CRANIUM (figs. 3–6)

DORSAL PART OF CALVARIA (fig. 3): The os frontale is narrowest just caudal to the os lacrimale and widens strongly and regularly toward the processus postorbitalis. The depressio frontalis deepens and widens toward the transverse rostral end of the cranium. The caudal part of the vault of the cranium is broadly rounded and devoid of marked eminence on either side. It shows a paired discontinuity that is best visible in the largest individuals as a faint groove (fig. 3A). Computed tomographic (CT) reconstruction of the endocranium of Dasornis toliapica has shown that the os frontale overlaps the os parietale caudally, and that the two bones are unfused at the caudal region of the os frontale (Milner and Walsh, 2009). In the light of these new data, the groove in the caudal part of the cranial vault is interpreted as an incompletely obliterated sutura frontoparietalis (see also Elzanowski and Galton, 1991). Rostral to this groove, the surface of the os frontale is transversely striated.

TABLE 2:

Measurements of the postcranium in Dasornis spp. Lengths in mm. * = estimated measurements.

continued

continued

continued

TEMPORAL REGION (figs. 4, 5): The processus postorbitalis projects rostrally and is rounded at the tip. It is continuous with the straight lateral border of the temporal region. The area of origin of musculus depressor mandibulae (fossa subtemporalis) is large, well defined, and continues onto the laterodorsal border of the processus paroccipitalis. Rostral to this structure is a shallow depression interpreted here as the area of origin of musculus adductor mandibulae externus, pars articularis (Zusi and Livezey, 2000). Both fossae extend halfway up to the occiput. There is no distinct processus zygomaticus. The area that supports the aponeurosis zygomatica (Elzanowski, 1987; Weber, 1996; Zusi and Livezey, 2000) is a low convexity.

OCCIPITAL REGION (figs. 3, 5) AND BASIS CRANII EXTERNA (figs. 3, 6): The sharp crista nuchalis transversa forms a double arch curving ventrally at the midline. The lateroventral part of this structure extends to the tip of the processus paroccipitalis. The prominentia cerebellaris is strongly convex in lateral aspect, and forms a sharp crista nuchalis sagittalis extending from the crista nuchalis transversa down to the foramen magnum. The os supraoccipitale dorsomedially forms a swollen zone with an oblique medial border.

The processus paroccipitalis is strongly developed and projects caudolateroventrally. The tip is vertical, rounded and forms a semilunar-shaped surface in lateral aspect. A slender processus lateralis parasphenoidalis connects the ventral border of the processus paroccipitalis with the lateral border of the lamina parasphenoidalis. The medial part of the processus paroccipitalis forms a smooth transition with the occipital plate and with the ventral corner of the prominentia cerebellaris; it shows a short crest and a tubercle close to the tip. The ventral side of the processus paroccipitalis is concave, with a lateral inclination in the medial part. In the London Clay specimens, the processus paroccipitalis is preserved only at the base (Harrison and Walker, 1976: pl. 1C).

FIGURE 3.

Dasornis toliapica, skull. A–F. Crania in dorsal view: A. OCP.DEK/GE 1044; B. D1-0027C; C. OCP.DEK/GE 1076; D. OCP.DEK/GE 1042; E. OCP.DEK/GE 1043; F. BMNH 44096. G. OCP.DEK/GE 1185, fragment of proximal part of maxilla, dorsal view. H–L. Crania in caudal view: H. OCP.DEK/GE 1044; I. OCP.DEK/GE 1076; J. OCP.DEK/GE 1042; K. OCP.DEK/GE 1043; L. BMNH 44096. Scale bars equal 10 mm.

FIGURE 4.

Dasornis toliapica, skull. A.–F. Crania in right lateral view: A. BMNH 44096; B. OCP.DEK/GE 1076; C. OCP.DEK/GE 1043; D. OCP.DEK/GE 1044; E. reversed OCP.DEK/GE 1044; F. reversed OCP.DEK/GE 1042. G. OCP.DEK/GE 1185, fragment of proximal part of maxilla, right lateral view. H. D1-0027E, distal end of maxilla, right lateral view. I–J. OCP.DEK/GE 1166, fragment of right mandibula: I. lateral view, J. medial view. Scale bar equals 10 mm.

FIGURE 5.

Dasornis toliapica, skull. A–D. Temporal regions in left lateral view: A. BMNH 44096; B. reversed OCP.DEK/GE 1042; C. reversed D1-0027B; D. OCP.DEK/GE 1076. E–F. Right middle ear regions: E. OCP.DEK/GE 1076; F. reversed OCP.DEK/GE 1044. G. OCP.DEK/GE 1076, region of the foramen opticum. H. D1-0027D, cavitas cranialis, dorsal view. I. D1-0027D, right wall of cavitas cranialis. J. D1-0027B, right osseous labyrinth. Scale bars equal 10 mm.

FIGURE 6.

Dasornis toliapica, skull. A–F. Crania in ventral view: A. BMNH 44096; B. OCP.DEK/GE 1043; C. OCP.DEK/GE 1042; D. OCP.DEK/GE 1076; E. D1-0027B; F. OCP.DEK/GE 1044. G. OCP.DEK/GE 1185, fragment of proximal part of maxilla, ventral view. H. D1-0027C, fragment of rostrum parasphenoidale, ventral view. Scale bars equal 10 mm.

A foramen venae occipitalis externae is found on either side at the ventral corner of the prominentia cerebellaris, at the level of the dorsal border of the foramen magnum and just medial to the inner border of the processus paroccipitalis. A short groove continues this foramen ventrally. A foramen rami occipitalis arteriae ophthalmicae externae that is continued dorsally by a long groove is located about two thirds of the way from the crista nuchalis sagittalis to the crista nuchalis transversa. The main groove branches into several smaller grooves.

The foramen magnum is higher than it is broad, with straight lateral borders (fig. 3J). Its plane is nearly perpendicular to that of the lamina parasphenoidalis, i.e., it is oriented downward only slightly. A small, depressed area is present on either side of the foramen magnum and ventral to the foramen venae occipitalis externae. The condylus occipitalis is very large, its width nearly equalling that of the foramen magnum. It is stemmed and slightly kidney shaped, with the dorsal facet showing deep triangular depression. The fossa subcondylaris is large and deep.

The medialmost foramen nervi hypoglossi is located in the stem of the condylus occipitalis. The tiny lateral foramen is far ventral and only slightly lateral to the medial one. The foramen nervi vagi is laterally oriented and its medial border is well defined, curving evenly to join the ventral border of the processus paroccipitalis and the base of the processus medialis parasphenoidalis. This crest is homologous to the crista fossae parabasalis. Milner and Walsh (2009) stated that the divergence of the nervus glossopharyngeus and nervus vagus is close to the exit of the latter, and that the nervus glossopharyngeus exits within the recessus scalae tympani. In one of the braincases, we found a small foramen in extreme marginal position, immediately lateral to the foramen nervi vagi, which may correspond to a foramen nervi glossopharyngealis (fig. 5E). It is not certain whether this is an artefact of preservation, however. There is no ostium canalis ophthalmici externi. A deep notch for the arteria carotis cerebralis lies just above the medial corner of the processus lateralis parasphenoidalis.

The lamina parasphenoidalis is triangular in shape, longitudinally narrow, and slightly concave. It has very sharp lateral borders and slants abruptly at the caudal edge, which is evenly curved. The prominent processus medialis parasphenoidalis occupies the lateral corner of the lamina parasphenoidalis and its lateral side shows a slit-shaped groove. The base of the processus lateralis parasphenoidalis forms a distinct horizontal platform lateral to the lamina parasphenoidalis. The tuba auditiva is completely closed. The ostium pharyngeale is located at the rostral corner of the lamina parasphenoidalis and continued rostrally by a shallow groove. The well-developed ala parasphenoidalis is continuous with the lateral border of the lamina parasphenoidalis and with the processus lateralis parasphenoidalis.

The foramen orbitale for the exit of arteria sphenoidea and nervus palatinus lies in the rostroventral part of the ala parasphenoidalis, close to the sharp ventral border of the basis rostri parasphenoidale (fig. 4). It is continued rostrally by a short, descending groove.

ROSTRUM PARASPHENOIDALE (figs. 4, 6): The rostrum parasphenoidale exhibits in its ventral corners a pair of elongated processus rostropterygoideus (Weber, 1996). These structures are roughly parallel to each other and have some lateral and rostral inclination. In the region of the processus rostropterygoideus, the rostrum parasphenoidale tapers upward to the lower edge of the septum interorbitale, and has concave lateral borders. A ridge continues medially the groove for the tuba auditiva and delimits a median surface. The latter structure evenly tapers rostrally and gradually rises to become a high crest at the level of the rostral half of the processus rostropterygoideus. Rostral to these structures, the section of the rostrum parasphenoidale gradually changes from triangular to round. In lateral aspect, a short straight ridge continues the processus rostropterygoideus rostrally.

MIDDLE EAR REGION (figs. 4, 5, 6): The arteria carotis cerebralis enters the middle ear region into a deep groove or partly closed canalis caroticus cranialis, deep to the ala parasphenoidalis and dorsal to the large ostium tympanicum (fig. 5). In BMNH 44096, the caudal part of a groove for the arteria carotis cerebralis is preserved on the left hand side. Our interpretation is congruent with that of Milner and Walsh (2009), which state that the arteria carotis cerebralis is enclosed in a bony tunnel. There is no canalis ophthalmicus externus, i.e., the arteria and vena ophthalmicae externae are neither encased in a bony canal in the medial wall of the tympanic cavity, nor is there a groove in which they rest.

The entrance of the recessus tympanicus rostralis is narrow and high (fig. 5). A strongly curved thin ridge separates the recessus tympanicus rostralis from the recessus columellae. A foramen nervi facialis is situated in the medial wall of the recessus tympanicus rostralis. This foramen is continued caudally by a groove that accommodates the nervus hyomandibularis. A shallow groove that continues this foramen rostroventrally accommodates the nervus palatinus. In the dorsal wall of the recessus tympanicus rostralis, an oval foramen that is probably pneumatic lies medial to the ala parasphenoidalis.

The recessus columellae is relatively deep (fig. 5). The fenestra vestibuli is rounded in shape. The oval fenestra cochleae is caudoventral to the fenestra vestibuli. The crista interfenestralis is narrow and oblique. The foramen pneumaticum caudale is very large and faces ventrally. The recessus tympanicus caudalis is well developed and probably communicates with the recessus tympanicus dorsalis. The pila otica is a flat surface facing ventrally.

The cotylae quadratica squamosi and otici cannot be distinguished from one another, because they merge rostrally with a smooth and evenly concave vertical surface (fig. 6). A prominent ridge that is roughly perpendicular to the median axis of the cranium delimits this structure rostrally. The cotyla quadratica squamosi and its lateral extension face ventrally. The lateral border of this extension is visible as a notch in lateral aspect, and continues caudomedially as a sharp ridge. The cotyla quadratica otici is sessile and faces lateroventrally. It is continuous with a flat surface that extends and widens onto the base of the processus paroccipitalis. This surface faces rostrally and has a rounded caudal border. A large foramen pneumaticum dorsale is situated between the cotylae quadratica and caudal to their rostral extension. A concave zone delimits this structure caudolaterally. The extensions of the cotylae quadratica are interpreted as such in Dasornis toliapica because these structures do not articulate with the processus oticus ossis quadrati in BMNH 44096. In the latter, the capitulum oticum and capitulum squamosum ossis quadrati merge rostrally with a narrow ridge that articulates with the rostral continuation of the cotylae quadratica (Harrison and Walker, 1976: pl. 2, fig. I). The processus oticus ossis quadrati is thus devoid of incisura intercapitularis, in contrast to most neornithine birds.

