The systematic position of the Ordovician calcareous microfossil Halysis Høeg, 1932 has long been uncertain. Only known from thin sections, its morphology has been suggested to be either a single chain of cells or a series of tubes and it has been regarded as a green alga or cyanobacterium. Here we propose that Halysis represents a single sheet of cells. This new morphological interpretation accounts for Halysis's appearance in thin section as an extended flexuous series of cells, some of which are not seen to be in mutual contact, exhibiting nonlinear cell-size variation. It is also consistent with the absence of tubiform sections unequivocally attributable to Halysis. This reassessment suggests comparisons between Halysis and Mesozoic–Cenozoic thin laminar unistratose coralline red algae. Halysis cells are relatively large (40–210 μm), but their lower range is comparable to cells of corallinaceans such as Lithoporella (Foslie) Foslie, 1909. Applanate thallus morphology in Halysis resembles that of thin laminar species of Lithophyllum Philippi, 1837 that were traditionally included in Titanoderma Nägeli, 1858. Interpretation of Halysis as a coralline-like alga strengthens the likelihood that a variety of corallines was present in the Ordovician, more than 300 Ma prior to the currently recognized major diversification of this important group of red algae in the Cretaceous.

We have studied the pattern of graptolite species turnover during the latest Ordovician mass extinction based on four continuous Ashgillian to earliest Llandovery sections together with data from more than 30 other published sections. The studied sections represent relatively shallow-water and deeper-water belts in the Yangtze Platform region. Using temporally scaled range data, species diversities and extinction and origination probabilities have been calculated using several analytical methods, including a capture-mark-recapture method. We test the statistical significance of these results and the apparent taxonomic selectivity of extinction and origination via Monte Carlo simulations and contingency analysis.

Graptolite species diversity within the Yangtze Platform rose steadily during the late Ashgill, until in the mid-late Paraorthograptus pacificus Chron, when rising extinction risk overtook origination. Diversity dropped to very low levels during the early Hirnantian when extinction probabilities attained significantly elevated rates for a period of 600–900 Ky. The period of high extinction risk was followed immediately by a short period of very high origination probability. A second, short period of high extinction risk occurred at the end of Hirnantian time. The Hirnantian extinction events marked a change from relatively low, steady origination and extinction probabilities to a prolonged period of elevated extinction risk and highly variable origination probability that extended well into the Rhuddanian. Extinction and origination was highly selective during the Hirnantian and favored both the survival and diversification of the Normalograptidae relative to the Dicranograptidae, Diplograptidae, and Orthograptidae.

The main phase of extinction in the latest Rawtheyan and early Hirnantian was coincident with continental glaciation in the Southern Hemisphere. The resulting changes in ocean circulation and oxygenation appear to have almost completely eliminated the preferred habitat for most graptolite species. The Yangtze Platform region, however, may have served as a refugium for many taxa that disappeared earlier in other regions as well as a host site for the initiation of graptolite rediversification. Following the end of the glaciation, conditions favorable for graptolite proliferation were restored but graptolite communities remained unstable for much of the late Hirnantian and early Rhuddanian. Accordingly, the Hirnantian mass extinction appears to have fundamentally altered graptolite species dynamics as well as clade dominance patterns. A full understanding of the history of life requires an expanded, hierarchical theory of evolution that gives to mass extinctions (and other levels of selection) an appropriate role in determining clade and diversity histories.

A faunule of silicified hypercalcified “sphinctozoan” sponges has been recovered from a clast of Upper Ordovician limestone out of the Early Devonian Karheen Formation on Prince of Wales Island in southeastern Alaska. Included in the faunule are abundant examples of the new genus Girtyocoeliana, represented by Girtyocoeliana epiporata (Rigby and Potter), and Corymbospongia adnata Rigby and Potter, along with rare Corymbospongia amplia n. sp., and Girtyocoelia(?) sp., plus common Amblysiphonella sp. 1 and rare Amblysiphonella(?) sp. 2. The assemblage is similar to that from Ordovician clasts from the eastern Klamath Mountains of northern California. This indicates that the Alexander terrane of southeastern Alaska is related paleogeographically to the lithologically and paleontologically similar terrane of the eastern Klamath Mountains.

This lithology and fossil assemblage of the clast cannot be tied to any currently known local rock units on Prince of Wales Island. Other clasts in the conglomerate appear to have been locally derived, so it is inferred that the limestone clasts were also locally derived, indicating the presence of a previously undocumented Ordovician limestone unit on northern Prince of Wales Island.

