Postcranial pneumaticity is interpreted as a weight saving adaptation in sauropod dinosaurs, especially in the vertebral column. In some derived sauropods pneumatic features also occur on vertebral ribs. While pneumatic ribs are considered diagnostic of the clade Titanosauriformes, they are also infrequently found in diplodocid sauropods. Here, we describe a partial dorsal rib IV or V referable to Apatosaurus sp. that exhibits a series of superficial pneumatic fossae along its posterior surface. These fossae differ from the morphology found in other pneumatic dorsal ribs of diplodocids, including other apatosaurines and Supersaurus. Moreover, the pneumatic features of this rib are more distally located from the capitulum and tuberculum than in other diplodocids and titanosaurs. Based on our findings, we propose that rib pneumaticity among apatosaurine sauropods (and potentially all diplodocids) is individually variable, in addition to being a function of ontogeny. More broadly, we conclude that rib pneumaticity among diplodocids is morphologically variable when present and individually expressed rather than being ubiquitous throughout the clade. Our findings are consistent with the hypothesis that pneumatic ribs evolved independently between Diplodocidae and Titanosauriformes and make for poor clade-level characters among diplodocids.

The Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada, is among the best-studied paleoecosystems in North America. However, its microvertebrate paleocommunity structure is relatively poorly known, partly because it lacks the abundant microsites of other Upper Cretaceous deposits of Alberta. An unusual microsite (FTS-2) from the Horsethief Member of the Horseshoe Canyon Formation is described that produces abundant anuran and troodontid material, alongside perinatal material from ornithischians and tyrannosaurs. Anuran specimens representing a minimum of two separate taxa and a metatherian molar suggest that these components of the fauna were more diverse than currently recognized. The assemblage is similar to three other North American sites that produce abundant troodontid teeth alongside perinatal dinosaurs. However, environmental and taphonomic conditions of these sites vary, supporting the notion of mixed biotic and abiotic factors driving the association of troodontids alongside perinates. In part, this may stem from similar nesting preferences between troodontids and other dinosaurs, as material collected from all three sites suggests proximity to troodontid nesting sites. Sites such as FTS-2 are important for revealing the rare and small components of paleoecosystems, and hold promise for revealing interactions between these parts of the fauna.

The Late Triassic archosauromorph Trilophosaurus buettneri is known from many sites in the Dockum Group and Chinle Formation of Texas and Arizona, spanning nearly 10 Ma from the Otischalkian to the Adamanian estimated holochrons. The holotype specimen, UMMP 2338, was described as a small fragment of a lower jaw in 1928 by E.C. Case. However, at the time no other specimens of the taxon were known. The present availability of several nearly complete skulls, mandibles, and postcranial skeletons referred to T. buettneri allows for reexamination of the anatomical context of the holotype. Here, we provide high-resolution photographs and 3D models of UMMP 2338 to justify our reidentification of the holotypic specimen of T. buettneri as an incomplete maxilla, which may have important implications for future work on trilophosaurid archosauromorphs.

We report a micro-CT study of a new specimen of Dryolestes priscus (Dryolestidae, Cladotheria) from the Upper Jurassic Morrison Formation of Wyoming. The fossil (KUVP 134101) is an incomplete lower jaw preserving eight intact teeth, including two premolars (p3, p4) and six molars (m1–6), along with double-alveoli for m7 and a single alveolus for m8. Its preserved teeth and molar alveoli are consistent with the dental formula in more complete jaws of this species (i4.c1.p4.m8–m9). Here we have newly characterized diagnostic features on the molar trigonid of Dryolestes priscus and other species of Dryolestidae. Our analysis places this specimen close to Dryolestes priscus in terms of phylogeny. CT scans and visualization made it possible to illustrate the distinctive root structures of lower molars of dryolestid species. The two-rooted lower molars of D. priscus show a hypertrophied anterior root that is spatulate and much broader and longer than the simpler posterior root of the same molar. The disparate shape and size of the two molar roots are a highly derived pattern of dryolestids, which is absent in closely related genera formerly assigned to “paurodontids.” It is also unique among all mammaliaforms with typically two-rooted molars. The hypertrophied anterior root corresponds to most of the molar crown, and likely provided better support for occlusal forces acting on the large trigonid of the molar.

