Well-preserved, articulated juvenile sauropod dinosaur material is very rare, hindering attempts to understand ontogenetic changes within the clade. Here, we describe an exceptionally preserved partial skeleton of a Barosaurus from the Morrison Formation of Dinosaur National Monument, Utah, U.S.A., that is only about one-third adult size. This small size and the lack of fusion of neurocentral and costovertebral sutures indicate that the individual is a juvenile. Apomorphy-based taxonomic identification of the specimen combined with the excellent preservation of its vertebral column allows documentation of both serial and ontogenetic morphological changes in Barosaurus. Each vertebra underwent substantial morphological change in the relative height of the neural spine and location of the zygapophyseal and diapophyseal articular facets during ontogeny but not in the degree of bifurcation of the neural spines. Pneumaticity in the dorsal vertebrae varies serially: large pneumatic fossae punctuate the centra of dorsal vertebrae 1–4 and 8–9, whereas these spaces are occupied by shallow depressions in dorsal vertebrae 5–7. This represents the first known caudal dorsal pneumatic hiatus in a sauropod dinosaur, which suggests that separate air sacs pneumatized the anterior and posterior regions of the dorsal vertebral column, congruent with the pattern observed in non-avian and avian theropod dinosaurs and the presence of an avian-style lung in sauropods.

We describe tritylodontid remains from the Lower Cretaceous Kuwajima Formation (Tetori Group) in central Japan as representing a new genus, Montirictus kuwajimaensis, gen. et sp. nov. Montirictus is a medium-sized tritylodontid genus characterized by upper cheek teeth having the cusp formula 2-2-2 with subequal cusps, buccal and lingual cusps retaining a crescentic shape with both buccal and lingual ridges anteriorly, and ‘V’-shaped buccolingual cross-sections of two anteroposterior grooves between the three cusp rows. Tentative dating of the Kuwajima Formation to the Barremian-Aptian makes it the stratigraphically youngest representative of a long-lived, globally distributed and abundant mammaliamorph lineage and extends the known geographic range of tritylodontids.

The emergence of a reversed hallux (first pedal digit) in the theropod lineage is regarded as an important indicator of increasing grasping ability and possibly arboreality. However, functions of the pes with a plesiomorphic, nonreversed hallux in non-avian theropods, other than the major role in supporting and propelling the body during the stance phase, have not been fully addressed. To clarify hallucal function, 21 specimens of non-avian theropods were examined in this study. Ancestrally in Theropoda, the proximal end of the first metatarsal reached the ankle joint as in extant crocodilians. The size of the first metatarsal was then reduced, lost direct contact with the ankle joint, and shifted more plantarly in basal neotheropods. In articulated coelophysoid specimens, the proximal end of the first metatarsal attaches to the medioplantar margin of the second metatarsal, whereas the distal part of the first metatarsal and phalanges of the hallux lies on the plantar aspect of the pes. In four articulated specimens of the dromaeosaurid Velociraptor, preserved positions of the first metatarsal on the second metatarsal vary from the medial to plantar aspects, and correspondingly the rotational axis of the extension/flexion movement at its distal articulation ranges from mediolateral to dorsoplantar. Similar conditions are also observed in troodontid specimens, suggesting the presence of intermetatarsal mobility between the first and second metatarsals enabled by a convex proximal articular surface of the first metatarsal in deinonychosaurians similar to the one present in extant birds.

Abelisauroids are the most abundant theropods in the Cretaceous beds of Patagonia. They are traditionally subdivided into large-sized Abelisauridae and smaller Noasauridae. Here, we describe a new specimen of the small enigmatic abelisauroid Velocisaurus unicus Bonaparte, 1991, which was previously known from a single incomplete specimen from Neuquén City, Neuquén Province, Patagonia. The new material comes from the Santonian Bajo de la Carpa Formation (Late Cretaceous) at the Paso Córdova locality, Río Negro Province. It comprises an almost complete left hind limb and offers novel information about the anatomy of this poorly known abelisauroid. The new material shows that Velocisaurus is remarkable in having a very short, stout, and anteriorly bowed femur, which has a notably subtriangular cross-section at its proximal end. The tibia is long and slender, and the anterior surface of the distal end is anteroposteriorly flat and transversely expanded, with an enlarged surface for the ascending process of the astragalus. The pes has a stout third metatarsal, rod-like metatarsals II and IV, and highly modified phalanges of digit IV. The unique combination of characters of Velocisaurus indicates that this taxon belongs to a still poorly understood radiation of gracile-limbed abelisauroids. The inclusion of Velocisaurus in a comprehensive phylogenetic analysis recovers a monophyletic Noasauridae, but with only very weak support. Detailed analysis of features supporting the inclusion of Velocisaurus within Noasauridae is discussed, and their implications for abelisauroid phylogeny are revisited.

