Lystrosaurus: Beast of the Week

This week we'll be checking out a wildly successful animal who's lineage managed to make it through the most powerful mass extinction in earth's history.  Say hello to Lystrosaurus!

Lystrosaurus was a plant-eating synapsid (group of animals that includes, but isn't limited to modern mammals) that lived during the late Permian era and the early Triassic period, between 255 and 250 million years ago.  Several species within the genus have been identified and their fossils have been found in Antarctica, China, India, Russia, and South Africa.  Among the species known, their sizes range from less than a meter (about 2 feet) up to 2.5 meters (about 8 feet) long from beak to tail.  The genus name translates to "Shovel Reptile" in reference to the wide, flat beaks they possessed.  

Lystrosaurus murrayi lived during the early Triassic in what is now South Africa.  Watercolor reconstruction by Christopher DiPiazza.

Lystrosaurus was a member of the dicynodont group of synapsids.  Dicynodonts walked on all fours and are notable for having squat robust bodies, broad short beaks, and two downward facing tusks that grew from either side of their upper beak.  Other than these tusks, they had no other teeth in their short jaws.  Lystrosaurus had thick limb bones and would have stood and walked with a semi-sprawling gait, similar to some reptiles today.  It is thought that at least some species of Lystrosaurus were strong diggers and may have lived in burrows.  

You may have noticed that the areas Lystrosaurus have been discovered spans a wide range.  Keep in mind that during the time Lystrosaurus was alive, the continents we now today were actually attached in one "supercontinent", called Pangea.  In fact, it the existence of Pangea and the concept of the continents moving over millions of years, called plate tectonics, was proven partially thanks to the same species of Lystrosaurus fossils all of the same age being discovered in Africa, India, and China, which would have been connected at the time it was alive. (either that or a short-limbed creature adapted to digging swam across oceans...which definitely didn't happen.)

Lystrosaurus georgi lived during the early Triassic in what is now Russia.  Skeletal mount on display at Museums Victoria in Australia.

Perhaps most impressive about Lystrosaurus, was the fact that it was just so abundant in the ecosystems that it lived. Even more impressive, some species, like Lystrosaurus curvatus, from Africa, managed to survive though the mass extinction event at the end of the Permian Era, into the Triassic, 251 million years ago.  Considered the most powerful extinction in earth's history, this event resulted in over 70% of land vertebrates being wiped out.  It included largest volcanic eruptions in earth's history, with 2 million square km (770 square miles) of earth's surface being covered in lava, and tons of carbon dioxide released in the atmosphere, choking out any animals that weren't outright incinerated.  Once into the Triassic, the surviving Lystrosaurus kept flourishing, becoming some of the most common and widespread land vertebrates in the fossil record.  In some fossil sites from the early Triassic, Lystrosaurus bones make up 95% of all the vertebrate fossils present.

So how did this little synapsid manage to survive the nastiest extinction event in earth's history? Scientists have a few ideas.  One of which is Lystrosaurus' burrowing lifestyle, and how hiding underground may have allowed it to avoid being choked out by all the extra carbon dioxide released that killed other land animals.  Another clue is that by looking at growth rings in cross sections of Lystrosaurus tusks, paleontologists can tell that Lystrosaurus could go into a torpor state, like hibernation, possibly allowing them to literally sleep through the global catastrophe while other animals starved to death. 

When alive, Lystrosaurus, would have probably relied on hiding underground or in the underbrush to avoid predators.  It also may have been able to use its tusks to defend itself if it needed to.  The late Permian Lystrosaurus would have watched out for sabre-toothed gorgonopsids.  The Triassic species were probably preyed on by the crocodile-like rauisuchians, and even some of the first dinosaurs.

That's all for this week! Feel free to leave a question or comment below!

References

Botha, J. & Smith, R.M.H. (2005). "Lystrosaurus species composition across the Permo–Triassic boundary in the Karoo Basin of South Africa". Lethaia. 40 (2): 125–137.

Cluver, Michael Albert (1978). Fossil reptiles of the South African Karoo. The South African Museum.

Damiani, R. J.; Neveling, J.; Modesto, S.P. & Yates, A.M. (2004). "Barendskraal, a diverse amniote locality from the Lystrosaurus assemblage zone, Early Triassic of South Africa". Palaeontologia Africana. 39: 53–62.

Surkov, M.V.; Kalandadze, N.N. Of & Benton, M.J. (June 2005). "Lystrosaurus georgi, a dicynodont from the Lower Triassic of Russia" (PDF). Journal of Vertebrate Paleontology. 25 (2): 402–413.

Trewick, Steve (2016). "Plate Tectonics in Biogeography". International Encyclopedia of Geography: People, the Earth, Environment and Technology. John Wiley & Sons, Ltd. pp. 1–9.

Whitney, Megan R.; Sidor, Christian A. (27 August 2020). "Evidence of torpor in the tusks of Lystrosaurus from the Early Triassic of Antarctica". Communications Biology. 3 (1): 471.