Meridiolestida is an endemic South American clade of non-therian mammals known to display a range of derived craniodental characteristics, such as complete cochlear coiling. Here we describe the morphology of an isolated petrosal we refer to Meridiolestida. This specimen was recovered from the Upper Cretaceous Allen Formation and includes an excellently preserved and fully coiled cochlear canal. However, both high resolution µ-CT imaging and a subsequent comparative geometric analysis of these data indicate the presence of an innervated lagenar sensory endorgan located at the apex of the cochlear canal. Since the lagenar macula is a plesiomorphic characteristic of the amniote inner ear (seen only in monotremes among extant mammals), its presence in a lineage close to crown therians highlights the evolutionary lability of inner ear characters in even late-diverging stem therians. The fossilizable bony correlates of cochlear coiling and lagenar innervation are therefore found to be more homoplastic and ambiguous than previously recognized.
The Etruscan wolf (Canis etruscus Forsyth Major, 1877) was one of the most widespread carnivorous mammals of the Early Pleistocene in southern Europe. Initially considered endemic to the Mediterranean basin, it has extended range to the Crimean Peninsula and the Netherlands. Here, we report the first discovery of C. etruscus remains in the Caucasus, representing the easternmost locality of this species to date. The material comes from the Muhkai 2 locality (Central Dagestan, Russia), dated to approximately 2.1–1.9 Ma. The sample includes three crania, four mandibles, and eight isolated teeth. Due to dense dolomitic encrustation, X-ray tomography was employed for non-destructive study. Morphological comparisons and principal component analysis clearly assign the specimens to C. etruscus. This species exhibits plesiomorphic traits, including a splanchnocranium longer than the neurocranium, parallel medial walls of the auditory bullae, and diastemata between all premolars. These features distinguish it from the wolf-like lineage. In our opinion, the traditional hypothesis C. etruscus–C. mosbachensis–C. lupus should be revised. The most probable trajectory leading to the gray wolf is C. borjgali–C. mosbachensis–C. lupus. The decline in canid diversity and body size at the end of the Early Pleistocene is attributed to competitive pressure from the hypercarnivorous genus Xenocyon, which displaced Canis from the niche of pack-hunting predators of medium-sized and large prey. The Caucasus served as a migration corridor between Asia and Europe, and further research in Central and Middle Asia is essential to fill gaps in the early evolutionary history of the genus Canis in Eurasia.
Cranial morphology in canids is characterized by a high degree of functional and ecological diversity despite a relatively conserved cranial architecture. In this study, we analyzed cranial anatomical networks in canid species representing a broad range of ecological niches, body sizes, and phylogenetic relationships to assess skull topological complexity, integration, and modularity using anatomical network analysis. Our results reveal substantial variation in network topology and connectivity patterns. Similarities in network parameters were detected among species occupying distinct ecological niches and belonging to different clades, whereas species with comparable diets or body sizes did not necessarily exhibit similar network configurations. These patterns suggest that dietary specialization, phylogeny, and body size alone are insufficient to explain the observed diversity in cranial network organization. We interpret these findings as consistent with a developmental scenario in which strong canalization constrains overall cranial architecture while allowing flexibility in the establishment and timing of sutural contacts among bones. Such flexibility may generate multiple alternative network configurations within a shared developmental framework, potentially promoting diversification in cranial network organization without substantial departures from a conserved cranial plan.
Palaeotragus is a widespread giraffid genus known from the Neogene and Quaternary (Early–Middle Pleistocene) deposits of Eurasia. However, its species-level taxonomy and overall generic composition remain controversial. Palaeotragus microdon and Palaeotragus cf. coelophrys have long been considered the two representative species of the Late Miocene of China, mainly distinguished from each other by differences in size and the presence or absence of ossicones. Here, several new cranial specimens of Palaeotragus from the Late Miocene of Linxia Basin, Gansu Province, China are described. Detailed morphological descriptions and measurements of the new material, along with a re-evaluation of previously reported Palaeotragus specimens from China, allow for a reassessment of the size range and morphological variability of the Chinese Palaeotragus. The taxonomic validity of the two Chinese species and other representative Eurasian taxa is also re-examined, together with their geological distribution and evolutionary trends. This study reveals that the features previously used to distinguish P. microdon from P. cf. coelophrys are not taxonomically stable, and both taxa should instead be referred to P. microdon. Individual variation in P. microdon suggests that the Linxia Basin may have served as an early evolutionary center for Chinese Palaeotragus, where larger individuals with longer ossicones predominated, whereas subsequent populations from other Chinese localities tend to be smaller with shorter ossicones. The European type species P. rouenii differs from the Chinese species in several cranial features, longer premolars, and more elongated limb bones, although ossicone differences require more cautious consideration. The holotype of P. coelophrys is comparable in size to P. microdon, but exhibits elongated premolars and more robust postcranial elements, likely representing a distinct larger species. Although the material currently assigned to P. coelophrys remains controversial, it may represent an ancestral lineage of P. microdon.
Reconstructing the dietary and habitat preferences of extinct taxa is essential to understand the selective pressures that drive morphological and behavioral evolution, which provides a necessary framework for understanding macroevolutionary patterns and how extinct lineages navigated ecological shifts across time and space. This study examines the degree to which environmental changes influence dietary intake by analysing dental microwear in Heteroxerus rubricati, an extinct xerine squirrel from the Middle Miocene (Aragonian) of the Iberian Peninsula. We examined 85 upper molars from multiple sites across two environmentally distinct geographic regions in Spain (the Madrid Basin and the Calatayud-Montalbán Basin), during a time of significant climatic change coinciding with the Middle Miocene Climatic Transition (15.0-13.5 Ma). Four microwear variables (fine scratches, wide scratches, small pits, and large pits) were quantified to proxy the consumption of grasses, seeds/dust, nuts, and arthropods. Notwithstanding the consistency of a mostly granivorous diet in both locations, H. rubricati exhibited notable spatiotemporal shifts in microwear signatures. While the Madrid Basin sample exhibited a high frequency of small pits, correlating with elevated environmental aridity and the subsequent ingestion of exogenous dust, the Calatayud-Montalbán Basin sample also showed a greater importance of fine scratches and large pits, which correlate with a more mesic, forested habitat with a higher dietary component of grasses. Additionally, signal variation related to the consumption of grasses shows temporal changes in both basins associated with variations in the amount of herbaceous vegetation in the landscape during this time interval. Therefore, the dietary signal of H. rubricati was not static; rather, it suggests a high degree of dietary plasticity fundamentally governed by localised resource availability in response to external environmental controls. Notably, the correlation between small pits and arid conditions highlights the utility of microwear as a high-resolution proxy for paleoclimate. Ultimately, these findings underscore the role of environmental aridity as a primary macroevolutionary force, shaping the ecological niche and evolutionary trajectory of small mammal lineages by modulating the interaction between the organism and its available food resources.
