Systematic analysis shows that the Southern Hemisphere bivalve genus Retrotapes includes the Antarctic species R. antarcticus, R. newtoni, and R. robustus and recognizes for the first time the presence of Katelysia represented by K. florentinoi. Two new genera were erected in this study: Marciachlys new genus to include M. inflata new combination, and Adelfia new genus, which includes A. austrolissa new combination and A. omega new species from the Eocene of Antarctica, and the late Eocene Chilean A. arenosa new combination. Eurhomalea carlosi was synonymized with K. florentinoi; Cyclorismina marwicki with R. antarcticus; Gomphina iheringi was considered an indeterminate species; and Cockburnia lunulifera was excluded from the Tapetinae. These systematic assignments are supported by a phylogenetic analysis, which recognizes an Austral clade of Tapetinae, comprising all the genera mentioned above, along with Marcia, Paleomarcia, Atamarcia, and Protapes.

During recent stratigraphical and micropaleontological investigations of the Gulupu section in Tüna, Yadong, of the Eocene Zhepure Formation, numerous holoplanktonic mollusks (pteropods) were recovered. Four species, assignable to two genera of pteropods (including Limacina yadongensis new species) were systematically described and illustrated, and a gastropod-bivalve biofacies was identified. This is the first report of Eocene (Ypresian) pteropods in southern Tibet; the same stratum also yields many other neritic faunas. The data presented in this study suggest that a semi-closed restricted gulf in the Tüna area existed and the occurrence of pteropods in Tüna may indicate transport from more open, deep water by oceanic currents during early Eocene. Based on the analysis of paleogeographical distribution of pteropods, it indicates that a Tethys seaway existed during the early Eocene (Ypresian).

Ptychites is among the most widely distributed ammonoid genera of the Triassic and is namesake of a family and superfamily. However, representatives of the genus mostly show low-level phenotypic disparity. Furthermore, a large number of taxa are based on only a few poorly preserved specimens, creating challenges to determine ptychitid taxonomy. Consequently, a novel approach is needed to improve ptychitid diversity studies. Here, we investigate Ptychites spp. from the middle and late Anisian of Nevada. The species recorded include Ptychites embreei n. sp., which is distinguished by an average conch diameter that is much smaller and shows a more evolute coiling than most of its relatives. The new species ranges from the Gymnotoceras mimetus to the Gymnotoceras rotelliformis zones, which makes it the longest-ranging species of the genus. For the first time, the ontogenetic development of Ptychites was obtained from cross sections where possible. Cross-sectioning highlights unique ontogenetic trajectories in ptychitids. This demonstrates that, despite showing little phenotypic disparity, Ptychites was highly ontogenetically differentiated, and thus the high taxonomic diversity at the species level is justified for the species investigated.

In the 1950s, Carlos Rusconi reported the biostratigraphically important Furongian trilobites Elvinia Walcott and Irvingella Ulrich and Resser from an exotic limestone block (La Cruz Olistolith) of the San Isidro area, Precordillera of Mendoza, western Argentina. Although several local species were erected by Rusconi at that time, most of them were later listed as junior synonyms of E. roemeri (Shumard) or I. major Ulrich and Resser, and this was followed in subsequent studies. A systematic revision of all the available specimens of Elvinia and Irvingella from the Rusconi collection at the Museo de Ciencias Naturales y Antropológicas J.C. Moyano (Mendoza) is provided herein. The occurrence of E. roemeri is supported by the present study, while the associated Irvingella species include I. jorusconii Rusconi, I. platycephala Rusconi, and Irvingella sp. The latter represent “advanced” forms in terms of morphological development in the Irvingella lineage, and these, together with E. roemeri, are typical of the uppermost part of the Elvinia Zone (uppermost Steptoean). Irvingella jorusconii, I. platycephala, and Irvingella sp. appear to be endemic to the Argentinian Precordillera, but are related to species from central Texas and northwest Canada.

The Ao Mo Lae Formation of the Tarutao Group crops out on Thailand's Tarutao Island and contains a diverse assemblage of late Furongian trilobite taxa, including several endemic forms. This study presents a new genus and species, Satunarcus molaensis, discovered at two locations on the island. A cladistic analysis of the kaolishaniid subfamily Mansuyiinae in light of Satunarcus and similar genera known from across upper Cambrian equatorial Gondwanan rocks suggests that the subfamily is polyphyletic in its current definition, and thus is not a natural group. Separating MansuyiaSun, 1924 from the other taxa conventionally placed in Mansuyiinae permits recognition of a previously unrecognized monophyletic subfamily Ceronocarinae new subfamily. As established herein, this kaolishaniid subfamily contains Satunarcus n. gen. and all genera previously recognized as Mansuyiinae. with the exception of Mansuyia itself. Ceronocarinae n. subfam. occur in middle Jiangshanian to middle Cambrian Stage 10 sedimentary rocks from Australia, South China, North China, and Sibumasu, with most genera endemic to Australia.

