Two new species of pseudo-horses, or palaeotheriidae, that lived 37 million years ago, have been identified by researchers.
The two mammals lived in the subtropical landscape of Zambrana (Álava) in the Basque Country, an autonomous community in northern Spain.
Researchers at the UPV/EHU-University of the Basque Country, led by Leire Perales-Gogenola, said the new species’ unusual dental features could point to a difference in environmental conditions between the Iberian and Central European areas.
Equids are today represented by only one genus (‘Equus‘) and just a handful of species of horses, donkeys and zebras, but they were more diverse during the Eocene epoch, between 56 and 33.9 million years ago.
One of the most widespread groups in Europe, which was an archipelago at that time, was the palaeotheriidae, named after the genus ‘Palaeotherium’, described in 1804 from fossils originating in the quarries of Montmartre, Paris, by the famous French naturalist George Cuvier.
Researchers with the university’s Vertebrate Palaeontology research group, writing in the Journal of Vertebrate Paleontology, named the new species Leptolophus cuestai and Leptolophus franzeni, in memory of palaeontologists Miguel Ángel Cuesta from Palencia, and Jens Lorenz Franzen from Bremen. The pair were specialists in mammal fauna of the Eocene epoch in Europe.
Pseudo-horses were represented across the European archipelago by more than half a dozen genera, more than half of which were endemic to the Iberian island. They became extinct during the climatic-biological crisis of the Eocene-Oligocene transition, also known as Stehlin’s Grande Coupure.
Palaeotheriidae were mammals similar in terms of body shape to today’s horses, but smaller in size.
“Can one imagine animals similar to horses with three toes, the size of a fox terrier, a Great Dane and a donkey living in a subtropical landscape in Alava?” said one of the team members, Dr Ainara Badiola.
“Many of these pseudo-horses have been described at the Zambrana site. Examples of them are the Pachynolophus zambranensis and Iberolophus arabensis species, which were first specified in this palaeontological enclave.”
The two new species not only expand the fossil record and the biodiversity of palaeotheriidae fauna, but also display dental features atypical for equids of the Eocene.
“Their molars have a very high crown and are covered with a thick layer of cementum,” explained Perales-Gogenola. “This type of dentition, also present in other endemic Iberian palaeotheriidae, 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 the presence of more open areas in Iberia.”
At the end of the Eocene in Europe, intertropical forests gradually disappeared, giving way to plant communities of a more temperate type with more open areas.
Modern horses or equids appeared in Europe later on during the Miocene, between 23 million and 5.3 million years ago. Their dentition, with very high crowns, is adapted for eating vegetation with a high grit content (grasses).
The new species Leptolophus cuestai also displays molars with atypically high crowns, similar to those of some of the earliest equids in Europe.
In addition to its palaeobiological interest, the diverse fossil association of mammals from Zambrana, which comprises primates, rodents, marsupials, carnivores, artiodactyla and perissodactyla, provides new information on the climatic and environmental changes that occurred in Europe and in the environment over geological time.
The university’s Vertebrate Palaeontology group is currently immersed in the description of more palaeotheriidae material, which could facilitate the description of new genera and species with unusual dental features among the equid perissodactyla.
Leire Perales-Gogenola, Ainara Badiola, Asier Gómez-Olivencia and Xabier Pereda- Suberbiola
New Leptolophus (Palaeotheriidae) species from the Iberian Peninsula and early evidence of hypsodonty in an Eocene perissodactyl
Journal of Vertebrate Paleontology DOI: 10.1080/02724634.2021.1912061