Coalescence Models Reveal the Rise of the White-Bellied Rat ( Niviventer confucianus ) Following the Loss of Asian Megafauna Abstract Rodents are the major remaining mammals in many terrestrial ecosystems after the historical loss of megafauna and large-bodied taxa. Niviventer confucianus is a dominant habitat generalist in natural forests in most of China. It is also recorded as an important vector of diverse zoonotic diseases. Here, three mitochondrial and one nuclear DNA fragments were sequenced from samples covering most of the species range to study intraspecific genetic diversification and demographic history. Molecular voucher specimens of N. confucianus revealed that its assumed distribution range has been overestimated because of the hitherto unrecognized separation from parapatric species. Phylogenetic inferences recognized three geographically delimited intraspecific lineages that diverged at approximately 1.28 and 0.68 Mya. Hengduan Mountains, the east margin of Qinghai Tibetan Plateau, and the mountains surrounding Sichuan Basin were recognized as the major geographical barriers. Demographic analysis revealed dramatic population growth in southwest, central, and northern China in the late Pleistocene, but only slight growth in Yunnan/Tibet. The population boom apparently coincided with the reduction of predation and competition from the loss of megafauna in the late Pleistocene. Distributional ranges were inferred to be fairly stable through the late Quaternary glacial-interglacial climatic oscillations, possibly enabled by the species’ seed hoarding behavior and wide climatic tolerance. The demographic history of N. confucianus suggests that these rodents directly profited from the loss of megafauna, while their most recent increases potentially led to the proliferation of zoonotic disease by this species.

New Virtual Endocasts of Eocene Ischyromyidae and Their Relevance in Evaluating Neurological Changes Occurring Through Time in Rodentia Abstract Little is known about the early evolution of the brain in rodents. We report on nine new virtual endocasts for one of the most primitive family of rodents, Ischyromyidae, based on five specimens of Pseudotomus and Notoparamys(Paramyinae) and four specimens of Reithroparamys and Rapamys (Reithroparamyinae), dating from the early Eocene to the late middle Eocene of North America (Colorado, Wyoming, Utah and Montana). The virtual endocasts were obtained from high-resolution X-ray micro-computed tomography data. Comparisons with previously described ischyromyid virtual endocasts allow us to make inferences about the ancestral condition of the brain in rodents. Since Reithroparamyinae are suggested to be more closely related to the squirrel-related clade than other Ischyromyidae, comparisons were also made with the oldest virtual endocast for a squirrel, which gave us the opportunity to look at finer neurological changes occurring in the early evolution of squirrels. These new data permit a preliminary assessment of the endocranial diversity in Ischyromyidae. The results do not show evidence for a clear increase in Encephalization Quotient through time for early rodents. Instead, variation among species could be due to ecological factors (e.g., locomotion). Significant expansion in the neocortex and increase in paraflocculi ratios may have occurred in the transition from Ischyromyidae to Sciuridae, as previously hypothesized. Large olfactory bulbs and exposed midbrain are inferred to have been features present in the common ancestor of rodents, while neocortical expansion is reconstructed as having occurred twice independently within Ischyromyidae.

Incisor Enamel Microstructure of Paleogene Caviomorph Rodents from Contamana and Shapaja (Peruvian Amazonia) Abstract We investigate the enamel microstructure of 37 isolated rodent incisors from several late middle Eocene and late Oligocene localities of Contamana (Loreto Department, Peruvian Amazonia), and from the early Oligocene TAR-01 locality (Shapaja, San Martín Department, Peruvian Amazonia). All incisors show an enamel internal portion with multiserial Hunter-Schreger Bands (HSB). The late middle Eocene localities of Contamana yield incisors with subtypes 1, 1–2, and 2 of multiserial HSB; TAR-01 yielded incisors with subtypes 1–2, 2, 2–3, and 3 of multiserial HSB; and the late Oligocene localities of Contamana, incisors with subtypes 1–2, 2, and 2–3 of multiserial HSB. Based on our current knowledge of the South American and African rodent fossil records and given the primitiveness of the Eocene caviomorph faunas, it may be expected that the hystricognath pioneer(s) who have colonized South America from Africa sometime during the middle Eocene, most probably had incisors that displayed a multiserial enamel with an interprismatic matrix arrangement characterizing the subtype 1 (or subtype 1 + the subtype 2 and/or the transitional 1–2) of multiserial HSB. In contrast, the derived subtypes 2–3 and 3 conditions were subsequently achieved but likely rapidly, as evidenced by its record as early as the ?late Eocene/early Oligocene (e.g., Santa Rosa, Shapaja, and La Cantera), and seemingly evolved iteratively but only in the Octodontoidea clade.