We describe an assemblage of isolated hybodontiform shark teeth from the nonmarine Upper Triassic (Carnian) Momonoki Formation in the town of Ominecho in Mine, Yamaguchi, Japan. These teeth were first reported in 1996 and tentatively referred to the genus Hybodus, but their taxonomy was not rigorously evaluated in an apomorphy-based context, and they have since been mostly overlooked. Herein, we assign them to a new species, Parvodus ominechonensis, based on a combination of synapomorphies of the lonchidiid genus Parvodus and autapomorphic character states. A diversity of Triassic hybodontiforms is known from Japan, but of these, Parvodus ominechonensis sp. nov. is the only taxon known from nonmarine deposits and the first reported occurrence of Lonchidiidae. Parvodus ominechonensis fills a gap in the stratigraphic record of Parvodus between occurrences in Middle Triassic (Anisian) and Middle Jurassic (Bajocian) strata. The global Triassic record of Parvodus comprises Parvodus huizodus from the Olenekian of China, Parvodus sp. from the Anisian of China, and Parvodus ominechonensis from the Carnian of Japan, of which Parvodus ominechonensis and Parvodus huizodus are known from nonmarine deposits. After the Triassic, Parvodus is known from marine and nonmarine strata across Laurasia and in South America until its extinction during the Early Cretaceous. This suggests that Parvodus may have originated in freshwater habitats in the South China region of Pangea following the end-Permian mass extinction and diversified throughout the Triassic in present day East Asia before attaining a global distribution later in the Mesozoic.

Current research suggests that ornithischians originated in the Middle–Late Triassic and achieved a global distribution by the Early Jurassic, but the Middle Jurassic was a pivotal period in which the clade underwent rapid diversification and radiation. However, Middle Jurassic ornithischian fossils are rare, with few named taxa and numerous occurrences of isolated teeth with disputed identifications. Here, we apply detailed morphological comparisons to a suite of isolated ornithischian teeth from Bathonian microvertebrate sites in the U.K., to assess their taxonomic affinities. These reveal a hitherto unknown, highly diverse ornithischian fauna that significantly increases the known diversity of ornithischians from this time period in the U.K. Comparisons indicate the presence of six ornithischian morphotypes: an indeterminate ornithischian, a heterodontosaurid, two indeterminate thyreophorans, a stegosaur, and an ankylosaur. These results confirm the predictions made by phylogenetic studies that Ornithischia rapidly diversified in the Middle Jurassic, fill in temporal gaps within lineages, and also include recognition of one of the oldest global occurrences of stegosaurs. In addition, the mixture of non-eurypodan and eurypodan morphotypes identified suggests that not only did non-eurypodans survive until at least the Middle Jurassic but they also co-existed with early eurypodans.

Understanding how biodiversity has changed through time and space is a central aim of paleobiology. To elucidate accurate biodiversity patterns in deep time, regional case studies, where sampling biases can be minimized, are needed. The Upper Jurassic Morrison Formation of the western U.S.A. crops out over 1.2 million km² and covers 12° of latitude. It was deposited over a ∼9-million-year time period, and was home to some of the most iconic dinosaurs. Utilizing a new, high resolution chronostratigraphic framework for the formation, tetrapod occurrences from the Paleobiology Database were temporally and spatially mapped to examine patterns of diversity change through time and space, and the geographic ranges of taxa were examined to shed light on niche partitioning. Latitudinally, diversity was found to peak in the center of the basin, perhaps due to the availability of water resources. Diversity increased over time in the Morrison Formation, and there is no evidence to indicate a decline in diversity prior to the extinction of the fauna at the end of the Jurassic. There appears to be some degree of geographic separation of faunas in the Morrison basin, with a southeastern and northwestern fauna, albeit with a number of overlapping taxa. High resolution climate models paired with detailed sedimentological analysis could help to elucidate the drivers of the patterns observed here.

—Edmontosaurus regalis is a hadrosaurid represented by abundant fossil material from the late Campanian–early Maastrichtian of what is now Alberta, Canada. Despite its prevalence, juvenile craniomandibular elements of E. regalis are poorly known. A newly collected partial skeleton from the Horseshoe Canyon Formation, UALVP 60425, represents a small saurolophine with a partial skull (skull length ∼500 mm). It can be referred to Edmontosaurini based on the presence of a postorbital fossa and anteroposteriorly long frontals that lack a dorsally oriented nasal contact and contribute significantly to the orbital margin. Despite its small size and presumed immaturity, UALVP 60425 is assigned to E. regalis based on a horizontal shelf on the postorbital process of the jugal. The deep postorbital fossa that, in part, diagnoses E. regalis is acquired during growth. UALVP 60425 shares many features with the Alaskan Prince Creek saurolophine (Ugrunaaluk kuukpikensis); both show consistent anatomical differences in the lacrimal, jugal, and postorbitals from E. annectens throughout their growth series. New data from UALVP 6025 supports referring the Alaskan saurolophine material to Edmontosaurus cf. regalis in the absence of large-sized cranial material from the Prince Creek Formation.

