The holotypic materials of the sauropod ‘Morosaurus' agilis—a partial skull, proatlases, and first three cervical vertebrae—have been a taxonomic and phylogenetic mystery since their initial description by O. C. Marsh in 1889 and redescription by C. W. Gilmore in 1907. Although most species of Morosaurus were subsumed into Camarasaurus in 1919, ‘M.' agilis was left in the defunct genus without a proper taxonomic assignment. Similarities have been noted between ‘M.' agilis and other Morrison Formation sauropod taxa, including Camarasaurus, Haplocanthosaurus, Diplodocus, and Brachiosauridae, but it had yet to be included in a phylogenetic analysis. Here we present new data following additional preparation and study that suggest ‘M.' agilis is a basally diverging member of Dicraeosauridae, along with the recently described sauropod Kaatedocus. Based upon its recovery as a distinct taxon, we propose that ‘M.’ agilis receive the new generic name Smitanosaurus, yielding the new combination Smitanosaurus agilis.

Phorusrhacidae, popularly known as ‘terror birds’, are the most speciose clade within the avian order Cariamiformes, with a fossil record that ranges from the Eocene to the Pleistocene. Although several species have preserved skulls, our understanding of their cranial morphology remains incomplete. Here, a comprehensive overview of the current knowledge of phorusrhacid skull anatomy is presented. The phorusrhacid skull bauplan includes salient features such as deep, triangular fossae temporales, a complex basipterygoid articulation and the loss of bending zones related to kinesis. Two skull morphotypes can be discriminated: the psilopterine and the ‘terror bird' type. The ‘terror bird’ skull type is here considered an evolutionary specialization, indicating that among phorusrhacids, medium-size to large phorusrhacids show more rigid and stiffer skulls. Nevertheless, studies have shown that the two morphotypes may have handled prey in a similar manner, suggesting that a trophic specialization with a unique hunting technique was the key driver of the evolution of the phorusrhacid skull.

Sphyraenidae is a cosmopolitan group of marine fishes represented by both extant and extinct taxa with occurrences spanning most of the Cenozoic. Although some species are known from well-preserved specimens with a considerable degree of completeness, most of the fossil record in the family consists of isolated teeth. Fossil occurrences of the genus Sphyraena are described from the Neogene Castilletes fauna of Colombia and the Palmetto and Torreya faunas in the United States. Symphysial teeth are found to differ serially, thus allowing us to refine anatomical descriptions of common isolated fossil remains in the genus Sphyraena. Comparisons with other marine taxa that show hypertrophied symphysial teeth are made in order to assess the taxonomic value of symphysial teeth as diagnostic structures of value in studies of isolated sphyraenid specimens.

The diversity in positions of nasal capsules has been well documented in various subgroups of placoderms or jawed stem gnathostomes. However, the condition in primitive antiarchs (i.e., the Yunnanolepidoidei) remains unclear, and the positional shift of nasal capsules in the Antiarcha has never been mentioned. Here we re-describe the headshield of Parayunnanolepis xitunensis, a yunnanolepidoid antiarch from the Lower Devonian of China, using X-ray computed tomography scanning. The study provides new anatomical details of the headshield including the sclerotic capsules, the visceral side of the rostral and pineal plates, and the dorsal profile of the endocranium. Parayunnanolepis xitunensis bears a pair of nasal capsules underlying the rostral plate between the eyes, resembling Romundina but differing from most euantiarchs, whose nasal capsules are encased in the preorbital recess in front of the eyes. A phylogenetic analysis based on a modified matrix indicates a stepwise forward migration of nasal capsules within antiarchs, accompanied by the innovation of the preorbital recess and the loss of the preorbital depression.

South America is well known for its abundance of Quaternary fossiliferous deposits, but well-preserved fossil remains from well-dated sites are scarce in the Atacama Desert and adjacent arid Andes. Here we report on a partially complete skeleton (46%) of a single young (ca. 3–4 years old) extinct horse discovered in the Salar de Surire, a salt flat located on the Andean altiplano of northern Chile (4,250 m asl). Comparative and osteometric morphological analyses identify the specimen as a South American endemic horse Hippidion saldiasiRoth, 1899. A direct AMS radiocarbon date on bone collagen yielded a calibrated age of 13,170 cal yr BP (2σ range: 13,300–13,060 cal yr BP) indicating that it lived near the end of the last glaciation. The body mass of the individual was calculated at approximately 326.4 kg, close to the upper limit of the larger sizes reported for the genus. Stable isotope evidence shows that the Salar de Surire horse relied on an almost 100% C3 diet that is mostly consistent with Hippidion specimens from other environments that also consumed either mixed C3/C4 or fully C3 diets. This finding is now the southernmost high-elevation record for this species and provides further evidence for the broad geographic and ecological distribution of this genus throughout southern South America.

