Triassic North Carolina
What was life like in North Carolina during the Triassic? That’s the time period between 252 and 199 million years ago, book-ended by two great mass extinctions (Permo-Triassic ~250ma , Triassic-Jurassic ~200MA) . To find out, I spoke with Dr. Andrew Heckert, Professor of Vertebrate Paleontology and Dinosaurs at Appalachian State University.
North Carolina and all up and down the eastern seaboard has a series of Triassic basins. These are a record of when North America and Africa split apart as Pangea began to split into what we now recognize as the modern continents. So when this happened, there were a great deal of mountain ranges uplifted and basins dropped down. Sediment eroded from those mountains and filled those basins. Which means that there were many opportunities for animals to get buried when they died, and then get preserved in the fossil record. What you would see 220 million years ago? We’re probably only a few degrees from the equator at this time, so it’s going to be very warm, all year round. It probably was very lushly vegetated. This is well before flowers evolved, so absolutely no flowering plants. In the larger ecosystem, it’s all dominated by reptiles more related to crocodiles than dinosaurs. Probably nothing more than about 4 meters long.
Archosaurs, or “Ruling Reptiles,” evolved 250 million years ago in the Triassic and have dominated life on land since. They evolved into crocodiles, dinosaurs, and birds. All of these, alive and extinct, are archosaurs.
During the Triassic, there’s all this evolution, this very rapid diversification of a variety of reptile lineages, and, through much of the Triassic, the dinosaurs, if they’re present, they are a relatively small portion of the the fauna. They’re relatively difficult to find, they tend to be smaller animals. There are many more on what we call the crocodile line, the Rauisuchids, aetosaurs, than we actually see on the dinosaurian line.
The dominant Triassic Tar Heel predators were crocodile-cousins, the Rauisuchids. We learned about one particularly cool two-legged one, called “The Carolina Butcher,” on an earlier episode. Another diverse croco-cousin was the heavily armored aetosaur.
Aetosaurs have very few teeth, and they’re not particularly well-pointed. Everything about their limbs suggests that they were not fast-moving. So we think that they were herbivores, or omnivores that ate, perhaps, insects. They were one of the larger animals around at the time, but there are a lot of animals in the Triassic that potentially fed on them. One is a group of reptiles called the Rauisuchians, made famous by postosuchus, in Walking With Dinosaurs.
The successful crocodilians outcompeted all other animals until the mass extinction at the end of the Triassic. Dinosaurs then filled their ecological niches, and dominated for more than 130 million years. This cycle happened again 65 million years ago, wiping out the dinosaurs and making way for mammals. They hadn’t evolved way back in the Triassic, but their closest reptile ancestors had.
There’s a group of proto-mammals called cynodonts. In late Triassic time, these are extremely small animals. What we do see is a jaw joint that is very similar to that of modern mammals. In picking through tiny sediment, we find teeth that do have the beginnings of double roots, like any good mammal has for their adult teeth. And relatively complex cusps.
Dr. Heckert’s specialty is finding the smaller animals that help complete the picture of the the Triassic ecosystem.
My students and I do a lot of work to look in sediments for pieces and parts of much smaller animals. Primarily teeth, but sometimes vertebrae and other bones like that. This gives us a picture of the actual ecosystem, because these small animals are extremely hard to find otherwise. This is how my colleagues found the first lungfish in North Carolina. We found tiny little lungfish teeth in these things. We found freshwater sharks in these microvertebrate assemblages.