Etymology: In reference to the extant genus Barbourula, associated with the prefix eo-, from Greek eus, dawn; referring to the age of the taxon.

Type species: Eobarbourula delflnoi sp. nov.; see below.

Diagnosis.—As for the monotypic type species.

Etymology: Named for Italian paleontologist Massimo Delfino, who alerted us to the presence of a particular articulation similar to a zygosphene-zygantrum complex on the vertebrae of this taxon.

Holotype: GU/RSR/VAS 5001 (Fig. 2A), nearly complete left ilium.

Type locality: Vastan Lignite Mine, Surat District, Gujarat, India.

Type horizon: Cambay Shale Formation, middle Ypresian, lower Eocene.

Referred material.—58 ilia: GU/RSR/VAS 5002 (Fig. 2B), GU/RSR/VAS 5003 (Fig. 2C), GU/RSR/VAS 5004–5059; 129 vertebrae: GU/RSR/VAS 5060–5065 (Fig. 4A–F), GU/ RSR/VAS 5066–5188; and 12 urostyles: GU/RSR/VAS 5189 (Fig. 4G), GU/RSR/VAS 5190–5200.

Diagnosis.—Differs from the other Bombinatoridae by having less laterally expanded sacral diapophyses on the vertebrae (antero-posterior/lateral length ratio, 1.1) and by having the tuber superius more developed dorsally, more asymmetric in lateral view and placed more anteriorly compared with the acetabulum. Differs further (in adults) from Bombina by being about twice as large, and by having a tuber superius situated anteriorly to the acetabulum; from Barbourula by being 1.5 times smaller and in having a more developed tuber superius.

Description.—In lateral view, the iliac shaft is almost straight and lacks a dorsal crest (Fig. 2A). The tuber superius is a long, prominent, asymmetric and slightly anterodorsally oriented tubercle, anteriorly situated with respect to the acetabulum (Fig. 3D). The junction between the acetabular area and the shaft is only slightly constricted. There is no subacetabular or supraacetabular fossa. The pars ascendens is short and posteriorly oriented. It forms an open angle (about 160°) with the tuber superius. The pars descendens is slightly developed and is obscured by the large acetabulum, which extends onto the pars descendens ventrally. The acetabulum is deep, slightly bell-shaped and bordered by a sharp rim. A shallow but well-marked protuberance is present near the anterior border of the acetabulum. In medial view, the acetabular area is bordered by shallow ridges. Between them, a triangular and medially prominent interiliac tubercle is developed. In dorsal view, the medial part of the acetabular area is prominent and the tuber superius projects laterally. This general shape is also visible on specimens that are nearly half the size of the first specimens (Fig. 2C). However, in lateral view, they differ from the first specimens by both less well-marked tuber superius and weaker protuberance near the anterior border of the acetabulum. The junction between the acetabular area and the shaft is slightly more constricted. In medial view, the interiliac tubercle is less developed. In dorsal view, the tuber superius is less laterally projected (Fig. 2A₄, B₄, C₄). Other specimens with the same morphology and presenting intermediate sizes between these two extreme sizes (Fig. 2B) are attributed to the same single taxon.

