Diet versatility and functional trade-offs shape tooth morphology in squirrels.

Identifying the drivers of adaptation is key to understanding the origin and evolution of diversity. Here we study the morphological evolution of tooth morphology, a classic example of a conserved structure, to gain insights into the conditions that can overcome resistance to evolutionary change. We use geometric morphometrics of the occlusal surface outline of the fourth lower premolar (p4) of squirrels, a paradigm of a stable tooth morphology, to explore morphological adaptations to diet. Although a versatile generalist dental morphology favors the retention of the ancestral shape, the acquisition of diets that require strong mechanical processing drives morphological change. In particular, species that eat both grass and dry fruits evolved disparate tooth shape morphologies, related to trade-offs between feeding performance that lead to a more or less pronounced change depending on the proportion of those items in their diet. Also, some folivores develop relatively large p4s, and most bark gleaners have relatively small p4s. Ultimately, despite the role of diet shaping these patterns, we showed that diet is not the only factor driving the evolution of tooth morphology.

Correction: Body-size structure of Central Iberian mammal fauna reveals semidesertic conditions during the middle Miocene Global Cooling Event.

[This corrects the article DOI: 10.1371/journal.pone.0186762.].

Body-size structure of Central Iberian mammal fauna reveals semidesertic conditions during the middle Miocene Global Cooling Event.

We developed new quantitative palaeoclimatic inference models based on the body-size structure of mammal faunas from the Old World tropics and applied them to the Somosaguas fossil site (middle Miocene, central Iberian Peninsula). Twenty-six mammal species have been described at this site, including proboscideans, ungulates, carnivores, insectivores, lagomorphs and rodents. Our analyses were based on multivariate and bivariate regression models correlating climatic data and body-size structure of 63 modern mammal assemblages from Sub-Saharan Africa and the Indian subcontinent. The results showed an average temperature of the coldest month higher than 26°C for the Somosaguas fossil site, a mean annual thermal amplitude around 10°C, a drought length of 10 months, and an annual total precipitation greater than 200 mm per year, which are climate conditions typical of an ecotonal zone between the savanna and desert biomes. These results are congruent with the aridity peaks described over the middle Aragonian of Spain and particularly in the local biozone E, which includes Somosaguas. The aridity increase detected in this biozone is associated with the Middle Miocene Global Cooling Event. The environment of Somosaguas around 14 Ma was similar to the current environment in the Sahel region of North Africa, the Horn of Africa, the boundary area between the Kalahari and the Namib in Southern Africa, south-central Arabia, or eastern Pakistan and northwestern India. The distribution of modern vegetation in these regions follows a complex mosaic of plant communities, dominated by scattered xerophilous shrublands, semidesert grasslands, and vegetation linked to seasonal watercourses and ponds.

Ecomorphological characterization of murines and non-arvicoline cricetids (Rodentia) from south-western Europe since the latest Middle Miocene to the Mio-Pliocene boundary (MN 7/8-MN13).

Rodents are the most speciose group of mammals and display a great ecological diversity. Despite the greater amount of ecomorphological information compiled for extant rodent species, studies usually lack of morphological data on dentition, which has led to difficulty in directly utilizing existing ecomorphological data of extant rodents for paleoecological reconstruction because teeth are the most common or often the only micromammal fossils. Here, we infer the environmental ranges of extinct rodent genera by extracting habitat information from extant relatives and linking it to extinct taxa based on the phenogram of the cluster analysis, in which variables are derived from the principal component analysis on outline shape of the upper first molars. This phenotypic "bracketing" approach is particularly useful in the study of the fossil record of small mammals, which is mostly represented by isolated teeth. As a case study, we utilize extinct genera of murines and non-arvicoline cricetids, ranging from the Iberoccitanian latest middle Miocene to the Mio-Pliocene boundary, and compare our results thoroughly with previous paleoecological reconstructions inferred by different methods. The resultant phenogram shows a predominance of ubiquitous genera among the Miocene taxa, and the presence of a few forest specialists in the two rodent groups (Murinae and Cricetidae), along with the absence of open environment specialists in either group of rodents. This appears to be related to the absence of enduring grassland biomes in the Iberian Peninsula during the late Miocene. High consistency between our result and previous studies suggests that this phenotypic "bracketing" approach is a very useful tool.

Global climate changes drive ecological specialization of mammal faunas: trends in rodent assemblages from the Iberian Plio-Pleistocene.

BACKGROUND: Several macroevolutionary hypotheses propose a synchrony between climatic changes and variations in the structure of faunal communities. Some of them focus on the importance of the species ecological specialization because of its effects on evolutionary processes and the resultant patterns. Particularly, Vrba's turnover pulse hypothesis and resource-use hypothesis revolve around the importance of biome inhabitation. In order to test these hypotheses, we used the Biomic Specialization Index, which is based on the number of biomes occupied by each species, and evaluated the changes in the relative importance of generalist and specialist rodents in more than forty fossil sites from the Iberian Plio-Pleistocene. RESULTS: Our results indicate that there was a decrease in the specialization degree of rodent faunas during the Pliocene due to the global cooling that triggered the onset of the glacial events of the Cenozoic (around 2.75 Ma). The subsequent faunal transition after this critical paleoenvironmental event was characterized by an increase of specialization related to the adaptation to the new environmental conditions, which was mainly associated with the Pleistocene radiation of Arvicolinae (voles). CONCLUSIONS: The pattern of faunal turnover is correlated with the development of the modern glaciations in the Northern Hemisphere around 2.75 Ma, and represents a reorganization of the rodent communities, as suggested by the turnover pulse hypothesis. Our data also support the resource-use hypothesis, which presumes the role of the degree of specialization in resources specifically related to particular biomes as a driver of differential speciation and extinction rates. These results stress the intimate connection between ecological and evolutionary changes.