Xenarthran Synsacrum Morphology and Evolution Abstract Xenarthra is unique in having striking features in the axial skeleton, usually very different from the rest of the eutherian clades. Some of these features are widely spread among the members of the group (e.g., the presence of xenarthrales in most cingulates and all pilosans, and the synsacrum with sacroischial union to the pelvis in almost all xenarthrans) and others are restricted to some taxa (e.g., deviated number of cervical vertebrae in Bradypus and Choloepus). In this study, we aim to explore the great diversity of vertebral elements composing the xenarthran synsacrum within a phylogenetic framework. Vertebral counts of the adult synsacrum was obtained from almost all extant genera, with the exception of Calyptophractus, and several fossils. The modal number of vertebrae from the adult synsacrum was mapped onto a composite phylogeny of Xenarthra. The ancestral number of synsacrals for Xenarthra was recovered as ambiguous, although one of the optimizations recorded a number of six synsacrals, probably three iliac and three post-iliac vertebrae. The clade Cingulata is characterized by a high number of vertebrae forming the synsacrum (eight synsacrals), which is fused to the ischium through the tip of the transverse processes of the most posterior vertebrae. In pilosans, the ancestral number of synsacral vertebrae seems to be lower, probably formed by five or six vertebrae, and the union with the ischium is achieved through the base of the transverse processes of the most posterior vertebrae. Two exceptions stand out, one involving the extant suspensory sloths and Megalocnus, and the other involving a family of ground sloths, the Mylodontidae. A probable relationship of the synsacral number in the different taxa to the lifestyles is discussed.

The Evolution of Climatic Niches and its Role in Shaping Diversity Patterns in Diprotodontid Marsupials Abstract The interplay between niche conservatism and niche evolution has been suggested to play a key role in shaping the biogeographical history of a given clade. Here, we integrate climatic data associated with the distribution range of 86 diprotodontid species and their phylogenetic relationships in order to examine the evolutionary dynamics of ecological niches of Diprotodontia and explore the link between diversification, niche evolution, and trends in biodiversity over space in this iconic group. Both mean annual temperature (MAT) and annual precipitation (AP) best-fitted punctuated modes of evolution indicate that climatic niche evolution in diprotodonts is speciational. Among-clade variation in rates of climatic niche evolution was correlated with variation in rates of lineage diversification, which reinforces the view that rapid shifts in climatic niches promote speciation. We found that both climatic attributes, AP and MAT, exhibited a pattern according to which species richness progressively declined along a gradient from ancestral to derived climatic conditions and, in turn, it was negatively correlated to niche breadth. However, correlation between niche breadth and niche position was not similar for both climatic traits, as these differ with respect to the relative position of the zone colonized by the most recent common ancestor within its corresponding axis. Diprotodontia diversity decreased while phylogenetic clustering increased, suggesting that niche conservatism associated with ancestral climate probably drives most of variation in species richness in this region. Our study shows that the diversification of diprotodontid marsupials appears to have occurred against a background of moderate phylogenetic niche consevatism, which largely determines the current distribution of this group.

Changes in Ontogenetic Allometry and their Role in the Emergence of Cranial Morphology in Fossorial Spiny Rats (Echimyidae, Hystricomorpha, Rodentia) Abstract All evolutionary modifications of morphology in adult animals presuppose occurrence of changes in developmental programming. While some developmental changes affect rates of trait growth during the entire ontogeny, other developmental changes modify timing and growth rates during limited stages, usually in early development. Identifying which kind of these alterations are more frequent during evolution is crucial for understanding processes influencing the emergence of phenotypic diversity and specializations. Here, we used an allometric approach to assess the relative impact of these two kinds of ontogenetic alterations in the emergence of specialized skull morphology in fossorial spiny rats, comparing them with closely related, more generalist, terrestrial species. Univariate and multivariate analyses of adult shape consistently showed that fossorial spiny rats remarkably differed from terrestrial species, mainly by showing shorter and lower rostrum and more expanded auditory bullae, a set of traits usually considered specializations for life underground. Slopes and elevations of allometric trajectories of cranial traits were estimated for each species and compared with Analysis of Covariance, Likelihood-ratio tests, and Analysis of Variance based on Burnaby-corrected data. These tests showed that changes in allometric elevations were more recurrent during evolution and more congruent with the change in adult morphology than change in allometric slopes. These findings indicated that developmental changes modifying timing and growth rates during limited stages of early development were more frequent than alterations of trait covariation patterns along the entire ontogeny. This kind of developmental change accounts for a large effect on diversification of adult morphology and emergence of burrowing specializations in spiny rats.