The vertebrae (Fig. 4) are imbricate (the elongate posterior part of the neural arch overlaps the anterior border of the subjacent vertebra like tiles on a roof), opisthocoelous, and present a particular articulation similar to the zygosphene-zygantrum complex of snake vertebrae (Fig. 5). The zygosphene-zygantrum articulation was defined by Romer (1956) as an accessory articulation composed of a dorsally tapered wedge of bone bearing articular surfaces on either side (zygosphene) that projects forward from the neural arch into a corresponding wedge-shaped cavity (zygantrum). However, on the Vastan specimens, the structure resembling the zygosphene looks like a pair of anterior processes separated by a notch and well differentiated from the neural arch (Fig. 5A) and the zygantrum is the corresponding cavity (Fig. 5B). Such a structure can also be found in the anuran Bombina, the salamander Salamandrina and some lacertilians such as lacertid, teiid, and cordylid lizards (Sanchìz 1988). A similar structure, the hyposphene-hypantrum complex, is also present in some dinosaurs and on cervical vertebrae of primitive birds (Rauhut 2003). The atlas of the Vastan taxon is fused with V2 and presents two large reniform cotyles narrowly separated and forming two distinct articular surfaces. This morphology is characteristic of type II of Lynch (1971). Posteriorly, a zygantrum-like cavity is slightly developed on V2, and the neural arch is postero-dorsally elongated and ends with three expansions or spikes, the medial one being the spinous process, and the two lateral expansions being the postzygapophyses (Fig. 4A₃-A₅). From the atlas to the fourth vertebra (Fig. 4B, C), the neural canal decreases in diameter, the transverse processes become more strongly developed, and the neural arch becomes flatter but is posteriorly well developed, presenting an acute spinous process. The neural arches of the other vertebrae up to the sacral are shorter posteriorly and become more rectangular in dorsal view (Fig. 4D, E). The sacral vertebra is biconvex and the sacral diapophyses are dorsoventrally flattened and moderately expanded laterally (Fig. 4F₄). The urostyle presents an anterior cotyle, a low dorsal crest, and two laterally and slightly anteroposteriorly elongated transversal processes (Fig. 4G; see Table 1).

Discussion.—All the bones described above are grouped together based on their morphology, size and relative abundance. The small form of ilium (Fig. 2C) is here interpreted as a juvenile stage of the larger form (Fig. 2A). Ilia of intermediate size, such as GU/RSR/VAS 5061 (Fig. 2B), are also present, supporting the interpretation of these as ontogenetic stages of the same species. The morphological characters of all these ilia are the same, with the exception of the tuber superius, which shows ontogenetic variability by being better developed and slightly inclined laterally in adult forms than in the juvenile forms, as can be seen in the posterior view of GU/RSR/VAS 5060 (Fig. 2A₄, B₄, C₄).

The presence of an open angle between the tuber superius and the pars ascendens (Rage and Hossini 2000) and. the imbricate vertebrae indicate that the Vastan taxon belongs to “Archaeobatrachia” and/or “Mesobatrachia” because they are only known in these groups (Prasad and Rage 2004). However, it does not belong to the most common “Discoglossus group”, including the genera Discoglossus, Eodiscoglossus, Paradiscogloss us, Latonia, and Paralatonia (Duffaud and Rage 1999; Rage and Hossini 2000) because the Vastan taxon lacks the dorsal crest on the iliac shaft (Rage and Hossini 2000) and the bicondylar sacro-urostylar articulation (Clarke 1987). It is similar to gobiatids, including the ilium attributed to ?Gobiatinae from the Late Cretaceous intertrappean beds of Naskal, India (Prasad and Rage 2004: fig. 1D), in having an asymmetric tuber superius (Roček and Nessov 1993: fig. 25). However, gobiatids present an acetabulum not extending over the pars descendens on the ilium and amphicoelous vertebrae (Roček and Nessov 1993; Prasad and Rage 2004), whereas the Vastan species presents a ventrally extensive acetabulum that obscures the pars descendens on the ilium and has opisthocoelous vertebrae.

