The Porcine Era – Lystrosaurs Ruled the World
An article recently published in the UK shed further light into the dominance of the Lystrosaurs in the Early Triassic after much of the terrestrial life had been wiped out by the Permian mass extinction. The cause of this mass extinction event is not clear, but the devastation it caused at the end of the Permian is very evident from the fossil record. Approximately 57% of marine families, especially those from low latitudes became extinct. Virtually all types of coral died out and reef life was decimated. The trilobites, those wonderful arthropods that had been around since the Cambrian, disappeared as did the last of the eurypterids (sea-scorpions). Sea lilies, brachipods, bivalves and gastropods suffered huge losses. On land; things were not much better as many groups of amphibians and reptiles also perished. Scientists estimate that 70% of all vertebrate genera living on land went extinct.
To read a related article on the Permian extinction and its effect on diaspid evolution and the development of the dinosaurs: Dinosaur Divergence – Long before the end of the Triassic.
Lystrosaurs were dicynodonts, short-tailed synapsid reptiles whose descendants were eventually to give rise to the mammals. Typically, these type of animals had short skulls, with a deep, powerful jaw, high nostrils and broad but stumpy limbs. This particular group of animals seems to have recovered very quickly following the Permian extinction event and rapidly diversified to become the dominant large, terrestrial life form.
There is evidence to suggest that these animals were mainly herbivorous (although other species may have been ominvores). The presence of tusks in the strong jaws, coupled with the strong forelimbs indicate that these animals may have dug up roots and even excavated burrows and dens. Perhaps this subterranean existence helped these animals survive the Permian extinction event.
It has been speculated that Lystrosaurs were able to hibenate or enter into a period of dormancy (estivation). This behaviour would have helped these relatively large animals survive a severe dry season for example. Some species of these mammal-like reptiles grew into giants. Fossils of Placerias, excavated from the petrified forest area of Arizona indicate animals as large as 3 metres long and weighing over 1,000 kilogrammes.
However, most of these types of animals went extinct themselves at the end of the Triassic, losing their “dead clade walking” tag as applied by many palaeontologists. The cynodonts themselves as a group survived until the end of the Jurassic.
Mystery still surrounds the causes of the Permian extinction and no doubt many more papers will be published examining the potential causes and the effects on fauna and flora. One thing is for sure, the Lystrosaurs with their jaws adapted for eating plants seized on the evolutionary opportunity and rapidly filled the ecological spaces vacated by extinct animals. It has been estimated that these animals were so successful that something like 50% of all large land animals were Lystrosaurs 240 million years ago.
To read a related article shedding light on a new theory regarding the Permian mass extinction: Can snails and oysters provide a clue to mass extinction events?