Byronosaurus: Beast of the Week

Let's check out a little dinosaur that not only taught us about how non-avian dinosaurs laid eggs and made nests, but also further solidified just how close-knit their relationship to modern birds really was.  Enter, Byronosaurus jaffei!

Byronosaurus was a meat-eating dinosaur that lived between 80 and 75 million years ago in what is now Mongolia.  It was a member of the troodontid family, similar to its North American relative, Troodon.  An adult Byronosaurus would have measured roughly four to five feet long from snout to tail, based on what has been found of it.  The genus and species names are in honor of Byron Jaffe, who was an important supporter of expeditions by the American Museum of Natural History into Mongolia.  These expeditions yielded a wealth of important dinosaur fossils, Byronosaurus, being one of them.  When alive, Byronosaurus would have shared its environment with other dinosaurs, like Velociraptor, Protoceratops, Oviraptor, and Citipati.

Byronosaurus life reconstruction by Christopher DiPiazza.

Being a troodontid, Byronosaurus had long legs, including proportionally long metatarsals (foot bones), indicating it was a fast runner in life.  On each foot, like its relatives, the dromaeosaurs, it would have had a retractable talon on each second toe.  These "killer claws" weren't as large as those seen on dromaeosaurs, like Velociraptor, but they would have still been helpful when hunting at least small prey.  Byronosaurus also had large eye sockets, suggesting it possessed good vision and further suggesting it could have been nocturnal or crepuscular.  This would make sense given the fact that where it lived was a desert at the time.  Many desert animals tend to be active when the sun isn't at its brightest to avoid the extreme heat.  Byronosaurus also had a long, slender snout filled with small, needle-like teeth, which were not serrated.  This style of tooth is typically seen in animals that are adapted for grasping and holding small prey.  This is interesting, since other troodontids are known to have had serrated teeth, which were more adept at cutting meat, rather than grasping.  Having good eyesight, a long snout, needle-like teeth, and a proportionally smaller, retractable talon, all suggest Byronosaurus may have specialized in hunting small, bite-sized prey, like invertebrates, mammals, small reptiles, and possibly baby dinosaurs, when available.

Adult Byronosaurus skull from the Mongolian Academy of Science.  Note the small, pointed teeth and large eye socket.

Another amazing thing about Byronosaurus is that paleontologists have discovered its nests, eggs, and babies!  The nests consist of eggs that were partially buried under sand, and were arranged in a cluster.  Eggs laid in clusters like this are also seen today from birds.  This is not the same as other known theropod nests, like those of Gigantoraptor, or Citipati, where the eggs are neatly arranged in a ring, in groups of twos.  Eggs laid in twos tells us that the dinosaur had two functioning oviducts.  Byronosaurus' eggs, which were not laid in twos, suggests, the mother did not have two functioning oviducts.  She likely only had one, like her modern bird relatives.  That, alone, is cool, but this information tells us a LOT more about bird evolution if you dig a little deeper.  For so long, it was thought that the reason why modern birds lost function in one of their oviducts was to become lighter in order to fly.  However, Byronosaurus didn't fly...and its descendants didn't either until finally going extinct.  Remember, when Byronosaurus was alive, during the Cretaceous, flying birds had already evolved.  This means that having one functioning oviduct evolved earlier than the first bird from a common ancestor of both birds and troodontids, and was not for flight originally.  It was simply utilized by the birds, for that purpose at some point later.  Why did troodontids, like Byronosaurus need to loose function of one oviduct if they weren't flying?  We still don't know!

Byronosaurus nest and baby skeleton on display at the American Museum of Natural History in New York.

Relatively newly hatched baby skeletons of Byronosaurus are also on the fossil record.  At first, these tiny skeletons were thought to be baby Velociraptors.  It was then discovered that they were actually Byronosaurus as more material was unearthed.  What's interesting is that as babies, Byronosaurus did not have the characteristic long snouts that the adults had.  Their faces were much shorter, with proportionally large eyes.  This is a trait also seen in modern bird babies, as well.  Animals that look like this as babies are typically taken care of by their parents for a period of time after hatching.  Were Byronosaurus attentive parents, too, perhaps?  Maybe more fossils will tell us one day!

That is all for this week!  As always, feel free to comment below or on our facebook page!

References

Bever, G.S. and Norell, M.A. (2009). "The perinate skull of Byronosaurus (Troodontidae) with observations on the cranial ontogeny of paravian theropods." American Museum Novitates, 3657: 51 pp.

Novacek, M.J., Norell, M.A, McKenna, M.C. and Clark, J.M, 1994, "Fossils of the Flaming Cliffs", Scientific American 271(6), 60-69

Norell, M.A., Makovicky, P.J. & Clark, J.M., 2000, "A new troodontid theropod from Ukhaa Tolgod, Mongolia", Journal of Vertebrate Paleontology 20(1): 7-11

Norell, Mark A.; Clark, James M.; Dashzeveg, Demberelyin; Barsbold, Rhinchen; Chiappe, Luis M.; Davidson, Amy R.; McKenna, Malcolm C.; Perle, Altangerel; Novacek, Michael J. (November 4, 1994). "A theropod dinosaur embryo and the affinities of the Flaming Cliffs dinosaur eggs". Science. 266 (5186): 779–782.