Metriorhynchidae is a family of highly specialized, extinct marine crocodylomorphs that inhabited the Paleopacific Ocean and the Tethys Sea during the Jurassic and the Early Cretaceous. Numerous metriorhynchid fossil specimens have been recovered from European and South American localities, but North American records of this family are still scarce. Here, we describe a recently recovered Kimmeridgian metriorhynchid from the Sabinal Formation, Tlaxiaco Basin, Oaxaca, Mexico, that is attributable to the genus Maledictosuchus. This genus was known previously from a single species, M. riclaensis, from the Middle Jurassic of Spain. The characteristics of this Mexican specimen support its identification as a new species, Maledictosuchus nuyivijanan, sp. nov. The two species differ in dental and skull-roof morphology. The frontal of M. nuyivijanan, sp. nov., has a wide, rounded anterior end that extends rostrally to the same level of the anterior end of the prefrontal, whereas the frontal of M. riclaensis has a narrow anterior end that is located posterior to the anterior end of the prefrontal. Additionally, the teeth of M. nuyivijanan, sp. nov., exhibit bicarinated crowns, a smooth labial surface, and a lingual surface ornamented with longitudinal ridges, whereas those of M. riclaensis lack carinae and the labial and lingual surfaces are covered with considerably more conspicuous ridges. The North American occurrence of M. nuyivijanan, sp. nov., suggests a wider temporal and geographic distribution for the genus Maledictosuchus across the Tethys Sea than previously thought: from the Callovian in Europe to the Kimmeridgian in southern North America.

An ontogenetically young fossil baleen whale from the lower part of the Horokaoshirarika Formation of Hokkaido, Japan, includes a partial skull, periotics, bullae, mandible, vertebrae, and a scapula. It is identified as Herpetocetus sp. because it exhibits a postglenoid process of the squamosal more transversely compressed than in Nannocetus, a deep and anteroposteriorly long fossa on the dorsal surface of the squamosal between the zygomatic process and the lateral wall of the brain case, and a prominent squamosal flange of the periotic. The Hokkaido specimen differs from currently described Herpetocetus species in having a large hiatus fallopii, and an angle at the anteromedial edge of the pars cochlearis, just medial to the hiatus fallopii. Because the lower part of the Horokaoshirarika Formation is late Miocene in age (approximately 7.7 to 6.8Ma), the Hokkaido Herpetocetus specimen is the only record of Miocene Herpetocetinae from the western Pacific. Previously, Miocene Herpetocetinae were reported from the eastern North Pacific and western Atlantic. Accordingly, this new record of Herpetocetus from the upper Miocene of the western North Pacific suggests an earlier origin for both the genus and the subfamily.

New cranial and postcranial remains of the Early–Middle Jurassic turtle, Condorchelys antiqua, are described here in detail, providing new insights into the early evolution of turtles. Unconstrained and constrained cladistic analyses in addition to newly developed total-evidence Bayesian analysis were performed to explore large-scale turtle relationships and evolutionary trends. All the analyses show a similar resolution at the base of the tree, recovering several species of small-sized, fresh water turtles of the Early–Middle Jurassic at the base of the tree following the most basal, large-sized, terrestrial turtles from the Late Triassic. The calibration of the cladistic analyses and the tip-dating analysis provided similar results in the main nodes Testudines, Pan-Cryptodira, Cryptodira, Pan-Pleurodira, and Pleurodira, corroborating that the Jurassic is a key period for turtle evolution. The significant reduction in size in Early–Middle Jurassic stem turtles and the combination of certain characters (e.g., presence of fontanelles, loss of bones, loss of scutes) shown by those taxa suggests heterochronic changes, paedomorphosis in particular, at the base of the turtle tree. These morphological novelties could have trigged, or facilitated, the occupation of the aquatic niche as seen in Jurassic stem turtles.

