The last North African hipparions – hipparion decline and extinction follows a common pattern

Abstract

Research on the Algerian localities of Ain Boucherit and Ain Hanech led to the dating of the oldest stone tools in North Africa, but also to the recovery of new material of the rare three-toed horse Hipparion ambiguum (Equidae) from its type locality of Ain Boucherit and the dating of the youngest North African hipparion record at Ain Hanech (1.7 Ma). Here we review the latest occurrences of the hipparions in the Old World and the problems concerning the taxonomical classification of the Pleistocene African hipparions. The decline and extinction of the hipparions (genus Hipparion, various subgenera) in the Old World occurred with a North-South gradient. Around 2.5 Ma, hipparions went extinct in Europe, West Asia and the Indian Subcontinent and the last dated record from North Africa is 1.7 Ma. There is evidence that at this time, there were still three species in Africa south of the Sahara and one in China. The last Chinese species went extinct before 1 Ma and the last African species between 0.6 and 0.4 Ma. Similar reduction of the diversity and extinction from North to South happened at different times in many other groups of vertebrates and was recognized already in the 18th century, when this pattern was explained with global cooling. Present data on temperature and atmospheric CO2 show a general decreasing trend and interfering Milankovich type cyclicities of different periodicities causing punctuated events major environmental change. The progressive demise of the hipparions seems to be related to such events. We discuss problems concerning the taxonomy of the last hipparions. The name Eurygnathohippus cornelianus is widespread, but the species name is a junior synonym. We classify this taxon with robust metapodials and elongated protocones as Hipparion (Eurygnathohippus) steytleri. The last North African hipparions are not a single species, but three: the large and very gracile H. (E.) libycum, the gracile H. (E.) ambiguum of intermediate size, and the small and very gracile H. (E.) massoesylium.