Journal of Mammalian Evolution最新文献

The Madras Treeshrew, Anathana ellioti (Waterhouse, 1850), is a small, poorly studied mammal from South Asia. It is the only treeshrew found across the southern half of the Indian subcontinent and is the westernmost member of its order (Scandentia). The phylogenetic relationship between Anathana and its putative sister genus, Tupaia, remains unresolved, and the morphological differences between these two genera have yet to be analyzed with craniometric data. Here we describe some features that distinguish Anathana from other treeshrews. However, our comparative morphometric analyses reveal that Anathana overlaps with Tupaia in morphospace; it is smaller than most species (including the only other species found on the Indian mainland, T. belangeri) but larger than T. minor, Dendrogale melanura, and Ptilocercus lowii. At the infraspecific level, there is some separation between eastern and western populations, but this requires further investigation with larger sample sizes. Unfortunately, Anathana is disproportionately scarce in museum collections relative to other scandentians, and additional biological surveys across South India will be critical for future research on the taxonomy, distribution, and conservation of this elusive taxon.

Fossil badgers of the genus Meles are known in Eurasia since the Late Pliocene but their record is utterly scarce, often represented by isolated remains. This led to taxonomic confusion and hindered phylogenetic reconstruction of the genus. Here we describe in detail all the material attributed to M. thorali from the Early Pleistocene locality of Saint-Vallier, including several new complete crania. The results of comparative morphological and morphometric analyses allow reaffirming the distinction of M. thorali from M. meles and reassessing the status of other fossil species. All the analyzed European specimens between ca 2.8 and 1.5 Ma can be reasonably accommodated in a single species, M. thorali, while in Asia the diversity is higher, with up to four taxa described. Our analyses support previous interpretations of a close relationship between M. teilhardi with M. thorali. The European Meles meles appeared around 1.5 Ma and became the only badger present in European sites. We can therefore assume that the radiation of the genus Meles occurred during the general climatic changes that took place during the latest Pliocene and the beginning of Pleistocene and resulting environmental shifts across Eurasia.

The stocky skeletons and post-cranial anatomy of many extinct kangaroos indicate that they might have engaged in varied locomotor behaviors, rather than bipedal hopping, as their primary mode of locomotion. This study investigates support for this idea by estimating femoral bone perfusion, which is a correlate of locomotor intensity, in extinct kangaroos compared to living hopping species. Femur blood flow rates can be estimated from the sizes of nutrient foramina on the femur shaft of living and extinct species, without preservation of soft tissue. Estimated femur blood flow rates among the extinct Macropus, Protemnodon and Sthenurinae (Sthenurus, Simosthenurus and Procoptodon) are not significantly different from one another but are significantly greater than in living hopping macropods after accounting for the effect of body mass, consistent with their purportedly different locomotor style. The giant sthenurines have more robust femora than extrapolated from data of living hopping macropods, possibly due to the larger sthenurines requiring relatively stronger leg bones to support their heavier body weights, especially if loaded onto a single limb during bipedal striding.

A comparative craniometric analysis among maned wolves (Chrysocyon brachyurus, n = 9), crab-eating foxes (Cerdocyon thous, n = 8) and domestic dogs (Canis lupus familiaris, n = 124) was performed. A total of 18 craniometric measurements were taken from these specimens, and eight craniometric indices were further computed from those measurements. Using correlation analysis, we found that the 26 variables could be clustered into four groups, namely: (1) indicators of rostro-caudal length; (2) ventro-dorsal height and latero-lateral width; (3) cranial indices; and (4) dimensions of the foramen magnum. Consequently, multivariate techniques were applied to the data in order to reduce dimensionality and thus facilitate the comparisons among domestic and wild species. The projection of the data into the lower-dimensional space created by a principal component analysis showed that skulls of crab-eating foxes resembled small mesaticephalic skulls of domestic dogs, whereas the skulls of maned wolves were closer to those of larger dolichocephalic dogs. However, both species shared similarities with the mesaticephalic and dolichocephalic morphotypes of domestic dogs when variables were considered individually. Importantly, the variation in skull morphology found in the wild specimens was significantly smaller than that found in domestic dogs. These findings suggest an evolutionary constraint to skull shape diversity in maned wolves and crab-eating foxes, which seems consistent with adaptation to a generalist omnivorous diet.