Eosauropterygians rapidly diversified in the Anisian (Middle Triassic), a period by which the invertebrates had already completely recovered from the end-Permian mass extinction. The Pelsonian (Anisian) deposits of the small Panxian and Luoping intraplatform basins in southwestern China alone yielded seven or more eosauropterygian taxa. A new Middle Triassic sauropterygian, Panzhousaurus rotundirostris, gen. et sp. nov., is here described based on an almost complete skeleton from the middle Anisian (Middle Triassic) of Panzhou (Guizhou Province, southwestern China). The upper temporal fenestra smaller than the orbit, the broad and flat parietal table, the cervical ribs with two proximal articular heads, the pachyostotic proximal ends of the dorsal ribs, and the unexpanded sacral ribs indicate that the specimen is a pachypleurosaur-like eosauropterygian. The new species also shows some differences from all other eosauropterygians, such as a rounded and shortened snout, 24 cervical and 20 dorsal vertebrae, a straight ulna with a concave posterior margin, and four distal carpals. Phylogenetic analysis also reveals that Panzhousaurus is an eosauropterygian, closely related to pachypleurosaur-like forms. The discovery of Panzhousaurus enriches our knowledge of the diversity of the Panxian fauna and provides new information to test phylogenetic relationships among known eosauropterygians.

Deposited over a short period of time during the Middle Miocene Climatic Optimum, the Sharktooth Hill Bonebed in California is one of the world's densest marine vertebrate concentrations. Pinnipeds are represented here by odobenids and desmatophocids, but some are still poorly known. Herein, the mandibular morphology of the odobenid Neotherium mirum is described in detail. Its morphology resembles that of early pinnipedimorphs, with postcanine teeth consisting of three or four longitudinally aligned cusps and double-rooted p2–m1, but shows derived characteristics such as reduced metaconid and bilobed canine root. Additionally, Neotherium is represented by two distinct size classes, which is likely the earliest evidence of sexually dimorphic body size in odobenids. Two additional mandibles represent other pinnipeds. One represents an unknown odobenid, with a unique suite of morphological characteristics setting it apart from contemporaneous odobenids such as Neotherium and Pelagiarctos. The other reconfirms the presence of Allodesmus cf. A. sadoensis, a species otherwise known from the middle Miocene of Japan. This species is distinguished from Allodesmus kernensis, based on anteriorly crowded and reduced postcanine dentition. This record adds further support for the presence of this taxon in the middle Miocene of California and represents the earliest evidence of trans-Pacific dispersal in pinnipeds. The Sharktooth Hill pinniped assemblage now consists of five species: the odobenids Neotherium mirum, Pelagiarctos thomasi, an unknown odobenid, and the desmatophocids Allodesmus kernensis and Allodesmus cf. A. sadoensis. Niche partitioning within this sympatric pinniped community was possible due to differences in body size, and feeding and foraging preferences.

Fossil whale material from the Oligocene-aged marine beds underlying the region around Charleston, South Carolina, has provided an unparalleled view of post-archaeocete cetacean evolution. Both the Chattian-aged Chandler Bridge Formation and the underlying Rupelian-aged Ashley Formation have yielded dozens of specimens, many yet-to-be described, that document an explosive evolutionary radiation at this time, particularly in odontocetes, but in early mysticetes as well. Specimens include early odontocetes, such as Ashleycetus planicapitis, Xenorophus sloanii, and Agorophius pygmaeus; the earliest baleen-bearing mysticetes, such as Eomysticetus whitmorei and E. carolinensis; and even multiple species of archaeocete-like toothed mysticetes, such as the recently described Coronodon havensteini. Herein, we describe yet another species of odontocete from the Ashley Formation, but one that is surprisingly derived relative to contemporary species noted above that maintain a pronounced intertemporal constriction, with broad exposure of the parietals across the skull roof. In contrast to those taxa, Ediscetus osbornei, gen. et sp. nov., shows an unexpectedly advanced degree of ‘telescoping’ whereby there is no exposure of the parietals across the vertex of the skull and only minimally exposed ‘parietal triangles’ at the lateral margins of the nearly lost intertemporal constriction. Phylogenetic analyses of a supermatrix of morphological and molecular data place E. osbornei slightly outside the odontocete crown group, with the presence of double-rooted teeth and a deep maxillary cleft, among other features, supporting this position. The holotype also has a well-developed articular ridge on the petrosal, typically considered a platanistoid synapomorphy, indicating that this character shows more homoplasy than generally realized.

