Postcanine dental form in the mustelidae and viverridae (Carnivora: Mammalia)

Preliminary description of a late Middle Pleistocene mammalian fauna prior to the extinction of Gigantopithecus blacki from the Yixiantian Cave, Guangxi ZAR, South China

In recent years, nearly 20 cave sites with rich assemblages of mammalian fossils have been found and excavated in the Chongzuo area, Guangxi Zhuang Autonomous Region, China. Their ages are distributed throughout the entire Pleistocene Epoch. These discoveries have greatly facilitated our understanding of the evolution of the Stegodon-Ailuropoda fauna and the environmental context of human evolution in southern China. Here, we present a preliminary report on a diverse late Middle Pleistocene mammalian fauna from the Yixiantian Cave in southern China, which is a typical representative of the Stegodon-Ailuropoda fauna (sensu lato). The fossil mammals are represented by isolated dental remains only. In 2010 and 2011, two seasons of systematic excavations at the Yixiantian Cave yielded a total of 4,958 identifiable mammalian teeth. They were identified as belonging to 37 species and 6 orders of mammals. In addition, the tooth type of all the teeth representing each species was also determined where possible. A single fragmentary molar was identified as belonging to Gigantopithecus blacki, indicating that its population had declined sharply at this time and was on the brink of extinction. Description of the Yixiantian fauna will not only help better characterize the composition of the Stegodon-Ailuropoda fauna during the late Middle Pleistocene, but also clarify our understanding of the paleoenvironmental context at a time just prior to the extinction of G. blacki.

The exceptionally high diversity of small carnivorans from the Late Miocene hominid locality of Hammerschmiede (Bavaria, Germany)

The present study deals with new material of carnivorans (Mustelidae, Mephitidae, Ailuridae, Potamotheriinae and Viverridae) from the basal Tortonian (Late Miocene, late Astaracian) hominid-bearing locality of Hammerschmiede (Bavaria, Germany). The small carnivoran fauna includes 20 species belonging to nine different subfamilies (Guloninae, Lutrinae, Mellivorinae, Potamotheriinae, Leptarctinae, Mephitinae, Simocyoninae, Genettinae and Viverrinae). The identified forms include: "Martes" sansaniensis, "Martes" cf. munki, "Martes" sp., Circamustela hartmanni n. sp., Laphyctis mustelinus, Guloninae indet., Eomellivora moralesi, Vishnuonyx neptuni, Paralutra jaegeri, Lartetictis cf. dubia, Trocharion albanense, Palaeomeles pachecoi, Proputorius sansaniensis, Proputorius pusillus, Alopecocyon goeriachensis, Simocyoninae indet., Potamotherium sp., Semigenetta sansaniensis, Semigenetta grandis and Viverrictis modica. The new species Circamustela hartmanni n. sp. is differentiated from the other members of the genus by its small size and the morphology of its dental cusps in the upper and lower carnassials. This is one of the highest reported taxonomic diversities for fossil small carnivorans in the Miocene of Europe, including also first and last occurrences for several genera and species. Additionally, the assemblage comprises some rare taxa such as Palaeomeles pachecoi and Eomellivora moralesi. An ecomorphological comparison of the discovered taxa reveals possible cases of competition and niche partitioning.

A comparative study of the Early Pleistocene carnivore guild from Dmanisi (Georgia)

The carnivore guild of the Early Pleistocene site of Dmanisi is among the most diverse of the Early Pleistocene of the entire Old World. It includes 14 carnivoran taxa: Homotherium latidens, Megantereon whitei, Panthera onca georgica, Acinonyx pardinensis, Lynx issiodorensis; Pachycrocuta brevirostris; Canis (Xenocyon) lycaonoides, Canis borjgali, Vulpes alopecoides; Ursus etruscus; Lutra sp., Martes sp., Meles sp., and Pannonictis sp. The analysis of this rich carnivore guild was carried out under different methodological approaches to compare the assemblage with other chronological coeval European, Asian, and African sites from a paleobiological perspective. To achieve the goal, we used a permutational hierarchical method called boostrapping cluster analysis based on taxonomic absence/presence matrices (at both generic and specific level) and on ecological matrices (considering dietary preferences/hunting strategies of each carnivoran) and carried out Mantels tests assessing magnitude of time, space, ecology, and taxonomy as source of difference between guilds. Our results suggest a close similarity among the Dmanisi carnivore assemblage and other guilds recorded from European late Villafranchian sites such as Pirro Nord, Venta Micena, and Apollonia 1 and, in a lesser extent, to European Epivillafranchian sites as Vallonnet, Untermassfeld, or the Vallparadís Section. Early to Middle Pleistocene Asian carnivore assemblages display several similarities with the Dmanisi guild mainly in the record and diversity of felid and the canid ecomorphotypes. Eastern African sites such as Olduvai and Omo, as well as South African sites, display a lower similarity with the studied sample, basically for the most diverse hyenid taphocoenoses. To sum up, the present study suggests a close similarity between the Dmanisi carnivore guild and other European Late Early Pleistocene assemblages without close parallels with African or Asian assemblages.