Dental Shape Variation and Phylogenetic Signal in the Rattini Tribe Species of Mainland Southeast Asia Abstract The Rattini tribe comprises some of the most specious genera in the mammalian kingdom. Many of these species are also highly morphologically conserved. As a result, identifying Rattini tribe animals, particularly those of the Rattusgenus, to species level is extremely difficult. Problems with identification of conservative morphologies, particularly of the skeleton, have led to difficulties in understanding the fossil remains and as a result the systematics of this group. Here, we apply geometric morphometrics to the first lower molar of 14 species of the Rattini tribe. We find that the morphological data present a strong phylogenetic signal. However, within Rattus, this signal is rather complex and possibly hints at rapid evolutionary shape and size changes. In modern species, it is possible to identify specimens to species level with a good degree of confidence. We find that using both size and shape together affords further confidence with identification. However, we caution against the over-reliance on size in environments with unknown species composition and climate, particularly in archaeological contexts. This approach should prove to be a useful tool for identifying fossil and sub-fossil remains, particularly where biomolecular markers are absent in circumstances of poor preservation.

Magnetic Resonance Imaging of the Brains of Three Peramelemorphian Marsupials Abstract Peramelemorphians (bandicoots and bilbies) are a unique and diverse group of digging Australasian marsupials, but their behavioral neurology and neuroanatomy is poorly known. Here, we have used Magnetic Resonance Imaging (MRI) to study the brains of three peramelemorphians: two bandicoots (Perameles nasuta and Isoodon obesulus) and the bilby (Macrotis lagotis), which is endangered. These brains had been stored in formaldehyde solution for more than 80 years and one of our goals was to demonstrate the feasibilty of extracting detailed comparative neuroanatomical information from the long-term preserved brains of rare, endangered, and extinct animals. High resolution anatomical and Diffusion Tensor Imaging was performed using a 9.4-T Bruker BioSpec 94/20 Avance III MRI system (Bruker, Ettlingen, Germany) located at the UNSW in Sydney. We were able to differentiate areal and laminar topography within isocortical areas (primary somatosensory – S1; and visual - V1, V2), as well as subdivisions within olfactory and limbic allocortical regions (cingulate, hippocampal). Resolution of subcortical structures was sufficient to differentiate α and β segments within the visual nucleus of the thalamus. We identified several previously unrecognized longitudinal association fiber systems as well as a rich array of sensory thalamocortical connections. Dense fiber pathways were observed to S1 and in the midbrain auditory pathways (mainly the lateral lemniscus, but also the brachium of the inferior colliculus). Our findings demonstrate the feasibility of using this sort of imaging of archived brains to analyze the neuroanatomy of rare and evolutionarily significant species and to relate these findings to the behavioral neurology of those species.

Incisor Enamel Microstructure of Hystricognathous and Anomaluroid Rodents from the Earliest Oligocene of Dakhla, Atlantic Sahara (Morocco) Abstract Seven hystricognaths and five anomaluroids have been recently described from the earliest Oligocene of the Dakhla (DAK C2) region of Morocco, based primarily on isolated cheek teeth. Here, we analyzed the enamel microstructure of thirty associated isolated fragments of incisors. Among these specimens, only three display an early stage of uniserial Hunter-Schreger bands (HSBs), with mostly a single prism per band, but also occasionally two prisms per band (in two specimens), and a thin interprismatic matrix (IPM) that runs parallel to the prism direction, thereby documenting incisors of anomaluroids. All other sampled incisors display an enamel with multiserial HSBs, thereby documenting hystricognaths. For these latter, we recorded primarily an IPM crystallite arrangement describing the subtype 2 of multiserial HSBs, but with variation including a wide amplitude in the angle (acute) formed between the crystallites of IPM and those of the prisms, some variations in the frequency of the IPM sheet anastomoses, in the number of prisms per HSBs, and variations in the inclination of the HSBs. The absence of the subtypes 2–3 and 3 of multiserial HSBs in DAK C2 suggests that African hystricognathous rodents had still not achieved these most resistant multiserial HSBs at that time. The drier, cooler climatic regime of the early Oligocene, having increased the fragmentation and opening of habitats, might have played a role in the subsequent selection of taxa having acquired a more resistant incisor enamel.

Cranial Biometrics of the Iberian Myotis myotis/Myotis blythii Complex: New Data for Studying the Fossil Record Abstract The Myotis myotis/M. blythii species complex, spread across the Western Palearctic, is a problematic group for which the taxonomy of the species is not yet satisfactorily resolved. The Iberian Peninsula played a key role in its evolutionary history as a Pleistocene refuge and as the starting point for the eastward expansion of M. myotis in the early Holocene, while M. blythii reached the Iberian Peninsula only during the middle Holocene. The study of Iberian populations and particularly of the Iberian fossil record is of high interest in this regard. However, there are few data available on the biometry of the skulls and teeth of Iberian populations (which differ somewhat in size from those of other regions of Europe and Asia) or tools for the identification of fragmentary cranial remains. Much of the Quaternary Iberian record of large Myotis remains unassigned. Here, we contribute to the task of determining fragmentary cranial remains by providing new cranial and dental biometric data from extant Iberian populations, predictive models for isolated upper molar identification, and a set of indices that allow quantitative evaluation of the differences in anatomical traits (in skull and molars) between the two species.

