Ancient Parrot-Beasts of Canada

Psittacotherium

Over 90% of living mammal species are placentals - that is, not marsupials or monotremes. The placentals can, using modern genetic data, be divided into four main groups, two of which originated in the Northern Hemisphere, and two in the southern. Naturally, when we look at unusual fossils for which we have no genetic data, it gets harder to figure out where in the family tree they might be placed. It's not always even obvious whether some of the early fossils are of placental mammals at all.

Such is the case with the taeniodonts. These were first identified as a distinct group of fossil mammals in 1876 by Edward Drinker Cope, so we've known about them for a long time. He placed them, based on perceived similarities to hedgehogs, as a suborder of the larger group then called the Insectivora. It eventually became clear that this wasn't valid, not least because "Insectivora" was one of the orders that had to be scrapped once we began to use genetic data to uncover deeper evolutionary relationships.

On the Origin of Ducks

Presbyornis

This is the post that will be current as of 1st April, when Synapsida traditionally hands over to the Lords of Misrule. Or, failing that, birds.

The fossil history of birds is less well-studied than that of mammals. This is hardly to say that it has been ignored, and we do know a reasonable amount about it. But a key problem with bird fossils is that, in order to fly, birds have light and fragile bones. These don't tend to survive the fossilisation process intact (bats don't do much better) and birds also lack the great standby of palaeontologists specialising in mammals - teeth.

Of course, a notable exception to this are the flightless birds, which can be enormous, and tend to have reasonably solid bones even when they aren't. It's a lot easier to find a reasonably intact skeleton of a terror bird, or even a penguin or fossil ostrich, than it is of something that flies. There's a reason that the previous posts in this April series have all focussed on the flightless sort.

But most birds do fly and are, let's be honest, well known for it. And, despite the difficulties, we do have a number of fossils of flying birds of various kinds - all the way back to Archaeopteryx - so that their evolutionary history is very far from being a blank book.

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.