Within the Discoglossoidea, the Vastan species closely resembles the Bombinatoridae. This family includes only the genera Bombina and Barbourula (Cannatella 2007). The presence of an articulation similar to a zygosphene-zygantrum complex and an interiliac tubercle are resemblances to Bombina (Sanchìz 1988; Gardner et al. 2010). However, in Bombina orientalis and Bombina bombina, the tuber superius is situated above the acetabulum (the anterior border of the acetabulum extends further to the anterior border of the tuber superius; Nokariya 1983a; Gardner et al. 2010; Fig. 3A, B), than in E. delfinoi in which case the anterior border of the acetabulum reaches only a third to a half of the length of the tuber superius (Fig. 3D). Moreover, the adult size of the ilium of E. delfinoi, measured at the level of the posterior suture with the ischium and pubis, is about twice that of B. orientalis (Nokariya 1983a) or B. bombina (Gardner et al. 2010). Little osteological information is available about the extant genus Barbourula. The Vastan specimens are close to Barbourula busuangensis in the general shape of the ilia and vertebrae (Clarke 1987; Přikryl et al. 2009). Indeed, both taxa have an ilium without a dorsal crest, a long prominent tuber superius, imbricate and opisthocoelous vertebrae, neural spines decreasing posteriorly in height, a monocondylar sacro-urostylar articulation, and a pair of well-developed transverse processes on the urostyle. However, the ilia of adult E. delfinoi are about 1.5 times smaller than those of B. busuangensis (Clarke 1987). Finally, the Vastan bombinatorid differs from both Bombina and Barbourula in having the tuber superius situated above the acetabulum (the anterior border of the acetabulum extends further to the anterior border of the tuber superius; Nokariya 1983a; Gardner et al. 2010; Fig. 3A–C), than in E. delfinoi in which case the anterior border of the acetabulum reaches only a third to a half of the length of the tuber superius (Fig. 3D). Moreover, in E. delfinoi, the tuber superius is more developed dorsally and more asymmetric in lateral view on the ilium and have sacral diapophyses that were likely less dilated laterally, like butterfly wings, than in Bombina and Barbourula (Clarke 1987; Gardner et al. 2010; Přikryl et al. 2009; Nokariya 1983a). In Barbourula busuagensis (Clarke 1987), the ratio of antero-posterior to lateral length in the sacral diapophyses is 2.1; in Bombina Orientalis (Nokariya 1983a), the ratio is 2.2, and in E. delfinoi, 1.1. Based on these comparisons, the Vastan taxon closely resembles the extant genus Barbourula.

The morphologies of the ilia and vertebrae correspond also exactly to those described from Vastan by Bajpai and Kapur (2008) as Discoglossidae indet. Indeed, the ilia IITR/SB/ VLM-LV/203-204 show the tuber superius as a swelling of the dorsal margin of the iliac shaft, the ventral margin of the acetabulum overhanging the pars descendens, and medially, the ilium bears an interiliac protuberance. The vertebra IITR/ SB/VLM-LV/208 is similar to the anterior trunk vertebra VAS 5061 in being opisthocoelous, bearing a dorso-ventrally flattened centrum, and presenting three posterior spikes on the neural arch. The same may be concluded for ilium IITR/SB/ VLM-LV/209 described from Vastan by Bajpai and Kapur (2008) and attributed to Leptodactylidae indet. based on general resemblances with the genera Telmatobius, Lymnodynastes, Kyarranus, and Philoria.

It is noteworthy that similarities were also observed with the genus Hatzegobatrachus from the latest Cretaceous of the Haeg Basin, Romania, and this has been already compared with bombinatorids (Venczel and Csiki 2003). They both share “a well-developed and undivided dorsal prominence” and a small pars descendens, but Hatzegobatrachus shows a thicker dorso-lateral margin and it also lacks “any waisting between the acetabular region and the iliac shaft”. Therefore, the Vastan taxon cannot be attributed to the Romanian genus Hatzegobatrachus.

Stratigraphic and geographic range.—Type locality and horizon locality only.

Type species: Eopelobates anthracinus Parker, 1929, latest Oligocene, MP 30, Rott, Germany.

Material.—GU/RSR/VAS 5201 (Fig. 6), a nearly complete right ilium.

Description.—Only the proximal (= anterior) part of the shaft and the ventral extremity of the pars descendens are missing. In medial and dorsal views, a partial dorsal crest extends onto the anterior half of the bone. There is no tuber superius, but a thin ridge bordered by two shallow spiral grooves extends posterolaterally-anteromedially. The junction between the acetabular area and the shaft is not constricted. There is no fossa around the acetabulum. The angle between the pars ascendens and the shaft is close to 180°. The pars ascendens is short. The pars descendens is broken but was likely flared. The acetabulum is oval and its border is very well marked. The angle between the shaft and the pars descendens is close to 90°. In medial view, an interiliac tubercle is well developed. Below this latter, a striated scar indicates that the contact between the two ilia was extensive (see Table 1).

