A new genus of echimyid rodent, †Ullumys, from the uppermost Miocene of northwestern Argentina is described. It includes two species, †U. pattoni, sp. nov., and †Ullumys intermedius, nov. comb. †Ullumys pattoni is known from a skull fragment and the corresponding right hemimandible coming from levels of Loma de Las Tapias Formation, underlying a tuff dated at 7.0 ± 0.9 Ma (Huayquerian age, San Juan Province). †Ullumys intermedius is represented by a left hemimandible from the ‘Araucanense’ of Valle de Santa María (Huayquerian age, Catamarca Province). A phylogenetic analysis in the context of octodontoids linked †Ullumys to the clade subtended by the extinct echimyids †Pampamys and †Eumysops and the living Thrichomys. †Ullumys has a peculiar craniomandibular morphology, shared only with †Eumysops among the Octodontoidea, involving specializations to open environments such as large and posteriorly extended orbits and related low mandibular condyles. Phylogenetic relationships of †Ullumys support the hypothesis that echimyids recorded since the latest Miocene in southern South America, and linked to those currently inhabiting Brazilian open biomes, represent a marginal sample of the great diversity evolving primarily in northern tropical areas.

We describe a new lagostomine rodent (Caviomorpha, Chinchillidae), Lagostomus telenkechanum, sp. nov., from the Arroyo Chasicó Formation (late Miocene; Buenos Aires Province, Argentina). Three characters permit its assignment to Lagostomus: suborbital canal for the infraorbital nerve limited by a bony lamina, well-developed posterior process of the palatine, and posterior maxillary foramen located at the midpoint of the M3. In addition, we identify the new species based on a unique character combination (e.g., small size, palatines reaching anterior to the level of the midpoint of P4, anterior margin of mesopterygoid fossa at the level of the anterior border of M3, upper cheek teeth more compressed anteroposteriorly and more obliquely implanted in the maxilla than in L. pretrichodactyla, L. compressidens, and L. maximus but less than in L. incisus, and thick cement layer in the hypoflexus). Because the early Miocene—middle Miocene genera, Prolagostomus and Pliolagostomus, are no longer recorded from the late Miocene, whereas the oldest record of the extant genus Lagostomus is recognized at that time, we consider this period as an important turnover time in the taxonomic composition of the Chinchillidae. This study increases understanding of the taxonomic diversity of the late Cenozoic lagostomines, contributing to the knowledge of the evolutionary and paleobiogeographic history of chinchillids.

Estimating the size of fossil organisms is essential for most paleontological studies, including studies of fossil squamates. Paradoxically, few works about the methods used to achieve this goal have been published. This study focuses on two genera of lizards found in the Lesser Antilles: Pholidoscelis and Anolis. We produced sets of size estimation equations based on skeletal measurements taken on modern specimens. We tested the effect of the anatomical part used and of the species composition of the comparative sample in order to produce reliable and statistically significant equations. We then compared our results with previously published estimates of fossil size for Anolis lizards. We found that past studies were inconsistent with each other in how body size was estimated even if the same value for a measurement was obtained independently. Further, we found that what others have described as Holocene dwarfism for Anolis bimaculatus is likely to reflect a methodological bias, and fossil representatives of this species likely had a similar size to modern individuals. Many conclusions made in previous studies could not be challenged, however, because even though body size estimates are given, the actual measurements made on skeletal elements remain largely unreported in the literature. These results show that more transparency and reproducibility are needed for studies concerning the body size of fossil squamates.

A new genus and species of crocodilian, Kalthifrons aurivellensis, is described from a channel sand deposit incised into the Oligo-Miocene Etadunna Formation on the western shore of Lake Palankarinna in the Lake Eyre Basin, South Australia. The channel sand is interpreted as an outcrop of theMampuwordu Sand Member of the Tirari Formation, which has been assigned an early Pliocene age. The taxon can be diagnosed by the extremely elongate and narrow anterior process of the frontal pair and a distinctively beveled and laterally expanded prefrontal contribution to the orbit margin. The broadly triangular rostrum, at least partially interlocking dentition, smooth dental carinae, and weak labiolingual compression resemble unspecialized crocodilian species, and it was probably a generalist aquatic predator. It possessed character states that indicate that it was not a member of Crocodylus, and it is referred to the endemic Australasian clade Mekosuchinae. The first overlying unit in the Lake Eyre Basin sequence to produce diagnostic crocodilian remains is the mid- to late Pliocene Pompapillina Member of the Tirari Formation. It contains a true species of Crocodylus but no indication of Kalthifrons aurivellensis or indeed any other mekosuchine, indicating that the lattermay have been driven to extinction via competitive replacement.