ORBITA (figs. 4, 5, 6): The lateral edge of the os frontale is sharp in the region where it widens toward the os lacrimale. The paries caudalis orbitae has only slight caudolateral slant and is not pierced by any fonticulus orbitocranialis. A groove that begins lateral to the fenestra associated with the fossa bulbi olfactorii curves toward the interorbital border of os frontale and turns caudally roughly paralleling the septum interorbitale (fig. 6). This groove probably accommodates the arteria supraorbitalis.

A deep square concavity is present in the region of the os laterosphenoidale, extending from the ala parasphenoidalis to the lateral border of the temporal region (fig. 6). A conspicuous prominentia lobi optici (Weber, 1996), which houses the globelike tectum mesencephali (see Milner and Walsh, 2009), forms most of its medial border. In the caudolateral part of the hollow is a drop-shaped depression interpreted here as the area of origin of musculus adductor mandibulae externus, pars coronoidea (Weber, 1996; Zusi and Livezey, 2000). The remainder of the hollow probably corresponds to the area of origin of musculus pseudotemporalis superficialis. The sharp crista orbitalis extends from the prominentia lobi optici to the tip of processus postorbitalis.

The foramen nervi maxillomandibularis is rostral to the ala parasphenoidalis. Just caudodorsally to the foramen nervi maxillomandibularis is a tiny recess that represents a remnant of the foramen for the vena cerebralis media (Elzanowski, 1987). The foramen opticum is small and rounded to oval in shape (fig. 5). There is a separate foramen nervi oculomotorii. It is not certain whether the nervus trochlearis is confluent with the nervus opticus. The foramen nervi opthalmici and the groove that continues the latter dorsally are located lateroventrally to the foramen opticum. The foramen nervi abducentis and its continuation are situated in a deep, rounded depression that is far ventral to the foramen opticum. A foramen arteriae ophthalmicae internae is present. At the angulus orbitae (Elzanowski, 1987), just above the foramen opticum, is a paired concavity from which the musculus rectus lateralis probably originates.

The fonticulus interorbitalis is evenly curved rostrodorsally and bounded dorsally by a narrow portion of septum interorbitale that shows a constant width (fig. 4). Its original aspect is not preserved in the Moroccan specimens. In OCP.DEK/GE 1042, the dorsal part of a bridge that probably separated the fonticulus interorbitalis from the foramen opticum is preserved (fig. 4F). Such a bridge is found in BMNH 44096. A small fonticulus orbitocranialis communicates with the fossa bulbi olfactorii and merges with the sulcus nervi olfactorii rostrally. The sulcus nervi olfactorii is wide, shallow, slightly curved, and of constant width. It bifurcates and widens slightly at its rostral extremity. The laterodorsal groove probably conducted the lateral ramus of nervus olfactorius, and the medioventral one conducted the medial ramus. The caudal border of the nasal cavity is a low and blunt crest, and the os ectethmoidale is absent. The lamina dorsalis is strongly developed with a rounded rostral end. It has a sharply defined outer edge, a deep depression for the concha caudalis in the caudal half and a conspicuous oblique column bordering this depression rostroventrally (fig. 6).

Os LACRIMALE (figs. 3, 4, 6): The os lacrimale is fused with the os frontale and possibly with a part of the os nasale, immediately caudal to the straight zona flexoria craniofacialis. The lateral border of the os lacrimale above the processus orbitalis is a slightly concave facet that is roughly parallel to the long axis of the cranium. The well-developed processus supraorbitalis is rounded at the tip and projects caudolaterally. This structure is damaged in the London Clay specimens (Harrison and Walker, 1976). The processus orbitalis is preserved only at the base in the Moroccan specimens.

CAVITAS CRANIALIS (fig. 5): The fossa cranii rostralis is wide, and houses the laterally expanded telencephalon (see Milner and Walsh, 2009). The fossa hypophysialis is small, rounded, and bounded caudally by a high dorsum sellae. Its shape agrees with the hypophysis morphology found in the virtual endocast of Dasornis toliapica (Milner and Walsh, 2009). The estimated angle between the plane of the lamina parasphenoidalis and a straight line connecting the dorsum sellae with the dorsalmost point of the condylus occipitalis is 20°. The fossa medullae oblongatae is strongly concave, rounded, devoid of median ridge, and fits well with the globe-shaped rhombencephalon of BMNH 44096 (Milner and Walsh, 2009). The foramen nervi abducentis is in medial position, and opens far ventral to the apex of dorsum sellae.

Milner and Walsh (2009) stated that the nervus trigeminus exits from the rhombencephalon and is contiguous with the ventral margin of the tectum mesencephali. In accordance with this, we found that the fossa ganglii trigemini opens exclusively to the fossa medullae oblongatae and is separated from the fossa tecti mesencephali by a thin ridge. The partial or complete separation of the fossa ganglii trigemini from the fossa tecti mesencephali occurs only in a few groups of neognathous birds among Neornithes (Elzanowski and Galton, 1991).

The bony labyrinth is widely separated from the fossa cranii rostralis by the protuberantia tentorialis (Elzanowski and Galton, 1991; Milner and Walsh, 2009). The eminentia arcuata canalis semicircularis rostralis (see Butendieck and Wissdorf, 1982) is of even width, oval, vertical, and smooth in the rostroventral corner. The rostral group of foramina of the fossa acustica interna is located in a deep well-defined concavity that is oval and higher than wide. There is no depression accommodating the caudal group of foramina. The fovea ganglii vagoglossopharyngealis is caudoventral to this caudal group. The canales nervorum hypoglossi opens slightly medial to the lateral border of the condylus occipitalis.

The fossa cerebelli is partly preserved. It is devoid of interfoliar ridges and sulcus medianus (Elzanowski and Galton, 1991), which correspond to the morphology of the cerebellum of BMNH 44096 (Milner and Walsh, 2009). The canalis semicircularis posterior projects very little into the fossa auriculae cerebelli, which occupies almost the entire area enclosed by the eminentia arcuata. The crista marginalis is prominent and sharp. A sulcus venae semicircularis running along the dorsal margin of the eminentia arcuata canalis semicircularis rostralis is clearly visible in one of the specimens (fig. 5J). This is not congruent with the work of Milner and Walsh (2009), who interpret the vena semicircularis rostralis as fully enclosed within an osseous tunnel.

MAXILLA (figs. 3, 4, 6)

A portion that roughly corresponds to the caudal third of the maxilla is preserved. It is heavily distorted and mediolaterally compressed. It lacks the caudalmost part and is broken just anterior to the apertura nasi ossea. Its structure is exceedingly similar to that of BMNH 44096 (Harrison and Walker, 1976). The distal end that corresponds to the rostral third of the maxilla is damaged at the tip and strongly crushed mediolaterally (fig. 4).

The maxilla is elongated, mediolaterally narrow, and dorsoventrally deep. In dorsal aspect, the culmen is broken at the zone where it begins to widen caudally toward the flat triangular region just rostral to the zona flexoria craniofacialis. This triangular structure is well preserved in BMNH 44096 (fig. 3) and BMNH A1 (see Harrison and Walker 1976: pl. 1, fig. B; pl. 4, fig. A). The maxilla has a deep lateral longitudinal groove ascending to the apertura nasi ossea and then paralleling the culmen before descending gradually to a point just behind the rostral tip, which does not seem to turn down strongly. The tiny apertura nasi ossea is longer than it is high (table 1) and situated 2 mm above the lateral groove, at approximately one third the distance from the zona flexoria craniofacialis to the tip of the maxilla. The crista tomialis is straight and thick, and bears numerous toothlike processes. These structures vary in size from mere spines to pointed, conical pseudoteeth. The large pseudoteeth are approximately evenly spaced (around 12 mm apart) on each ramus, and their heights are comparable to those of BMNH 44096. Between each large projection is a small pseudotooth, sometimes flanked rostrally by a still smaller process. Most of the large projections are broken, showing a central hollow within. The large projections of the proximal region slant forward, as in BMNH 44096 (Harrison and Walker, 1976). In the rostral end of the maxilla, however, they arise vertically from the crista tomialis. The lateral surface of the maxilla and the cristae tomiales including the toothlike projections bear numerous canaliculi neurovasculares that open into foveae corpusculorum nervosorum, which consist of shallow, irregular furrows.

The ventral aspect of the proximal maxilla is very similar to that of BMNH 44096 (fig. 6). The straight, wide processus maxillaris of os palatinum curves ventrally from front to back and is separated from its counterpart by a narrow median furrow, which is the rostral continuation of the fossa choanalis. Rostral to this groove, the processus maxillaris of os palatinum merges with the processus palatinus of os premaxillare and possibly with the processus maxillopalatinus of os maxillare, which fuse with their counterpart to form a unique structure, the “central palatal region” (Harrison and Walker, 1976). The latter structure shows a median groove, the “interpalatal groove” (Harrison and Walker, 1976). On either side of the central palatal ridge is a deep longitudinal “lateral palatal groove” that accommodated the crista tomialis and toothlike projections of the mandibula when the jaws were closed (see Harrison and Walker, 1976). The central palatal ridge appears to decrease in depth and width toward the rostral end of the maxilla, which is deeply hollowed.

MANDIBULA (fig. 4)

A lateromedially crushed portion of pars intermedia is preserved (OCP.DEK/GE 1166). It tapers gradually toward the distal end. The crista tomialis and toothlike processes are similar to those of the maxilla. Only two large toothlike projections are preserved. They slant forward and their heights are comparable to those of the large maxillar projections. The lateral surface of the mandibula, crista tomialis, and pseudoteeth bear canaliculi neurovasculares and foveae corpusculorum nervosorum that are similar to those found in the maxilla. In lateral aspect, a deep straight longitudinal groove gradually gets closer to the ventral margin: in the proximal part, it is located at about one third of the depth of the mandibula above ventral margin; in the distal one, it is located at about one fifth of the depth of the mandibula. The lateral side of the jaw is nearly flat. The medial one is smooth, slightly convex, and a shallow longitudinal hollow occupies the lower third of it.

CORACOIDEUM (fig. 7)

The processus acrocoracoideus is lateromedially narrow and noticeably elongated dorsoventrally. The facies articularis clavicularis is proximodistally high with a bent, sharp sternal border, and faces medioventrally. The impressio ligamenti acrocoracohumeralis is probably shallow or indistinct. Two parallel crests are located in the caudal part of the apex of processus acrocoracoideus. The medial side of the long collum acrocoracoidei (Ballmann, 1969) is devoid of pneumatic foramina and bears a shallow groove in its dorsal half. This groove is most probably an artifact of preservation, because it is not found in a coracoideum from the Middle Eocene of Belgium tentatively assigned to Macrodontopteryx oweni (Mayr and Smith, 2010). The processus acrocoracoideus and its neck project cranially, so that the whole structure makes an angle with the long axis of the corpus.

The facies articularis humeralis is not preserved. The cotyla scapularis is deep and cup shaped. The well-developed processus procoracoideus is proximodistally thick and strongly projects ventrally. Its base is noticeably convex just medial to the cotyla scapularis. A short, sharp crest continues the processus procoracoideus sternally. A pneumatic foramen is just sternal to the cotyla scapularis. Its ventral opening lies in a round concavity. The corpus coracoidei has a strongly curved margo medialis. The lateral extremity of the extremitas sternalis is blunt, with a low facies interna that is nearly perpendicular to the facies dorsalis. The facies externa is a thick convexity in this region. The fragmentary coracoidea described here match well with the complete coracoideum putatively assigned to M. oweni (a junior synonym of Dasornis toliapica) by Mayr and Smith (2010: fig. 3).