Discussion.—The morphology of this ilium is reminiscent of Pelobatidae. This family includes only the living genus Pelobates and the fossil genera Elkobatrachus (middle Eocene, Elko Formation, Nevada, USA; Henrici and Haynes 2006) and Eopelobates (see distribution below). Pelobatid ilia are characterized by the absence of the dorsal crest, the tuber superius and the subacetabular and supraacetabular fossae (Rage and Hossini 2000) and by the presence of an oblique spiral groove on the middle surface (Evans and Milner 1993). All these characters are visible in the Vastan specimen. The Miocene specimens of Pelobates and Eopelobates have a small interiliac tubercle whereas the Recent specimens of Pelobates do not (Rage and Hossini 2000). Moreover, following Rage and Hossini (2000), the presence of striated scars on the postero-mesial border of the ilia is indicative of the genus Pelobates. However, striated scars are also present in Eopelobates (personal observation on specimens of E. wagneri, SMF Me-11262a and 2795). In addition, there is a partial dorsal crest extending on the anterior half of the bone, which is only known in the genus Eopelobates. For these reasons, the ilium GU/RSR/VAS 5201 from Vastan is here attributed to the genus Eopelobates. The type species of the latter genus, E. anthracinus from the latest Oligocene of Rott (MP30), Germany, differs from all the other Eopelobates species by being about half the size of the other species (Roček and Rage 2000). Following Rage and Roček (2003), three other species are recognized in the genus. Two species are known from the middle Eocene of Germany, E. wagneri from Messel (MP11) and E. hinschei from Geiseltal (MP 13), the latter possibly a synonym of E. wagneri (Roček and Rage 2000). The third species is E. bayeri from the late Oligocene of Bechlejovice, Czech Republic, which is smaller than E. wagneri (Roček and Rage 2000) and bigger than E. anthracinus (Estes 1970).

The identification of the different species of Eopelobates is based on cranial characters, especially the frontoparietal; whereas ilia of Eopelobates are not diagnostic enough for determination below the genus level (Evans and Milner 1993; Rage and Roček 2003). Nevertheless, the single ilium from Vastan was compared with IRSNB A 2 (field number BE 2-126), an exceptionally well preserved specimen of Eopelobates wagneri from the middle Eocene of Messel, which preserves the two ilia in dorsomedial view (Fig. 6A). The ilia of both the Indian and German specimens are very close in size and morphology (Fig. 6A₂, B). They share a similar acetabular area, the presence of a thin ridge instead of the tuber superius, a dorsal crest extending on the anterior half of the bone, and a well-developed interiliac tubercle. Comparisons with other specimens attributed to Eopelobates wagneri (HLMD-Be-171 and SMF Me-11262a, SMF Me-2795, SMF Me-2562, SMF Me-189) confirm these observations. The vertebrae, cranial bones and other skeletal elements of this Indian taxon are unknown. It is therefore not possible to give a more precise identification of the Vastan pelobatid frog until a revision of Eopelobates is undertaken.

Material—Eight nearly complete ilia: GU/RSR/VAS 5202 (Fig. 7), GU/RSR/VAS 5203–5209); seven vertebrae: GU/ RSR/VAS 5210–5212 (Fig. 8A–C), GU/RSR/VAS 5213– 5216; and two urostyles: GU/RSR/VAS 5218 (Fig. 8D), GU/RSR/VAS 5217.

Description.—In lateral view, the iliac shaft is cylindrical and is separated from a high dorsal crest by a well-marked groove (Fig. 7A). The tuber superius, a thickening of the proximal (= anterior) part of the dorsal crest, is ovoid and projects slightly laterally (Fig. 7D). The junction between the acetabular area and the shaft is constricted. A shallow, small, rounded supraacetabular fossa is present at the proximal (= anterior) base of the tuber superius. The angles between the tuber superius and the pars ascendens and between the shaft and the pars descendens are both close to 90°. The pars ascendens is short. The pars descendens is broken on GU/RSR/VAS 5202, but was likely short and flared. The acetabulum is rounded and its border is accentuated by a sharp rim. There is no subacetabular fossa. In medial view, there is no distinction between the tuber superius and the dorsal crest (Fig. 7C). Two ridges extend along the pars ascendens and pars descendens. Proximally (= anteriorly), the dorsal crest and the iliac shaft are separated by a groove. There is no interiliac tubercle. In dorsal view, the dorsal crest is posterolaterally to anteromedially oriented on the shaft (Fig. 7D).