Chondrichthyan-like scales with simple, single-odontode crowns, reminiscent of those of euselachians, have been reported from Silurian strata in a number of previous studies. These specimens comprise the genera Elegestolepis (from Siberia, Mongolia, and Tuva) and Kannathalepis (from the Canadian Arctic) and have been considered to exhibit contrasting patterns of ontogenetic development. A study of elegestolepid microremains from the Chargat Formation of Mongolia (Llandovery—lower Wenlock) and the Baital Formation of Tuva (Wenlock—Ludlow) has been undertaken using scanning electron microscopy and micro-computed tomography to examine scale canal system and hard tissue structure. These investigations revealed scales at different stages of development, whose morphogenesis is characterized by growth (elongation) of the crown odontode and formation of neck canals. This ontogenetic pattern (Elegestolepis-type morphogenesis) is also recognized in Kannathalepis and the Lower Devonian species Ellesmereia schultzei and forms the basis for the unification of these taxa into a new chondrichthyan order Elegestolepidida, ordo nov. Similarities in crown vascularization (branching pulp, single neck canal) shared by Elegestolepis, Ellesmereia, and Deltalepis, gen. nov. (D. magna, sp. nov., and D. parva, sp. nov., erected herein for Mongolian specimens), require the erection of the family Elegestolepididae, fam. nov., that is distinguished from the monogeneric Kannathalepididae (non-branching pulp, multiple neck canals). Elegestolepid scales exhibit characteristics (neck canal formation and lack of enamel and basal bone osteons) consistent with those of the chondrichthyan dermal skeleton. This establishes Elegestolepidida as the stratigraphically oldest chondrichthyan taxon to develop monodontode scales, which, in contrast to the ‘placoid’ scales of euselachians, are growing structures.

Buitreraptor gonzalezorum is a paravian theropod from the Late Cretaceous of Patagonia that has been recovered as an unenlagiine dromaeosaurid in several phylogenies. It was preliminarily described in a brief article, but a detailed osteology has not been published to date. Here we provide a thorough osteological description of the skull of the holotype, which preserves the maxillae, nasals, frontals, parietals, postorbitals, quadrates, and many mandibular bones, together with some in situ and isolated teeth. The isolated occipital condyle is the only element preserved from the braincase. Diagnostic cranial characters of this taxon include elongate skull; maxillary fenestra not dorsally displaced; posteriorly expanded postantral wall; quadrate with expanded lateral flange and a posterior pneumatic foramen; straight anterior border of the supratemporal fossa; nutrient foramina within a well-marked lateral groove on the dentary; and small, fluted teeth without denticles. Buitreraptor shares traits with Austroraptor cabazai, the only other unenlagiine to preserve cranial remains, although they also differ in the morphology of the maxillary fenestra and the presence/absence of interdental plates. A phylogenetic analysis was performed, recovering Buitreraptor as an unenlagiine dromaeosaurid, in agreement with previous works. The phylogenetic implications of some characters are discussed, including characters not previously considered for this taxon, such as the presence of the mylohyoid foramen. The distribution and codings of some characters are reconsidered, with an evaluation of how they influence the phylogenetic position of Buitreraptor and paravian relationships overall.

