The Hemphillian-age Mehrten Formation has yielded several fossil dogs (family Canidae). Initial study had identified all larger canids as Borophagus secundus ( = Osteoborus cyonoides), a bone-crushing borophagine (a diverse subfamily of extinct canids), and all smaller canids as Canis cf. C. davisi, a canine (a subfamily including all living canids). Later analysis split B. secundus into two taxa and reassigned Canis cf. C. davisi to Eucyon davisi, yet omitted fragmentary remains of possible vulpines. Despite this wealth of Mehrten canid materials, a detailed systematic treatment is lacking. More recently, additional specimens have become available, further necessitating a systematic examination of the canids at this site. The present study finds four canid species: two borophagines (Borophagus parvus and B. secundus) and two canines (E. davisi and Vulpes stenognathus, newly identified). We support the division of ‘B. secundus’ into the smaller B. parvus and the larger, more hypercarnivorous B. secundus and find two morphotypes within B. parvus. A specimen from the Coyote Hill fauna, earliest in the Mehrten sequence, is reassigned to B. secundus, extending the temporal range of the species in California into the early Hemphillian. Borophagus parvus co-occurs with B. secundus only in the lower Modesto Reservoir Member; higher in the sequence, B. parvus co-occurs only with canines. Despite the apparent turnover in its co-inhabitants, B. parvus exhibits no size change. Given that the characteristics of B. parvus and B. secundus are intermediate among other Borophagus, the Mehrten canids may represent a rapid transition early in the evolution of the Borophagus lineage.

Stegosauria is a clade of ornithischian dinosaurs characterized by a bizarre array of dermal armor that extends from the neck to the end of the tail. Two genera of stegosaur are currently recognised from North America: the well-known Stegosaurus stenops and the much rarer Hesperosaurus mjosi. A new specimen of Hesperosaurus mjosi was discovered in some of the most northerly outcrops of the Upper Jurassic Morrison Formation near Livingston, Montana. The new specimen includes cranial, vertebral, and appendicular material as well as a dermal plate, and the excellent state of preservation of the palate reveals new anatomical information about this region in stegosaurs. Histological examination of the tibia indicates that the individual was not skeletally mature at time of death. Comparison with previously studied Stegosaurus and Hesperosaurus individuals indicates that Hesperosaurus mjosi may have been a smaller species than Stegosaurus stenops. Physiological processes scale with body mass, M, according to the relationshipM^0.75 in extant megaherbivores; thus, larger animals are better able to cope with more arid environments where forage is less abundant. Under this scenario, it is possible that Stegosaurus stenops and Hesperosaurus mjosi were environmentally partitioned, with the larger S. stenops occupying more arid environments. Analyses of the temporal overlap and latitudinal range of Morrison stegosaurs would allow this hypothesis to be investigated.

The upper Maastrichtian elasmosaurid plesiosaur Aristonectes quiriquinensis from central Chile is here redescribed following further preparation of the holotype. New cranial characters include a flattened skull with a caudal extension of the mandibular articulation far posterior to the occipital condyle; a very long, horizontal, and posteriorly oriented paroccipital process; mandible with restricted gape angle; and teeth oriented rostrally and not interlocking during occlusion. Postcranial features include the presence of very long extremities (ca. 3 m), whereas features of the caudal-most vertebrae suggest the presence of a horizontal caudal fin. Additionally, neuroanatomical features of Aristonectes are for the first time described based on a braincase cast. Integration of osteological features, anatomical comparisons, as well as taphonomic and environmental data strongly suggests that the foraging behavior of Aristonectes quiriquinensis incorporated a mix of engulfment and feeding from benthic sediments. This is a novelty among elasmosaurids, so far considered as mainly epipelagic feeders.

Fossil vertebrae from the early Miocene of France (Loire Basin) are described. They show several characters generally regarded as varanid synapomorphies. A phylogenetic analysis of these vertebrae is performed with a subset of morphological data taken from several large morphological data sets (vertebral characters) and it confirms an attribution to varanid lizards. Moreover, referral of isolated vertebrae from the Eocene-Oligocene of Egypt to varanids is confirmed. The use of subsets of large morphological data sets in phylogenetic analysis of fossils (especially incomplete remains) is discussed and advocated for, and we argue that convergence between tree topologies obtained from different kinds of data sets is a key issue in inferring the phylogenetic position of fossil taxa.