The posterior part of the presacral region of the vertebral column can be reconstructed. The vertebrae are not imbricate. The presacral vertebrae, except the last one, are procoelous and rather short antero-posteriorly (Fig. 8A); the neural arch bears a strong medial ridge and presents a notch on its anterior border that is anteriorly widened. The last presacral vertebra is amphicoelous, presenting an anterior and a posterior cotyle (Fig. 8B). The sacral vertebra is biconvex with two posterior condyles (Fig. 8C). The sacral diapophyses are well separated from the prezygapophyses, are posteriorly directed and are cylindrical (not laterally or antero-posteriorly expanded). This vertebra is also characterized by a well-developed medial ridge on the neural arch, which is laterally bounded by two well-marked and posteriorly concave ridges. The urostyle is free and presents two anterior cotyles and a well-developed dorsal crest (Fig. 8D; see Table 1).

Discussion.—Some ilia of this taxon present a tuber superius that is more elongated and anterodorsally oriented. The supraacetabular fossa is also deeper on some specimens. These differences are interpreted as intraspecific variations.

The presence of a dorsal crest, the acute angle between the tuber superius and the pars ascendens, the tuber superius that is a thickening of the dorsal crest, and the absence of an interiliac tubercle (Prasad and Rage 2004) indicate that these specimens belong to a ranoid frog. These characters are also present in the ilia of Ranoidea indet. (IITR/SB/VLM-LV/ 201–202) described from Vastan by Bajpai and Kapur (2008), and both probably represent the same taxon.

The bicondylar sacro-urostylar articulation is consistent with a ranoid affinity (Rage and Hossini 2000). This group is considered here to include families “Ranidae”, Rhacophoridae, “Hyperoliidae” and Microhylidae and excludes Dendrobatidae (sensu Cannatella 2007).

The ranoid from Vastan differs from the ranoid described by Prasad and Rage (2004) from the Upper Cretaceous inter trappean beds of Naskal, India, by having a more constricted junction between the acetabular area and the shaft, and by the presence of a supraacetabular fossa. It also differs from the Microhylidae and the Rhacophoridae (except Mantidactylus, Buergeria, Chiromantis, Polypedates; Liem 1970) and is close to the “Ranidae” and “Hyperoliidae” in the presence of a diplasiocoelous assemblage of the vertebrae (all vertebrae are procoelous, except the last presacral vertebra which is amphicoelous and the sacral vertebra which is biconvex; Liem 1970; Rage and Hossini 2000; Rödel et al. 2009). Moreover, it differs from the rhacophorids Buergeria, Chiromantis, and Polypedates by a more developed tuber superius and by a more acute angle between the tuber superius and the pars ascendens. It differs also from the Microhylidae and “Hyperoliidae” by the presence of a well-developed dorsal crest on the iliac shaft (Nokariya 1983a; Scott 2005). Finally, following Rage and Hossini (2000), non-imbricate vertebrae, cylindrical sacral diapophyses and a free urostyle with a well-developed dorsal crest are a typical character assemblage for the family “Ranidae”. The ilium and vertebrae described above from Vastan can thus be attributed to “Ranidae”. The posterior border of the dorsal crest sloping precipitously into the dorsal acetabular area and the acute angle between the tuber superius and the pars ascendens are similar in general morphology to the green frog Rana clamitans (Holman 2003).

It might seem that the quantity and quality of the specimens assembled here should allow us to create a new taxon. However, below the familial level, there are few diagnostic osteological characters of the different “ranid” genera, which are mainly distinguished on external morphological characters. It is thus premature to create a new taxon or to include this material in an already existing taxon until there is a detailed revision of the family “Ranidae” that identifies generically distinctive osteological traits.

Etymology: In reference to India and rana, a suffix for the ranoid taxa.

Type species: Indorana prasadi sp. nov.; see below.

Diagnosis.—As for the monotypic type species.

Etymology: For Indian paleontologist Guntupalli V.R. Prasad, for his contributions to the knowledge of Indian frogs.

Holotype: GU/RSR/VAS 5220 (Fig. 9A), a nearly complete left ilium associated with the two ischia and pubis.

Type locality: Vastan Lignite Mine, Surat District, Gujarat, India.

Type horizon: Cambay Shale Formation, middle Ypresian, lower Eocene.