Palacrodon, a near-crown stem reptile, is known from several Triassic sites across the globe, and is easily recognized by its dentition characterized by labiolingually expanded molariform teeth coupled with acrodont tooth implantation. Here we explore the nature of tooth implantation and attachment in specimens of Palacrodon from South Africa and Arizona, U.S.A. using µCT. We note the presence of unusual ridges located underneath the tooth crowns in Palacrodon browni. Such ridges are not present in specimens from Arizona, which warrants the naming of a new species P. parkeri. We conducted a broad survey of internal tooth morphology across extant and extinct pan-reptiles (n = 212), and we conclude that homologous ridges like those we observe in P. browni are not present in any other species of reptile. As such, our ability to determine the function of the ridges is limited, though we hypothesize it is related to tooth attachment via unmineralized soft tissues.

The vertebrate assemblages of the Albian to Cenomanian Wayan Formation of southeastern Idaho and southwestern Montana's coeval Vaughn Member of the Blackleaf Formation are dominated by the small, burrowing orodromine dinosaur Oryctodromeus cubicularis. Here, we describe in detail the osteology of Oryctodromeus based on new specimens from Idaho and Montana that add substantially to the preliminary description of the types from Montana, and provide a suite of additional diagnostic characters for the taxon: ilium with elongate preacetabular process; elongate cervical vertebra centra with an anteroposterior length 1.6 times the dorsoventral height; elongate dorsal vertebra centra with an anteroposterior length 1.4 times the dorsoventral height; more than 55 elongate caudal vertebrae enveloped in hypaxial and epaxial ossified tendons; and a femoral head on an elongate neck—similar to that of Koreanosaurus—projecting from the greater trochanter at about 35°. The tail, comprising two-thirds of the animal's roughly 3 meters length, and associated tendon sheaths in the axial column indicate greater flexibility than previously supposed for ossified tendons or, alternatively, suggest that the Oryctodromeus burrows had separate, or multiple entrances and exits. The elongated and angled femoral head likely facilitated digging via a braced splayed-leg posture. Our phylogenetic analysis incorporates new characteristics and supports the monophyly of Orodrominae, a clade of neornithischian dinosaurs from the middle to Late Cretaceous of Asia and western North America that utilized burrowing.

A transfer-prepared specimen of Lepidotes (Actinopterygii, Lepisosteiformes) from the Posidonia Shale Formation of south Germany is tentatively identified specifically as L. gigas. The genus and its species are insufficiently defined and in need of revision. The new specimen reveals details of the cranial and pectoral girdle skeletal architecture and previously unknown osteological features of Lepidotes, such as a large foramen on the maxilla and the formation of two tooth-bearing clavicle elements (serrated appendages). Maxillary foramina are also known in the related contemporaneous lepisosteiform Mengius and possibly served for passage of nerve branches supplying either a maxillary pit-line or cutaneous sense organs (taste buds) in a thickened upper lip or barbels. The clavicle elements agree morphologically with those of the Recent Amia. Their function remains obscure.

The skull of Plioplatecarpus possesses large orbits and a large parietal foramen. Although the large orbits suggest that Plioplatecarpus possessed large eyes with enhanced visual performance, none of the previously described skulls include a sclerotic ring, and so it has been impossible in the past to reconstruct their size or optical properties. A recently collected skull with a sclerotic ring preserved in situ provides for the first time the data to do so. The dimensions of the sclerotic ring demonstrate that, although the f-number of the eyeball was not low enough to support the hypothesis that Plioplatecarpus was adapted to low light conditions, the eyeball was nevertheless large and possessed increased visual acuity and sensitivity that enabled the mosasaur to operate efficiently in both light-rich and light-poor conditions and possibly other conditions of reduced visibility. Proportions of this skull also suggest that Plioplatecarpus possessed a relatively wide binocular field of vision, providing stereoscopic vision, and further increasing both acuity and sensitivity, enhancing its ability to effectively detect and track quickly moving objects under a wide range of light conditions. A greatly enlarged parietal foramen implies the presence of a large parietal eye, the significance of which is uncertain, but it may have enhanced the ability to regulate migratory behavior.

The larger species in many mammalian clades have relatively longer faces than their smaller relatives. This has been shown to be true for extant kangaroos (Macropodinae), who follow the CREA rule of positive facial allometry; but the extinct short-faced kangaroos (Sthenurinae) have not so far been examined. Using linear measurements, rather than CREA techniques, we show here that sthenurine face lengths scale with negative allometry, thus differing from the trend seen in their extant relatives.