Claws of the Bear-Dogs

Arctocyon primaevus

Over the four or so years that this blog has been running, I have covered a number of discoveries of or about fossil mammals. These have come from various epochs within, and beyond, the Age of Mammals, and so are a wide range of different ages. But I don't believe that I've ever previously discussed a fossil from the very first epoch of the Age of Mammals, the Paleocene.

This is partly because, being the oldest, it's not an epoch from which very many good quality fossils survive - at least, as compared with later epochs (as opposed to, say, comparably short periods during the Permian). On the other hand, though, it's obviously an important one, because this is the time during which mammals rose to inherit the Earth in the wake of extinction of the dinosaurs. The great diversity of mammals that we see today had much of its origin in the explosive radiation of new forms that first occurred during the Paleocene. Few modern groups are recognisable from this time, but we do see a number of immediate ancestors of those later groups.

Sonar and the Fossil Brain

Most species of large, placental herbivore belong to a group broadly defined as the "ungulates". There are exceptions; animals such as elephants, which were once thought to be related to the ungulates, but later turned out to have a completely different origin, some of the larger primates, and the occasional oddity such as the panda. In general though, outside of Australia, the ungulates have been the most successful of the large mammalian herbivores. The group includes two, related, orders of mammals. The even-toed ungulates, including antelopes, cattle, deer, and pigs, among others, are by far the larger group today, while the odd-toed ungulates, which include horses, rhinos, and tapirs, are less numerous, but just as familiar.

Both of these groups, and possibly some of the weird-looking prehistoric herbivores of South America, are descended from a general type of animal called "condylarths". The condylarths are probably not a real evolutionary group of animals, in that they aren't all necessarily closely related, and even if they were, they would just be a rough assemblage of things related to the modern groups, rather than a group in their own right. They may well be what is called a "wastebasket taxon" - a handy place to put some animal whose relationship to other animals you aren't really sure of yet.