Macgeea is a cosmopolitan genus of Devonian rugose corals that includes numerous, generally highly variable, species. Because of its wide skeletal variation and additional trabecular dilation it is difficult to recognize taxonomically relevant characters and to separate those from ecologically induced modifications. The high variability is probably related to radiations following phases of sea level rise and is connected to bioevents. Length of major septa in ontogenetic stages allows a separation of different populations within the Macgeea dubia species group. However, it remains questionable if septal length is a reliable taxonomic character, indicating a phylogenetic trend, or if it is subject to large individual variability. By revising Macgeea dubia, we reveal its synonymy with Macgeea heterophylloides sensu Birenheide. In addition, Macgeea recta (type species of Pexiphyllum Walther, 1929) is discussed as an insufficiently defined taxon of problematic status. Macgeea crassiseptata n. sp. is also described from the Late Givetian of Morocco.

The erection of the new pseudocolumellate genus Baculophyllum with type species Pexiphyllum ultimum Walther, 1929 requires a comparison with Protomacgeea from Poland and Australia as well as a phylogenetic discussion of the solitary Phillipsastreidae. The new genus most probably belongs to a separate lineage of the Upper Devonian Macgeea group but could also be considered as a descendant of the Australian Lower Devonian columellate solitary phillipsastreid species group, that has not yet been recorded from the Middle Devonian. Because of large stratigraphic gaps between the occurrences of both genera, preference is given to the interpretation of a development of polycronomorph taxa (homeomorphic taxa living at a different time) not belonging to a single lineage. This shows again the significance of stratigraphic age when comparing similar-looking taxa, which should be considered in any phylogenetic reconstruction.

Seven genera and eight species of lingulate brachiopods were recovered from the House Limestone and lower Fillmore Formation, Ibex area, Utah, USA. These strata are assigned to the upper Skullrockian Stage and lower Stairsian Stage of the Ibexian Series (Iapetognathus Conodont Zone to Low Diversity Interval) and are correlated with the Tremadocian Series of the Acado–Baltic Faunal Province. The fauna includes two new linguloid species, Spinilingula prisca and Wahwahlingula sevierensis, one new siphonotretoid species, Schizambon obtusus, and two new acrotretoid species, Eurytreta fillmorensis and Ottenbyella ibexiana. The last species is the first record of the genus in North America and suggests a correlation of the basal Fillmore Formation with the Ceratopyge Limestone in Sweden. A Siphonobolus? covered by long hollow spines may be one of the oldest siphonotretides with such ornament. This fauna and those described previously from older Utah strata document the biodiversification of the Cambrian–Ordovician lingulate brachiopods and demonstrate their potential for regional and intercontinental correlation.

This paper describes 19 brachiopod species (including six indeterminate species) in 15 genera and one indeterminate genus from the basal Itaituba Formation at the Caima Quarry 1 section of Itaituba, Amazon Basin, Brazil. The faunal correlations of the brachiopods and the associated fusulinids and conodonts indicate a late Chesterian (late Serpukhovian) age for the described fauna, therefore confirming for the first time the presence of uppermost Mississippian rocks in the Amazon Basin. A new species, Composita caimaensis, is created, and two species, Inflatia cf. gracilis and Marginovatia cf. catinulus, are described for the first time from the Amazon Basin. The Amazon brachiopods appear to be of strong affinity with coeval faunas of the North American midcontinent.

This paper describes a unique deepwater brachiopod fauna from the upper part of the Talung Formation at the Dongpan Section, southern Guangxi, South China. This brachiopod fauna includes 10 species belonging to 10 genera. New taxa are Anidanthus mucronata n. sp., Dongpanoproductus elegans n. gen. and sp., Costatumulus dongpanensis n. sp., and Spinomarginifera semicircridge n. sp. This fauna is characterized by small, thin-shelled species with high abundance and low diversity, and therefore is different in generic and species composition from the coeval faunas of the Late Permian limestone facies in South China. The brachiopod fauna can be safely assigned to the latest Changhsingian as indicated by the presence of abundant Paracrurithyris pigmaea, the immediately underlying radiolarian Neoalbaillella optima Zone of late Changhsingian age, and the overlying ammonoid Ophiceras sp. cf. O. tingi Tien of the lowest Triassic. This fauna is most likely to have lived in a deepwater environment as indicated by coexistence with the radiolarian Latentifistularia, small thin-shelled brachiopods, and the dominance of silica-bearing mudstone.