HUMERUS (figs. 7–10)

The caput humeri is craniocaudally narrow (fig. 8). It shows a distinct dorsal prominence on its cranial facies and tapers ventrally to the wide incisura capitis. An oblique groove is present on its dorsal slope. Its caudal border is well defined. The tuberculum dorsale is well separated from and slightly distal to the caput; it consists of a smooth, indistinct facet that faces proximally. An even convexity continues this structure far distally. The well-developed crista deltopectoralis extends far distally on the shaft and has an evenly curved dorsal border. The low impressio musculi pectoralis is in proximal position on the crista deltopectoralis (fig. 9). It is dorsally indistinct and has an evenly curved distoventral border. The tuberculum ventrale is not completely preserved, but appears well developed (fig. 8). It is oriented somewhat proximally and dorsally, with an oblique concave ventral facet. Its proximal facet is slightly concave with a distinct pit in its dorsal corner. The crista bicipitalis is low and oblique.

The fossa pneumotricipitalis is very large and faces caudally (fig. 8). The crus dorsale fossae is distally continuous with the margo caudalis. The thick crus ventrale fossae is convex in its distal part and forms a flat surface just distal to the tuberculum ventrale. This flat surface exhibits a distinct scar for the insertion of musculus scapulohumeralis caudalis. Two pneumatic foramina are widely separated from each other by a thick ridge. The proximal foramen pneumaticum is roughly oval in shape. The distal one is narrow, proximodistally elongated with tapering extremities.

FIGURE 7.

Dasornis toliapica. A–E. Left ossa coracoidei: A. OCP.DEK/GE 1195, dorsal view; B. reversed OCP.DEK/GE 1088, corpus, dorsal view; C. reversed OCP.DEK/GE 1088, processus acrocoracoideus, medial view; D. reversed OCP.DEK/GE 1088, processus acrocoracoideus, lateral view; E. OCP.DEK/GE 1195, ventral view. F. Reversed OCP.DEK/GE 1070, right humerus, cranial view. G. OCP.DEK/GE 1240, right humerus, caudal view. H. OCP.DEK/GE 1233, right humerus, caudal view. I. MHNL 20-149215, left ulna, cranial view. Scale bars equal 10 mm.

The short, deep sulcus transversus ends dorsally at the level of the incisura capitis (fig. 9). It is perpendicular to the long axis of the corpus, sharply defined, with tapering ventral extremity. The planum intertuberculare is nearly flat. The low intumescentia humeri is poorly developed dorsally, proximodistally elongated, and shows two prominences that are loosely separated from each other. The proximal one is just distal to the sulcus transversus. The roughly rounded distal one is the higher. The impressio coracobrachialis is very shallow. Its dorsal border is visible as a low, blunt crest. Tiny vascular foramina are present in the distal part of planum intertuberculare, at the level of the impressio coracobrachialis and the distal prominence of the intumescentia.

The corpus humeri is straight (fig. 7) and oval in transverse section. Close to the extremitas proximalis, the margo caudalis is prominent, so that the transverse section of the humerus is triangular (fig. 8). The linea musculi latissimi dorsi is dorsal to the margo caudalis and divided into two widely separated parts. The distal part of the linea is thick, well defined, and continues far distally to the crista deltopectoralis. The section of linea distal to the crista deltopectoralis is close to the margo dorsalis. The proximal part of the linea musculi latissimi dorsi is an almond-shaped facet that is ventral to the distal part. It faces caudally and is parallel to the margo caudalis. The slitlike, proximodistally elongated foramen nutritium (Ballman, 1969) is in distal position on facies cranialis and close to the margo ventralis (figs. 7, 9). The margo dorsalis sharpens close to the distal extremity (fig. 10).

The condylus dorsalis is long, straight, blunt at the tip, and distally prominent (fig. 10). The condylus ventralis is roughly rounded with a low, oblique crest on its ventral side. It is distally prominent and has an abrupt caudal border. It does not extend distally to the condylus dorsalis. The incisura intercondylaris is wide. The fossa musculi brachialis is shallow and roughly oval in shape. The epicondylus dorsalis is a very prominent, proximodistally short convexity. The tuberculum supracondylar dorsale is a small pit just proximal to this structure. The origin of musculus extensor carpi ulnaris is caudodistal to the epicondylus dorsalis and it consists of two deep concavities that are bounded caudally, cranially, and distally by a thick and smooth prominent ridge. There is a distinct separation between this ridge and the condylus dorsalis. The proximal concavity is slightly cranial to the distal one. The epicondylus ventralis is a blunt ridge that is perpendicular to the long axis of the corpus. The facies ventralis just proximal to the former is markedly concave. The large surface of attachment of the ligamentum collaterale ventrale faces cranially, is oval in shape and higher than it is wide. The surface of origin of musculus pronator superficialis is a small pit proximal and slightly caudal to the latter. The processus flexorius is poorly developed and distinctly proximal to the condylus ventralis. The origin of musculus flexor carpi ulnaris consists of two scars that face slightly cranially, the more cranial one the larger and the deeper. The fossa olecrani is fairly shallow. The sulci humerotricipitalis and scapulotricipitalis are shallow. The latter is wide, without prominent borders.

The partial humeri tentatively assigned to Macrodontopteryx oweni (a junior synonym of Dasornis toliapica) by Mayr and Smith (2010: fig. 5) match fairly well with the Moroccan specimens except for three features: the caput humeri protrudes more proximally and there is a conspicuous muscle attachment scar on the dorsal edge and at mid height of the fossa pneumotricipitalis, which is smaller than in D. toliapica. These elements indicate that the Belgian specimens belong to a different species, and might be assigned to a different genus.

FIGURE 8.

Dasornis toliapica, proximal part of left humeri. A, D. Dorsal view: A. MHNL 20-149229; D. OCP.DEK/GE 1003. B, C, E–I. Caudal view: B. MHNL 20-149229; C. reversed OCP.DEK/GE 1164; E. OCP.DEK/GE 1003; F. reversed OCP.DEK/GE 1194; G. OCP.DEK/GE 1216; H. reversed OCP.DEK/GE 1128; I. OCP.DEK/GE 1229. J, K. Proximal view: J. OCP.DEK/GE 1229; K. reversed OCP.DEK/GE 1164. Scale bar equals 10 mm.

FIGURE 9.

Dasornis toliapica, proximal part of left humeri in cranial view. A. OCP.DEK/GE 1229; B. OCP.DEK/GE 1216; C reversed OCP.DEK/GE 1194; D. OCP.DEK/GE 1003; E. reversed OCP.DEK/GE 1183; F. OCP.DEK/GE 1086; G. MHNL 20-149229; H. OCP.DEK/GE 1116 Scale bar equals 10 mm.

FIGURE 10.

Dasornis toliapica, distal part of right humeri. A–D. MHNL 20-149214, extremitas distalis: A. dorsal view; B. ventral view; C. distal view; D. cranial view. E–H. Reversed MHNL 20-149216, extremitas distalis: A. dorsal view; B. ventral view; C. distal view; D. cranial view. I. Reversed OCP.DEK/GE 1164, extremitas distalis, ventral view. J–N. Cranial view: J. OCP.DEK/GE 1075; K. reversed OCP.DEK/GE 1218; L. reversed OCP.DEK/GE 1203; M. OCP.DEK/GE 1107; N. MHNL 20-149211. O. MHNL 20-149211, caudal view. Scale bar equals 10 mm.

FIGURE 11.

Dasornis toliapica, proximal part of left ulnae. A, B, F, G. Caudal view: A. BMNH A224; B. reversed OCP.DEK/GE 1002; F. OCP.DEK/GE 1005; G. MHNL 20-149215. C–E. Fragments of corpus in caudal view: C. OCP.DEK/GE 1257; D. reversed OCP.DEK/GE 1207; E. reversed OCP.DEK/GE 1160. H, I. Ventral view: H. OCP.DEK/GE 1005; I. BMNH A224. J–Q. Cranial view: J. BMNH A224; K. reversed OCP.DEK/GE 1002; L. OCP.DEK/GE 1283; M. OCP.DEK/GE 1135; N. OCP.DEK/GE 1005; O. OCP.DEK/GE 1039; P. MHNL 20-149215; Q. reversed MHNL 20-149218. R-T. Proximal view: R. BMNH A224; S. reversed OCP.DEK/GE 1002; T. OCP.DEK/GE 1039. Scale bars equal 10 mm.

ULNA (figs. 7, 11, 12)

The extremitas proximalis ulnae and the proximal part of the corpus are exceedingly similar to those of BMNH A224, but more or less caudocranially crushed. Most probably, the original aspect of the ulna is preserved in BMNH A224 (fig. 11R). The impressio musculi brachialis is small, indistinct, and distally tapering (fig. 11). The facies caudodorsalis is strongly convex. The impressio musculi scapulotricipitalis is in distodorsal position and roughly parallel to cotyla dorsalis. The cotyla dorsalis is flat with a straight cranial border and a pointed extremity without any dorsal projection. The cotyla ventralis is round. The crista intercotylaris is well developed, wide, and blunt. The depression for attachment of meniscus radioulnaris is poorly developed. The incisura radialis is rather shallow, with a rounded dorsal edge. The olecranon is prominent, caudocranially narrow, with a bluntly rounded tip that is slightly deflected ventrally. The tuberculum ligamenti collateralis ventralis is prominent, proximodistally elongated, and in distal position.

The corpus is straight (fig. 7), without marked cranial curvature at the proximal end (fig. 11). It is wider than deep, with a well-marked, smooth margo caudalis. Its proximal part shows a low margo interosseus. The sharp linea intermuscularis of facies cranialis extends from the dorsal border of the cotyla dorsalis to the tuberculum carpale (fig. 71). It is evenly curved in the proximal part and parallel to the margo dorsalis distal to the foramen nutritium (Ballmann, 1969). The papillae remigales are low and longitudinally striated tubercles (figs. 11, 12). A slight caudocranial flattening of the corpus occurs not far from the extremitas distalis (fig. 12).

The extremitas distalis ulnae is somewhat flattened caudocranially and roughly corresponds to an isosceles triangle (fig. 12). The condylus dorsalis, condylus ventralis, and tuberculum carpale are of same width. The condylus dorsalis extends rather far proximally and protrudes caudoventrally. In its ventral part, the smooth condylus ventralis shows a low prominence in cranial position. It has a bluntly pointed ventral extremity. The sulcus intercondylaris is wide and shallow. Its proximal continuation on facies cranialis is a wide flat surface bounded ventrally by a distinct sinuous ridge that extends far proximally. The apex of this ridge is visible in distal view and gives a truncated aspect to the cranial border of the ulna. The distal edge of the smooth tuberculum carpale is straight to slightly curved and slopes only slightly proximally. The ventral edge of the tuberculum extends far proximally on the corpus. The facies cranialis is not deeply excavated between the tuberculum carpale and the continuation of the sulcus intercondylaris. The depressio radialis is shallow with a well-marked proximal edge. The incisura tendinosa is shallow with a straight caudal edge and a curved cranial one. A low tubercle lies at its proximal corner.

The proximal part of the ulna tentatively referred to Macrodontopteryx oweni (BMNH A3692) by Harrison and Walker (1976) is identical to that of Dasornis toliapica and its size corresponds to that of the largest individuals of this species (table 2). This justifies the assignment of BMNH A3692 to D. toliapica.

FIGURE 12.

Dasornis toliapica, distal part of ulnae. A, B. Left ulnae, cranial view: A. MHNL 20-149215; B. MHNL 20-149217. C–E. Right ulnae, dorsal view: C. reversed MHNL 20-149237; D. MHNL 20-149218; E. OCP.DEK/GE 1035. F–H. Right ulnae, ventral view: F. MHNL 20-149218; G. OCP.DEK/GE 1035; H. OCP.DEK/GE 1198. I, J. Right ulnae, cranial view: I. OCP.DEK/GE 1198, J. MHNL 20-149218. K, L. Fragments of right corpus ulnae, caudal view: K. reversed MHNL 20-149220; L. reversed OCP.DEK/GE 1153. M–O. Right ulnae, distal view: M. MHNL 20-149218; N. OCP.DEK/GE 1035; O. OCP.DEK/GE 1198. Scale bars equal 10 mm.

