Reconstruction of the common herbivorous therapsid Diictodon, a victim of the Permian extinction. The degree of its “mammalness” can only be determined now by characteristics that rarely fossilize, such as hair and internal organs.

Triassic, they were present in late Permian strata. The oldest Triassic member of the group is Proterosuchus from the Karoo of South Africa. Its appearance coincides with the oxygen minimum, and it might be the first of its lineage to have been endothermic.


As we have seen above, the Permian extinction has been proposed as a time of lowering oxygen. This hypothesis stimulated paleontologist Ken Angelyck of Berkeley to look at various therapsid fossils from the late Permian and lower Triassic to see if there were any anatomical adaptations to lowering oxygen, either long-term or short-term. He examined the skull of every known taxon of therapsid in the latest Permian and early Triassic in various museum collections and came up with a fascinating result. While he could find no short-term changes, the size of the nasal passages and the size of the secondary palate area showed significant increases in size from the late Permian into the lower Triassic. This anatomical change is consistent with and supports

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement