The gang discusses two examples where extinction may have been very important in directing the evolution of mammals through time. The first paper looks at the impact of other mammals groups on the morphology of earlier therians, and the second paper looks at how extinction could explain some of the patterns observed in the Great American Interchange. Meanwhile, James learns some things, Curt steps out, Amanda imagines the end.

Up-Goer Five (Amanda Edition):

Today our friends talk about animals with hair. The first paper talks about animals with hair, and that ideas were had a while ago about how old kinds of animals with hair just weren't as good as new kinds of animals with hair, and that the very big angry animals with lots of teeth and no hair made the animals with hair from the same time stay small and not good. But it turns out that even after the very big angry animals with lots of teeth and no hair went away the animals with hair were still all very much the same and didn't do anything fun until much longer after the very big angry animals with lots of teeth and no hair were gone. That means that the very big angry animals with lots of teeth and no hair didn't really keep the animals with hair from being any good. The other paper talks about animals with hair from the upper part of the colder area of land in the "new" half of the world (which is not new but that's the only word we can use in this stupid word thing) moved into the usually warmer lower area of land in the "new" half of the world. It talks about how upper animals with hair moved into lower areas of land, and how lower animals with hair moved into upper areas of land. However, more upper animals moved into lower areas of land. And they wanted to know why. It turns out that more animals with hair that lived in the lower part of the "new" half of the world were dying as the places changed and got colder. We used to think just that it was upper animals with hair were better at living than lower ones, but that isn't true. It's just that there was space for upper animals to move in, and they could use the area better than lower animals with hair that moved to the upper part of the "new" half of the world.

References:

Carrillo, Juan D., et al. "Disproportionate extinction of South American mammals drove the asymmetry of the Great American Biotic Interchange." Proceedings of the National Academy of Sciences 117.42 (2020): 26281-26287.

Brocklehurst, Neil, et al. "Mammaliaform extinctions as a driver of the morphological radiation of Cenozoic mammals." Current Biology (2021).