RADIUS (fig. 13)

The cotyla humeralis is almond shaped, dorsoventrally elongated, and caudocranially flattened. Its cranial edge is distinctly proximal to the caudal one. Its ventral border forms a conspicuous overhang that is continuous with the prominent caudal edge of the tuberculum bicipitale. The caput radii is prominent and well developed dorsoventrally. In dorsal aspect, it is oblique and very sharply defined proximally A crest on the facies caudalis extends from the top of the latter structure to a point slightly distal to the tuberculum bicipitale. This crest together with the tuberculum bicipitale and the facies articularis ulnaris delimit a slightly concave and triangular plateau.

Several isolated fragments of corpus radii are preserved. The corpus is very straight with only a slight ventral curvature toward the extremitas proximalis. Its facies cranialis shows sharply defined lineae intermusculares in its proximal part. A straight groove (caudodorsal groove) continues the caudal part of sulcus tendinosus through most of the length of the corpus.

The extremitas distalis is wide and has a strong ventral curvature. The ligamental prominence (Howard, 1929) is strongly convex and protrudes ventrally Its proximal border is well defined and sinuous. The depressio ligamentosa and the region proximal to the cranial part of the ligamental prominence are strongly concave and separated from each other by the smooth and curved distal end of the margo ventralis. The protuberance cranial to the sulcus tendinosus (dorsal convexity) is high and caudocranially wide. The caudal border of facies articularis radiocarpalis evenly curves toward the tuberculum aponeurosis ventralis. A small tubercle (ventral tubercle) is just proximal to the depressio ligamentosa, close to the margo interosseus. The sulcus tendinosus is smooth and shallow.

CARPOMETACARPUS (fig. 14)

The os metacarpale ahilare does not show any strongly protruding processus extensorius. It forms a somewhat elongated structure parallel to the long axis of os metacarpale majus. A very elongated processus alularis with an orientation comparable to that of Dasornis toliapica is found in Gaviidae. The caudodorsal extremity of the trochlea carpalis forms a thick tubercle. The sharp caudoventral border of the trochlea carpalis extends as far distally as this tubercle. The dorsal margin of the trochlea carpalis shows a small prominence just caudal to the welldefined surface of attachment of ligamentum radiocarpo-metacarpale dorsale. The fossa supratrochlearis exhibits a short furrow that can be referred to the facies ligamenti externa (Ballmann, 1969). The proximoventral corner of the trochlea carpalis is thick and overhangs the deep fossa infratrochlearis. The processus pisiformis is very prominent with an oblique proximal margin that reaches the trochlea carpalis caudally Its cranial border forms a conspicuous overhang that extends far distally. A sharp crest cranial to the processus pisiformis constitutes the caudal edge of the depressio muscularis interna (Ballmann, 1969).

FIGURE 13.

Dasornis toliapica, radii. A–E. Proximal parts of left radii in caudal view: A. OCP.DEK/GE 1055; B. MHNL 20-149215; C. MHNL 20-149219; D. OCP.DEK/GE 1175; E. OCP.DEK/GE 1212. F–H. Proximal parts of left radii in cranial view: F. OCP.DEK/GE 1212; G. OCP.DEK/GE 1175; H. MHNL 20-149215. I. OCP.DEK/GE 1212, left radius, proximal view. J. OCP.DEK/GE 1121, fragment of corpus radii, dorsal view. K. OCP.DEK/GE 1153, fragment of left corpus radii, dorsal view. L–N. Distal ends of left radii in dorsal view: L. reversed OCP.DEK/GE 1058; M. reversed OCP.DEK/GE 1118; N. reversed OCP.DEK/GE 1199. O–R. Distal ends of left radii in ventral view: O. reversed OCP.DEK/GE 1157; P. reversed OCP.DEK/GE 1199; Q. reversed OCP.DEK/GE 1118; R. reversed OCP.DEK/GE 1058. Scale bars equal 10 mm.

FIGURE 14

Dasornis toliapica, left carpometacarpi. A–H. Dorsal view: A. reversed OCP.DEK/GE 1241; B. OCP.DEK/GE 1152; C. reversed OCPDEK/GE 1255; D. OCP.DEK/GE 1139; E. OCP.DEK/GE 1172; F. OCP.DEK/GE 1100; G. reversed OCP.DEK/GE 1101; H. reversed OCP.DEK/GE 1102. I–K. Caudal view: I. OCP.DEK/GE 1152; J. OCP.DEK/GE 1012; K. OCP.DEK/GE 1139. L–R. Ventral view: L. OCP.DEK/GE 1152; M. reversed OCP.DEK/GE 1255; N. OCP.DEK/GE 1012; O. OCP.DEK/GE 1137; P. OCP.DEK/GE 1139); Q. reversed OCP.DEK/GE 1101; R. reversed OCP.DEK/GE 1102. S, T. Distal view: S. reversed OCP.DEK/GE 1101; T. reversed OCP.DEK/GE 1102. Scale bars equal 10 mm.

FIGURE 15.

Dasornis toliapica. A, B. OCP.DEK/GE 1045, partial right femur: A. caudal view; B. cranial view. C, D. OCP.DEK/GE 1144 fragment of distal end of right femur: C. lateral view; D. caudal view. E, F. Right tibiotarsi in caudal view: E. OCP.DEK/GE 1013; F. MHNL 20-149238 G–I Right tibiotarsi in lateral view: G. reversed OCP.DEK/GE 1011; H. OCP.DEK/GE 1013; I. MHNL 20-149238. J–N. Right tibiotarsi in cranial view I. MHNL 20-149238; K. reversed OCP.DEK/GE 1040; L. OCP.DEK/GE 1204; M. OCP.DEK/GE 1013; N. reversed OCP.DEK/GE 1011. O–P. Right tibiotarsi in medial view: O. OCP.DEK/GE 1013; P. MHNL 20-149238. Q. OCP.DEK/GE 1013, right tibiotarsus, distal view. Scale bar equals 10 mm.

FIGURE 16.

Dasornis toliapica, left tarsometatarsi. A–D. Dorsal view: A. MHNL 20-149231; B. reversed OCR DEK/GE 1176; C. OCP.DEK/GE 1155; D. OCP.DEK/GE 1146. E, F. Lateral view: E. OCP.DEK/GE 1146; F. reversed OCP.DEK/GE 1176. G–J. Plantar view: G. MHNL 20-149231; H. reversed OCP.DEK/GE 1176; I. OCP.DEK/GE 1155; J. OCP.DEK/GE 1146. K–L. Medial view: K. OCP.DEK/GE 1146; L. reversed OCP.DEK/GE 1176. M. Reversed OCP.DEK/GE 1176, proximal view. Scale bar equals 10 mm.

The corpus is long and slender. The straight os metacarpale majus is roughly triangular in shape, because it shows a smooth median ridge on facies ventralis (ventral ridge) that curves caudally close to the facies articularis digitalis major. Just cranial to the distal end of this median crest is a triangular concavity. The sulcus tendinosus distinctly deepens and widens at distal extremity. There is no processus intermetacarpalis. The os metacarpale minus is oval in transverse section and fused proximally to the os metacarpale majus over a long distance. It is nearly straight and parallel to os metacarpale majus, so that the spatium intermetacarpale is narrow. In ventral aspect, it shows a sharp crest and a tubercle just proximal to the spatium intermetacarpale. On the proximal slope of the tubercle is a large surface of attachment of ligamentum ulnocarpo-metacarpale ventrale that can be referred to the facies ligamenti interna (Ballmann, 1969).

The symphysis metacarpalis distalis is long and slightly concave in ventral aspect. The sulcus interosseus is deep and narrow. The facies articularis digitalis major has a regularly curved dorsal margin that extends far caudally. In some specimens, this margin forms a bridge above the sulcus interosseus. The facies articularis digitalis major exhibits a high and well-defined caudal protuberance that is continuous with the distal end of the ventral crest of os metacarpale majus. The facies articularis digitalis minor is oval in shape, dorsally protruding, and distinctly separated from the body of os metacarpale minus.

FEMUR (fig. 15A–D)

Most of the corpus and a small part of the extremitas distalis are preserved. The corpus is straight and slender. At mid height of the latter is a distinct triangular facet located on facies caudalis and close to the medial edge. The sharp linea intermuscularis caudalis is in extreme medial position and continuous with the crista supracondylaris medialis. It is interrupted proximal to the triangular facet. The linea intermuscularis cranialis is straight and roughly parallel to the lateral border of the corpus.

In caudal aspect, the trochlea fibularis is wide and faces caudally. Just above the condylus fibularis is a distinct notch. The tuberculum musculi gastrocnemialis lateralis is high and conspicuous. The distal impressio ansae musculi iliofibularis is just distal to the latter. The fossa poplitea appears deep. In cranial aspect, the sulcus patellaris and sulcus intercondylaris are deep and wide, and the crista medialis sulci patellaris is narrow and prominent. Proximal to the crista lateralis sulci patellaris is the proximal impressio ansae musculi iliofibularis.

TIBIOTARSUS (fig. 15E–Q)

The proximal part of the tibiotarsus is preserved only in MHNL 20-149238 (fig. 15F, I, J, P). The partly damaged cristae cnemiales are well developed. The cranial margin of the crista cnemialis cranialis was straight to slightly curved. The facies articularis lateralis protrudes proximally and caudally and is continuous with a very prominent facies articularis fibularis. The fossa flexoria is deep. The caudal incisura between the facies articularis medialis and the facies articularis lateralis is well defined. The impressio ligamenti collateralis medialis is a very prominent and proximodistally elongated tubercle.

The crista fibularis is damaged. The part of the facies caudalis level with the latter structure is convex. The conspicuous tuberositas poplitea consists of three sharp ridges that are parallel to each other. The linea extensoria is well marked. The well-defined lineae musculi fibularis form a wide platform that tapers toward the crista fibularis proximally and toward the sulcus musculi fibularis distally.

The condylus lateralis has a nearly straight caudal margin and projects rather far cranially The epicondylus lateralis is a blunt oblique ridge that is variably developed. The depressio epicondylaris lateralis is shallow. The condylus medialis is perpendicular to the long axis of the corpus, strongly projects cranially, and has a convex proximal border. It protrudes more cranially and is narrower than the condylus lateralis. The epicondylus medialis is a distinct protuberance that extends beyond the proximal edge of the condylus medialis. A tiny circular pit is present at the extremitas distalis and on the internal side of the condylus medialis. Both condylae are devoid of distal notches. The incisura intercondylaris is very wide with a marked impressio ligamenti intercondylaris. It extends onto the proximal part of the condylus medialis. The deep, sharply defined sulcus musculi fibularis faces craniolaterally. The zone between the latter and the epicondylus lateralis is depressed. The trochlea cartilaginis tibialis is shallow and its proximal end forms a smooth transition with the corpus. The cristae trochleae are poorly developed.

The sulcus extensorius is deep and occupies the median third of the facies cranialis, with the medial border distinctly higher than the lateral one. The lateral tuberositas retinaculi extensori forms a vertical triangular surface that communicates with the lateral margin of the pons supratendineus through a sharp edge. It is located just above the condylus lateralis and separated from the latter by a distinct pit. The medial tuberositas retinaculi extensori is a sharp oblique ridge that is proximodistally elongated. The pons supratendineus is wide and slightly oblique. The distal opening of the canalis extensorius is large, oval, and tapers a little laterally. It is slightly medial to the sulcus extensorius.

