New species of pseudo-horses from 37 million years ago

Although currently hypomorphic (or ecuoid) mammals are only represented by one genus (‘Equus’) and a few species of horses, donkeys and zebras, in the Eocene period (between 56 and 33.9 million years ago) there were a greater diversity of them. One of the most widespread groups in Europe – at that time an archipelago – were the paleoterids, named after the genus ‘Palaeotherium’ described in 1804, from fossils from the quarries of Montmartre (Paris), by the famous French naturalist George Cuvier.

In a new research directed by Leire Perales-Gogenola, from the University of the Basque Country / Euskal Herriko Unibertsitatea (UPV / EHU), two new species of paleoterid mammals that inhabited the subtropical landscape of Zambrana (Álava) about 37 million ago are described. of years. Together with his collaborators from the UPV / EHU Vertebrate Paleontology research group, he has described the new species, ‘Leptolophuscosti’ and ‘Leptolophus franzeni’, dedicated to the memory of paleontologists Miguel Ángel Cuesta, a native of Palencia (Spain ), and Jens Lorenz Franzen, a native of Bremen (Germany), specialists in mammalian faunas from the Eocene of Europe.

Paleoterids (or pseudohorses) were represented in the European archipelago by more than half a dozen genera, more than half endemic to the Iberian island, and they became extinct during the climatic-biological crisis of the Eocene-Oligocene transit, also called the ‘Grande Coupure ‘by Stehlin. Due to their bodily appearance, paleoterids were mammals similar to current horses, but smaller in size. “Can you imagine animals similar to three-toed horses the size of a fox terrier, a German bulldog and a donkey inhabiting a subtropical landscape of Álava? A large part of these pseudohorses have been described in the Zambrana site – points out Dr. Ainara Badiola, a member of the team. For example, the species ‘Pachynolophus zambranensis’ and ‘Iberolophus arabensis’, which were defined for the first time in that paleontological enclave ”.

The two new species not only expand the fossil record and the biodiversity of paleoterid faunas, but also present atypical dental characteristics for Eocene equoids. “Their molars have a very high crown and are covered by a thick layer of cement. This type of dentition, also present in other endemic Iberian paleotherids, could be indicative of a difference in environmental conditions between the Iberian and Central European areas, with more arid conditions or less dense or closed forests and with the presence of more open areas in Iberia ”, explains Perales-Gogenola.

At the end of the Eocene, in Europe, the intertropical forests were disappearing and gave way to plant communities of a more temperate hue, with more open areas. Modern horses or equidae appeared in Europe later, in the Miocene (between 23 and 5.3 million years ago). Its dentition, with very high crowns, is adapted to the intake of vegetation with a high content of silica (grasses). The new species ‘Leptolophuscosti’ from the Upper Eocene site of Zambrana (Álava) also shows molars with atypically high crowns, similar to those of some of the first equidae in Europe.

Detail of the margin of Lake Zambrana (Álava) from 37 million years ago. On the left, the new species of paleoterid ‘Leptolophus cosai’ and in the center and on the right another equoid perissodactyl, ‘Pachynolophus zambranensis’, also defined for the first time in the Alava paleontological enclave. (Paleo-illustration: Ulises Martínez Cabrera)

In addition to its paleobiological interest, the diverse fossil association of mammals in Zambrana, which is made up of primates, rodents, marsupials, carnivores, artiodactyls and perissodactyls, provides new information on climatic and environmental changes that have occurred in Europe over geological time.

Currently, the UPV / EHU Vertebrate Paleontology group is immersed in the description of more paleoterid material, which could allow the description of new genera and species with unusual dental characters among equoid perissodactyls.

The study is titled “New Leptolophus (Palaeotheriidae) species from the Iberian Peninsula and early evidence of hypsodonty in an Eocene perissodactyl”. And it has been published in the academic journal Journal of Vertebrate Paleontology. (Source: UPV / EHU)

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