Reexamination of Sciurotamias gromovi from the upper Miocene of Ukraine stimulated revision of Sinotamias, a problematic Neogene sciurid of uncertain affinities and previously documented only from the middle-upper Miocene of Asia. A reanalysis of the Ukrainian material and other morphologically similar taxa shows Sinotamias to be a member of the xerine tribe Marmotini. Sciurotamias gromovi and Tamias atsali are shown to be members of Sinotamias. Tamias anatoliensis from the upper Miocene of Turkey is a junior subjective synonym of Sinotamias primitivus. Sinotamias minutus and Sinotamias maximus are excluded from the genus. The latter species is referred to Kherem. Prospermophilus is synonymized with Sinotamias. Phylogenetic analysis of 23 xerine genera using 66 craniodental characters places Sinotamias among the basal Marmotina as a sister group to the living members of the subtribe. The species of the genus are united by obliquely striated lower incisors, posteriorly expanded metaconules of M1–2, and posteriorly tapered ectolophid of m1–2. The late Oligocene-early Miocene Asian genus Plesiosciurus, previously classified in the sciurid subfamily Sciurinae, is instead a member of the Marmotini and is recovered as the sister taxon to Miospermophilus and Sinotamias. The genera Ammospermophilus, Cynomys, Marmota, Miospermophilus, Paenemarmota, Plesiosciurus, Sinotamias, and Spermophilus s.l. form a monophyletic subtribe Marmotina, supported by the absence of the mesoconid in m1–3. Miospermophilus is identified as the basal-most member of this group of genera, suggesting a Nearctic origin for the Marmotina. Sinotamias, considered to be a descendant of Plesiosciurus, appears to have originated in Asia and entered Europe around 8.5 Ma.

Unknown, well-preserved fish specimens from the Upper Jurassic Plattenkalk of Cerin, France, found in the historical collection in Muséum d'Histoire Naturelle de Lyon, France, and from the excavation site of the Collections de Géologie, Université Claude Bernard Lyon 1, France, permit description of Cerinichthys koelblae, gen. et sp. nov. This new genus differs from all other Halecomorphi in the following combination of features: 27 caudal principal rays; 51 vertical scale rows; presence of broadened basal fin segments in the posterior rays of the pectoral, pelvic, anal, and dorsal fins and the median rays of the caudal fin; complete absence of vertebral centra in adult-sized individuals and multiple small scales in the median and ventral parts of the caudal peduncle. Investigations concerning the phylogenetic setting of the new genus Cerinichthys led to a proposal for a revision of the Halecomorphi, with Cerinichthys as a basal member of the new order Ophiopsiformes. The new family Ophiopsiellidae, as replacement for Ophiopsidae, within the Ophiopsiformes, are ganoinscaled Halecomorphi with one horizontally elongated dorsal fin or two dorsal fins. The Ionoscopidae are proposed to belong in the Amiiformes, and the order Ionoscopiformes needs to be reconsidered. The more basal Halecomorphi with massive ganoin scales remain poorly known, compared with the more advanced halecomorph group of the Amiidae. Closer investigation of their morphology and taxonomic relationships is therefore important for understanding broader patterns of halecomorph evolution.

Whereas ornithomimosaurs (ostrich-mimic dinosaurs) are well known from Asia during the Early Cretaceous, they are less well known from this time in North America. Represented by a single specimen consisting of pedal elements, a new North American taxon, Arkansaurus fridayi, gen. et sp. nov., consists of a nearly complete right foot, recovered from the Lower Cretaceous (Albian-Aptian) Trinity Group of Arkansas. Arkansaurus fridayi can be distinguished from other ornithomimosaurs based on differentiated pedal unguals, a laterally compressed third metatarsal that is ovoid in proximal view, and a distal ungual with a very weak flexor tubercle, lacking spurs. The condition of this third metatarsal suggests that Arkansaurus fridayi is more basal than Asiatic ornithomimosaurs of similar age, but consistent with older North American forms. This specimen provides knowledge of a poorly understood radiation of ornithomimosaurs in Appalachia and is the only known saurischian dinosaurian fossil from the state of Arkansas.