TARSOMETATARSUS (fig. 16)

In the Moroccan fossils, the tarsometatarsus is preserved in its entirety except for the extremitas proximalis and hypotarsus, which are slightly damaged. In contrast, these parts are well preserved in BMNH A134 (Harrison and Walker, 1977: pl. 1), which was initially referred to Odontopteryx toliapica by Lydekker (1891) and later assigned to Neptuniavis minor by Harrison and Walker (1977). The cotyla medialis is round and its inner plantar corner forms a prominent ridge (plantar prominence) extending to the crista medialis hypotarsi. The cotyla lateralis has a marked dorsodistal slant and its lateroplantar corner shows a prominent tuberculum musculi fibularis brevis. The eminentia intercotylaris is dorsally prominent and laterally deflected with a slight overhang on the lateral side. The hypotarsus is in lateral position, its lateral border in line with the medial edge of the cotyla medialis. It consists of three cristae hypotarsi and two sulci (Harrison and Walker, 1977: pl. 1G). The crista medialis extends further proximally and distally than the two lateralmost cristae. The sulcus medialis is deeper and wider than the sulcus lateralis. The plantar aperture of the lateral foramen vasculare proximale is deeply set at the side of the distal end of the crista lateralis hypotarsi. The plantar aperture of the medial foramen vasculare proximale is proximal and dorsal to the lateral one. The impressio ligamenti collateralis lateralis is a proximodistally elongated scar on facies lateralis, not far beneath the lateral edge of the cotyla lateralis.

The corpus is almost square in transverse section and flares out more widely at the proximal end of the facies subcutanea medialis. The cristae plantares are low and sharply defined. The crista medianoplantaris is straight. The facies medialis shows an evenly curved line ending proximodorsally into a small oval scar that is probably for the origin of musculus extensor hallucis longus. The fossa metatarsi I is very shallow, nearly indistinct.

The fossa infracotylaris dorsalis and the proximal part of the sulcus extensorius are deep. The dorsal opening of the medial foramen vasculare proximale is only a little higher than the lateral one. The tuberositas musculi tibialis cranialis consists of two parts, the lateral one slightly distal to the medial one. The latter is continuous with a sharp ridge extending to the proximal part of the fossa infracotylaris dorsalis and partly hiding the medial foramen vasculare proximale.

The foramen vasculare distale is large and higher than it is wide. In dorsal aspect, it is continued proximally by a deep sulcus musculi extensoris brevis digiti IV (Ballmann, 1969). In plantar aspect, it is recessed and in low position.

All three trochleae are grooved and the external sides of trochleae metatarsi II and IV are smooth. The trochlea metatarsi II shows a very strong proximal and plantar displacement and is tilted plantarolaterally. Its rounded inner edge extends barely a third of the length of trochlea metatarsi III. The external flange of trochlea metatarsi II is displaced proximally and forms plantarly a proximally pointed projection. The external fovea ligamenti collateralis is very shallow.

The trochlea metatarsi III is dorsally elevated in dorsal aspect, and its base is incised by the foramen vasculare distale. In plantar aspect, the trochlea metatarsi III is proximodistally elongated and slightly oblique, with a pointed extremity. The trochlea metatarsi IV extends about two-thirds the length of the trochlea metatarsi III. Its internal flange is round. Its external flange shows a strong proximoplantar displacement and forms a bluntly rounded plantar projection. The external fovea ligamenti collateralis is a shallow concavity. The incisura intertrochlearis lateralis is wider than the incisura intertrochlearis medialis.

The proximal end of tarsometatarsus tentatively assigned to Macrodontopteryx oweni (a junior synonym of Dasornis toliapica) by Mayr and Smith (2010: fig. 6) differs from D. toliapica and Dasornis emuinus in several features: the cotylae are subequal (the cotyla lateralis is distinctly smaller than the cotyla medialis in Dasornis), the eminentia intercotylaris is less prominent dorsally, the cristae hypotarsi are more prominent and subequal in height, the corpus is more slender, the crista plantaris lateralis is more sharply defined, and the sulcus extensorius is wider and deeper. These elements indicate that the Belgian specimen belongs to a different species, which might be assigned to a different genus.

CRANIUM (figs. 17–20)

The new skull material referred to Dasornis emuinus includes six imperfect crania. The processus paroccipitalis, os lacrimale, and fonticulus interorbitalis are incompletely preserved, but were probably similar to those of the London Clay skulls (Harrison and Walker, 1976; Mayr, 2008). The recessus columellae is not preserved (fig. 20). The foramen nervi trochlearis is at mid height and just lateral to the foramen opticum. It is continued dorsally by a long groove (fig. 20). The structure of the cranium of D. emuinus is exceedingly similar to that of Dasornis toliapica. Apart from the larger size, the former differs from the latter in a few features: the sutura frontoparietalis is more distinct, and forms a curved groove that marks the caudal edge of the transversely striated zone of the os frontale (fig. 17). The prominentia cerebellaris is narrower with a wide and blunt crista nuchalis sagittalis, but this might be due to preservation (fig. 18). The lamina parasphenoidalis is caudorostrally shorter (fig. 19; see also Mayr, 2008: fig. 3B). The os exoccipitale forms a thick flange extending lateral to the distinct foramen nervi glossopharyngealis, and there is no evidence of notch, groove, or canal for the arteria carotis cerebralis (figs. 18, 20). The caudal extension of the cotyla quadratica otici is longer and twisted ventrally (figs. 19, 20). The foramen pneumaticum dorsale is smaller and occupies the rostralmost third of the surface delimited by the cotylae quadratica plus their extensions (fig. 19). The laterosphenoid hollow (fig. 19) is triangular owing to the relatively smaller size of the prominentia lobi optici (Weber, 1996). The foramen for the exit of the nervus abducens is not situated in a deep pit. The foramen nervi ophthalmici is in more rostral position (fig. 20). The cranial differences between D. emuinus and D. toliapica must be taken with caution, given the artifacts of preservation and the limited number of available skulls.

HUMERUS (fig. 21)

The available material covers most of the humerus, and includes two complete humeri embedded in matrix (fig. 21A, B). In these two specimens, the major part of the facies cranialis is visible, but the corpus humeri is crushed (fig. 21A, B). Taking into account all specimens, visible structures of the extremitas proximalis include the caput, tuberculum dorsale, base of crista deltopectoralis, a part of the dorsal margin of the foramen pneumaticum, and a part of the planum intertuberculare plus impressio coracobrachialis. Most of the corpus is preserved, including the linea musculi latissimi dorsi. Most of the extremitas distalis is conserved, including the shallow oval fossa musculi brachialis and the condylae. Apart from the larger size, the structure of the humerus of Dasornis emuinus is exceedingly similar to that of Dasornis toliapica. Mayr and Smith (2010) tentatively assigned an incomplete humerus from the Middle Eocene of Belgium to D. emuinus. However, two features of the Belgian specimen suggest that it might not belong to Dasornis: the caput humeri is caudocranially wider than in the Moroccan fossils and the facies cranialis exhibits a prominent tubercle for the origin of the humeral head of musculus biceps brachii (Mayr and Smith, 2010: fig. 7).

ULNA (fig. 22A)

The specimen OCP.DEK/GE 1242 preserves the distal two thirds of a crushed ulna embedded in matrix, including the partially hidden extremitas distalis. Apart from the larger size, the structure of the ulna of Dasornis emuinus is very similar to that of Dasornis toliapica.

RADIUS (fig. 22B–J)

Available material includes the proximal two thirds of a crushed radius embedded in matrix (fig. 22A), the proximal third of the corpus (fig. 22B–E, H–J), plus isolated fragments of corpus (fig. 22G). In dorsal aspect, the distal edge of the caput radii forms a distinct tubercle, but this is uncertain whether this structure is present in Dasornis toliapica. The dorsal extremity of the cotyla humeralis joins the caput radii and the oblique crest of the facies caudalis via a smooth ridge. This structure is not preserved in D. toliapica. Apart from the larger size, the structure of the radius of Dasornis emuinus is very similar to that of D. toliapica.

FEMUR (fig. 23A)

The extremitas proximalis is badly preserved. The caput femoris is distinctly proximal to the plane of the facies articularis antitrochanterica. The proximal part of the crista trochanteris is very feebly developed. The cranial part of the crista trochanteris is low and fairly elongated. A small portion of the corpus is preserved. Its structure is similar to that of the previous species. The linea intermuscularis cranialis is continuous with the distal end of the crista trochanteris.

TIBIOTARSUS (fig. 23B–G)

The distal half of the tibiotarsus including the extremitas distalis and the facies articularis fibulae is preserved. In Dasornis emuinus, the medial tuberositas retinaculi extensori is less sharply defined and the sulcus musculi fibularis extends further proximally than in Dasornis toliapica. Apart from this and the larger size, the morphology of the tibiotarsus is identical in the two species.

FIGURE 17.

A–E. Crania in dorsal view: A. Dasornis toliapica (OCP.DEK/GE 1042); B. Dasornis emuinus (BMNH A3691); C. D. emuinus (OCP.DEK/GE 1004); D. D. emuinus (OCP.DEK/GE 324); E. D. emuinus (D1-0027A). Scale bars equal 10 mm.

FIGURE 18.

Dasornis emuinus, skull. A–D. Crania in caudal view: A. OCP.DEK/GE 1004; B. D1-0027A; C. BMNH A3691; D. BMNH 31929. E, F. Crania in right lateral view: E. D1-0027A; F. reversed OCP.DEK/ GE 1004. Scale bar equals 10 mm.

FIGURE 19.

Crania in ventral view. A–C. Dasornis emuinus: A. D1-0027A; B. OCP.DEK/GE 1004; C. OCP.DEK/GE 324. D. Dasornis toliapica, OCP. DEK/GE 1076. Scale bar equals 10 mm.

FIGURE 20.

A, B. Left middle ear regions: A. Dasornis toliapica (reversed OCP.DEK/GE 1076); B. Dasornis emuinus (OCP.DEK/GE 1004). C, D. Ventral view of left articular surfaces with os quadratum: C. D. toliapica (OCP.DEK/GE 1044); D. D. emuinus (OCP.DEK/GE 1004). E. D. emuinus, caudolateral view of the cavitas cranialis (OCP.DEK/GE 1004). F, G. Regions of the foramen opticum: F. D. toliapica (reversed OCR DEK/GE 1076); G. D. emuinus (D1-0027A). Scale bars equal 10 mm.

FIGURE 21.

A-H. Dasornis emuinus, right humeri: A. reversed OCP.DEK/GE 1237, cranial view; B. OCR DEK/GE 1236, cranial view; C. reversed OCP.DEK/GE 1109, cranial view; D. OCP.DEK/GE 1333, caudal view; E. OCP.DEK/GE 1334, caudal view; F. OCP.DEK/GE 1334, cranial view; G. OCP.DEK/GE 1072, proximal view; H. OCP.DEK/GE 1072, caudal view. Scale bars equal 10 mm.

FIGURE 22.

A. Dasornis emuinus, OCP.DEK/GE 1242, ulna and radius embedded in matrix. B–E. D. emuinus, proximal parts of left radii: B. OCP.DEK/GE 1224, proximal view; C. OCP.DEK/GE 1224, ventral view; D. OCP.DEK/GE 1224, caudal view; E. reversed OCP.DEK/GE 1046, caudal view. F. Dasornis toliapica, OCP.DEK/GE 1212, proximal part of left radius, caudal view. G. D. emuinus, reversed OCP.DEK/GE 1221, fragment of left corpus radii, caudal view. H–J. D. emuinus, proximal parts of left radii: H. reversed OCP.DEK/GE 1046, cranial view; I. OCP.DEK/GE 1224, cranial view; J. OCP.DEK/GE 1224, dorsal view. Scale bars equal 10 mm.

FIGURE 23.

A. Dasornis emuinus, OCP.DEK/GE 1059, proximal end of right femur, cranial view. B-G. Distal parts of right tibiotarsi: B. Dasornis toliapica, MHNL 20-149238, cranial view; C. D. emuinus, OCP.DEK/GE 1123, cranial view; D. D. emuinus, reversed OCP.DEK/GE 534A, cranial view; E. D. emuinus, OCP.DEK/GE 1123, medial view; F. D. emuinus, reversed OCP DEK/GE 534A, lateral view; G. D. emuinus, reversed OCP.DEK/GE 534A, distal view. H. D. emuinus, OCP.DEK/GE 1106, left tarsometatarsus in proximal view. I. D. toliapica, OCP.DEK/GE 1146, distal end of left tarsometatarsus in dorsal view. J–M. D. emuinus, OCP.DEK/GE 1106, complete left tarsometatarsus: J. dorsal view; K. plantar view; L. lateral view; M. medial view. Scale bars equal 10 mm.

