An exceptionally well-preserved skeleton of Palaeothentes from the Early Miocene of Patagonia, Argentina: new insights into the anatomy of extinct paucituberculatan marsupials

International audienc

Conservatism and adaptability during squirrel radiation : what is mandible shape telling us?

SYNTHESYS Project from the European Community Research Infrastructure (NL-TAF-4084)Both functional adaptation and phylogeny shape the morphology of taxa within clades. Herein we explore these two factors in an integrated way by analyzing shape and size variation in the mandible of extant squirrels using landmark-based geometric morphometrics in combination with a comparative phylogenetic analysis. Dietary specialization and locomotion were found to be reliable predictors of mandible shape, with the prediction by locomotion probably reflecting the underlying diet. In addition a weak but significant allometric effect could be demonstrated. Our results found a strong phylogenetic signal in the family as a whole as well as in the main clades, which is in agreement with the general notion of squirrels being a conservative group. This fact does not preclude functional explanations for mandible shape, but rather indicates that ancient adaptations kept a prominent role, with most genera having diverged little from their ancestral clade morphologies. Nevertheless, certain groups have evolved conspicuous adaptations that allow them to specialize on unique dietary resources. Such adaptations mostly occurred in the Callosciurinae and probably reflect their radiation into the numerous ecological niches of the tropical and subtropical forests of Southeastern Asia. Our dietary reconstruction for the oldest known fossil squirrels (Eocene, 36 million years ago) show a specialization on nuts and seeds, implying that the development from protrogomorphous to sciuromorphous skulls was not necessarily related to a change in diet

Ecogeographical and phylogenetic effects on craniofacial variation in macaques.

The widespread and complex ecogeographical diversity of macaques may have caused adaptive morphological convergence among four phylogenetic subgroups, making their phylogenetic relationships unclear. We used geometric morphometrics and multivariate analyses to test the null hypothesis that craniofacial morphology does not vary with ecogeographical and phylogenetic factors. As predicted by Bergmann's rule, size was larger for the fascicularis and sinica groups in colder environments. No clear size cline was observed in the silenus and sylvanus groups. An allometric pattern was observed across macaques, indicating that as size increases, rounded faces become more elongated. However, the elevation was differentiated within each of the former two groups and between the silenus and sylvanus groups, and the slope decreased in each of the two northern species of the fascicularis group. All allometric changes resulted in the similar situation of the face being more rounded in animals inhabiting colder zones and/or in animals having a larger body size than that predicted from the overarching allometric pattern. For non-allometric components, variations in prognathism were significantly correlated with dietary differences; variations in localized shape components in zygomatics and muzzles were significantly correlated with phylogenetic differences among the subgroups. The common allometric pattern was probably influenced directly or indirectly by climate-related factors, which are pressures favoring a more rounded face in colder environments and/or a more elongated face in warmer environments. Allometric dissociation could have occurred several times in Macaca even within a subgroup because of their wide latitudinal distributions, critically impairing the taxonomic utility of craniofacial elongation