Abstract
The sequence of cheek teeth mineralization, eruption, and replacement of an extinct horse species is here documented with radiological techniques for the first time thanks to the exceptional preservation of Hipparion sp. mandibles from Cerro de los Batallones (Madrid Basin, Spain). The sequence of dental ontogeny in mammals provides valuable insights about life history traits, such as the pace of growth, and about the mode of formation of fossiliferous assemblages. We have determined that the order of permanent cheek teeth mineralization and eruption of hipparionine horses is m1, m2, (p2, p3), p4, m3. Cheek teeth mineralization timing of hipparionine horses coincides with the one observed in modern equids. In turn, there are differences in the eruption timing of the p4 and m3 between horses belonging to the Anchitheriinae and Hipparionini compared to equids of the Equus genus that might be related to the shorter durability of the deciduous tooth dp4 in anchitheriine and hipparionine horses and, more broadly, to an increased durability of equid teeth through their evolutionary history. Based on the dental eruption sequence, hipparionine horses are slow-growing, long-living mammals. The Hipparion sp. assemblage from Batallones-10 conforms to an attritional model, as individuals more vulnerable to natural mortality predominate.
Highlights
Horses constitute key taxa to investigate past terrestrial ecosystems because their fossils are very abundant in the Cenozoic fossil record, identifiable, and represent wide geographic and temporal ranges
This is the case of Cerro de los Batallones fossil sites, which are known for containing diverse and extremely rich mammalian fossil assemblages[30,31]
The aim of this study is to describe for the first time with radiological techniques the postcanine dentition ontogeny of hipparionine horses, a fundamental taxonomic group for the equid evolutionary scheme and a very common faunal element in Neogene sites worldwide
Summary
Horses constitute key taxa to investigate past terrestrial ecosystems because their fossils are very abundant in the Cenozoic fossil record, identifiable, and represent wide geographic and temporal ranges. The long, continuous, and intercontinentally widespread Equidae fossil sequence has long been used to prove, dispel, and analyse evolutionary patterns and processes[1,2,3,4,5,6] Horse fossils, specially their teeth, have been the object of numerous paleoecological studies that try to infer past environmental conditions. Paleontological sites with exceptionally rich and well-preserved fossil assemblages provide an adequate number of specimens (including juvenile individuals) to describe ontogenetic series[16,19,20,21,22,23,24,25,26,27,28,29]. Remains from Batallones-10 belong to a single Hipparion species that is still under study
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