Featured Topic 7/12: Sciurumimus

Earlier this month, paleontologists described the newly-discovered feathered dinosaur Sciurumimus from the late Jurassic period.  Several paleoartists have already depicted this animal, including our own other admin here.  Enough feathered dinosaurs have been discovered at this point that finding yet another one might not seem to be a big deal, but Sciurumimus is unique in several ways.

First, while most of the feathered dinosaurs known at this point have been found in China, Sciurumimus was discovered in Germany.  This makes it the first nonavian dinosaur with preserved feathers discovered outside of China.  (This is not including dinosaurs where the evidence of feathers is indirect, such as the Velociraptor with quill knobs.)

Second, Sciurumimus is currently classified as a megalosaurid, although this may change in the future—it isn’t easy to tell what group of theropods it belonged to because it was so young when it died.  If it’s a megalosaurid, it is only distantly related to most of the other feathered dinosaurs discovered up to this point.  All of the other known feathered theropods are coelurosaurs, and if they share a feathered common ancestor with megalosaurids, it would mean feathers were probably an ancestral trait to all tetanuran theropods.  Tetanurans include the coelurosaurs that have been known to be feathered for several years, but they also include theropods like Spinosaurus and Allosaurus.  In other words, it would be likely that Allosaurus had a feathered ancestor, and may itself have had feathers one some part of its body, at least when it was a chick.

But the implications of Sciurumimus for how widespread feathers may have been among dinosaurs go way beyond feathered allosaurs or spinosaurs.  This is because of the third significant thing about Sciurumimus: it has what are known as “stage 1” feathers, simple hollow fibers that are the most primitive feather-like structures known to exist.  Stage 1 feathers similar to those on Sciurumimus have previously been discovered on Tianyulong, a basal ornithischian dinosaur.

Sciurumimus and Tianyulong are related to one another as distantly as it’s possible for two dinosaurs to be.  They are on opposite sides of the divide between ornithischia and saurischia, the single largest division that exists in dinosaurs.  If both Sciurumimus and Tianyulong inherited their feathers from their common ancestor, that ancestor was also the ancestor of sauropods, stegosaurs, ankylosaurs, and hadrosaurs.  It would mean that every one of these groups of dinosaur was descended from an ancestor that had feathers.

That doesn’t mean all of these dinosaurs were actually feathered—on some of them, such as the hadrosaur Edmontosaurus, skin impressions exist for the animal’s entire body showing only the scutes that dinosaurs have traditionally been depicted with.  But it would mean that feathered hadrosaurs, stegosaurs or sauropods are no longer out of the question, and also that every one of them which lacked feathers would have lost its feathers secondarily.

With that in mind, here is this month’s question: Do you think it is likely that Sciurumimus and Tianyulong inherited their feathers from their common ancestor, which was the common ancestor of all dinosaurs?  Or is it more likely that this type of feather evolved more than once?

I don’t personally have an opinion about this yet.  Sciurumimus is so recently-described that many things about it are still considered uncertain, although I’m sure that over the next few months paleontologists will be putting a lot of thought into the answer to this question.  At the moment, only one thing is certain: Sciurumimus shows that we’re still a long ways from knowing everything there is to know about dinosaurs, so new discoveries will continue bringing surprises.