Fossils of an insectivorous bat from the early Miocene of Panama are described as a new genus and species, Americanycteris cyrtodon (Chiroptera: Phyllostomidae: Phyllostominae). Americanycteris is a large phyllostomine bat, similar in size to the living species Chrotopterus auritus. Americanycteris cyrtodon can be distinguished from other closely related species by a posteriorly curved p4 and a thick labial cingulum on m1. Americanycteris cyrtodon occurs in two early Miocene vertebrate faunas from Panama. The holotype mandible with p4–m1 and an isolated p3 of A. cyrtodon were recovered from the early Hemingfordian (19–18 Ma) Centenario Fauna, and a mandible with p2 was found in the older late Arikareean (21 Ma) Lirio Norte Local Fauna. A similar large phyllostomine bat is known from the early Miocene Gran Barranca Fauna in Argentina. The presence of early Miocene phyllostomids in both North America and South America confirms the overwater dispersal of bats between the Americas before the late Miocene onset of the Great American Biotic Interchange. Pre-late Miocene chiropteran dispersals between the Americas were previously documented for the Emballonuridae and Molossidae. Although the five endemic New World families in the Noctilionoidea, including Phyllostomidae, were previously thought to be South American in origin, the oldest fossil records of noctilionoids (Mormoopidae and extinct Speonycteridae) are from the early Oligocene of Florida and one of the earliest records of the Phyllostomidae is from the early Miocene of Panama. The currently available fossil records from Panama and Florida suggest a possible North American origin for the Noctilionoidea.

Fossil teeth representing four species of Lophiomeryx are identified from early Oligocene strata in the Saint Jacques area of Nei Mongol, including L. shinaoensis, L. gracilis, L. cf. chalaniati, and L. triangularis sp. nov. This represents the highest species richness of this early traguline from a single stratigraphic sequence. The new materials expand the spatiotemporal ranges of L. shinaoensis and L. gracilis, which are previously known from the late Eocene of Guizhou, south China. We present further morphological details that support the validity of the original taxonomy for the Guizhou materials. L. cf. chalaniati resembles the type species morphologically but is smaller than European specimens. L. triangularis sp. nov. is the last to appear in the sequence, and it is notably larger and more high-crowned than all the other known species of Lophiomeryx. Aside from the dental materials, we report the first known skull of L. gracilis, collected from a nearby locality, Qianlishan. While the overall skull morphology is primitive for tragulines, the specimen preserves a closed postorbital bar, a derived feature that was previously thought to be absent in Lophiomeryx. Our new specimens shed light on the diversity, biogeography, and ecology of this basal ruminant as well as on the evolution of early tragulines.

Explorations in the past 20 years in the Plio-Pleistocene Zanda Basin (3,800–4,500 m above sea level) along the northern slopes of the Himalaya Mountains have substantially enriched our understanding of the paleoenvironments of the Tibetan Plateau and associated biologic evolution. Many elements of the mammalian fauna recovered are either new to science or shed new light about their special adaptations in this high elevation basin. Here we describe a new species of twisted-horned antelope, Gazellospira tsaparangensis, with a heteronymous spiral. Its small size and primitive morphology, such as relatively short horncore with less twisting, thin frontal bones, a lack of frontal and horncore sinuses, small size of supraorbital foramina, and lack of an anterior keel, helps to place it at the base of genus Gazellospira, substantially more stem-ward than the type species G. torticornis from the Plio-Pleistocene of Europe and western Asia. With an estimated age of 3.62 Ma, this also places G. tsaparangensis as one of the early occurrences in Eurasia, although some fragmentary records in Turkey may be slightly earlier. Considering this early appearance and primitive morphology, G. tsaparangensis once again may be a case of the ‘out-of-Tibet’ model of megafauna origin, with earlier progenitors adapted to cold environments in high Tibet before expanding their range to the rest of Eurasia.