Articulated fishes are rare in Late Cretaceous non-marine deposits of the Western Interior; fishes are more often represented by disarticulated elements in vertebrate microfossil localities. A new Maastrichtian locality of the Scollard Formation in central Alberta, Canada, has been named Pisces Point to reflect the diversity of articulated fishes that are now being recovered from this site. Material collected from the Pisces Point locality includes a percopsiform, a semionotiform, at least one esociform, and at least two osteoglossomorphs. One of these is described here as a new genus and species, †Wilsonichthys aridinsulensis. A phylogenetic analysis shows this new taxon to be the sister group of most other Osteoglossiformes. The new articulated material allows us to identify some of the microfossil remains previously collected from other Late Cretaceous sites as belonging to the same or a similar taxon.

The locality of Sant Jaume de Frontanyà (Eastern Pyrenees, Catalonia, northeastern Spain) includes four fossil-bearing levels with an extraordinary abundance of mammal remains, representing the most significant middle Eocene site from the Iberian Peninsula. Despite this, the fauna from this locality has not been studied in detail. Recent work has mostly focused on the primates from the oldest levels, including the description of two new species, Anchomomys frontanyensis and Pseudoloris pyrenaicus. Recently, study of the primate remains from the uppermost level, Sant Jaume de Frontanyà-1 (SJF-1), has led to the description of a new species of Necrolemur. On the other hand, other mammal groups such as rodents are practically undescribed. In this work, rodent remains from SJF-1 are described for the first time. Three different forms have been identified: one glirid, referred to Glamys aff. robiacensis, and two theridomyids that have allowed the erection of the new species Paradelomys santjaumensis and Elfomys catalaunicus, suggested to be the most primitive members of the genera Paradelomys and Elfomys. These three forms show more primitive traits than other species from upper Bartonian (MP16) localities such as Robiac, Grisolles, and Le Bretou. Locality SJF-1 is therefore assigned to the lower Bartonian (MP15), with an age slightly older than Chéry-Chartreuve, and represents the first occurrence of the genera Paradelomys and Elfomys. Moreover, this dating allows us to place the only record of Necrolemur from the Iberian Peninsula in a correct chronological framework, shedding new light on the evolution of this primate genus.

We describe fossil kogiid periotics from the Lower Pliocene upper Bone Valley Formation in central Florida and the Lower to Upper Pliocene Yorktown Formation at Lee Creek Mine, North Carolina. The fossils show diagnostic characters that identify them as belonging to Kogiidae, such as three spines in the anterior process, presence of an incudal process, and a posterior process oriented along the long axis of the bone. Morphological comparisons and morphometric and statistical analyses of periotic proportions confirm the presence of a large and a small morphotype within the sample. The large morphotype (mean length = 39.76 mm) belongs to an unknown kogiid that occurs in both formations, whereas the small morphotype (mean length = 28.64 mm), referred to aff. Kogia sp., occurs only in the Yorktown Formation. The cooccurrence of two taxa in North Carolina may represent one of the earliest evidences of sympatry in kogiids and may demonstrate that this ecological behavior has been part of the natural history of this group at least since the deposition of the Yorktown Formation at Lee Creek (∼4.8–3.1 Ma). In addition, the occurrence of the large morphotype in the upper Bone Valley Formation, herein reported for the first time, shows that we are still far from understanding the diversity of marine mammals of that formation and that revision of newly acquired material is necessary.

A new Pliocene river otter is described from the Hagerman Fossil Beds (Hagerman Fossil Beds National Monument), Idaho. Lontra weiri, sp. nov., exhibits notable lutrine traits that closely align it to Old World Lutra and New World Lontra, which are morphologically similar but diphyletic. It is further assigned to Lontra based on known otter biogeography and molecular phylogenetic data. The Hagerman Fossil Beds are characterized by a Blancan North American Land Mammal Age fauna, and radiometric dates for the otter-bearing deposits are inferred as >3.79 Ma, making this the first pre-Pleistocene occurrence of Lontra. Hagerman has a rich and diverse carnivoran fauna with at least five families and 17 species represented, including a much larger otter, Satherium piscinarium. This new otter increases carnivoran richness at Hagerman and provides insight into the evolution of New World river otters.

