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Teeth are frequently used in phylogeny in order to better characterize the evolution of extinct mammal species. While most studies have focused on the adult dentition, the consideration of characters from the deciduous dentition could also contribute to reinforce phylogenetic assumptions or disentangle phylogenetic issues. We chose to investigate the characters of the deciduous dentition in cetartiodactyl taxa in relation to the disputed relationships within hippopotamoids, especially the position of Hippopotamidae. We describe the deciduous dentition of 51 species, among a dataset of 70 cetartiodactyls. We noticed that second and third deciduous premolars have a much lower degree of molarization, and are more suitable for coding than fourth deciduous premolars. Thirty-nine resulting characters were thus added to a previously published matrix, and parsimony and maximum-likelihood analyses were performed. Both analyses provided a better resolved topology for most taxa than without these characters, and with better support for most nodes in the parsimony analysis. Moreover, this analysis provides additional characters supporting the hypothesis of an emergence of hippopotamids within bothriodontine anthracotheres from the Palaeogene of Africa. The promising use of characters from the deciduous dentition in phylogeny should allow discussion of the underlying ontogenetic mechanisms at the origin of dental homology. [ABSTRACT FROM AUTHOR]

Sustainable coexistence of similar, related species is generally expected to be achieved through character displacement, resulting in niche partitioning. The species Apodemus sylvaticus and Apodemus flavicollis are very similar both morphologically and ecologically, and have a large geographical overlap. Whether functional or biomechanical differences between these two species contribute to their coexistence remains unknown. A biomechanical model was created based on muscle data derived from dissections to estimate the maximum bite force. In addition, the dental microwear was analysed to test for evidence of a divergence in diet. Finally, geometric morphometric approaches were used to compare mandibular shapes. The results indicate that A. flavicollis, the slightly larger species, is optimized for biting at a larger gape angle. Apodemus sylvaticus appears to be slightly more specialized for grinding and biting at a narrower gape angle. However, the majority of shape variation in the mandible across both species follows the same pattern. No significant differences in microwear were observed between species, and thus, they appear to consume similar food types. These results suggest that character divergence resulting in niche partitioning has not occurred, possibly due to low resource competition. Alternatively, resource partitioning may occur through behavioural differences or differences in activity patterns. [ABSTRACT FROM AUTHOR]

When it comes to mouse evo-devo, the fourth premolar-firstmolar (P4-M1) dental complex becomes a source of longstanding controversies among paleontologists and biologists. Muroidea possess only molar teeth but with additional mesial cusps on their M1. Developmental studies tend to demonstrate that the formation of such mesial cusps could result from the integration of a P4 germ into M1 during odontogenesis. Conversely, most Dipodoidea conserve their fourth upper premolars and those that lost these teeth can also bear additional mesial cusps on their first upper molars. The aim of this study is to assess this developmental model in both Muroidea and Dipodoidea by documenting the morphological evolution of the P4-M1 complex across 50Ma. Fourteen extinct and extant species, including abnormal and mutant specimens were investigated. We found that, even if their dental evolutionary pathways strongly differ, Dipodoidea andMuroidea retain common developmental characteristics because some of them can present similar dental morphological trends. It also appears that the acquisition of a mesial cusp on M1 is independent from the loss of P4 in both superfamilies. Actually, the progressive decrease of the inhibitory effect of P4, consequent to its regression, could allow the M1 to lengthen and mesial cusps to grow in Muroidea. Apart from these developmental explanations, patternings of the mesial part of first molars are also deeply constrained by morpho-functional requirements. As there is no obvious evidence of such mechanisms in Dipodoidea given their more variable dental morphologies, further developmental investigations are needed. [ABSTRACT FROM AUTHOR]

An ecomorphological approach of mandible shape through Fourier analyses combined with a paleodietary analysis of dental microwear patterns is used to reconstruct the diet of the extinct endemic Canariomys bravoi Crusafont, Pairó & Petter, 1964 and Canariomys tamarani López-Martínez & López-Jurado, 1987. These two large rodents, respectively, lived on Tenerife and Gran Canaria, the central islands of the Canarian Archipelago. Mandible shape and dental microwear respectively inform us on the volume of vegetal matter and on the presence of grass in the diet. Both Canariomys, which are of similar size, possess relatively similar mandible outlines and microwear patterns. For each species, a diet based on plant materials except grass is the most likely. Such results chime with the similar environments offered by the islands in which the species lived. On the contrary, molar morphology suggests different feeding habits of the two Canariomys. Thus, this suggests a case of mosaic evolution between teeth and mandibles, as well as the likely sensitivity of mandible shape to a combination of ecological and allometric factors. These new data obtained from the fossil record underline the propensity of island endemic mammals to yield surprising examples of phenotypic evolution. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 28–40. [ABSTRACT FROM AUTHOR]

The origin of the Cricetidae and the relationships among earliest species from Central and East Asia are still disputed. The taxonomic status of some Eocene cricetid taxa is also doubtful. A parsimony analysis based on 65 cranial and dental characters and including 22 early Myomorpha was performed to elucidate these issues. As a result, the North American Elymys, known as the first Myodonta, belongs to dipodoid rodents, although it shares a suite of characters with the first cricetids. This implies that the split between dipodoids and muroids occurred in North America during the early middle Eocene, as previously supposed. The disputed Simimys and Nonomys could constitute an early dipodoid radiation. It appears that the earliest offshoot of the cricetid clade is the Asian genus Palasiomys. This taxon has a more advanced cricetid plan than contemporaneous dipodoids. The genus Raricricetodon no longer exists here because it is polyphyletic; the species are included in Palasiomys ( P. minor, P. trapezius) and Pappocricetodon ( P. zhongtiaensis). The genus Pappocricetodon displays a complete cricetid plan associated with both the loss of P4 and the development of an anterocone on M1. The disputed genera Eocricetodon and Oxynocricetodon characterize the beginning of the Oligocene radiations of Eucricetodontinae throughout the Holarctic continents. [ABSTRACT FROM AUTHOR]