Although squamates are commonly found in Cenozoic South American deposits, most findings correspond to fragmentary cranial materials or isolated vertebrae. Among the known South American vertebrate fossil localities, the lower section of the Chichinales Formation (Early Miocene, Colhuehuapian South American Land Mammal Age [SALMA]), in Paso Córdoba Protected Natural Area, Río Negro Province, Argentina, recently yielded an almost complete skull of a previously unknown teiid lizard. Here, we provide a detailed description of this new fossil, based on stereoscopic and high-resolution X-ray computed tomography (CT scan) analyses. Our phylogenetic analysis recovered the new fossil within the monophyletic genus Callopistes, as the sister group of the fossil C. bicuspidatus from upper Miocene–lower Pliocene sediments (Montehermosan SALMA) of the Monte Hermoso Formation. The new species antedates the oldest previously known fossil record of the genus by at least 14 Ma, providing a minimum age of origin for the genus of approximately 20.1Ma (based on recent revisions of the Cenozoic fossil record of SALMA). The current distribution of the two known extant species of Callopistes and the locality from which the new taxon was recovered indicate that this genus had a much broader distribution in the past that included cis-Andean areas of Patagonia during the Miocene. Our phylogenetic results further suggest that Tupinambis uruguaianensis should be allocated to the genus Dracaena.

The holotype of Concavenator corcovatus (MCCM-LH 6666) is a carcharodontosaurid skeleton from the Lower Cretaceous Las Hoyas fossil site in Spain. The appendicular skeleton of Concavenator is the most complete for any Carcharodontosauridae, with only a few regions absent. We describe the limb osteology of Concavenator and carry out an anatomical comparison with other theropods. The results show that Concavenator presents several allosauroid and carcharodontosaurid synapomorphies. Concavenator shares with other allosauroids symmetric glenoid rims of the scapulacoracoid, a canted orientation of the proximal and distal humeral ends, an anterior position of the humeral condyle on the distal end, a long manus relative to the forearm, curved ungual phalanges, a posteriorly broad brevis fossa in the ilium, a reduced ischial tuberosity, a posterior flange on the iliac peduncle of the ischium, and a reduced distal tubercle in the ischium. A concavity on the middle of the proximomedial surface of the humeral head is postulated as a new synapomorphy of carcharodontosaurids. We propose some autapomorphies of Concavenator regarding the length of the phalanges of digit III, the height of the olecranon process relative to ulna length, the proportions of the deltopectoral crest, and the projection of the preacetabular hook in the ilium. The osteological description of the complete appendicular skeleton of Concavenator provides some novelties in the limbs of carcharodontosaurids and is relevant to understanding its general phylogenetic relationships.

Cranial and postcranial elements attributed to the alligatoroid Bottosaurus harlaniMeyer, 1832, are described from the Rowan Fossil Quarry, a Cretaceous–Paleogene locality in Mantua Township, New Jersey, U.S.A. This specimen (NJSM 11265) represents the most complete individual attributable to the species and includes significant postcranial elements not found in other specimens. Posterior elements of the skull are described for the first time, and the species is placed into a phylogenetic context. Aspects of the skull table, including constricted supratemporal fenestrae, a linear frontoparietal suture, and a large trapezoidal dorsal supraoccipital exposure, are similar to those of caimans. Bottosaurus harlani is included within Caimaninae due to its possession of a linear frontoparietal suture between the supratemporal fenestrae. Optimal trees from phylogenetic analysis recover B. harlani in three different positions, as a sister either to the modern dwarf caimans (Paleosuchus), to living species of Paleosuchus, or to both. That a substantial stratigraphic gap separates B. harlani from both species of Paleosuchus, which first appears in the Miocene, along with low character and nodal support, raises questions about this relationship. The phylogenetic placement of B. harlani may reflect incomplete knowledge of the taxon, and further study might support placement outside of Caimaninae. More complete analyses of B. harlani and other Cretaceous–Paleogene alligatoroids will help to illuminate the relationships among these forms and their living relatives.

