Intraspecific variation of Eolophiodon laboriense, a basal Lophiodontidae (Mammalia, Perissodactyla) from the early Eocene of Southern France

Abstract

The Lophiodontidae is an emblematic and well-documented Eocene family of perissodactyls from Western Europe. However, after more than a century and a half of studies, lophiodontids still display a complex systematics associated with blurry intraspecific variation and a poorly known early radiation. The locality of La Borie, located near the city of Toulouse, France, has yielded numerous remains of Eolophiodon laboriense. This abundance of remains allows for the first time the study of the intraspecific variation of a basal lophiodontid. The variation has been investigated for dental and cranio-mandibular characters, notably dental polymorphism, size variation and sexual dimorphism. The intraspecific variation of E. laboriense is high with more than 20 polymorphic characters of the dentition, including many additional crests and conules. This dental polymorphism is similar to the one observed in the Bartonian lophiodontid Lophiodon lautricense. E. laboriense also displays an important degree of sexual dimorphism, with male specimens having broader and longer mandibles with larger canines than females. Despite this high intraspecific variation, the low size variation of teeth and the consistency of diagnostic characters strengthen the validity of the genus Eolophiodon and does not impact the previous lophiodontid phylogeny.