Time heals all wounds, even if you're extinct

Injuries are surprisingly common in the fossil record. Some specimens even get their fame from the amount or severity of their pathologies - the famous Allosaurus "Big Al," as well as the Tyrannosaurus "Sue" are both riddled with contusions and fractures which they carried with them in life as in death. We can tell by looking at these fossils if an animal died due to its injuries, or was able to recover and live a relatively normal, albeit more painful, life.

I was hoping to find this picture online! A pack (woo!) of Tyrannosaurus pursuing a herd of Edmontosaurus. The artist's signature is at bottom-right, but I can't read it. If you know who painted this masterpiece, please let me know.

Finding evidence of bite marks or scrapes on the fossils of deceased animals is not surprising - carnivore's gotta eat something, right? Numerous Triceratops fossils sport gashes and cuts from (big surprise) Tyrannosaurus teeth (though these did not heal - the prey was already dead), and some Edmontosaurus vertebrae display signs of healing after close encounters with the tyrant-lizard.

Yesterday, evidence of an even more fascinating brush with death was published. Skin impressions from the head of an Edmontosaurus revealed something truly remarkable: a scar.

The Edmontosaurus skull (top) and skin impression (bottom). The area highlighted in red represents where the animal was attacked. The scar can clearly be seen on the impression. From Rothschild and Depalma, 2013.

Now, a scar may not seem that exciting. Each of us (animals in general) has our fair share of them, caused by anything from cuts to scratching at chicken pox. But we seldom realize that scars are indications that our immune systems are working well, and that our body is working to patch up a minor tear or scrape so that we can move on. The Edmontosaurus in question not only had a brush with death, but it survived and healed to see another day in Hell Creek.

Fossilized skin impressions of non-avian dinosaurs are uncommon, but they are becoming increasingly less so. They reveal a wealth of information about the outward appearance of these animals, as well as their biology. The preserved scar was ringed in circular scales which were disruptive, compared to the overall patterning of the rest of the skin; this trend of disruptive scales forming around healing wounds can also be found in modern reptiles.

This beautifully preserved patch of scales reminds us that dinosaurs were no different than modern animals: hunters were not always successful, and prey was not defenseless. Oh, and the culprit behind the scar? Yeah, you guessed it - probably a Tyrannosaurus.

References

Rothschild, B. M., and Depalma, R. Skin pathology in the Cretaceous: Evidence for probable failed predation in a dinosaur, Cretaceous Research.