TARSOMETATARSUS (fig. 23H–M)

The extremitas proximalis, hypotarsus, and extremitas distalis agree in morphology and size with those of the material described as Neptuniavis miranda by Harrison and Walker (1977: figs. 2, 3) and recently synonymized with Dasornis emuinus by Mayr (2008). The curved line and the scar for the origin of musculus extensor hallucis longus on facies medialis are barely distinct in D. emuinus, in contrast to Dasornis toliapica. Apart from this and the larger size of D. emuinus, the structure of the tarsometatarsus is identical in the two species.

HUMERUS (fig. 24A–I)

The humerus is well preserved, except for the caput, tuberculum dorsale, crista deltopectoralis, and tuberculum ventrale, which are partly damaged. The extremitas distalis is identical to that of Dasornis toliapica. The shallow fossa musculi brachialis is better preserved than in D. toliapica: its ventral edge is straight and its dorsal one is curved. The extremitas proximalis and corpus are similar to those of D. toliapica, but differ from the latter in several important features: the distal almond-shaped foramen pneumaticum of D. toliapica is absent and replaced by a tiny slit. The proximal foramen pneumaticum is larger than in D. toliapica. There is no distinct crista bicipitalis. The intumescentia humeri is displaced proximally and much more prominent. The proximal part of the linea musculi latissimi dorsi is a faint ridge that is continuous with the distal part.

FIGURE 24.

A, I. Dasornis toliapica, OCP.DEK/GE 1194, proximal end of right humerus: A. cranial view; I. caudal view. B–H. Dasornis abdoun, sp. nov., right humeri: B. reversed OCP.DEK/GE 1031, cranial view; C. reversed MHNL 20-149225, cranial view; D. reversed MHNL 20-149225, distal view; E. OCP.DEK/GE 1033, cranial view; F. reversed MHNL 20-149225, caudal view; G. OCP.DEK/GE 1033, caudal view; H. reversed OCP.DEK/GE 1031, caudal view. J–L. D. abdoun, sp. nov., OCP.DEK/GE 1022, two fragments of right ulna: J. distal end in dorsal view; K. distal end in caudal view; L. corpus ulnae in caudal view. M, N. Right ulnae in distal view: M. D. abdoun, sp. nov., OCP.DEK/GE 1022; N. D. toliapica, OCP.DEK/GE 1035. O–R. Distal parts of left radii: O. D. toliapica, reversed OCP.DEK/GE 1118, ventral view; P. D. abdoun, sp. nov., OCP.DEK/ GE 1030, ventral view; Q. D. abdoun, sp. nov., OCP.DEK/GE 1030, dorsal view; R. D. toliapica, reversed OCP.DEK/GE 1118, dorsal view. S–V. Distal parts of left carpometacarpi: S. D. abdoun, sp. nov., OCP.DEK/GE 1121, dorsal view; T. D. abdoun, sp. nov., OCP.DEK/GE 1121, ventral view; U. D. toliapica, reversed OCR DEK/GE 1101, ventral view; V. D. abdoun, sp. nov, OCP.DEK/GE 1121, distal view. W, X. D. abdoun, sp. nov., OCP.DEK/GE 1096, fragment of right corpus femoris: W. cranial view; X. caudal view. Y-AA. Right tibiotarsi: Y. D. abdoun, sp. nov., OCP.DEK/GE 1191, fragment of corpus, cranial view; Z. D. abdoun, sp. nov., OCP. - DEK/GE 1151, fragment of corpus, caudal view; AA. D. toliapica, MHNL 20-149238, proximal end, caudal view. Scale bars equal 10 mm.

ULNA (fig. 24J–N)

Only a short fragment of corpus and the distal end lacking the tuberculum carpale are preserved. The structure is similar to that of Dasornis toliapica. However, Dasornis abdoun differs from the latter in the more prominent papillae remigales. Furthermore, the papillae remigales caudales are smooth and narrow.

RADIUS (fig. 24O–R)

The radius consists of a complete distal half. The structure is similar to that of Dasornis toliapica, but differs from that of the latter in several important features: the corpus is less flattened dorsoventrally; the extremitas distalis is wider; the convexity cranial to the sulcus tendinosus is more prominent and its ventral border is more strongly curved; the margo interosseus shows a marked convexity at the tuberculum aponeurosis ventralis that is absent in D. toliapica; the proximal border of the ligamental prominence (Howard, 1929) is less sinuous; the tubercle above the depressio ligamentosa, close to the margo interosseus, is in more distal and ventral position.

CARPOMETACARPUS (fig. 24S–V)

The extremitas distalis and distal half of os metacarpale majus are preserved. They are similar to those of Dasornis toliapica, except that the os metacarpale majus is more flattened caudocranially.

FEMUR (fig. 24W, X)

A fragment of corpus femoris is preserved. It resembles the corresponding part in Dasornis toliapica in the presence of a distinct triangular facet and the position of the lineae intermusculares plus nutrient foramen.

TIBIOTARSUS (fig. 24Y–AA)

Two caudocranially crushed fragments of corpus are preserved. The proximal one includes a part of the crista fibularis and the distal end of the impressio ligamenti collateralis medialis. The distal one includes the lineae musculi fibularis. The structure is very similar to that of Dasornis toliapica. The crista fibularis is better preserved than in D. toliapica. It is high with a thick margin that is sharply defined caudally.

CRANIUM (fig. 25A, B)

The cranium of Pelagornis/Osteodontornis (see also Olson, 1985: fig. 10; Chavez et al., 2007: fig. 3) differs from that of Dasornis in the following features: the sutura frontoparietalis is more sharply defined; the os frontale is wider in the interorbital region, and the rim of this bone is convex just caudal to the os lacrimale; a large deep impressio glandulae nasalis is present in the mediorostral part of the roof of the orbita; the straight sulcus nervi olfactorii is wider and in lower position.

MAXILLA AND MANDIBULA

The maxilla and mandibula of Dasornis resemble those of other pseudotoothed birds (Spulski, 1910; Lambrecht, 1930; Howard, 1957, 1978; Howard and White, 1962; Hopson, 1964; Howard and Warter, 1969; Harrison and Walker, 1976; Harrison, 1985; Matsuoka et al., 1998; Aslanova and Burchak-Abramovich, 1999; Olson and Rasmussen, 2001; Stidham, 2004; Chavez et al., 2007; Tambussi and Hospitaleche, 2007; Mourer-Chauviré and Geraads, 2008; GoGeometry, 2009). The reconstruction of the maxilla of Dasornis toliapica by Harrison and Walker (1976: fig. 15B) does not agree with that proposed here (fig. 4; see also Bourdon, 2005: fig. 1a). Indeed, the distal end of the maxilla of D. toliapica is very similar to that of Osteodontornis orri (Stidham, 2004) and two less complete and undescribed fragments from the Miocene of Maryland (USNM 237203). Pelagornis/Osteodontornis shows a transverse groove in the dorsal part of the tip of the maxilla (Olson, 1984; Stidham, 2004), which is absent in D. toliapica. In Osteodontornis and Pseudodontornis longirostris, the longitudinal groove of the maxilla is in more dorsal position than in Dasornis, presumably related to the larger toothlike projections and deeper internal grooves (Harrison and Walker, 1976: 39). In P. longirostris and Neodontornis, the central palatal ridge is strongly convex and more prominent than in Dasornis (Harrison and Walker, 1976: figs. 20, 21A), a feature that is also possibly related to the large pseudoteeth and deep internal grooves. An undescribed specimen (USNM 335463) from the Miocene of Oregon that most probably belongs to the Pelagornis/Osteodontornis assemblage shows the same features (EB, personal obs.). In D. toliapica, the caudal end of the longitudinal groove of the mandibula curves dorsally toward the zona flexoria intramandibularis caudalis, whereas this is not the case in Osteodontornis (Harrison and Walker, 1976: figs. 15, 32). The pseudoteeth of D. toliapica are smaller than in the other odontopterygiform genera, and also exhibit a distinctive forward slant (fig. 4A, G, I). We are not convinced, however, that the pseudotooth arrangement can be a good discriminating feature (e.g., Harrison and Walker, 1976: fig. 25). Even the forward orientation of the pseudoteeth in D. toliapica must be taken with caution, since these processes seem vertical in the distal end of the maxilla of this species (fig. 4H).

FIGURE 25.

A, B. Crania in left lateral view: A. cf. Pelagornis (USNM 335463); B. Dasornis toliapica (OCP.- DEK/GE 1194). C–E. Proximal parts of left humeri in caudal view: C. Pelagornis sp. (USNM 425111); D. cf. Pelagornis (USNM 335794); E. D. toliapica (reconstructed after OCP.DEK/GE 1229 and MHNL 20-149229). F–H. Proximal parts of left humeri in cranial view: F. D. toliapica (reconstructed after OCP.DEK/GE 1116, OCP.DEK/GE 1229, and MHNL 20-149229); G. cf. Pelagornis (USNM 335794); H. Pelagornis sp. (USNM 425111). I–L. Distal ends of right humeri: I. Pelagornis miocaenus (uncataloged holotype, MNHN), dorsal view; J. D. toliapica (MHNL 20-149214), dorsal view; K. Osteodontornis (LACM 128423), cranial view; L. D. toliapica (MHNL 20-149214), cranial view. M–P. Proximal extremities of left ulnae: M. cf. Pelagornis (LACM 128462 [initially referred to Argillornis]), cranial view; N. D. toliapica (BMNH A224), cranial view; O. cf. Pelagornis (LACM 128462), proximal view; P. D. toliapica (BMNH A224), proximal view.

PTERYGOIDEUM

The structure found in Pelagornis (Olson and Rasmussen, 2001: specimen USNM 425110 figured in pl. 11d; Mourer-Chauviré and Geraads, 2008) is similar to that of Dasornis toliapica BMNH 44096 (Harrison and Walker, 1976: pl. 2K–M). Pelagornis sp. (Olson and Rasmussen, 2001: specimen USNM 425110 figured in pl. 11d) differs from the latter in the following features: the articulatio pterygopalatina is only slightly concave and bears a pointed process (see also Mourer-Chauviré and Geraads, 2008: 181), whereas it is strongly concave and devoid of a sharp process in D. toliapica; the facies articularis parasphenoidalis is large, oval, and sessile, whereas it is pedunculate in D. toliapica; the corpus shows a stronger widening toward the processus quadraticus; the dorsal flange of the corpus is more developed than in D. toliapica. Except for the articulatio pterygopalatina, the pterygoideum of Pelagornis mauretanicus (Mourer-Chauviré and Geraads, 2008) is distinct from that of Pelagornis sp. (USNM 425110) and superficially similar to that of D. toliapica, because it exhibits a slender corpus and a pedicellate facies articularis parasphenoidalis.

QUADRATUM

The quadratum of Dasornis toliapica (Harrison and Walker, 1976: pl. 1) closely resembles that of Pelagornis/Osteodontornis (Ono, 1989: fig. 1; Olson and Rasmussen, 2001: pl. 11f; Mourer-Chauviré and Geraads, 2008: figs. 4, 6). The latter differs from the former in having a flatter caudal facies of the corpus, a more prominent condylus pterygoideus, and a more rounded and sharply defined capitula.

