Bipedalism evolved more than twice among archosaurs, and it is a characteristic of basal dinosaurs and a prerequisite for avian flight. Nevertheless, the reasons for the evolution of bipedalism among archosaurs have barely been investigated. Comparative analysis using phylogenetically independent contrasts showed a significant correlation between bipedality (relative length of forelimb) and cursoriality (relative length of metatarsal III) among Triassic archosaurs. This result indicates that, among Triassic archosaurs, bipeds could run faster than quadrupeds. Bipedalism is probably an adaptation for cursoriality among archosaurs, which may explain why bipedalism evolved convergently in the crocodilian and bird lineages. This result also indicates that the means of acquiring cursoriality may differ between archosaurs and mammals.

In reference to the evolutionary trend of increasing cheek tooth height in herbivorous ungulates, the causes of dental abrasion have long been debated. Interspecific comparisons of extant ungulates have revealed that both phytoliths in grass and external abrasive matter may play important roles. Using analysis of extant sika deer living in various environments and showing continuous latitudinal variation in food habits from northern grazing to southern browsing, we quantitatively evaluated the influence of dietary and environmental properties on three dental variables: mesowear score (MS), molar wear rate, and M3 hypsodonty index. We used 547 skulls and 740 mandibles from 16 populations of sika deer to obtain the dental measurements. We found that only graminoid proportion in diet correlated with MS and the molar wear rate, implying that phytoliths in grass abrade dental tissues. In contrast, annual precipitation in habitat was not correlated with any of the dental variables. We also found a significant correlation between the molar wear rate (selective pressure for high-crowned molars) and the M3 hypsodonty index of extant sika deer, implying an evolutionary increment in molar height corresponding to the molar wear rate. Our intraspecific comparative analyses provide further support for use of mesowear analysis as a paleodiet estimation method; it not only reveals staple food types (graminoids or dicots) but also implies regional or seasonal variation in the diet of the species.

In the present study, we estimated age at death of extinct deer (Cervus astylodon) excavated from two Late Pleistocene sites in Okinawa Island (the Hananda-Gama Cave and Yamashita-cho Cave I sites) from degree of molar wear. This was done using a regression equation of extant sika deer of known age, and deriving an age estimation equation based on M 3 crown height applicable to fossil specimens. We then reconstructed mortality profiles using 45 and 88 individuals of the Hananda-Gama and Yamashita-cho assemblages, respectively, and compared the profiles with those of extant and archaeological (Jomon period) sika deer (C. nippon) populations. The reconstructed age profiles of both sites were strikingly different from the living and hunted Jomon period profiles in relative abundance of old adults. They were more similar to the attritional mortality profiles of the extant sika deer that died by natural causes (i.e. not by human or animal predation), but showed a further shift towards older age. Combined with the fact that there is no fossil evidence of medium-to large-sized carnivores on Okinawa Island during the Late Pleistocene, our results suggest that C. astylodon populations had extended longevity because of low predatory pressure, including that by Paleolithic human hunters.

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Silesaurus opolensis belongs to Muroko, Katsuyama, Japan;, The University Museum, The University of Tokyo,