First 3D Dental Topographic Analysis of the Enamel-Dentine Junction in Non-Primate Euarchontans: Contribution of the Enamel-Dentine Junction to Molar Morphology Abstract Molar morphology plays a key role in the systematics and behavioral interpretation of fossil taxa, so understanding the developmental patterns that shape occlusal morphology in modern taxa is of central importance to informing analysis of the fossil record. The shape of the outer enamel surface (OES) of a tooth is largely the result of the forming and folding of the inner enamel epithelium, which is preserved in fully formed teeth as the enamel-dentine junction (EDJ). Previous research on living primates has shown that the degree of correlation between the EDJ and OES can be used to inform our understanding of developmental patterns because lower correlations imply that later developmental events modify the template provided by the EDJ more extensively. Here, we use three topographic metrics to investigate the degree of correlation between the EDJ and OES across living euarchontans by analyzing treeshrews and dermopterans in addition to primates. We found that all living euarchontans show a high degree of topographical correlation, whereas non-primates, especially basally divergent taxa such as Ptilocercus lowii, show the highest degree of correlation between these two surfaces. Our results indicate, that while it is the earlier stages of dental development that have the most influence on overall crown morphology in euarchontans generally, among primates, anthropoids have a lower degree of correlation, implying a greater emphasis on later phases of dental development. This provides insight relevant to interpreting the evolutionary context of the diversity of dental form observed within Euarchonta.

New Fossil Suid Specimens from the Terminal Miocene Hominoid Locality of Shuitangba, Zhaotong, Yunnan Province, China Abstract Fossil suid specimens recovered from the latest Miocene site of Shuitangba, Zhaotong Basin, Yunnan Province, provide new information on the classification and relationship of Chinese Miocene Suinae. Most of the recovered specimens are referred to a relatively advanced and large species of Suinae, Propotamochoerus hyotherioides, based on dental dimensions and morphology. Detailed morphological comparisons were made between the Shuitangba Pr. hyotherioides and other Asian Miocene suines. From these comparisons, we suggest that Pr. hyotherioides from Shuitangba and northern China may be relatively derived compared to the specimens from Lufeng and Yuanmou, southern China and that Pr. hyotherioides and Pr. wui represent separate branches of the genus in China. Furthermore, Microstonyx differs from Pr. hyotherioides in p4/P4 and m3/M3 characters. Molarochoerus is suggested to represent a relatively derived taxon due to the uniquely molarized upper and lower fourth premolars. Miochoerus youngi is suggested to have a closer relationship to Sus and Microstonyx than to Propotamochoerus due to its small size and p4 morphology. Hippopotamodon ultimus, Potamochoerus chinhsienense, Dicoryphochoerus medius, and D. binxianensis exhibit complex morphologies that variously resemble Propotamochoerus, Microstonyx, and Sus and are suggested to be possible transitional forms between Propotamochoerus, Microstonyx, and Sus. However, the resolution of their classification requires further analysis when more material is recovered.

A Dental Microwear Texture Analysis of the Early Pliocene African Ursid Agriotherium africanum (Mammalia, Carnivora, Ursidae) Abstract The craniodental morphology of the early Pliocene ursid Agriotherium africanum has been studied extensively to reveal aspects of its dietary ecology. Results suggest that this large-bodied, long-legged, short-faced African native primarily consumed vertebrate matter. While many carnivoran families exhibit a clear functional relationship between craniodental form and performance on the one hand, and dietary behavior on the other, this is not always the case with Ursidae. Because of uncertainties regarding the appropriateness of using craniodental form to investigate ursid diets, questions still linger about the dietary ecology of Ag. africanum. Here, we report on a dental microwear texture analysis of six Ag. africanum lower second molars from the South African fossil site of Langebaanweg. Results support morphological evidence that suggests a diet focused on vertebrate soft tissue and bone. Unfortunately, results cannot clarify questions about mode of acquisition.