Argenthina emilyae is a new genus and species of extinct muricid gastropods from the early Middle Miocene of southern Argentina. Most of its shell features are consistent with those of the Acanthina-clade of Thais-like ocenebrines, including a broad, rounded body whorl, a large aperture lacking ornamentation, and a short, open siphonal canal, although other characters are consistent with the Ocinebrina-like ocenebrines, such as the differentiation of axials into varices and intervaricals and complex spiral sculpture. This combination of traits is unique in the Ocenebrinae. It is not yet clear whether this new taxon represents an episode of morphological experimentation by a stem group of Thais-like ocenebrines resulting in convergence on the Ocinebrina-like shell form or an evolutionarily intermediate step between Thais-like and Ocinebrina-like ocenebrines. Intermediates are expected from previously published phylogenetic hypotheses for the Ocenebrinae that suggest Ocinebrina-like ocenebrines have evolved multiple times from Thais-like ocenebrines. Until now, however, such intermediates have not been reported from the fossil record.

A detailed morphometric approach applied to the diversity (interspecific variation)/disparity (intraspecific range of variation) was developed. It was based on outline analysis, and it was applied to 41 cross sections of Kosmoceras from the Upper Callovian of eastern France (Prusly). The cross sections represent an excellent basis for evaluation of the global shape of the shell: the main morphologic descriptors include the proportion of umbilical diameter/conch diameter and the thickness of the whorl; they also indirectly describe the ornament that influences the aspect of the whorl section. This analysis was conducted to quantify the size and shape variations and to determine the relations among some of the ‘morphological species’ defined by Tintant: K. bizeti, K. fibuliferum, K. phaienum? and K. interpositum? Numerous analyzed individuals may not belong to these categories.

The results suggest that despite a wide range of variability four main morphotypes can be ascribed a probable taxonomic status, whose mean representatives can be properly assigned to Tintant's four ‘species.’ Moreover, three of them could constitute a morphological series, continuously related through ontogeny. The fourth (K. interpositum) may be an independent species, rarely recovered in the studied area.

A single specimen of a likely sphaeromatoid isopod is described from the Upper Bathonian of northern France at Ranville, Normandy. The remarkable three-dimensional preservation consists of only the head and first pereionite, but clearly constitutes a new genus and species, Reboursia ranvillensis.

A new species of clawed lobster, Hoploparia albertaensis, is reported from the late Coniacian, shallow-marine Bad Heart Formation of northwestern Alberta, Canada. Hoploparia is a well-known, clawed lobster genus with a record extending from Early Cretaceous (Valanginian) to Miocene. Fifty-one species of Hoploparia are known worldwide; 13 from the North American Western Interior Seaway. None of the 12 other Interior Seaway species, of any age, closely resembles the new species. The new species strongly resembles Hoploparia gabbi Pilsbry, 1901 from the upper Santonian–lower Campanian of the U.S. Mid-Atlantic Coastal Plain.

A new species of polycotylid, Dolichorhynchops herschelensis, is described based on a well-preserved skeleton from the Upper Cretaceous (Campanian–Maastrichtian) Bearpaw Formation of Herschel, Saskatchewan. Its small size as an adult, the sharp rise in front of the parietal crest, and the straight ilium with narrow dorsal end are diagnostic features of this taxon. This is the first polycotylid plesiosaur described from the Bearpaw Formation, deposited during the critical period when polycotylids were disappearing from the Western Interior of North America.

Dianchungosaurus lufengensis was erected on the basis of fragmentary isolated jaw elements (a left premaxilla and left and right partial lower jaws) from the Lower Lufeng Formation (Lower Jurassic) of Yunnan Province, China. Yang referred Dianchungosaurus to the Heterodontosauridae (Ornithischia, Ornithopoda), as several features appeared to indicate affinity with the southern African genus Heterodontosaurus. However, reexamination of the type material demonstrates that the holotype specimen of Dianchungosaurus represents a chimaera of prosauropod dinosaur and mesoeucrocodylian remains: the mesoeucrocodylian premaxilla is distinctive and allows the genus to be diagnosed on the basis of several autapomorphic features. Revision of this genus thereby invalidates the only reported occurrence of a heterodontosaurid dinosaur from Asia.

Articulated scleritomes of the chancelloriids Archiasterella fletchergryllus new species and Chancelloria cf. eros Walcott, 1920 are described from the Early Cambrian (Branchian) Sekwi Formation, Mackenzie Mountains, Northwest Territories, Canada. Early diagenetic, microbially mediated lithification has resulted in unusual three-dimensional preservation of the body surface, which potentially allows consideration of the evolutionary affinities of these enigmatic organisms. Sclerites are mounted on short stalks of the integument, connected to the undersurface of the central disc, and are external to the body surface.