The killer’s toolkit: remarkable adaptations in the canine teeth of mammalian carnivores

Often the first point of contact between predator and prey, mammalian canine teeth are essential for killing, dismembering and consuming prey. Yet despite their importance, few associations among shape, function and phylogeny are established. We undertook the first comprehensive analysis of canine tooth shape across predatory mammals (Carnivora, Didelphimorphia and Dasyuromorphia), integrating shape analysis with function of this fundamental feature. Shape was quantified using three-dimensional geometric morphometrics and cross-sectional sharpness. Canines vary in three main ways (sharpness, robustness and curvature) which vary with diet, killing behaviour and phylogeny. Slender, sharp canines are associated with carnivores such as felids that target the neck of their prey and primarily consume the ‘softer’ parts of a carcass. Robust, blunt canines are found in mustelids and dasyurids that typically consume ‘harder’ materials, such as bone, or bite into skulls. Differences in the killing behaviours of felids and canids probably result in more curved canines in the latter, which act as hooks to hold prey. We find functional specialization in the upper and lower canines of individuals and across the major mammalian clades. These patterns demonstrate how canine teeth are adapted to suit diverse diets and hunting styles, enabling mammals to become some of nature's most successful predators.

On the Dental Formulae of Brazilian Terrestrial Carnivora (Mammalia)

Key compendia of Neotropical mammals contain conflicting information regarding the dental formulae of Brazilian carnivores. The objective of the present study was to review the dental formulae of Brazilian Canidae, Felidae, Mephitidae, Mustelidae and Procyonidae. We illustrate the dental morphology of all Brazilian genera, and report intra and interspecific tooth variation, and supernumerary teeth. We examined skulls and mandibles of 710 Brazilian terrestrial carnivores, including juvenile and adult specimens. Adults of all genera have three incisors and one canine in each quadrant. Members of the canid family have the following postcanine formula P 4/4 and M 2/3, except Speothos venaticus (M 1/2); felids have P 3/2 and M 1/1; mephitids present P 2/3 and M 1/2; mustelids show P 2-4/2-3 and M 1/2; and finally, procyonids have P 4/4 and M 2/2, except Potos flavus (P 3/3). Supernumerary teeth were found in individuals of seven genera in every family except Procyonidae. Although our results corroborate previous descriptions based on vouchered material, we detected several incongruences being replicated, possibly due to the lack of examination of museum vouchers, propagating erroneous information without critical analysis. Finally, we present a dichotomous key based on the review of dental morphology.

Quantifying the link between craniodental morphology and diet in the Soricidae using geometric morphometrics

Dietary adaptations have often been associated with heightened taxonomic diversity. Yet, one of the most species-rich mammalian families, the Soricidae, is often considered to be ecologically and morphologically relatively homogenous. Here, we use geometric morphometrics to capture skull and dentary morphology in a broad sample of shrew species and test the hypothesis that morphological variation among shrew species reflects adaptations to food hardness. Our analyses demonstrate that morphology is associated with dietary ecology. Species that consume hard food items are larger and have specific morphological adaptions including an anteroposteriorly expanded parietal, an anteroposteriorly short and dorsoventrally tall rostrum, a mediolaterally wide palate, buccolingually wide cheek teeth, a large coronoid process and a dorsoventrally short jaw joint. The masseter muscle does not appear to play an important role in the strong bite force of shrews and the dentary is a better indicator of ecology than the skull. Our phylogenetic flexible discriminant function analysis suggests that the evolutionary history of shrews has shaped their morphology, canalizing dietary adaptations and enabling functional equivalence whereby different morphologies achieve similar dietary performances. Our work makes possible future studies of niche partitioning among sympatric species as well as the investigation of the diet of extinct soricids.