Cranial Geometric Morphometric Analysis of the Genus Tapirus (Mammalia, Perissodactyla) Abstract Tapirs are perissodactyl ungulates of the genus Tapirus. The family Tapiridae was more diverse in the past. Genus Tapirus include five living species: T. indicus, T. pinchaque, T. bairdii, T. terrestris, and T. kabomani. Despite all the information available about tapirs, evolutionary relationships among species within the genus are still uncertain. Recent works suggest that T. terrestris may be a species complex. A better understanding of the evolutionary history of this clade is essential to better support conservation strategies for the species of this genus, which are keys in the dynamics of tropical forests in Southeast Asia and Central and South America. Geometric morphometry has been proved to be a useful tool for the study of morphological evolution in mammals, but studies involving cranial geometric morphometry of tapiroids have never been done. We hereby propose landmarks for the study of tapir cranial shape through 2D geometric morphometric technique, including 20 in lateral cranial view (n = 71), 14 in dorsal cranial view (n = 51), and 21 in ventral cranial view (n = 44), followed by PCA multivariate statistical analysis that ordinated specimens from each of the three data groups along the major axis of shape variation. Lateral and dorsal view landmarks proved to be the most diagnostic for the species studied, providing interesting insights and trends on tapiroid cranial evolution. Ventrally, the species analyzed do not differentiate significantly. In this paper, we add new information to the current cranial morphometric database of tapirs, which can help elucidate questions about their evolutionary history.

Generalized Osteosclerotic Condition in the Skeleton of Nanophoca vitulinoides , a Dwarf Seal from the Miocene of Belgium Abstract In the fossil record, it has been shown that various clades of secondarily aquatic tetrapods experienced an initial densification of their bones in the early stages of their evolution, and developed spongier and lighter bones only later in their evolution, with the acquisition of more efficient swimming modes. Although the inner bone structure of most secondarily aquatic tetrapods has already been studied, no research hitherto focused on true seals, or Phocidae. However, preliminary observations previously made on a Miocene species, Nanophoca vitulinoides, suggested that this taxon showed pronounced specialization of bone structure as compared to other seals. This feature justifies a specific comparative study, which is the purpose of this article. Microanatomical analysis of bones of N. vitulinoides shows compactness values nearing 100%, which is much higher than in other semi-aquatic mammals, pinnipeds included. Osteohistological analyses show virtually complete remodeling of the medullary territory by Haversian substitution. Extreme bone compactness locally resulted from an imbalance, towards reconstruction, of this process. Cortical regions were less intensely remodeled. In a number of specimens, the cortex shows clear growth marks as seasonal lines of arrested growth. The results suggest that, despite the extreme compactness of long bones of N. vitulinoides and the small size of this taxon, the growth rate of the cortex, and that of the bones in general, did not differ strongly from that of other, larger phocids. Extreme skeletal compaction and densification must have increased body density in Nanophoca. Consequently, speed, acceleration, and maneuverability must have been low, and this taxon was most likely a near-shore bottom-dwelling seal. Consequently, dietary preferences were most likely oriented towards benthic food sources.

Reigitherium (Meridiolestida, Mesungulatoidea) an Enigmatic Late Cretaceous Mammal from Patagonia, Argentina: Morphology, Affinities, and Dental Evolution Abstract New dental and dentary fossils collected in the Upper Cretaceous La Colonia Formation in central Patagonia provide new evidence on the morphology, feeding ecology, and relationships of the enigmatic mammal Reigitherium. The newly discovered specimens described here include elements of the upper dentition and several partial dentaries, elucidating fundamental questions of serial homology and postcanine dental formula (four premolars and three molars). This new evidence supports a nested position of Reigitherium within the advanced meridiolestidan clade Mesungulatoidea. Apomorphic features of the upper and lower molariform elements include intense enamel crenulation circumscribed within the primary trigon and trigonid, elevated cingulids, and the neomorphic appearance of cusps/cuspulids, all of which increase overall crown complexity. A Dental Topography Analysis comparing Reigitherium and its sister taxon Peligrotherium to Cretaceous and Cenozoic therians demonstrates functional similarity between the mesungulatoids and South American marsupial taxa that succeed them in the small-to medium-sized herbivore niche during the Paleocene. Previous taxonomic attributions of Reigitherium are discussed and comparisons with other meridiolestidans highlight the remarkable radiation of this group in the Cretaceous of South America.