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.