Avian remains are rare from Paleogene sediments in the Great Plains region of North America, especially those that can be identified taxonomically. Here, we describe avian eggshell fragments from the Fitterer Ranch locality within the Oligocene Brule Formation of North Dakota and assign them to ootaxonomy. The specimen examined (NDGS 1934) exhibits low tubercles that form undulating surface ornamentation; 650–900-µm-thick eggshell composed of three structural layers of calcite; abrupt transition between mammillary and continuous layers; prisms visible in continuous layer; squamatic texture primarily visible in lower half of continuous layer; and mammillary-to-total shell thickness ratio of 1:2.70–2.75. Due to this unique combination of characters, we establish the new oospecies Metoolithus jacksonae, oosp. nov. This new oospecies extends both the geographic and temporal ranges of the oogenus Metoolithus and demonstrates the importance of oological research in revealing the diversity of Oligocene avifauna in this region.

A new species of the ‘isectolophid’ Chowliia, C. europea, sp. nov., is described from the lowermost Eocene (MP7) Le Quesnoy locality of the Paris Basin. The new species is exclusively known by dental material, and it represents the earliest tapiromorph occurrence in Europe. The morphology of its bunolophodont molars indicates that C. europea is a tapiromorph, and it is here included in the primitive and probably paraphyletic family ‘Isectolophidae.’ Chowliia was previously restricted to the lowermost Eocene Wutu Formation (eastern China), and its occurrence in Europe indicates faunal interchange between continental Asia and western Europe as early as the earliest Eocene. A preliminary analysis of the phylogenetic position of C. europea supports the hypothesis that Chowliia is most closely related to Cardiolophus and to Homogalax wutuensis.

Although fragmentary remains of sturgeon, such as scutes and pectoral spines, are relatively common in fossil deposits, articulated fossilized skeletons are rare in Upper Cretaceous sediments of North America. Currently, there are four extinct species referred to Acipenseridae reported from the Upper Cretaceous of North America; two of them (†Acipenser eruciferus and †A. albertensis) are of doubtful validity because they are based on isolated elements that are probably not diagnostic. Only two species, †Priscosturion longipinnis and †Protoscaphirhynchus squamosus, have been described based on articulated skeletons. In June 2016, an articulated sturgeon specimen was discovered in the Campanian Dinosaur Park Formation of Dinosaur Provincial Park, Alberta, Canada. This specimen preserves the skull and anterior half to two-thirds of the body but is missing the pelvic, dorsal, anal, and caudal fins. This new specimen cannot be included in any of the previously named taxa, so we describe it here as a new genus and species, †Anchiacipenser acanthaspis. A combination of several characters allows us to diagnose the new sturgeon from Dinosaur Provincial Park as a new taxon, including the dermal cranial bones being strongly ornamented with straight and anastomosing ridges, the dorsal scutes being large and laterally expanded and bearing median spines, and the presence of an extensive cover of smaller dermal scales on the flanks. A phylogenetic analysis indicates that this new taxon belongs in Acipenseridae, although its precise relationships within this clade are not clear.

Protosuchids are known from the Late Triassic to the Early Cretaceous and form a basal clade of Crocodyliformes. We report here a new protosuchid crocodyliform, Coloradisuchus abelini, gen. et sp. nov., from the middle Norian Los Colorados Formation, La Rioja, northwestern Argentina. Our phylogenetic analysis recovers Coloradisuchus abelini within Protosuchidae, as the sister group of the clade formed by Hemiprotosuchus and two species of Protosuchus (P. richardsoni and P. haughtoni). The new protosuchid C. abelini increases the diversity of crocodyliforms in the Late Triassic and, together with H. leali from the same stratigraphic levels of the Los Colorados Formation, shows that the diversification of basal crocodyliforms was probably faster and/or older than thought previously.

