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Therapsids and You

April 21, 2016

Gina Viglietti

Testing… Testing…
As this is my first post on LITC I’d like to say “Hello!” I live in South Africa, in the south- western windy end that’s known as the Cape of Good Hope (You know, the place the survivors travel to at the end of the 2012 movie…)
Anyway, I’ve pretty much always been a fossil nerd. As kids my twin sister and I would set up our own excavations. We’d dig up things we thought were dinosaur fossils with tools we found in our parents garage. Nowadays my love of paleontology is not restricted to dinosaurs. In South Africa we have a diverse range of geological formations that have preserved many different creatures from all across the expanse of time. One such group of creatures is a group that is very close to my heart, a group of animals that is not very well known: Therapsids.
What are Therapsids?
Therapsids evolved in the middle Permian, around 260 million years ago. Therapsid fossils are not unique to South Africa. There are rich finds of these animals in Russia, though South Africa is where these Therapsids were first discovered. The Therapsids belong to a larger group of animals called the Synapsids (of which mammals are the only living examples) and a particularly well known Synapsid from North America is Dimetrodon.
But Dimetrodon is a dinosaur right? Nope, wrong. But then why have I been finding Dimetrodon figurines alongside T.rex since childhood? Because Therapsids are so poorly understood. Also, let’s admit they do look pretty wild with that giant, colorful fan stuck to their backs. But Dimetrodon is not a dinosaur. So what was it, a reptile? Let’s return to the definition of a Synapsid.

Everybody Let’s Not Walk the Dinosaur
Synapsid is an umbrella term referring to a lineage of animals both living and extinct that evolved from Amniotes, early tetrapods that were terrestrial and bred on land. Reptiles and Synapsids both have this common ancestor; however, they were two different lines of descent and this cannot be stressed enough. Lizards, snakes, crocodiles, dinosaurs and the avian dinosaurs, birds, are all groups of animals we’re familiar with tracing their ancestry back to Reptiles.
But what are Synapsids? While early ones like Dimetrodon superficially resembled reptiles and dinosaurs, they were not reptiles. These animals were the ancient relatives and ancestors of mammals, including Humans. In South Africa, a group of Synapsids named the Therapsids reigned as the dominant fauna for over 40 Million years, and included a bizarre group of animals that could have come straight out of a science-fiction novel. Gorgonospians and Therocephalians had long sabre-like canines, similar to the sabre-toothed cats that evolved much later and prowled the primeval flood plains of the Great Karoo, at a time when South America, Africa, India, Antarctica, and Australia were joined forming a single giant southern continent called Gondwana. Dog to cow-sized dicynodonts were tusk-bearing herbivores, who fed using a tortoise like beak. They were also the main prey of the gorgonopsians and therocephalians. Smaller meerkat-sized animals called Cynodonts included the ancestors of mammals and may even have had whiskers.
However, life on Earth never came closer to complete annihilation than it did at the end of the Permian period 252 million years ago, when 90% of all life (including the therapsids) was eradicated due to a run-away greenhouse warming event at that time. Fossil remains of these animals are found in the Karoo Basin today, and tell their story to Palaeontologists. A few of the small, burrowing therapsids species managed to survive and their descendants, the mammals, eked out a living through the Mesozoic (perhaps dodging the gargantuan steps of sauropods and T. rex!) The amazing part of this story is that the only group of Synapsids alive today are mammals, and us. Perhaps if our minute burrowing ancestors were not so resourceful we would not be here.
Therapsids and other synapsids are amazing evidence for the wonder of evolution. The fact that we humans can trace our ancestry back to these animals… I can’t get over how amazing that is. It’s something we should all know about. In South Africa the fossil preservation is of such high resolution that the transition from therapsid to mammal can be tracked through time using these animals. Also we can now safely say that there are no reptile- people after all because humans did not evolve from reptiles…



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