HUMERUS (fig. 25C–L)

The humerus of Pelagornis/Osteodontornis differs from that of Dasornis in many features: the cranial prominence of the caput humeri is wider, protrudes further cranially, and has a straight abrupt distal border; the caudal prominence of the caput humeri is higher and tapers far distally; the latter structure is smooth at the distal end and has sharp lateral and medial borders; the incisura capitis is deeper and much wider; the tuberculum dorsale is wide and protrudes proximally to the level of the caput; it forms a distinct surface that faces caudolaterally and that is continued by a tapering ridge; finally, it is separated from the caput by a marked depression; the crista deltopectoralis begins very far distal to the tuberculum dorsale and makes an angle at each extremity; the crista bicipitalis is replaced by a flat prominence located in the medial part of the planum intertuberculare, just proximal to the crista deltopectoralis; the sulcus transversus is wider, shorter, and shallower; there is a sharp process that lies on the proximal border of the sulcus transversus, between the caput humeri and the tuberculum ventrale; the intumescentia humeri is exceedingly small, with no distal and dorsal extension, so that the planum intertuberculare is flat; the fossa pneumotricipitalis is apneumatic and the crus ventrale fossae is nearly straight; the area of insertion of musculus scapulohumeralis caudalis is a flat facet facing ventrally; the margo caudalis is lower in the region of the fossa tricipitalis; the linea musculi latissimi dorsi is straighter and less distinct; the epicondylus dorsalis is oval and more prominent; a furrow delimits the latter proximally and cranially; the distal part of the ridge that delimits the two fossae for origin of musculus extensor carpi ulnaris is not distinctly separated from the condylus dorsalis.

FIGURE 26.

A, B. Distal ends of right ulnae in ventral view: A. cf. Pelagornis (USNM 335794); B. Dasornis toliapica (MHNL 20-149218). C–F. Proximal ends of left radii: C. Pelagornis sp. (USNM 183512), proximal view; D. Dasornis emuinus (reversed OCP.DEK/GE 1224), proximal view; E. Pelagornis sp. (USNM 183512), caudal view; F. D. emuinus (reversed OCP.DEK/GE 1224), caudal view. G–J. Right tarsometatarsi: G. cf. Pelagornis (reversed USNM 237200), proximal view; H. D. emuinus (reversed OCP.DEK/GE 1106), proximal view; I. Osteodontornis (LACM 128424), dorsal view; J. D. emuinus (reversed OCP.DEK/GE 1106), dorsal view. K–O. Left carpometacarpi: K. Osteodontornis orri (LACM 53906), ventral view; L. D. toliapica (OCP.DEK/GE 1152), ventral view; M. D. toliapica (OCP.DEK/GE 1139), ventral view; N. O. orri (LACM 53906), caudal view; O. D. toliapica (OCP.DEK/GE 1152), caudal view. Scale bars equal 10 mm.

ULNA (fig. 25M–P, 26A, B)

The ulna of Pelagornis/Osteodontornis (see also Chavez et al., 2007) differs from that of Dasornis in many respects: the cotyla ventralis is larger and makes an angle far ventral to the olecranon; the olecranon is not prominent; the tuberculum ligamenti collateralis ventralis does not extend as far distally and forms a flat surface; the corpus ulnae is stouter with a sharper margo cranialis. The extremitas distalis ulnae of an undescribed specimen of Pelagornis sp. (USNM 335794) is distinct from that of Pelagornis mauretanicus (Mourer-Chauviré and Geraads, 2008: 183), especially concerning the aspect of the tuberculum carpale. The extremitas distalis ulnae of Pelagornis, however, differs from that of Dasornis in that the condylae end very sharply proximo caudally, and at the same level.

Goedert (1989) tentatively assigned the late Eocene specimen LACM 128462 from Oregon (fig. 25M, O) to the genus Argillornis, which is now synonymized with Dasornis (Mayr, 2008). However, this ulna matches well with that of Pelagornis/Osteodontornis in the morphology of the cotyla ventralis, tuberculum ligamenti collateralis ventralis, and corpus. Thus, this specimen is regarded as belonging to Pelagornis.

RADIUS (fig. 26C–F)

In Pelagornis/Osteodontornis, the extremitas proximalis radii is well preserved in USNM 183512 (fig. 26C, E), and the proximal part is badly preserved in LACM 127875. These specimens differ from Dasornis in several features: the cotyla humeralis is oval in shape and less caudocranially flattened; its ventral overhang is less prominent and proximodistally longer; there is no ridge joining the dorsal extremity of the cotyla humeralis and the caput radii, which is more prominent; the oblique crest that continues the caput radii on the facies caudalis is less prominent in its distal part; the caudal edge of the tuberculum bicipitale is more prominent. The extremitas distalis radii is partially visible in Pelagornis mauretanicus (Mourer-Chauviré and Geraads, 2008: 183): it differs from Dasornis in the more angular ligamental prominence (Howard, 1929) and in the lower convexity cranial to the sulcus tendinosus.

CARPOMETACARPUS (fig. 26K–O)

The proximal part of carpometacarpus of Osteodontornis orri (fig. 26K, N) described by Howard (1978) markedly differs from that of Dasornis in several features: the os metacarpale alulare is much longer; the processus pisiformis is larger, blunter, and more rounded in shape; a large pneumatic foramen occupies most of the fossa infratrochlearis; the symphysis of os metacarpale minus and os metacarpale majus is longer (also seen in Pelagornis mauretanicus; Mourer-Chauviré and Geraads, 2008); distal to this symphysis, the os metacarpale minus is pressed against the os metacarpale majus, so that the spatium intermetacarpale is absent; the proximal part of the os metacarpale minus does not show any ventral tubercle; the fovea carpalis caudalis is larger and interrupts the caudal extremity of the trochlea carpalis; the facet for ligamentum radiocarpo -metacarpale dorsale is less distinct.

FEMUR

The femur of Pelagornis/Osteodontornis differs from that of Dasornis in several features: the corpus is shorter and stouter; the triangular facet is smaller; the linea intermuscularis caudalis is indistinct proximal to the triangular facet; the tuberculum musculi gastrocnemialis lateralis is less prominent and in more lateral position; a small depression that is absent in Dasornis toliapica delimits the tuberculum musculi gastrocnemialis lateralis caudally; the sulcus patellaris is shallower, and the cristae sulci patellaris are less prominent.

TIBIOTARSUS

The tibiotarsus of Pelagornis/Osteodontornis differs from that of Dasornis in several features: the condylus medialis is shorter with a more rounded distal margin; the epicondylus medialis is more proximodistally developed; the cristae trochleae are more prominent; the sulcus musculi fibularis faces cranially and has a higher lateral border; the lateral tuberositas retinaculi extensori is oval and medially displaced, and the pons supratendineus is narrower.

TARSOMETATARSUS (fig. 26G–J)

The tarsometatarsus of Pelagornis/Osteodontornis differs from that of Dasornis in many features: the sulcus ligamentosus is wider and deeper; the eminentia intercotylaris is wider; the hypotarsus shows two canales hypotarsi; the crista lateralis hypotarsi forms a distinct flat surface facing laterally; an oblique groove extending from the base of the hypotarsus through the cotyla lateralis is present; the corpus tarsometatarsi is shorter, stouter, and dorsoplantarly compressed, so that its transverse section is rectangular; the zone between the crista medianoplantaris and the crista plantaris lateralis forms a longitudinal groove; the fossa metatarsi I is deep (best visible in LACM 128422); the trochlea metatarsi II is less displaced proximally, and is bounded plantaroproximally by a distinct oval depression; the external edges of trochleae metatarsi II and IV are more prominent; the trochlea metatarsi III is not dorsally elevated, so that the surface above the trochleae is flatter; in dorsal aspect, the foramen vasculare distale is smaller and not prolonged proximally by a deep groove; the plantar opening of the foramen vasculare distale is larger.

TAXONOMIC AND NOMENCLATURAL CONSIDERATIONS

The abundance of the collected material offers insight into intraspecific size and shape variation of early odontopterygiform species (tables 1, 2; figs. 3–24), especially in Dasornis toliapica, which is the most common species found in the Moroccan phosphates. For instance, some cranial structures (e.g., the condylus occipitalis and processus medialis parasphenoidalis) vary in shape and dimension in D. toliapica. These structures, however, show some variability within examined species of extant birds (E.B., personal obs.). Thus, we could not provide convincing evidence for more than three species in the Moroccan phosphates, which are distinguished from one another mainly by size. Some cranial structures also differ between the London Clay and Ouled Abdoun specimens of the two larger Dasornis species, such as the shape of the foramen magnum, processus rostropterygoideus, and foramina for exit of the cranial nerves (table 1; figs. 3, 4, 6, 18, 19; see also Harrison and Walker, 1976: pl. 1, fig. C; pl. 3, fig. D). However, these features are variable within extant species, and cannot be sufficient to erect two new species for the larger Moroccan fossils.

Most Moroccan specimens are crushed or flattened to varying extent. Compared with the London Clay specimens, the crania show a more or less important degree of dorsoventral flattening (table 1). The undistorted aspect of the braincase of D. toliapica may be found in OCP.DEK/ - GE 1042, which is enclosed in a very hard, silicified nodule (figs. 3–6). In BMNH 44096, the braincase is slightly bent downward, and this results in the following features: the fossa subtemporalis extends less dorsally than the area of origin of musculus adductor mandibulae externus pars articularis (fig. 5), the foramen magnum faces slightly ventrally (fig. 3), and the laterosphenoid hollow faces rostrally (fig. 6). These features are probably due to preservation and thus cannot justify the definition of a new Moroccan species comparable in size to D. toliapica.

Taking into account intraspecific variability in size and morphology as well as distortion, we adopt here a conservative taxonomy. A large part of the fossils described herein are assigned to D. toliapica (Owen, 1873) and Dasornis emuinus (Bowerbank, 1854), which were previously known from the Lower Eocene London Clay of Sheppey (Harrison and Walker, 1976; Mayr, 2008). A few Moroccan remains are assigned to a new, smaller species of Dasornis.

Previous taxonomists often proposed new names for very incomplete (e.g. Harrison and Walker, 1976; Harrison, 1985; Averianov et al., 1991) or badly crushed (Aslanova and Burchak-Abramovich, 1982) odontopterygiform specimens. Harrison and Walker (1976) defined no fewer than 11 species, 9 genera, and 4 families inside the Odontopterygiformes, without convincing justification (Olson, 1985; Mayr, 2008). The Ouled Abdoun specimens provide a considerable amount of new morphological information concerning the morphology of early odontopterygiforms. On this basis, we revise the “over split” taxonomy of the London Clay odontopterygiforms proposed by Harrison and Walker (1976) and partly simplified by Mayr (2008). We propose that the two species from the Paleogene of England and Morocco are congeneric, the name Dasornis having priority over the name Odontopteryx.

Owen (1873) first described Odontopteryx toliapica in 1873 on the basis of a single incomplete skull. Lydekker (1891) referred a proximal end of ulna and a proximal end of tarsometatarsus to this species, and these were later figured by Lambrecht (1933). Harrison and Walker (1976) redescribed O. toliapica and referred a second incomplete skull to this species. These authors did not retain the tarsometatarsus with the material of O. toliapica (Harrison and Walker, 1976, 1977). They referred this specimen to a new species, Neptuniavis minor, because “the tarsometarsus is much too large and has procellariiform characters only” (Harrison and Walker, 1977). Both the morphology and size of this proximal tarsometatarsus, however, fit with the new Moroccan specimens referred to D. toliapica (table 2). On the basis of these new data, N. minor Harrison and Walker, 1977, is synonymized with D. toliapica (Owen, 1873). Harrison and Walker (1977) also attributed a distal end of femur to N. minor, because this specimen “would appear to be the size and character that might be expected for this species.” However, we refrain from assigning it to D. toliapica because we were unable to examine this femur, which is neither figured nor precisely described in Harrison and Walker (1977).

