A new Pronotolagus (Lagomorpha: Leporidae) and other leporids from the Valentine Railway quarries (Barstovian, Nebraska), and the archaeolagine-leporine transition

We analyzed 108 adult lower third premolars and 38 upper second premolars of leporids from the late Barstovian (ca. 13 Ma) Valentine Railway quarries in north-central Nebraska. Remains of two species of the archaeolagine genus Hypolagus are overwhelmingly abundant in four of five quarry samples. Both the large, primitive Hypolagus parviplicatus and the smaller, more derived H. fontinalis are represented by larger samples than have previously been available, including upper and lower jaws. At a fifth site remains of leporines, including a new species of Pronotolagus and a probable new species of Alilepus, outnumber those of Hypolagus. The leporines are characterized by lingual reentrants and/or an enamel lake on p3 and, possibly, by three anterior reentrants on P2. The new Pronotolagus is less derived than the oldest leporine previously known, P. apachensis of Clarendonian age (ca. 10 Ma), and probably descended from an earlier population of H. parviplicatus. The unnamed Alilepus, on the other hand, shows closer affinity to H. fontinalis. The existence of two well-differentiated leporine species in the late Barstovian of the Great Plains strongly supports a North American rather than Palaearctic origin for the Leporinae, the oldest Eurasian representatives of which are at least five million years younger than the Valentine species. The abundance of brachydont ungulates at the leporine-rich Valentine site indicates a more wooded paleoenvironment than those represented at the remaining archaeolagine-rich sites, suggesting that the Leporinae may have first evolved in a forested environment.