A stegosaurian humerus from the Oxfordian–Tithonian(?) Cañadón Calcáreo Formation of Chubut, Argentina, extends the fossil record of this clade of thyreophoran ornithischian dinosaurs to the Upper Jurassic of South America. The element shares the derived character of an oblique ridge extending from the deltopectoral crest towards the medial distal condyle with taxa such as Kentrosaurus and Stegosaurus and thus represents a derived representative of the clade. The presence of stegosaurs in the Cañadón Calcáreo Formation underlines the similarities of its dinosaur fauna with other Late Jurassic dinosaur faunas, such as the Morrison Formation of North America or the Tendaguru Formation of Tanzania, in at least broad systematic terms.

Our understanding of Typothorax coccinarum is primarily based on postcranial material, along with a few isolated cranial elements. Here we describe the first complete articulated skull of Typothorax coccinarum from the Owl Rock Member of the Late Triassic Chinle Formation in Petrified Forest National Park. We assessed the relationships and defining synapomorphies for some of the major clades within Aetosauria by using a combination of morphological characters in the cranium of Typothorax coccinarum. Based on the descriptions of skulls from a variety of aetosaur species including Aetosaurus ferratus, Aetosauroides scagliai, Coahomasuchus chathamensis, Neoaetosauroides engaeus, Paratypothorax andressorum, Stagonolepis olenkae, Stenomyti huangae, Scutarx deltatylus, and now Typothorax coccinarum, it is apparent that the two major aetosaurian clades vary in their overall skull morphologies. The stagonolepidoids share a more robust, elongate skull, with varying degrees in the lateral expansion of the premaxillary tips. On the other hand, aetosaurines share an overall shorter, more gracile skull with tapered premaxillae. These new characters are mapped onto a revised phylogenetic tree for the Aetosauria. Historically, aetosaurs were interpreted as being predominantly herbivorous. In recent years, the discovery of new aetosaur cranial material, like that of Neoaetosauroides engaeus and Aetosauroides scagliai, suggested an omnivorous diet for at least some aetosaur taxa. The dentition of Typothorax coccinarum possesses the most strongly developed heterodonty for an aetosaur, therefore challenging the historical interpretation by expanding the range of dentition types within Aetosauria. This supports the more recent hypothesis that aetosaurs exhibited diverse feeding strategies beyond just herbivory.

Abelisaurids are among the most abundant and diverse Patagonian Late Cretaceous theropods. Here, we present a new furileusaurian abelisaurid, Llukalkan aliocranianus gen. et sp. nov., represented by cranial remains from the Bajo de la Carpa Formation (Santonian) at La Invernada fossil area, northwestern Patagonia. Features characterizing this taxon include a possible caudal tympanic recess posterior to the columellar recess, a T-shaped lacrimal with jugal ramus lacking a suborbital process, and large foramina for caudal middle cerebral veins widely separated from the median supraoccipital crest. In addition to this, a bulge on the anteromedial border of the supratemporal fossa, tall and posteriorly projected paroccipital processes, basal tubera interconnected distally, a triangular basisphenoid recess, and a single foramen for the sphenoidal artery on the basisphenoid, differentiate Llukalkan from Viavenator exxoni. The latter is the other furileusaurian taxon from the same area and stratigraphic unit. Although the holotype of Llukalkan probably corresponds to a sub-adult—as the lacrimal morphology suggests— the possibility that it represents a juvenile of V. exxoni is discarded based mainly on the presence of a caudal tympanic recess (which is absent in V. exxoni). The probable coexistence of two abelisaurid taxa demonstrates that the abelisaurids were one of the most important—and likely the main—predator component of the ecosystems, not only in this area, but also in all of Patagonia, during the Late Cretaceous.

The dissorophid genus Conjunctio (Temnospondyli) is poorly characterized, known only from two incomplete specimens from the upper El Cobre Canyon Formation (lower Permian), Cutler Group, New Mexico, U.S.A. Nonetheless, the taxon's conserved morphology and stratigraphic occurrence near the Carboniferous–Permian boundary (ca. 299 million years ago) make it an important datum to resolve the early diversification of dissorophids. We report the first occurrence of Conjunctio cf. C. multidens in the adjacent undivided Cutler Formation of San Miguel County, Colorado, which also represents only the second dissorophid from southwestern Colorado's historic Placerville assemblage. The new specimen highlights the plesiomorphic anatomy of Conjunctio, with newly described mandibular and postcranial data, and provides further evidence for a relationship to the Eucacopinae. We performed a phylogenetic analysis of 34 temnospondyl taxa by modifying a previously published matrix of 102 craniodental and postcranial characters, scoring Conjunctio at the specimen-level, and found a monophyletic Conjunctio at the base of Eucacopinae. The clade also included the earliest Permian Reiszerpeton and Scapanops in relatively basal positions, and an unresolved polytomy among the later Permian Cacops, Kamacops, Zygosaurus, and Anakamacops. Geographically, the discovery of Conjunctio among the Placerville assemblage is consistent with a broader southwestern U.S. Wolfcampian fauna, correlative to that of the upper El Cobre Canyon Formation in northern New Mexico, and may underscore previously proposed regional provincialism among early Permian tetrapod assemblages.

