Your Daily Fossil

Cynognathus

When: Early to Middle Triassic (247 - 237 million years ago)

Where: Frolicking over Gondwana (an ancient super continent) Fossils have been documented on South Africa, South America, and Antarctica. 

What: Cynognathus is a cynodont. Historically these taxa were called ‘mammal-like-reptiles’, as they were on the evolutionary line leading to mammals, but had not yet acquired the characteristics we use to define Mammalia. Cynognathus was a fairly far along towards being mammalian, as the cynodonts are some of the most derived synapsids (for a basal synapsid, click here). This triassic carnivore had hind-limbs held directly under its body in a mammal like fashion, but its forelimbs still sprawled outwards. Cynognathus had multiple bones in its lower jaw, unlike the single bone of mammals, but the ‘extra’ bones were heavily reduced compared to basal synapsids.  Mammal-like characteristics were a complete secondary palate (the bony roof of our mouths) and multiple types of teeth with differentiated cusps in its jaws.  Reconstructing non-bony features for this 3 feet (1 meter) long animal is a bit tougher, but we can confidently say they still laid eggs and did not nurse their young. One of the biggest questions is ‘Did Cynognathus have fur?’ there is no direct evidence proving this one way other the other, but morphology suggestive of a large amount of blood vessels and nerves on the snout could indicate the presence of whiskers, which may in turn imply a covering of fur. 

Beyond giving us critical information on the evolutionary history of mammals, Cynognathus was important to the development of the geologic theory of plate tectonics (though at the time it was called continental drift). A tremendous numbers of fossils of this animal are known, most on the now very distant continents of South America and Africa. Specimens from each land mass are virtually identical, meaning there had to be a lot of gene flow between each population, if they were separate populations. This is impossible for groups of terrestrial mammals  with an ocean between them. Thus, these fossils (and other taxa) were used to argue that there had to have been a time in Earth’s history when these landmasses were one. This ancient landmass is now known (along with Antartica, India, and Australia) as the paleo continent of Gondwana.