The late Miocene and Pliocene Middle Awash fish fauna is one of the earliest known Neogene fish faunas in eastern Africa and is the earliest known from the Horn of Africa. The fauna was recovered as part of the Middle Awash research project, which was designed to investigate the Mio-Plio-Pleistocene deposits along the shores of the Awash River, Ethiopia. Remains of eight fish taxa were recovered: Clarotes, Cichlidae, and Parachanna, which are native to the African continent where they have a long fossil record, and cf. Labeo, Barbus, Labeobarbus, Bagrus, and Clarias, whose origins were in Asia. These genera and families are all extant; however, certain fossil elements of cf. Labeo and Bagrus differ morphologically from modern species. When and how the Asian-derived taxa moved into Africa is enigmatic. The Middle Awash fossil deposits are located within the Horn of Africa, long suggested as a possible crossing point between Africa and the Arabian Peninsula in the late Miocene. Data presented in this paper suggest that in the late Miocene, the Horn of Africa region was accessible from the southern Arabian Peninsula via the Bab el-Mandeb Strait land bridge, which was (only) viable in the late Miocene. This land bridge has been implicated in the migration of other freshwater and terrestrial animals between Africa and Arabia. The subsequent movement of Barbus sp., Labeobarbus sp., Bagrus sp., and Clarias sp. into eastern Africa had a large impact on the diversity and abundance of later populations of African freshwater fish.

Nasal regions of the non-mammalian cynodonts Massetognathus, Probainognathus, and Elliotherium were reconstructed from micro-computed tomography scans and compared with scans and published accounts of more derived forms, including Brasilitherium, Morganucodon, Haldanodon, and extant mammals. The basic structure of the modern mammalian nose, already present in non-mammalian cynodonts of the Early Triassic, underwent little modification during the Triassic. A respiratory chamber opened into a nasopharyngeal passage through an enlarged primary choana bordered posteriorly by a transverse lamina that formed the floor to a more posterior olfactory chamber. Cartilaginous respiratory turbinals initially provided a surface for evaporative cooling during periods of increased activity in the exceptionally high ambient temperatures of the Triassic. A similar mechanism for heat loss is present in extant crocodilians, squamates, and mammals. In the Late Triassic and Early Jurassic non-mammaliaform cynodonts (Elliotherium) and mammaliaforms (Morganucodon), the pterygopalatine ridges behind the hard secondary palate extended ventrally and formed the lateral walls to a narrow nasopharynx, as pterygoid hamuli do in extant mammals. Ridges in this position suggest the presence of a palatopharyngeus muscle in late non-mammaliaform cynodonts that could hold the larynx in an intranarial position during rest or low activity levels to prevent inhaled air from entering the oral cavity, thus allowing cartilaginous respiratory turbinals to assume an additional role as temporal countercurrent exchange sites for heat and water conservation. Ossification of respiratory turbinals in mammals enhanced their efficiency for conserving heat and water at rest, as well as their ability to dissipate heat during thermal stress.

We describe an exceptionally well preserved skull of a small anthracothere from the late middle Eocene of the Pondaung Formation that can be confidently attributed to Siamotherium pondaungensis, a species that was first diagnosed on the basis of a fragmentary maxilla preserving two upper molars. The new material confirms that Siamotherium pondaungensis is an anthracothere and not a helohyid as repeatedly suggested. According to its dentition and skull structure, Siamotherium pondaungensis was most likely a terrestrial, open-forest animal with an omnivorous diet that showed no significant adaptation to folivory. A phylogenetic analysis that includes both species of Siamotherium confirms their basal position within the Hippopotamoidea.

We describe five new specimens of Hippopotamidae from the Miocene of Napudet, a new site in southwestern Turkana Basin, Kenya. These specimens include fragmentary maxillae with teeth and a well-preserved mandibular symphysis. We attribute them to Kenyapotamus ternani, the least known species within Kenyapotamus, on the basis of relatively small dental dimensions and a clear distinction between the parastyle and the mesiostyle on the upper molars. This attribution suggests an age older than 10 Ma for Napudet. A cladistic analysis integrating these new data makes it possible to evaluate the relationships between middle Miocene hippopotamids and later representatives. The mandibular symphysis from Napudet, defining the plesiomorphic condition for mandibular morphology in Hippopotaminae, could be crucial for future phylogenetic reconstructions of the family. Mandibular morphology is a fast-evolving complex of characters, key in reconstructing the behavior and the past diversity of Hippopotamidae. Finally, this material demonstrates the potential of Napudet for augmenting the fossil record for a relatively ill-documented time interval (13–10 Ma).