The Osteostraci are an early clade of jawless vertebrates widely regarded as the sister group of all jawed vertebrates. Despite their prominent role in the Silurian to Devonian marginal marine ecosystems, the early evolutionary history of this subclass remains poorly understood. Here we report the discovery of a head shield (part with broken right margin and counterpart) of Kalanaspis delectabilis gen. et sp. nov. from the Kalana Quarry in Central Estonia. Reliably dated to the Pranognathus tenuis Conodont Zone, Raikküla Regional Stage, mid-Aeronian, mid-Llandovery, the specimen is about 10 million years older than the previously known oldest record of the Osteostraci. Kalanaspis delectabilis gen. et sp. nov. is identified as belonging to the new Family Kalanaspididae fam. nov., Order Ateleaspidiformes. It has a relatively large dorsal head shield, which is somewhat wider than long, with very small and very closely placed orbits, short prepineal length, one pair of notably long lateral fields, and gently undulating posterior margin. It lacks a posteromedian dorsal ridge as well as cornual processes and pectoral sinuses. No impressions of nasohypophyseal and pineal features were detected. The preservation of the specimen is unusual; the energy-dispersive spectroscopy (EDS) elemental analysis revealed that calcium phosphate, the original major constituent of the dermal skeleton of vertebrates, has disappeared and has been substituted by carbonaceous matter.

Xotodon caravela, a new species of toxodontid from northwestern Argentina, is presented. The material studied consists of a well-preserved and nearly complete mandible and a maxillary fragment, recovered in the Aconquija Formation (late Miocene-early Pliocene) at the El Molino locality (Tucumán Province, Argentina). The fossil diversity of the levels is concordant with an early Pliocene fauna. The general features of the dentition and mandible (e.g., concave ectoloph and single lingual fold on upper molars, anterior fold mesially displaced relative to the hypoflexid in the lower molars, sigmoid lateral outline of chin, and continuous enamel on M3) allow the inclusion of this specimen in the genus Xotodon. In turn, some traits indicate unequivocally that this is a new species, such as the anterior region without constriction at the premolar level, the approximately 13° angle of implantation of the i3 in relation to the ventral edge of the mandibular body (without lateral divergence), and the presence of an intra-alveolar projection of the incisive crown extending laterally below the premolars to the level of the p4 and forming a robust projection or lateral ledge. The new taxon was included in a matrix of 59 characters and compared with 32 notoungulate genera. The phylogenetic position and comparative analysis support the taxonomic interpretation of the studied specimen as a new species of Xotodon. This represents the first record of a toxodontid in the Neogene lowlands of northwestern Argentina and contributes to our knowledge of this family in the region.

Dinosauromorphs evolved a wide diversity of hind limb skeletal morphologies, suggesting highly divergent articular soft tissue anatomies. However, poor preservation of articular soft tissues in fossils has hampered any follow-on functional inferences. We reconstruct the hip joint soft tissue anatomy of non-dinosaurian dinosauromorphs and early dinosaurs using osteological correlates derived from extant sauropsids and infer trends in character transitions along the theropod and sauropodomorph lineagues. Femora and pelves of 107 dinosauromorphs and outgroup taxa were digitized using 3D imaging techniques. Key transitions were estimated using maximum likelihood ancestral state reconstruction. The hips of dinosauromorphs possessed wide a disparity of soft tissue morphologies beyond the types and combinations exhibited by extant archosaurs. Early evolution of the dinosauriform hip joint was characterized by the retention of a prominent femoral hyaline cartilage cone in post-neonatal individuals, with the cartilage cone independently reduced within theropods and sauropodomorphs. The femur of Dinosauriformes possessed a fibrocartilage sleeve on the metaphysis, which surrounded a hyaline core. The acetabulum of Dinosauriformes possessed distinct labrum and antitrochanter structures. In sauropodomorphs, hip congruence was maintained by thick hyaline cartilage on the femoral head, whereas theropods relied on acetabular tissues such as ligaments and articular pads. In particular, the craniolaterally ossified hip capsule of non- Avetheropoda neotheropods permitted mostly parasagittal femoral movements. These data indicate that the dinosauromorph hip underwent mosaic evolution within the saurischian lineage and that sauropodomorphs and theropods underwent both convergence and divergence in articular soft tissues, correlated with transitions in body size, locomotor posture, and joint loading.