Referred material.—GU/RSR/VAS 5219 (Fig. 9B), an incomplete left ilium associated with the pubis, left ischium and half of the right ischium.

Diagnosis.—Ilium differs from Rhacophorus and Polypedates by a very weak dorsal crest on the iliac shaft, and from Buergeria buergeri in having an ossified pubis fused with the ilium and ischium, a wider acetabulum and a thicker iliac shaft.

Description.—In lateral view, the iliac shaft is almost straight and bears a weakly developed elongated tuber superius (Fig. 9A₁). The acetabular area is relatively large dorsoventrally in comparison with the shaft. There is no subacetabular or supraacetabular fossa. The angle between the tuber superius and the pars ascendens is close to 180°, whereas the angle between the shaft and pars descendens is close to 90°. The pars ascendens is short. The extremity of the pars descendens is flared. The acetabulum is deep, slightly bell-shaped, and has a sharp rim. A shallow groove extends from the tuber superius to the anteroventral part of the shaft. The suture with the ischium is nearly dorsoventrally oriented. An ossified pubis is fused with the ilium and ischium but its limits are not readily visible. The ischium is reniform and its dorsal border is laterally thickened. The acetabulum is deep and presents a rim as sharp as on the ilium. On its posterior border, the ischium bears a tubercle that projects laterally. This structure is clearly visible in posterior view (Fig. 9A₂, B₂). In medial view, there is no ornamentation (e.g., striae or foramina) on the ilium except for a weak dorsal crest (Fig. 9A₃, A₄, B₃, B₄). The latter begins on the dorsal part of the shaft, close to the tuber superius, and extends on the medial side of the shaft. There is no interiliac tubercle. In dorsal view, the iliac shaft is slightly laterally compressed, and the tuber superius, and the dorsal crest project laterally, and medially, respectively (Fig. 9A₃, A₄, B₃, B₄; see Table 1).

Discussion.—This specimen presents features that differ from those of most major groups of frogs. A weak or low dorsal crest is present in some non-ranoid frogs such as Hylidae and Leptodactylidae (Lynch 1971; Holman 2003). However, both families differ from the Vastan taxon by a more developed and globular tuber superius (Bailon 1999).

This taxon does not belong to “Ranidae” or Discoglossidae of the “Discoglossus group” because the dorsal crest of the iliac shaft is less developed in particular in the posterior area of the ilium (Rage and Hossini 2000). It most resembles Rhacophoridae (which is here considered a family of the superfamily Ranoidea, sensu Cannatella 2007) in having a weakly developed tuber superius and a relatively elongate pars descendens (Nokariya 1983b: fig. 4.5). The laterally projecting tubercle on the posterior border of the ischium is another character shared with rhacophorids, such as several species of Rhacophorus (Nokariya 1983b) and the species Polypedates leucomystax (MNHN n°1871–187, Recent, Philippines). Moreover, it resembles the species Buergeria buergeri (previously referred to Rhacophorus) in having a weak dorsal crest and the anterior border of the acetabulum that extends to half the length of the tuber superius. However, the pubis of the Vastan specimen is better developed. Indeed, based on Nokariya (1983b: fig. 4.5), the pubis of B. buergeri is cartilaginous, whereas it is ossified and fused with the ilium and the ischium in the Vastan taxon. Moreover, the acetabulum is wider, and the shaft is thicker than in B. buergeri. These morphological differences and the temporal gap between extant B. buergeri and the Vastan form allow us to erect the new name Indorana prasadi, gen. and sp. nov., for this early Eocene frog and to tentatively attribute it to the family Rhacophoridae.

Liem (1970) considered the genus Buergeria as a primitive rhacophorid frog because it presents several putative plesiomorphies among Asiatic rhacophorids, such as the presence of musculus adductor longus, an arch-shaped anterior horn of the hyoid, and the presence of second and fourth phalangeal slips of the musculus humerodorsalis. Subsequently, Channig (1989) erected the subfamily Buergeriinae for this genus, restricted to Taiwan and Japan, indicating that it is the sister taxon of the other Rhacophoridae. These data are in agreement with the possibility that Indorana prasadi represents a primitive rhacophorid.

Stratigraphic and geographic range.—Type locality and horizon only.