We present a comprehensive qualitative and quantitative study of the manus of a new therocephalian specimen referable to Tetracynodon from the Early Triassic of South Africa. We examined 18 specimens, representing at least 12 genera, including basal therocephalians (Lycosuchidae and Scylacosauridae) and eutherocephalians (Akidnognathidae, Whaitsioidea and Baurioidea). A temporal range of 23 million years through the Permo-Triassic (Wordian to Anisian) was surveyed. A principal component analysis of the therocephalian manus indicates that (1) metacarpals II, III, and IV acted as a module of which the medial and lateral elements (metacarpals I and V) were independent from each other; and (2) the proximal carpals, ulnare, and radiale lengths show contrasting variation in their measurements (e.g., groups with longer ulnares tend to have shorter radiales). The manus of Permian and Triassic taxa occupy separate regions in morphospace. This segregation pattern suggests selection for a manus with slender, elongated second to fourth metacarpals during and after the Permo-Triassic mass extinction. We show a heterogeneous condition of the fifth distal carpal bone. Although usually interpreted as fused to the fourth distal carpal or absent, the fifth distal carpal was present as a cartilaginous element in Tetracynodon. Strong and proportionally long unguals in relation to length of digits III and IV, wide and stocky basal phalanges, and short non-ungual phalanges strongly suggest that Tetracynodon was a scratch-digger. This supports the proposition that burrowing was an important behavioral strategy of terrestrial taxa during and after the Permo-Triassic mass extinction.

Titanosauria is a clade of sauropod dinosaurs that includes species ranging from the largest known terrestrial vertebrates to insular dwarfs no bigger than elephants. Although most sauropod dinosaurs exhibit highly vascularized fibrolamellar bone signaling rapid growth rates comparable to those of extant mammals, diminutive titanosaurs apparently exhibit histological traits consistent with reduced primary growth rates and/or truncated active growth to reach small adult body sizes. A better understanding of the evolution of titanosaur body size requires additional sampling of the 40 + known titanosaur species. The best-preserved and most complete titanosaur yet discovered is Rapetosaurus krausei from the Maastrichtian Maevarano Formation in Madagascar. Skeletal material from many individuals spanning a wide range of ontogeny, from neonates to very large body sizes, makes Rapetosaurus an ideal candidate for an analysis of growth. We analyzed Rapetosaurus histology using a growth series of 25 forelimb, hind limb, and girdle elements representing different ontogenetic stages, including samples from the largest Rapetosaurus known (femur length = 143 cm). Primary bone histology in Rapetosaurus is highly vascularized fibrolamellar tissue, such as is found in other sauropods and most sampled titanosaurs. Secondary remodeling begins early, as noted in other titanosaur taxa, and by mid-ontogeny is pervasive in most sampled elements. The largest known Rapetosaurus was still growing, whereas some small juveniles exhibit an unusual pattern of bone erosion and replacement in the context of peripheral lines of arrested growth that signal a temporary pause in bone apposition. We hypothesize that these signals may relate to the drought-stressed ecosystem inhabited by Rapetosaurus.

A series of pterosaur bones from the Upper Cretaceous (Campanian) of Velaux (Bouches-du-Rhône, southeastern France) is described. This material, including both cranial and postcranial elements found in close association and likely belonging to a single immature individual, is assigned to a new genus and species of azhdarchid pterosaur, Mistralazhdarcho maggii. This large-sized taxon (wingspan ca. 4.5 m in the holotype, possibly reaching 5–6 m in mature individuals) is characterized by a slightly downturned mandibular symphysis that shows a ‘V’-shaped cross-sectional profile and bears a well-developed, anteriorly located median eminence on its dorsal surface. The presence of a median eminence suggests that Mistralazhdarcho might be closely related to Alanqa from the Cenomanian of Morocco. The material described here represents the first partial skeleton of a pterosaur recovered from the Late Cretaceous deposits of western Europe, and the new taxon is one of the most completely known European azhdarchids. Mistralazhdarcho is intermediate in size between the medium-sized genus Eurazhdarcho and the giant-sized genus Hatzegopteryx, two azhdarchids from the Maastrichtian of Romania. The discovery of Mistralazhdarcho suggests the presence of a third azhdarchid size class in the continental ecosystems of the latest Cretaceous European archipelago.