Before Cats Could Purr

Hyperailurictis

Although the differences are obvious when we can see the spots or stripes on their fur, the various species of cat are often very similar in form, and it can be hard to tell them apart based on the skeleton alone. For this reason, through much of the 20th century, all of the "purring cats" except the cheetah were placed in the single genus Felis. That's not the case today, when we distinguish genera not only for the larger purring cats, such as pumas and lynxes, but others that modern genetic evidence tells us are distinct, such as the group that includes the ocelot.

Given this, it's hardly surprising that the same should go for fossil species, too. It may well be that if we had genetic evidence on those, or could even just see their coat colour, we would be more willing to distinguish them but, when all you have is an often fragmentary skeleton, there isn't much to go on.

Squirrels, Advance!

The rapid growth of human population over the last century or so has led to a decline in many species. As I talked about last month, however, some animals can live alongside us even in urban environments, and there are many more than can tolerate us in rural - yet not truly wild - habitats, such as cropland or pasture. Any species that can do this clearly has an advantage, in many cases being able to move into new parts of the world previously inhabited by some similar, but less human-tolerant species. Thus, we can see some native species replaced by foreign invaders, as has happened, for example, with mink in continental Europe and jackrabbits in the American southwest.

In Britain, the most familiar example of this is probably the replacement of our native red squirrels (Sciurus vulgaris) by invasive eastern grey squirrels (Sciurus carolinensis). Red squirrels were once common across the British Isles, but have now vanished from most of England and Wales, surviving in the far north of England and a few pockets elsewhere, but otherwise replaced by the greys. In large part this is due to the greys carrying a virus to which they are immune but the reds are not, but simple competition is another factor.