Skull Ontogeny of the Hyraxes Procavia capensis and Dendrohyrax arboreus (Procaviidae: Hyracoidea) Abstract Extant hyraxes are small, rabbit-sized, herbivorous paenungulates, with a notable feeding mechanism: they crop with the molars instead of the incisors, unlike most modern hoofed mammals. We investigated the postnatal development of the skull, and their functional correlates, in two extant representative forms of hyraxes, the terrestrial grazer Procavia capensis and the arboreal browser Dendrohyrax arboreus. We measured 18 linear variables representing fundamental descriptive and functional aspects of the skull, and estimated allometric equations on the basis of bivariate and multivariate analyses of an ontogenetic series of 32 specimens of P. capensis and 27 specimens of D. arboreus. Results showed that the ontogenetic trajectories of both species are similar in overall shape and size, but differ in localized regions of the skull associated with the masticatory apparatus. Examples include both differences in degree of allometry (upper postcanine row more positively allometric in Procavia) as well as opposing trends (positive allometry of diastema length in Dendrohyrax versus negative allometry in Procavia). In the mandible, the height of mandible and the length of the lower postcanine row showed significant differences. These changes could be associated with the acquisition of contrasting herbivorous specialization along the browsing-grazing gradient as exemplified in hyraxes.

Morphology of the Middle Ear Ossicles in the Rodent Perimys (Neoepiblemidae) and a Comprehensive Anatomical and Morphometric Study of the Phylogenetic Transformations of these Structures in Caviomorphs Abstract The extinct clade of caviomorph rodents Neoepiblemidae includes forms that lived in South America from the early Miocene to Pliocene. Among them is Perimys. The exceptional preservation of ear ossicles in this rodent is described and analyzed in a study of the phylogenetic transformations of these structures in caviomorphs including 21 extant and two extinct genera. Caviomorphs exhibit a conserved malleoincudal complex, with synostosis of the malleus and incus, “bullet-shaped” mallear head, and absence of orbicular apophysis. They also show a reduction of the mallear anterior process, in some cases even lacking this structure. The malleoincudal complex of Perimys shows an elongation of the head, but not as marked as in Chinchillinae. The incudal long process of Perimys is slightly more prolonged than the short process, as in chinchillids. In contrast, dinomyids have the incudal long process disproportionally more prolonged than in most caviomorphs. Concerning the disparity of caviomorph middle ear ossicles, Perimys shares the morphospace with chinchillids and other small forms. Within chinchilloids, Perimys is closer to chinchillids than to neoepiblemids.

A Nearly Complete Juvenile Skull of the Marsupial Sparassocynus derivatus from the Pliocene of Argentina, the Affinities of “Sparassocynids”, and the Diversification of Opossums (Marsupialia; Didelphimorphia; Didelphidae) Abstract “Sparassocynids” are small, carnivorously-adapted marsupials known from the late Miocene and Pliocene of South America, thought to be relatives of living didelphid opossums but of otherwise uncertain phylogenetic relationships. Here, we describe a nearly complete juvenile skull of the “sparassocynid” Sparassocynus derivatus, from the Pliocene (~5–3 million years old) Chapadmalal Formation, Argentina. It provides new information on the morphology of Sparassocynus, including the deciduous dentition, and (together with previously collected specimens) allows reinterpretation of the derived auditory region of “sparassocynids.” The new specimen also exhibits several distinctive apomorphies characteristic of Didelphidae and of subclades within the family. Undated Bayesian phylogenetic analysis of a total evidence dataset (132 craniodental characters, 7.3 kb of DNA sequence data from five nuclear genes) places “sparassocynids” within the didelphid genus Monodelphis, whereas “tip-and-node” dating analysis of the same dataset with an Independent Gamma Rates (IGR) clock model places them as sister to Monodelphis, showing that temporal information influenced the resultant topology. We conclude that “sparassocynids” warrant tribal separation only, as Sparassocynini, new rank. Based on our dated phylogeny, we also provide a revised scenario for didelphid diversification. Crown-clade didelphids probably originated close to the Oligocene-Miocene boundary. We agree with previous proposals that the appearance of carnivorously-adapted didelphids in South America during the late Miocene, including sparassocynins, is likely related to a decline in diversity of the sparassodonts at this time, and that the disappearance of these carnivorously-adapted didelphids at the end of the Pliocene may have been due to the arrival of placental carnivorans, such as mustelids, from North America.