Ray-finned fishes of the Saurichthyidae radiated rapidly after the end-Permian mass extinction event and became important predators within Triassic marine and freshwater ecosystems. Despite their extensive fossil record, the early evolution of saurichthyids still remains obscure. In an attempt to address this problem, we restudied Saurichthys madagascariensis, a key species from the Early Triassic of Madagascar (maximum age range middle Dienerian-early Smithian according to the available biostratigraphic data discussed herein), on the basis of ∼160 specimens, including several new, nearly complete individuals. Saurichthys madagascariensis is a medium-sized (ca. 60 cm) saurichthyid with a wellossified circumorbital series, a suborbital, an antoperculum, one pair of branchiostegal rays, all fins with segmented, branched lepidotrichia and fringing fulcra, and an extensive squamation consisting of specialized scales arranged in six longitudinal rows, with rhombic scales in between. A series of ‘L’-shaped ventrolateral scales may be apomorphic for the Madagascan species. Comparisons among early saurichthyids reveal some shared traits, based upon which we hypothesize that the primitive condition of Saurichthyidae includes (1) broad scutes along the dorsal and ventral midlines articulating with one another via a specialized ‘keel and groove articulation’; (2) high, anteriorly inclined flank scales subdivided by the lateral line sensory canal into a tuberculated dorsal and a vertically striated ventral portion; (3) posteriorly inclined ventrolateral scales; and (4) a 1:2 relationship between the mid-lateral scales and the neural arches. These data may help to resolve problems in phylogenetic studies concerning synapomorphies and convergences of saurichthyids with other taxa.

Our understanding of caenagnathids has benefited from recent discoveries, including nearly complete skeletons from the Hell Creek Formation of Montana. However, their phylogenetic relationships remain unclear. A new specimen from the Horseshoe Canyon Formation of Alberta has implications for the phylogeny and paleobiology of these creatures. The partial skeleton is articulated and includes a mandible, a full cervical and dorsal series of vertebrae, a right pectoral girdle and arm, a sternum, gastralia, a partial ilium, and a partial hind limb. The mandible is edentulous and the articular ridge is intermediate in form between Caenagnathus collinsi and Chirostenotes pergracilis. The neck is long and composed of at least 11 well-pneumatized cervical vertebrae with fused cervical ribs. The dorsal ribs have finger-like uncinate processes dissimilar in shape to those of other oviraptorosaurs. The pectoral girdle is large and typically maniraptoran, except that the glenoid of the scapulocoracoid faces laterally instead of posteroventrally. The arm is well muscled and can be interpreted to have been a pennibrachium, as indicated by ulnar papillae on the ulna. The manus is characterized by a short first metacarpal but an elongate phalanx I-1 and oviraptorid-like phalangeal proportions in the second digit. These and other features indicate that the specimen represents a new taxon, Apatoraptor pennatus, gen. et sp. nov. Phylogenetic analysis resolves the complicated relationships of Caenagnathidae and allows the evolution of display features to be traced throughout Oviraptorosauria.

The Eocene La Meseta Formation on Seymour Island, Antarctic Peninsula, is known for its remarkable wealth of fossil remains of chondrichthyans and teleosts. Chondrichthyans seemingly were dominant elements in the Antarctic Paleogene fish fauna, but decreased in abundance from middle to late Eocene, during which time remains of bony fishes increase. This decline of chondrichthyans at the end of the Eocene generally is related to sudden cooling of seawater, reduction in shelf area, and increasing shelf depth due to the onset of the Antarctic thermal isolation. The last chondrichthyan records known so far include a chimeroid tooth plate from TELM 6 (Lutetian) and a single pristiophorid rostral spine from TELM 7 (Priabonian). Here, we present new chondrichthyan records of Squalus, Squatina, Pristiophorus, Striatolamia, Palaeohypotodus, Carcharocles, and Ischyodus from the upper parts of TELM 7 (Priabonian), including the first record of Carcharocles sokolovi from Antarctica. This assemblage suggests that chondrichthyans persisted much longer in Antarctic waters despite rather cool sea surface temperatures of approximately 5°C. The final disappearance of chondrichthyans at the Eocene—Oligocene boundary concurs with abrupt ice sheet formation in Antarctica. Diversity patterns of chondrichthyans throughout the La Meseta Formation appear to be related to climatic conditions rather than plate tectonics.

