FIGURE 7. Schematic diagram illustrating some of the issues raised by the discovery of the hybrid origin of Late Pleistocene North American mammoths (nominal Mammuthus columbi). First, genomic analysis indicates hybridisation, in North America, of endemic mammoths with M. primigenius in the Middle Pleistocene, but there are no fossils of that species identified from the Middle Pleistocene of North America. Second, if the hybridisation is taken to be the 'origin' of M. columbi, then earlier North American mammoths should be a different species ('xxx'). However, it would be hard to diagnose such a species or choose a type specimen, because we have not yet morphologically differentiated it from later M. columbi, we have no DNA from it, and the date of its transition to M. columbi is uncertain.