Big-Headed Carnivore a Sign of Triassic Recovery

I’ve spent much of my weekend writing about Jurassic World. I won’t rehash the details here – you can read those over at VICE – but it struck me how easy it is to talk about paleontology when everyone knows the animals you’re discussing. I don’t have to explain who Tyrannosaurus or Velociraptor were, and, from museums and movies, most everyone has some idea of what a dinosaur is.

But if Colin Trevorrow were directing Triassic World, my job would be a lot more difficult. With the exception of the first dinosaurs, and maybe the “armadillodiles“, most of the strange creatures that thrived between 252 and 200 million years ago don’t have common names or much presence at all in the public consciousness. So you’re going to have to bear with me for a second while I introduce you to Garjainia madiba.

Discovered in the 247 million year old rock of South Africa, and described by Natural History Museum, London paleontologist David Gower and colleagues in PLoS One, Garjainia madiba belonged to a group of carnivores called erythrosuchid archosauriforms. Let’s unpack that.

You know birds and crocodiles? They’re the two living lineages of a group of animals called archosaurs – the “ruling reptiles” – that, in turn, were part of a larger radiation of critters called archosauriforms. So lower down on the tree, close to the roots, there was a lineage of predatory archosauriforms called erythrosuchids to which Garjainia belonged. To give it a little more context, Garjainia madiba was archaic enough that, in hindsight, we can say it’s equally-closely-related to birds and crocodiles. Garjainia and its carnivorous kin evolved before that great split in the archosauriform family tree.

The animal that Gower and coauthors describe is not the first of its kind. The first species of Garjainia was described in 1958 from fossils uncovered in Russia. What makes the new species special is that it’s a little older and living in a different region, and, as long as you’re looking at the skull, it’s easy to tell the two species apart. The South African species, Garjainia madiba, has bulbous bosses of bone behind its eye and on its cheek that are lacking in the other species. Why this animal had these bumps isn’t yet clear – perhaps they were sign of maturity, differences between the sexes, or something else – but they’re among the traits that mark Garjainia madiba as a new species.

And in terms of size, Garjainia madiba was large enough to take on a variety of prey. Gower and colleagues estimate that the animal grew to over eight feet long, with a significant portion of that being a big, narrow-snouted skull. But what makes Garjainia madiba remarkable is not its fearsome appearance. The real story is in its bones.

Thin sections of Garjainia madiba bones, showing signs of rapid growth. From Gower et al., 2014.
Thin sections of Garjainia madiba bones, showing signs of rapid growth. From Gower et al., 2014.

Gower and colleagues examined thin sections of seven Garjainia madiba limb bones from individuals of different sizes. Inside, they found signs of rapid growth – relatively messy organization riddled with vascular canals and newly-made bone structures called primary osteons. Even in Garjainia that had periodic stopping points in their growth, likely in response to dry seasons or other times of stress, the bone in between those lines show quick growth spurts.

These starts and stops might explain why the archosauriforms, and not the surviving protomammals, came to rule the Triassic. Garjainia madiba and its relatives may have outpaced our own ancestors and cousins in terms of their life cycle, growing faster and reaching sexual maturity earlier. Simply put, the archosauriforms may have simply out-reproduced the protomammals, letting them evolve more quickly and limiting niches the protomammals could then create.

This archosauriform takeover happened quickly. Garjainia madiba lived a scant five million years after the worst mass extinction of all time – the end-Permian catastrophe that eliminated over 90% of species in the seas and over 75% of species on land. It’s a sign of a rapid burst of evolutionary novelty that paleontologists are truly just beginning to track. In the earliest days of the Triassic, life was bouncing back, with the archosauriforms leading the way.

[For more, read Mark Witton’s account of illustrating Garjainia.]

Reference: Gower, D., Hancox, P., Botha-Brink, J., Sennikov, A., Burlet, R. 2014. A new species of Garjainia Ochev, 1958 (Diapsida: Archosauriformes: Erythrosuchidae) from the Early Triassic of South Africa. PLoS One. 9, 11: e111154. doi: 10.1371/journal.pone.0111154

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