Els Casots is one of the richest fossil vertebrate sites of the Vallès-Penedès Basin (Catalonia, Spain). It was discovered in 1989 and excavated briefly during the 1990s, resulting in the recovery of thousands of remains and the erection of several new mammal species.Excavations resumed in 2018 and continue to date. Here we provide updated results regarding the age, stratigraphy, biota and palaeoenvironment of the site. The age of the site is well constrained to ~15.9 Ma thanks to recent bio-and magnetostratigraphic data, thus coinciding with the onset of the Miocene Climatic Optimum (MCO). The stratigraphic succession at the site area indicates lacustrine to palustrine environments with cyclically oscillating water level.There are several fossiliferous layers that have yielded a vertebrate fauna comprising up to 74 different vertebrate species including amphibians, reptiles, birds and mostly mammals. The finding of several articulated partial skeletons indicate that the site records an autochthonous to parautochthonous assemblage. The abundance and completeness of the vertebrate remains together with a well-constrained age and detailed stratigraphic and palaeoenvironmental data, make els Casots a key site for understanding wetland ecosystems in southern Europe during the MCO.
F I G . 1 . Phylogenetic relationships and age for Sciuridae and Ischyromyidae discussed in the text. Within the Sciurinae, the flying (Pteromyini) and tree squirrel (Sciurini) clades are highlighted and Miopetaurista crusafonti is indicated in bold. Tree topology is mostly based on Korth & Emry (1991), Meng et al. (2003) and Casanovas-Vilar et al. (2018) (see text for details). This tree is used to perform the phylogenetic generalised least squares (PGLS) analyses (see text for details).F I G . 8 . Endocasts of various extinct and extant rodents in dorsal, ventral and right lateral views. A, Petaurista petaurista (USNM 589079). B, Glaucomys volans (AMNH 240290). C, Cedromus wilsoni (USNM 256584). D, Protosciurus cf. rachelae (YPM 14737). E, Paramys delicatus (AMNH 12506). Scale bars represent 10 mm.
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