The hurdiid radiodont Cambroraster is characterized by a prominent horseshoe-shaped head carapace, which bears conspicuous posterolateral spinous processes and covers half of the body length, and a pair of frontal appendages possessing rake-like endites. Here we report the discovery of characteristic central and lateral elements as well as a possible appendage endite for Cambroraster from the Cambrian Wuliuan Mantou Formation of North China. This discovery suggests that Cambroraster had dispersed over a wide biogeographic range and expands the geographic range of Hurdiidae. The increasing discoveries of exceptionally preserved fossils in the Upper Shale Member of the Mantou Formation indicate that this horizon is a promising Burgess Shale–type Lagerstätte.

A locality in the Upper Cretaceous Two Medicine Formation of Montana preserves abundant and variable horseshoe crab tracks and trails of the ichnotaxon Kouphichnium isp. These specimens span six morphologies differing in track form and trail configuration. These differences likely reflect variations in track-maker locomotion and behavior, substrate consistency, epichnial versus hypichnial preservation, and undertrack versus true tracks. Several tracks preserve the first clear appendage impressions for an extinct horseshoe crab. This discovery adds new information to the fossil horseshoe crab diversity in the Cretaceous Period. Trackway dimensions, such as the external width across the pusher legs or of the prosomal drag mark, provide information on the track-maker size. Most trackways correspond with crabs 9–14 cm wide; the abundance but limited size range of the traces suggests the large assemblage corresponds to a mating aggregation. The trace fossil record of xiphosurids indicates that throughout their history, horseshoe crabs inhabited both marine and nonmarine settings. They were definitively present in freshwater habitats from the lower Carboniferous through at least the Paleogene. Horseshoe crab trace abundance is highest from the upper Carboniferous through the Jurassic and likely reflects two factors: true upper Carboniferous taxonomic diversity and a preponderance of suitable sites for trackway preservation in the Late Triassic and Jurassic. Cretaceous traces are uncommon, and this Two Medicine locality is the first occurrence of horseshoe crab traces in the Late Cretaceous worldwide. Overall, track abundance and diversity would seem to correspond well with the reported horseshoe crab body fossil record.

Gonatocaris decora (Clarke, 1901) is an unusual, highly ornamented Silurian phyllocarid from the Pittsford Shale Member of the Vernon Formation, Salina Group of New York, that has been allied with Emmelezoe in the past due to the possession of an ‘optic tubercle.’ The systematic positions of Gonatocaris and Emmelezoe have been difficult to assess due to the lack of complete remains, attributions based on spurious characters, and missing and unfigured specimens. Relatively recent collections of Gonatocaris decora, along with a relocation of the original type material of Emmelezoe, have allowed a reexamination of all relevant genera and a more robust systematic placement for G. decora. Characters of generic importance for Gonatocaris include a greatly elongated abdomen; an acute angle of the ventral carapace margin separating distinct anteroventral and posteroventral margins from each other; and distinctive, multiscale horizontal ridge-like ornament of the carapace valves. Growth was found to be isometric. Experimental work done using a model of the scale-like ornament and multiple grain sizes of substrate indicates that cuticle ornament may have served to increase friction between the animal and a fine sand substrate, although resistance to predation is the currently favored hypothesis. Because Gonatocaris species are currently known only from the eastern margin of Laurentia and northern South China, it is likely that this genus was nektonic. Accumulations of similarly sized carapaces and other disarticulated sclerites in shallow-water settings may indicate spawning events following molting en masse.

A new trace fossil, Feoichnus martini new ichnospecies, from the Two Medicine Formation is here described. This ichnotaxon is reported from the upper Campanian deposits of the Egg Mountain locality (Montana) and consists of a hemispherical to hemiellipsoidal structure with a truncated upper edge, and a regular, rounded lower edge marked by a lined border composed of stained layers. The trace maker likely impregnated the border using organic fluids. The simple lined wall observed in F. martini n. isp. suggests that the structure was produced by an invertebrate soil-dwelling organism, likely an insect. Specimens are preserved as casts in calcitic Inseptisols alongside an abundant vertebrate fossil record composed by dinosaurian and nondinosaurian fossil remains, dinosaur eggs and nest structures, and pervasive insect bioturbation. Feoichnus martini n. isp. represents an additional, minor component of the impoverished Celliforma ichnofacies reported at Egg Mountain and expands the paleogeographical distribution of the ichnogenus FeoichnusKrause et al., 2008 to the Upper Cretaceous deposits of Montana, USA.

