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Survival During the ‘Mother’ of Mass Extinctions

Most people are familiar with the catastrophic extinction that saw the end of the non-avian dinosaurs some 65 million years ago. But few are aware of an even greater biodiversity crisis that occurred about 250 million years ago, stamping out more than 90% of species on Earth, and setting the stage for the “age of dinosaurs”: the End-Permian Extinction. In the Karoo Basin of South Africa, Permo-Triassic rocks document a period of extreme drought and plant die-off, with many herbivores and their attendant predators becoming extinct. Some of the former included the bizarre beaked, dicynodont synapsids and their relatives, the eutheriodonts. The latter group included many small, weasel-like carnivores such as the therocephalians (literally “beast-heads”).

The discovery of a small therocephalian skeleton just a few feet above the Permian-Triassic boundary in the Karoo Basin of South Africa prompted UW graduate student, Adam Huttenlocker, and Burke Museum vertebrate paleontology curator, Christian Sidor, along with their South African colleague, Dr. Roger Smith, to reinvestigate the stratigraphic distribution of carnivores throughout the boundary interval. Careful study of the new specimen showed that it belonged to the Permian therocephalian genus Promoschorhynchus, making it the youngest documented occurrence of that animal. In other words, this was the first time a representative of this species was found after the Permo-Triassic boundary. Consequently, the list of extinction survivors had to be changed and extinction dynamics reassessed. Although they were less abundant than contemporary herbivorous dicynodonts (their distant relatives) therocephalians were more diverse during the extinction interval and may have played an important role in stressed Triassic communities. Why they were so successful and what led to their ultimate extinction in the Middle Triassic remains unknown. Huttenlocker, Sidor, and Smith (who discovered the specimen) published their findings in the Journal of Vertebrate Paleontology.

The Burke Museum houses over 54,000 specimens of fossil vertebrates.  Most of these are original fossils, but about 1% are casts (or replicas). These, including copies of Promoschorhynchus, are used as educational resources to promote the conservation of fossil vertebrates and as instructional resources in various graduate and undergraduate courses in paleontology offered at University of Washington (Vertebrate Paleontology, Evolution of Mammals & their Ancestors). 

 

Publication

 

Huttenlocker, A. K., C. A. Sidor, and R. M. H. Smith. 2011. A new specimen of Promoschorhynchus (Therapsida: Therocephalia: Akidnognathidae) from the Lower Triassic of South Africa and its implications for theriodont survivorship across the Permo-Triassic boundary. Journal of Vertebrate Paleontology 31:405–421.

 

Related Websites

 

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Scientific illustrator, Jude Swales, prepares a cast of the first Triassic Promoschorhynchus specimen (UWBM 95001). The original specimen is housed at the Iziko: South African Museum in Cape Town, South Africa.
The therocephalian, Promoschorhynchus, was found approximately five feet above the Permian-Triassic boundary near Bethulie, South Africa.