Unique pattern of dietary adaptation in the dentition of Carnivora: its advantage and developmental origin

Carnivora is a successful taxon in terms of dietary diversity. We investigated the dietary adaptations of carnivoran dentition and the developmental background of their dental diversity, which may have contributed to the success of the lineage. A developmental model was tested and extended to explain the unique variability and exceptional phenotypes observed in carnivoran dentition. Carnivorous mammalian orders exhibited two distinct patterns of dietary adaptation in molars and only Carnivora evolved novel variability, exhibiting a high correlation between relative molar size and the shape of the first molar. Studies of Bmp7-hetero-deficient mice, which may exhibit lower Bmp7 expression, suggested that Bmp7 has pleiotropic effects on these two dental traits. Its effects are consistent with the pattern of dietary adaptation observed in Carnivora, but not that observed in other carnivorous mammals. A molecular evolutionary analysis revealed that Bmp7 sequence evolved by natural selection during ursid evolution, suggesting that it plays an evolutionary role in the variation of carnivoran dentition. Using mouse experiments and a molecular evolutionary analysis, we extrapolated the causal mechanism of the hitherto enigmatic ursid dentition (larger M₂ than M₁ and M₃). Our results demonstrate how carnivorans acquired novel dental variability that benefits their dietary divergence.

Divergent Skull Morphology Supports Two Trophic Specializations in Otters (Lutrinae)

Variation in terrestrial mammalian skull morphology is known to constrain feeding performance, which in turn influences dietary habits and ultimately fitness. Among mustelids, otters have evolved two feeding specializations: underwater raptorial capture of prey (mouth-oriented) and capture of prey by hand (hand-oriented), both of which have likely associations with morphology and bite performance. However, feeding biomechanics and performance data for otters are sparse. The first goal of this study was to investigate the relationships between feeding morphology and bite performance among two mouth-oriented piscivores (Pteronura brasiliensis and Lontra canadensis) and two hand-oriented invertebrate specialists (Enhydra lutris and Aonyx cinerea). Since other vertebrate taxa that are mouth-oriented piscivores tend to possess longer skulls and mandibles, with jaws designed for increased velocity at the expense of biting capability, we hypothesized that mouth-oriented otters would also possess long, narrow skulls indicative of high velocity jaws. Conversely, hand-oriented otters were expected to possess short, blunt skulls with adaptations to increase bite force and crushing capability. Concomitant with these skull shapes we hypothesized that sea otters would possess a greater mandibular bluntness index, providing for a greater mechanical advantage compared to other otter species investigated. A second goal was to examine morphological variation at a finer scale by assessing variation in cranial morphology among three sea otter subspecies. Since diet varies among these subspecies, and their populations are isolated, we hypothesized that the magnitude of mandibular bluntness and concomitant mechanical advantage, as well as occlusal surface area would also vary within species according to their primary food source (fish versus hard invertebrates). Functional expectations were met for comparisons among and within species. Among species the phylogeny suggests a deeply rooted transition to alternative foraging types. Yet within foraging types alternative species were also strongly variable, suggesting either selective differences in the extent or nature of realized foraging mode, or an accumulation of non-adaptive changes during the long independent evolutionary history. At the finest scale, variation among subspecies indicates that trophic adaptation occurred rapidly, making it interesting that we happened to find both deeply and shallowly-rooted transformations associated with diet type in otter species and subspecies.

Shape variation in the skull and lower carnassial in a wild population of raccoon dog (Nyctereutes procyonoides)

Individual variations in skull and lower carnassial morphology within a wild population of raccoon dog were examined using geometric morphometric techniques. We compared individual morphological variations by using relative warp analysis, and then tested morphological integration between the skull and carnassial by using partial least square (PLS) analysis. The most marked variation in skull shape was the dorsoventral flexion; i.e., deformation from klinorhynchy to airorhynchy. Two remarkable variations were observed, including tilting between the trigonid (or carnassial blade) and the talonid in the lower carnassial, and the relative sizes of the trigonid and the talonid. This observed variation in skull shape was similar to previous reports of variations among dog breeds that correlate with a polymorphism of the Runx2 gene. This polymorphism has also been reported to correlate with snout length, which is strongly related to carnivorous or omnivorous dietary adaptations, across the entire order Carnivora. Our results in the lower carnassial were also similar to previously reported patterns observed for carnivorous or omnivorous dietary adaptations among Carnivora. However, in our PLS analysis between skull and carnassial shapes, we only found a significant correlation in a lower dimension, suggesting a lower degree of integration. These results indicate that shape variations, which could be sources of natural selection in the skull and carnassial, were present in a wild population, suggesting high evolvability of these variations in the raccoon dog and the order Carnivora in general.

Unique inhibitory cascade pattern of molars in canids contributing to their potential to evolutionary plasticity of diet

Developmental origins that guide the evolution of dental morphology and dental formulae are fundamental subjects in mammalian evolution. In a previous study, a developmental model termed the inhibitory cascade model was established. This model could explain variations in relative molar sizes and loss of the lower third molars, which sometimes reflect diet, in murine rodents and other mammals. Here, I investigated the pattern of relative molar sizes (inhibitory cascade pattern) in canids, a taxon exhibiting a wide range of dietary habits. I found that interspecific variation in canid molars suggests a unique inhibitory cascade pattern that differs from that in murine rodents and other previously reported mammals, and that this variation reflects dietary habits. This unique variability in molars was also observed in individual variation in canid species. According to these observations, canid species have greater variability in the relative sizes of first molars (carnassials), which are functionally important for dietary adaptation in the Carnivora. In conclusion, an inhibitory cascade that differs from that in murine rodents and other mammals may have contributed to diverse dietary patterns and to their parallel evolution in canids.

Morphological innovation, diversification and invasion of a new adaptive zone

How ecological opportunity relates to diversification is a central question in evolutionary biology. However, there are few empirical examples of how ecological opportunity and morphological innovation open new adaptive zones, and promote diversification. We analyse data on diet, skull morphology and bite performance, and relate these traits to diversification rates throughout the evolutionary history of an ecologically diverse family of mammals (Chiroptera: Phyllostomidae). We found a significant increase in diversification rate driven by increased speciation at the most recent common ancestor of the predominantly frugivorous subfamily Stenodermatinae. The evolution of diet was associated with skull morphology, and morphology was tightly coupled with biting performance, linking phenotype to new niches through performance. Following the increase in speciation rate, the rate of morphological evolution slowed, while the rate of evolution in diet increased. This pattern suggests that morphology stabilized, and niches within the new adaptive zone of frugivory were filled rapidly, after the evolution of a new cranial phenotype that resulted in a certain level of mechanical efficiency. The tree-wide speciation rate increased non linearly with a more frugivorous diet, and was highest at measures of skull morphology associated with morphological extremes, including the most derived Stenodermatines. These results show that a novel stenodermatine skull phenotype played a central role in the evolution of frugivory and increasing speciation within phyllostomids.

The hog-badger is not an edentate: systematics and evolution of the genus Arctonyx (Mammalia: Mustelidae)

Hog-badgers (mustelid carnivorans classified in the genus Arctonyx) are distributed throughout East and Southeast Asia, including much of China, the eastern Indian Subcontinent, Indochina and the large continental Asian island of Sumatra. Arctonyx is usually regarded as monotypic, comprising the single species A. collaris F. Cuvier, 1825, but taxonomic boundaries in the genus have never been revised on the basis of sizeable series from throughout this geographical range. Based on a review of most available specimens in world museums, we recognize three distinctive species within the genus, based on craniometric analyses, qualitative craniodental features, external comparisons, and geographical and ecological considerations. Arctonyx albogularis (Blyth, 1853) is a shaggy-coated, medium-sized badger widely distributed in temperate Asia, from Tibet and the Himalayan region to eastern and southern China. Arctonyx collaris F. Cuvier, 1825, is an extremely large, shorter-haired badger, distributed throughout Southeast Asia, from eastern India to Myanmar, Thailand, Vietnam, Cambodia and Laos. The world's largest extant badger, A. collaris co-occurs with A. albogularis in eastern India and probably in southern China, and fossil comparisons indicate that its geographical range may have extended into central China in the middle Pleistocene. The disjunctly distributed species Arctonyx hoevenii (Hubrecht, 1891), originally described within the order ‘Edentata’ by a remarkable misunderstanding, is the smallest and darkest member of the genus and is endemic to the Barisan mountain chain of Sumatra. Apart from A. hoevenii, no other Arctonyx occurs on the Sunda Shelf below peninsular Thailand. The natural history of each species of Arctonyx, so far as is known, is briefly reviewed. No claim to original US Government works.