Abundant new material of articulated asteroids from the Taba Starfish Bed (Lower Cretaceous, Barremian) of the Agadir Basin, western Morocco, allows reappraisal of this important fauna, and the recognition, to date, of five taxa belonging to the Astropectinidae, Odontasteridae, Goniasterididae, Terminasteridae, and Asteriidae. Betelgeusia orientalisBlake and Reboul, 2011 is shown to be a junior synonym of Coulonia platyspinaHess and Blake, 1995, and Dipsacaster africanusBlake and Reboul, 2011 comprises material of C. platyspina and a new odontasterid, here described as Odontaster tabaensis n. sp. Alkaidia megaungula n. sp. is described and its ontogeny and affinities discussed. From this, it is concluded that the Terminasteridae, revised to include the genera Terminaster and Alkaidia, is sister taxon to the extant family Zoroasteridae, and both are placed in the suborder Zorocallina of the Forcipulatida. The Taba fauna is a representative of a distinctive Lower Cretaceous asteroid assemblage that existed in northern Tethys from the Barremian to the Cenomanian and is also well known from the Albian and lower Cenomanian of Texas.

The latest Ordovician to earliest Silurian graptolite Avitograptus avitus is important in the biostratigraphy of the Ordovician–Silurian boundary interval. Two additional species of Avitograptus are described from the sponge-dominated Anji Biota of the Upper Ordovician Wenchang Formation (Metabolograptus persculptus Biozone) of Zhejiang Province, South China. One species, Avitograptus akidomorphus new species, is new; the other, Avitograptus acanthocystus new combination, which was previously placed in Climacograptus, is herein assigned to Avitograptus. The former species may represent the ancestral akidograptid because it is identical in thecal form to Akidograptus, but differs in the development of the proximal end. The evolutionary changes from Avitograptus avitus to Akidograptus and Parakidograptus involved distal movement of the origins of th1¹ and th1², thecal elongation, and greater outward inclination of the thecal walls.

The Hawkesbury Sandstone (Hawkesbury Series, Sydney Basin) on the southeastern coast of New South Wales, Australia, preserves a depauperate but important vertebrate tetrapod body-fossil record from the Early and Middle Triassic. As with many fossil sites around the world, the ichnological record has helped to shed light on the paleoecology of this interval. Herein, we investigate historical reports of a trackway pertaining to a putative short-tailed reptile found at Berowra Creek in the 1940s. Reinvestigation of the surviving track-bearing slabs augmented by archival photographs of the complete trackway, suggests that these impressions, which consist primarily of didactyl tracks (plus less common monodactyl and tridactyl traces), represent the earliest example of a swimming tetrapod found in Australia. Another isolated specimen (possibly from a nearby locality at Annangrove) appears to represent similar didactyl swim traces of a second, larger individual. Although the identities of the trackmakers are unknown, the Berowra Creek individual had an estimated body length of between ∼80 cm (short-coupled) and 1.35 m (long-coupled), and produced the subaqueous trackway while travelling upslope (against the current) on a sandbar within a braided river system of the Hawkesbury Sandstone. These trackways partially resemble amphibian swim traces in the so-called Batrachichnus C Lunichnium continuum, but appear to represent a unique locomotion trace. This reanalysis of the Berowra Creek trackway provides insight into the locomotion of tetrapods of the Triassic Hawkesbury Series, which remains a poorly understood aspect of their life history.

The Microsyopidae are extinct mammals from the late Paleocene–late Eocene of North America and the late Paleocene of Europe. While results from phylogenetic analyses support euarchontan affinities, specific relationships of microsyopids to other plesiadapiforms (plausible stem primates), Euprimates (crown primates), Scandentia (treeshrews), and Dermoptera (colugos) are unresolved. An exceptionally well-preserved cranium of Microsyops annectens includes a basicranium that is generally primitive relative to that of other extinct and extant euarchontans in having: (1) a transpromontorial groove for an unreduced internal carotid artery (ICA) entering the middle ear posteromedially; (2) grooves (not tubes) on the promontorium, marking the course for both stapedial and promontorial branches of the ICA; (3) a foramen faciale that opens into the middle ear cavity, with the facial nerve exiting through a stylomastoid foramen primitivum; and (4) unexpanded caudal and rostral tympanic processes of the petrosal. The absence of any preserved bullar elements in the middle ear contrasts with that of other plesiadapiforms for which the region has been recovered, all of which have evidence of an ossified bulla. Microsyops lacks many of the specialized cranial characteristics of crown scandentians and dermopterans. The basicranial anatomy of microsyopids does not provide evidence in support of a clear link to any of the extant euarchontans, and suggests that the primitive morphology of this region in Euarchonta was little differentiated from that observed in the primitive placental mammals.