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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. [ABSTRACT FROM AUTHOR]

El Cerro de los Batallones is one of the most important fossil sites of the Miocene. The quantity and preservation of its fossil remains have allowed us to describe many new mammal species. One of these is Hispanomys moralesi, a derived species of the Tribe Cricetodontini, a wide group of rodents with great importance in the faunal assemblage during the Miocene. Unlike most fossil micromammals in this fossil site, we have obtained skull remains that preserve never recorded anatomical structures in this time interval. Due to the fragility of the material, it could only be studied in detail using X-ray micro-computed tomography (µ-CT Scan). With this technique, we obtained three-dimensional models of 12 skulls of Hispanomys moralesi, in which different osteological parts have been described. In this way, we compared the morphological variation of the skull with other fossil cricetids and concluded that Batallones' species is an opisthodont rodent, with a relatively elongated rostrum, a robust base of zygomatic arches and big-sized tooth rows. Opisthodont incisor characterises omnivore and herbivore diets in rodents. Therefore, these new findings of Hispanomys moralesi could allow us to describe the dietary affinities of this extinct species. [ABSTRACT FROM AUTHOR]

The shape of the tree of life is the result of shifting diversification rates, and identifying the factors driving these shifts is one of the main aims in evolutionary biology. Various biotic and abiotic factors have been proposed to have an impact on mammal diversification, such as climatic and tectonic changes, the acquisition of new traits, and expansion into new ecosystems or landmasses.We used phylogenetic comparative methods to quantify the influence of potential drivers on diversification patterns in extant squirrels (Sciuridae, Rodentia). We conducted a multilayer approach, comparing diversification rates among squirrel lineages depending on their degree of biome specialisation, biogeographic realm occupancy, locomotion adaptations, and presence in mountainous regions.We generated the most complete phylogeny of squirrels to date, encompassing almost 80% of the extant species, and applied multiple and binary state‐dependent diversification models. All the traits examined showed an influence on diversification rates.The biome specialist lineages showed the highest speciation rates, suggesting a major role of bioclimatic specialisation on macroevolutionary patterns. A single major event, the Miocene–Pleistocene radiation of terrestrial‐adapted lineages in North America, left a signal that was recovered in two of our analyses. Both the Nearctic lineages and the terrestrial‐adapted lineages showed high speciation rates, highlighting the fact that that major evolutionary episodes may produce confounding effects in state‐dependent diversification models.Ancestral reconstructions showed that cold and warm intervals in Earth's history had different effects on squirrels' diversification, depending on their climatic affinities. Tropical and arboreal squirrels evolved predominantly in the warm intervals, while terrestrial and cold‐adapted squirrels radiated in the cold intervals.Our findings suggest that, while global climatic shifts are key for the speciation processes in mammalian lineages, lineage‐specific ecological adaptations are critical modulators of the responses of lineages to such environmental shifts, in an interplay that ultimately affects their diversification patterns. [ABSTRACT FROM AUTHOR]

The tribe Cricetodontini is a common cricetid group found in several European basins from the Miocene. Here we present a study of the fossils of this group found in the Duero Basin. We updated the biostratigraphical assignation of some of the localities in which several species of Cricetodontini have been found. Cricetodontini remains from eight localities from the central sector of the Duero Basin have been described, measured and assigned to a species. The presence in these localities ofHispanomys aguirrei,H. lavocati,H. nombrevillaeandH. aragonensishas allowed correlating them to the biostratigraphic scale built for the Miocene in Calatayud-Daroca Basin, identifying biozones G3, H and I (MN7/8 – MN10, Late Aragonian – Early Vallesian, Middle – Late Miocene). Furthermore, this study constitutes the first citation of this species in this basin, exceptH. aguirrei, previously described in the Duero Basin. After this work, the biostratigraphical assignation of the studied sites is now well known. We evidenced the resemblance of Duero and Calatayud-Daroca basins. [ABSTRACT FROM PUBLISHER]

The most updated stratigraphical distributions of the Cricetodontini from the Calatayud–Daroca Basin are presented. Cricetodon sansaniensis (local biozone F, MN6, middle Aragonian) and Cricetodon jotae (local biozone G1, G2 and G3, MN6-MN7/8, Middle–Upper Aragonian) from the middle Miocene are described and discussed. Generally, the genera of Cricetodontini were used to define large time intervals, whereas the species were neglected in the local biostratigraphical studies. The results presented herein show that, for the Calatayud–Daroca Basin, most of the stratigraphical distributions of the species of Cricetodontini are strongly linked with the local biozonation. That reveals that they could be used as good biostratigraphical indicators. Moreover, the unusually long local biozone G3 could be redefined and subdivided based on the distributions of the four species of Cricetodontini present in it. However, it is recommended to complete the study of the whole rodent fauna before proposing a new biozonation. [ABSTRACT FROM AUTHOR]