The Lophiodontidae are endemic perissodactyls from Europe that flourished during the Eocene. Despite their preponderance in the European fossil record, their exact origin and relationships within the perissodactyls remain unknown due to the rare and fragmentary material in the early Ypresian, the time of their earliest radiation. Lophiaspis maurettei is the oldest and earliest diverging lophiodontid known to date but is unfortunately poorly known. We describe here the results of new excavations of the type locality of Palette. Important new material including complete skulls, mandibles, post-cranial elements and juvenile specimens lead us to revise Lophiaspis maurettei from Palette and other localities and to describe novel morphology for this species. According to an original phylogenetic analysis, based on a revised matrix of dental, cranio-mandibular and postcranial characters, Ls. maurettei is an early diverging lophiodontid morphologically close to Protomoropus and Paleomoropus, two basal chalicotheres, known from Asia and North America, respectively. Our resulting topology does not support the previously proposed inclusion of the lophiodontids within the Ceratomorpha and supports a position within the suborder Ancylopoda, close to some Eomoropidae representatives. These results imply that Ls. maurettei was restricted to Southern Europe during the early Eocene, which would be compatible with an Asian origin for lophiodontids in accordance with the evolutionary history of other perissodactyls and placental mammals.

A chimaeroid species, Edaphodon eyrensisLong, 1985 (Holocephali, Chimaeroidei), from the Lower Cretaceous Bulldog Shale of the Eromanga Basin, South Australia, is reassessed as Ptyktoptychion eyrensis (Long, 1985), comb. nov. This is the oldest representative of the endemic Australian chimaeroid genus PtyktoptychionLees, 1986. An ancestor of this genus could be the Early Cretaceous chimaeroid Ischyodus thurmanniPictet and Campiche, 1858 from the northern hemisphere. Ptyktoptychion eyrensis survived in Australia in southern polar environment conditions.

Fossil tracks should theoretically capture differences in pedal anatomy between growth stages of the same taxon, particularly those related to the soft tissue of the foot, providing a more realistic view of pedal ontogeny than skeletal material alone. However, recognizing these ontogenetic trajectories is complicated by the influence of preservation and kinematics on track morphology, as well as the inherent difficulty of referring different tracks to a single taxon. Here, we explore differences in track morphology from a collection of tracks attributed to tyrannosaurids from Unit 4 of the Wapiti Formation (upper Campanian) in western Canada. Along with morphology, close geographic and stratigraphic associations suggest that the tracks pertain to similar tyrannosaurid trackmakers. A geometric morphometric analysis of the track outlines reveals size-dependent increase in relative track robusticity, driven primarily by an increase in ‘heel' breadth and surface area. This relationship is lost when the dataset is expanded to include tyrannosaurid tracks globally, which we attribute to increased stratigraphic and taxonomic ‘noise’ within the global dataset that masks the tightly constrained patterns obtained from the Wapiti Formation tracks. Although there is some substrate and kinematic influence on certain aspects of track morphology, we hypothesize that the observed size-dependent relationship reflects genuine expansion in the breadth of the heel soft tissues and probably their overall surface area associated with growth. Increased pedal robusticity likely assisted with weight bearing and locomotor stability as body mass increased over ontogeny, supporting previous hypotheses that some tyrannosaurids underwent a growth-related reduction in relative agility and/or cursorial performance.

The early Barremian Iberian ornithopod Iguanodon galvensis was described for the first time in 2015. However, much of its anatomy, such as the axial skeleton in mature specimens, remains unknown. Here, the partially articulated presacral vertebrae and ribs belonging to a large adult ornithopod (DS-1 ornithopod) from the lower Barremian (Lower Cretaceous) that were found in Teruel Province (northeast of the Iberian Peninsula, Spain) are investigated by a systematic study and a phylogenetic analysis. The only cervical vertebra preserved is strongly opisthocoelus, as is typical of styracosternans. In fact, the phylogenetic analysis resolves DS-1 ornithopod as an hadrosauriform styracosternan. The assemblage also includes ten anterior-to-posterior dorsal vertebrae that strongly resemble those of the contemporary European iguanodontoid Iguanodon, particularly in having amphiplatyan and higher-than-long centra and dorsal neural spines two times the lateral height of their centra and slightly sigmoid in the posterior vertebrae. In addition, the dorsal centra are moderately compressed between the articular faces and lack a ventral keel, unlike the late Barremian type species I. bernissartensis but resembling the sympatric I. galvensis. For these reasons, DS-1 ornithopod is ascribed here as I. cf. galvensis. Moreover, this specimen has costovertebral ankyloses likely related to the specimen's maturity. Finally, the fossils of I. galvensis including those referred to it as DS-1 ornithopod, as well as evidence provided by bones and tracks in other places, indicate that the genus Iguanodon frequently occupied areas around rivers, lakes, estuaries, or lagoons.