A new species of rheid, Opisthodactylus kirchneri, sp. nov., is erected on the basis of associated elements of both hind limbs from the late Miocene in northwestern Argentina. The new species extends the biochron of Opisthodactylus from early Miocene to late Miocene and its distribution from Patagonia to northwest Argentina. Cladistic analysis recovered an Opisthodactylus-Pterocnemia clade as sister to a Rhea americana clade. The Opisthodactylus-Pterocnemia clade would have inhabited the most southern, central, and western regions of southern South America throughout the early-middle Neogene, whereas the Rhea stock would have had a north-northeastern or Brazilian ancestral distribution in the lowlands of the continent. The similar biogeographic patterns of living and fossil rheids, cariamids, and tinamids seem to roughly reflect the environmental shift from closed to open habitats that took place at the southern end of South America during the Neogene and Pleistocene, and at least in the former two families the effects of isolation produced by the ‘Paranaense' sea. Closed-habitat taxa of these three families are recorded at early Miocene localities in Patagonia (O. horacioperezi, O. patagonicus, Noriegavis santacrucensis, and Crypturellus reai), whereas open-habitat taxa come from late Miocene—early Pliocene sites at central (Pterocnemia sp. and Eudromia sp.), northwestern (O. kirchneri and Pterocnemia cf. mesopotamica), and northeastern (Pterocnemia mesopotamica) regions in Argentina.

Colymbosaurus is a genus of long-necked plesiosaurian represented by two valid species: C. megadeirus from the Upper Kimmeridge Clay Formation (Kimmeridgian-Tithonian) of the United Kingdom and C. svalbardensis from the Slottsmøya Member of the Agardhfjellet Formation (Tithonian-Berriasian) of Svalbard, Norway. Due to the lack of complete and articulated skeletons and a near absence of cranial material, Colymbosaurus has been problematic to characterize morphologically. Here, we describe and conduct a phylogenetic analysis on an informative new specimen referable to C. svalbardensis from the Slottsmøya Member, preserving a large portion of the axial and appendicular skeleton. The new material contributes important new osteological data for the species and together with an extensive examination of congeners in British museums, clarifies the diagnostic characters of the genus. We provide two new diagnostic characters of the epipodials for the genus and reevaluate the utility of an anteroposteriorly oriented bisecting ridge on the distal end of the propodials. We also present two new diagnostic features for C. svalbardensis regarding the neural canal and femoral morphology. A phylogenetic analysis recovers a monophyletic and well-supported Colymbosaurus. The new specimen of C. svalbardensis confirms that this species is not synonymous with other described Slottsmøya Member plesiosauroids, demonstrating considerable diversity of the clade at high latitudes close to the Jurassic-Cretaceous boundary.

Hegetotheriidae are one of the most derived families of the Order Notoungulata. It is composed of two subfamilies: Hegetotheriinae, which resolves as paraphyletic in most recent phylogenies, and Pachyrukhinae, which historically is considered monophyletic. The family is recognized from late Oligocene to Pliocene and is well diversified from its earliest records. Most papers on the family are systematic studies and, to a lesser degree, investigate its phylogenetic relationships, but paleobiogeographic approaches are rare. A phylogenetic analysis was carried out using TNT, based on a previous matrix that was augmented with additional taxa and characters. Previous results are supported, viz., the paraphyly of Hegetotherium Ameghino and Paedotherium Burmeister, and the monophyly of Pachyrukhinae, but new conclusions arise, such as the paraphyly of Hemihegetotherium Rovereto and the monophyly of Prohegetotherium Ameghino and Hegetotheriinae. In this work, a paleobiogeographic analysis on hegetotheriids is carried out by means of the Bayesian method using the RASP program, with the aim of estimating the possible ancestral area and vicariance, dispersal, and extinction events. This analysis shows that Hegetotheriidae and both subfamilies originated in central Patagonia (southeast of Chubut and northeast of Santa Cruz provinces). The analysis also reveals that dispersals were the predominant events, and they are related to Cenozoic dispersals to lower latitudes as global cooling advanced and new lands emerged.