The cranium BMNH Al initially described as Macrodontopteryx oweni by Harrison and Walker (1976) matches well with D. toliapica and its size corresponds to that of the largest individuals of this species (table 1). BMNH Al differs from D. toliapica in the following features: the groove that continues the foramen orbitale is oriented slightly dorsally (Harrison and Walker, 1976: pl. 4, fig. E); the processus rostropterygoideus is oriented more laterally; the dorsal edge of the fonticulus interorbitalis is straight and makes an angle with the rostral one; the dorsal corner of the foramen opticum is confluent with a large fonticulus orbitocranialis. These small differences are most probably due to individual variation and are not sufficient to justify the placement of BMNH Al in a separate genus and species. Thus, M. oweni Harrison and Walker, 1976, is regarded here as a junior synonym of D. toliapica (Owen, 1873).

Most recently, Mayr and Smith (2010) described new odontopterygiform remains from the Middle Eocene of Belgium. The sternum, pectoral girdle bones, and humeri of a single individual were tentatively assigned to M. oweni, and an incomplete humerus was tentatively identified as D. emuinus. A preliminary comparison with the material described here shows that the two Belgian species are distinct from D. toliapica and D. emuinus (see above). Because we were unable to examine the Belgian specimens, it is uncertain whether these can be confidently assigned to the genus Dasornis.

While comparing other pseudotoothed birds with Dasornis, we found that there were no differences between the genera Pelagornis and Osteodontornis Howard, 1957, and we regard all the Pelagornis and Osteodontornis specimens as pertaining to a single taxonomic entity, which corresponds to the Pelagornis morphotype. Osteodontornis is most probably a junior synonym of Pelagornis, but this synonymy cannot be established without a complete revision of the Odontopterygiformes.

As shown above, Pelagornis markedly differs from Dasornis in skeletal characters of the skull, forelimb, and hind limb. Despite this, we have chosen to place these genera in one single family, Pelagornithidae, rather than maintaining the two families Pelagornithidae and Odontopterygidae. The reason for this is that oversplit taxonomy often complicates the assignment of new specimens to the family level, especially when most species are based on very fragmentary fossils, as is the case for Odontopterygiformes. Indeed, aside from Dasornis and Pelagornis, odontopterygiform specimens were given a variety of names, such as Cyphornis magnus Cope, 1894, Gigantornis eaglesomei Andrews, 1916, Palaeochenoides miocaenus Shufeldt, 1916, Tympanonesiotes wetmorei Hopson, 1964, Neodontornis stirtoni (Howard and Warter, 1969), Caspiodontornis kobystanicus Aslanova and Burchak-Abramovich, 1982, and no fewer than four species assigned to the genus Pseudodontornis Lambrecht, 1930 (Spulski, 1910; Harrison and Walker, 1976; Harrison, 1985; Averianov et al., 1991). Whether some or all of these names are actually synonymous with either Dasornis or Pelagornis must await a thorough taxonomic revision of the group. At present, the number of species assigned to the Odontopterygiformes remains uncertain, but it is obvious that the number of names proposed in the literature exceeds the number of taxa. However, we maintain the pseudotoothed birds in the Odontopterygiformes, because of their sister-group relationship with Anseriformes (Bourdon, 2005), combined with a highly specialized morphology, which diverges greatly from that of ducks and allies.

PALEOECOLOGY AND PALEOENVIRONMENT OF DASORNIS

The Ouled Abdoun phosphatic deposits correspond to an epicontinental sea that communicated to the West with the Atlantic Ocean (Salvan, 1986; Herbig, 1991; Trappe, 1991). The strong concentration of phosphates in the Moroccan phosphate sea permitted the preservation of an exceptionally rich fauna. Upper Paleocene and Lower Eocene deposits have yielded a huge amount of marine vertebrates (e.g., Arambourg, 1952; Noubhani and Cappetta, 1997; Jalil et al., 2006; Jouve et al., 2008), including seabirds (Bourdon et al., 2008a, 2008b; this study). The strong condensation of the phosphate series in the northeastern margin of the basin indicates the proximity of the shore and is in accordance with the presence of mammals (Gheerbrant et al., 2006; Gheerbrant, 2009; Solé et al., 2009).

The species of Dasornis, especially the two larger ones, are very common in the level “Intercalary beds II/I” made of hard phosphatic limestone and dated as lowermost Eocene (fig. 2). This suggests that these seabirds formed large breeding colonies near the shore of the northeastern part of the Ouled Abdoun Sea, some 55 million years ago, as has been hypothesized for the extinct tropicbird Lithoptila abdounensis (Bourdon et al., 2008b). Upwellings on the Atlantic margin permitted the formation of Moroccan phosphatic deposits (Lucas and Prévôt-Lucas, 1995). Low-latitude upwelling zones are among the most productives (Ashmole, 1971), and this may have favored the occurrence of vast seabird breeding colonies.

A large part of the collected specimens are isolated bones, which suggests a postmortem dispersion of bones, with a possible role of marine predators. An important size variation is observed in the postcranial material and skulls referred to Dasornis toliapica (tables 1, 2). The smallest Moroccan specimens approximated the size of BMNH 44096 and corresponded to a bird with a 2 m wingspan (that of a small albatross, e.g., Diomedea nigripes). The medium-sized specimens, which are the most common, reached a wingspan of around 2.5 m (that of a medium-sized albatross, e.g., Diomedea cauta). The largest individuals had a wingspan of about 3 m (that of a large albatross, e.g., Diomedea epomophora). The largest specimens are thus approximately 1.5 times larger than the smallest ones. Because these seabirds probably formed large breeding colonies, it is likely that some fragments of long bones pertain to juvenile specimens. Nevertheless, well-preserved specimens belong to adult individuals: epiphyses are fully ossified and sutures are obliterated in available skulls, except for the sutura frontoparietalis (see above).

The presence of several closely related species living in the same environment cannot be excluded given the material at hand. The largest individuals (around 3 m wingspan) could be assigned to Dasornis oweni (Harrison and Walker, 1976), initially described as Macrodontopteryx oweni by Harrison and Walker (1976) and synonymized here with D. toliapica. However, skeletal morphology does not provide evidence for the presence of two species within the D. toliapica complex (see above). Secondly, the sizes of braincases and most long bones are continuous between the smallest and the largest specimens, which renders the distinction of two species arbitrary (tables 1, 2). In addition, individual variation and sexual dimorphism can explain size disparity among adults. An important size variation is found, e.g., in Anseranas semipalmata (wingspan 125–180 cm, ratio 1.44), Diomedea exulans (wingspan 254–351 cm, ratio 1.38) or Pelecanus onocrotalus (wingspan 226–360 cm, ratio 1.59) (del Hoyo et al., 1992). Sexual size dimorphism is well known in seabirds, and has been linked to a variety of factors such as sexual selection (Serrano-Meneses and Székely, 2006).

Dasornis emuinus is distinctly larger in size than D. toliapica (tables 1, 2). The wingspan of the smallest individuals is approximately 3.5 m, equaling that of a large individual of D. exulans (see above). The wingspan of the largest individuals approximates 4.5 m, which is smaller than the estimated winspan for Osteodontornis orri (5.5 to 6 m; Olson, 1985). Size variation is less important than in D. toliapica, since the largest specimens are approximately 1.3 times larger than the smallest ones. This may be explained by a variety of factors, including sampling bias and relative scarcity of D. emuinus with respect to D. toliapica. Dasornis abdoun is much smaller is size than D. toliapica, and constitutes the smallest species of pseudotoothed bird ever discovered. The estimated wingspan is 1.5 to 1.7 m, which is comparable to that of a Northern Gannet (Sula bassana).

The morphology of the humerus in Dasornis strikingly differs from that of Pelagornis/ Osteodontornis (fig. 25C–L). In Pelagornis, the morphological peculiarities of the humerus that are supposedly related to gliding flight are more pronounced than in Dasornis: the caput humeri is caudocranially wider; the tuberculum dorsale and tuberculum ventrale are more prominent and in more proximal position; the crista deltopectoralis is somewhat square in outline and located far distally from the caput. The Pelagornis sternum (Mayr et al., 2008) exhibits a more derived morphology than a sternum putatively assigned to Dasornis (Mayr and Smith, 2010): it is strongly vaulted and the carina sterni shows a marked cranial projection for the articulation with the furcula. These features probably reduced loadings linked to gigantic size and sustained gliding flight (Mayr et al., 2008). Moreover, Pelagornis had relatively shorter and stouter legs than Dasornis (especially concerning the tarsometatarsus; fig. 26I, J), and was possibly more clumsy on land. Altogether, these differences suggest that Dasornis was less narrowly specialized for soaring flight than Pelagornis. Pseudotoothed birds pertaining to the Dasornis morphotype were more generalists and could probably use flapping flight, even if limited. In contrast, the Pelagornis morphotype included exceedingly specialized gliders which were most likely unable of sustained flapping flight and relied almost entirely on winds to provide lift (Olson, 1985).

Our work provides evidence that Dasornis was widespread by the Lower Paleogene, as it is currently known from the Lower Eocene of England (Harrison and Walker, 1976; Mayr, 2008) and Upper Paleocene/Lower Eocene of Morocco (this study). Nessov (1992: fig. 5O, P) described a distal end of ulna from the Upper Paleocene of Kazakhstan. This author suggested anseriform affinities for this ulna, but comparison with our material shows that it belongs to Dasornis. The size of the Kazakhstanish ulna matches well with the smallest species described from the Moroccan phosphates, D. abdoun, but the latter is represented by too fragmentary material to allow direct comparison. Fragmentary specimens of Odontopteryx (a junior synonym of Dasornis) have been described from the Lower Eocene of North America (Olson, 1999) and Middle Eocene of Mexico (González-Barba et al., 2002), but these records are tentative. In the current state of knowledge, Middle Eocene remains from Belgium recently described by Mayr and Smith (2010) cannot be assigned confidently to Dasornis (see above). D. toliapica and D. emuinus were present in both the Moroccan phosphates and the London Clay by the Lower Eocene, which is congruent with their paleoecology: both species were pelagic feeders specialized for gliding flight, and could disperse on large territories like extant albatrosses (Diomedeidae). Interestingly, prophaethontid remains have been recorded from exactly the same Lower Paleogene localities as Dasornis (Bourdon et al., 2008b).

The Lower Eocene London Clay Formation of southeast England is a succession of marine silty clays and sandy silts that constitute a remnant of a larger depositional area covering much of the North Sea in the early Tertiary (King, 1981; Allison, 1988). Numerous plant remains indicate a subtropical to tropical climate (Reid and Chandler, 1933; Collinson, 1983; Collinson and Hooker, 1987; Poole, 1993). Upper Paleocene deposits from Kazakhstan formed in a shallow bay with a high biological productivity that was connected with upwelling processes (Nessov, 1992). The climate of the Zhylga locality was humid and nearly tropical, with forests and small freshwater or brackish water bays near the shore (Nessov, 1992). Some studies suggest a warm, humid climate and tropical forests near the shore of the Moroccan phosphate sea (Boureau, 1951; Herbig and Gregor, 1990). This is compatible with the discovery of various folivorous mammals such as proboscideans and hyracoids (Gheerbrant et al., 2003; Gheerbrant, 2009). Moreover, a palynological study of the Moroccan phosphates has shown the uniformity of Moroccan and European floras in the Paleocene and Lower Eocene (Ollivier-Pierre, 1982). In sum, paleoenvironmental studies show that the Ouled Abdoun, London Clay, and Zhylga marine deposits formed in a tropical climate. This is congruent with the fact that avian taxa nowadays restricted to the intertropical zone were found in northern Europe in the Lower Paleogene, as exemplified by the avifaunas from the London Clay and Fur Formation (Dyke, 2001; Kristoffersen, 2001; Dyke and Van Tuinen, 2004; Mayr, 2005, 2009; Lindow and Dyke, 2006; Waterhouse et al., 2008). This could also explain the occurrence of both Dasornis and prophaethontids in all three Paleogene localities.