The genus Wakaleo represents a close outgroup to the charismatic marsupial hypercarnivore Thylacoleo carnifex. While early species of Wakaleo were likely arboreal, or at least scansorial, the ecology of later species of Wakaleo is not well understood. Here we present descriptions of new postcranial material of W. vanderleueri and W. alcootaensis from mid- and late-Miocene fossil deposits from the Australian Northern Territory. New calculations suggest that these taxa were smaller than previously thought, around 30 kg and 50 kg respectively. The postcrania reveal increasing adaptation towards terrestrial locomotion and felid-like grappling predation within this lineage, in contrast to the more canid-like adaptations occurring at around the same time in the other major group of terrestrial marsupial carnivores, the thylacinids. This hypothesis seems to reflect similar patterns of divergent morphological adaptation towards large carnivorous forms among placental mammals, and highlights a greater diversity in the evolutionary history of medium to large sized marsupial carnivores during the Miocene in Australia than previously recognized.

Although Neogene crocodylians were well documented from Indo-Pakistan, few fossils were known from Southeast Asia, precluding the understanding of their evolutionary and biogeographic history. Here, we describe crocodylians from the Neogene Irrawaddy Formation of central Myanmar and evaluate their taxonomic status. Tebingan, SE of Magway (lower Upper Miocene) yields Gavialis and Crocodylus that differ from the previously known species of each genus, and the Gwebin area, SW of Bagan (Upper Pliocene) produces Crocodylus cf. palaeindicus. Taking into account the materials without provenance data, Neogene crocodylians from Myanmar include at least three gavialids and two Crocodylus that are characterized by different craniomandibular and postcranial features. The body length estimates for the gavialines from Tebingan and an unknown locality in central Myanmar are 7.5 m and 8.6 m, respectively, which exceed the maximum size limit of extant Gavialis gangeticus. Together with the previously reported large taxa, gavialids repeatedly evolved large body sizes in the Neogene of Asia. Gavialis from the Miocene of Myanmar is one of the oldest records of the genus, and its unraised orbital rim suggests that the “telescoped” eyes derived later during the genus evolution. Crocodylus cf. palaeindicus from the Pliocene of Myanmar indicates the species range was extended from western India to Myanmar during the Neogene. The absence of Crocodylus siamensis in the Neogene of India and central Myanmar implies the species originated east of central Myanmar.

We examined a selection of three-dimensionally preserved quadrate bones from representatives of all major clades of mosasauroid reptiles, an extinct group of marine lizards inclusive of aigialosaurs and mosasaurs (Squamata, Mosasauroidea). The quadrate bones appear to be very diverse within and across mosasauroid clades, and show variable combinations of ridges, crests, and processes. Because of its complex features and diversity, taxonomists have often relied quite heavily on quadrate morphology both in alpha-level classification of mosasauroids and for use as characters in phylogenetic analyses. However, the terminology applied to some quadrate features has been inconsistent, in particular regarding the ‘infrastapedial process.’ Such a lack of clarity of even anatomical terms hampers our understanding of the evolution of the morphology of this complex bone. Here we provide a comprehensive comparison of mosasauroid quadrates contextualized against a recent phylogeny of the group, and demonstrate that some features of the posteroventral region of these bones are likely homoplastic and require the establishment of a new set of anatomical terms.

We describe a new taxon of lepidosauromorph reptile, Vinitasaura lizae, based on a nearly complete dentary and the posterior portion of a second dentary from the Upper Triassic (upper Carnian) Vinita Formation in east-central Virginia. It offers new insights into the morphological diversification and spatiotemporal distribution of lepidosauromorphs during the Triassic. The lepidosauromorph assemblage from the Vinita Formation include at least two other taxa and reveals connections to others in Europe and North America. It currently provides the best record of the early diversification of these reptiles in equatorial Pangaea, highlighting the potential importance of similar assemblages from still poorly sampled regions such as western North America for addressing questions concerning the origin and evolutionary history of this major diapsid clade during the Triassic.