We describe new plotopterids (Aves, Plotopteridae) from late Eocene and Oligocene strata in western Washington State, U.S.A. The specimens belong to four new species of these flightless, wing-propelled seabirds, three of which are named and assigned to two new supraspecific taxa, Olympidytes, gen. nov., and Klallamornis, gen. nov. We confirm previous observations on a high diversity of plotopterids in the Paleogene of North America, but because the fossils are from different formations, it remains elusive how many of the six currently recognized species from western Washington actually coexisted. Tonsala, the only previously described plotopterid taxon from the Olympic Peninsula, is likely to occupy a more basal phylogenetic position than the other plotopterids of this geographic area. Olympidytes and Klallamornis may be successive sister taxa of Copepteryx and Hokkaidornis from the late Oligocene of Japan, but a determination of the exact affinities of the new taxa requires the discovery of further fossils. Notably, the geochronologically youngest plotopterid, the early Miocene Plotopterum, differs from earlier taxa in plesiomorphic features and is here considered to be among the phylogenetically most basal plotopterids. The late Eocene basal Phocavis likewise temporally overlaps with more derived plotopterid taxa. The coexistence of basal and more derived plotopterids in the late Eocene may indicate a rapid evolution of plotopterids towards the late Eocene. The factors that allowed the persistence of basal taxa into the Miocene remain, however, elusive, and so are those that triggered the evolution of wing-propelled diving in these highly specialized birds.

A new skull representing the oldest record of the genus Lariosaurus in the Germanic Basin is described. The small-sized skull originates from the early middle Anisian (Bithynian) of the Winterswijkse Steengroeve (Winterswijk, The Netherlands) and is assigned to L. vosseveldensis, sp. nov. Supplementation of a recently established phylogeny with L. vosseveldensis, sp. nov., recovered it within Lariosaurus as the sister taxon to Nothosaurus winkelhorsti and L. buzzii. The generic assignment of N. juvenilis, N. youngi, and N. winkelhorsti to Nothosaurus must be reevaluated to reestablish support for a monophyletic Lariosaurus, and only a definitive resolution of the polytomy including Germanosaurus could recover a monophyletic Nothosauridae. The Winterswijk locality has previously yielded a rich and diverse marine reptile fauna, including an endemic basal placodont. The nearly contemporaneous occurrence of L. vosseveldensis, sp. nov., and L. hongguoensis from the middle Anisian (Pelsonian) of China indicates a very rapid dispersal of the group, but does not resolve the origin of Sauropterygia (eastern Tethyan faunal province vs. western Tethyan faunal province).

Geometric morphometrics (GM) and finite element analysis (FEA) are increasingly common techniques for the study of form and function. We show how principles of quantitative evolution in continuous phenotypic traits can link the two techniques, allowing hypotheses about the relative importance of different functions to be tested in a phylogenetic and evolutionary framework. Finite element analysis is used to derive quantitative surfaces that describe the comparative performance of different morphologies in a morphospace derived from GM. The combination of two or more performance surfaces describes a quantitative adaptive landscape that can be used to predict the direction morphological evolution would take if a combination of functions was selected for. Predicted paths of evolution also can be derived for hypotheses about the relative importance of multiple functions, which can be tested against evolutionary pathways that are documented by phylogenies or fossil sequences. Magnitudes of evolutionary trade-offs between functions can be estimated using maximum likelihood. We apply these methods to an earlier study of carapace strength and hydrodynamic efficiency in emydid turtles. We find that strength and hydrodynamic efficiency explain about 45% of the variance in shell shape; drift and other unidentified functional factors are necessary to explain the remaining variance. Measurement of the proportional trade-off between shell strength and hydrodynamic efficiency shows that throughout the Cenozoic aquatic turtles generally sacrificed strength for streamlining and terrestrial species favored stronger shells; this suggests that the selective regime operating on small to mid-sized emydids has remained relatively static.

Therocephalians were an ecologically diverse group of therapsids whose long stratigraphic record and widespread distribution during Permian and Triassic times make them important for understanding biogeographic patterns during a major faunal transition. Here, we describe a new therocephalian, Mupashi migrator gen. et sp. nov., from the upper Madumabisa Mudstone Formation (upper Permian) of Zambia's Luangwa Basin. The specimen has a long snout with a maxilla-vomerine contact on the hard palate, a high antecanine tooth count and numerous postcanines, and a conspicuous boss on the dentary angle whose structure is identical to that of the Russian baurioid Karenites. Additional endocranial anatomy, including palatal and braincase features, are revealed by high-resolution X-ray computed tomography and described in detail in light of the growing availability of tomographic data for therapsids. A phylogenetic analysis of 56 therapsid taxa and 136 cranial and postcranial characters recovers Mupashi as the sister taxon to Karenites, placing the pair between basal ictidosuchid-grade baurioids and the later Triassic bauriamorphs. Parsimony optimizations of geographic occurrences are ambiguous regarding the origination centers of therocephalian subclades. However, the patterns are suggestive of either (1) rapid, early dispersal events of Eutherocephalia and its major subgroups from a Laurasian center during the early-late Permian or, more likely, (2) within-province diversifications with occasional dispersal events occurring between provinces. Regardless, these associations strengthen the hypothesis that unknown but effective dispersal routes to high latitudes were available to therapsids and other tetrapods at least until early-late Permian times.