Gorgon

YESTERDAY I posted about the evolution of mammals from synapsids, which definitely were not “mammal-like reptiles”! Long before the mammals appeared the therapsids descended from basal synapsids. These animals were highly successful during the Permian, and if they had not been almost eradicated by the Permian-Triassic extinction the dinosaurs might never have had their chance at preeminence. Blogger Will Baird, who dropped by to read that article, has published on his blog an excellent overview of the gorgonopsids, a group of robust carnivorous therapsids.

You can read more about the gorgonopsids and other therapsids in Gorgon: Paleontology, Obsession, and the Greatest Catastrophe in Earth’s History. While Ward unfortunately does spend more time talking about himself than I’d like, he also devotes a lot of time to these carnivores, the alien ecosystem they inhabited, and the catastrophe that brought about their extinction.

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The Term “Mammal-Like Reptiles” Enrages Me

I RECENTLY READ a paleontology book that irked me by referring to the basal synapsids as “mammal-like reptiles”. This term pre-dates modern phylogenetics. It violates several rules of phylogenetics, the first being that all clades (groups of related organisms) should contain organisms sharing a single common ancestor in that clade, and the second being that clades should nest within each other, so that each more recent clade fits into its ancestors’ clades as well. In other words, clades should not be polyphyletic, but monophyletic. An example of a polyphyletic group is the pachydermata, an obsolete category containing elephants, hippopotami, rhinoceri, horses, tapirs, and pigs simply on the basis that these organisms have thick skin and hooves. Now these animals are placed into separate clades since they do not share a recent common ancestor. Polyphyletic groups are a great embarrassment to phylogenicists.