Tianyulong: Beast of the Week

This week we'll be checking out a fascinating little creature that changed the way we imagine dinosaurs.  Let's get to know Tianyulong confuciuci! 

Tianyulong was a plant-eating (or maybe omnivorous) dinosaur that lived in what is now Northeastern China, during the late Jurassic period, between 158 and 159 million years ago.  It was tiny, only measuring a little over two feet long from beak to tail. (about 70cm) The genus name translates to "Tianyu Dragon", named after the Tianyu Museum of Nature, where the first discovered skeleton of this dinosaur is housed. 

Tianyulong life reconstruction in watercolors by Christopher DiPiazza.

Tianyulong was a member of the heterodontosaurid family of dinosaurs.  Heterodontosaurids were small, plant-eating or possibly omnivorous, dinosaurs that flourished during most of the Jurassic period.  They are widely thought of being from the base of the ornithiscian branch of dinosaurs, which later includes ceratopsians (like Triceratops), ornithopods (like Iguanodon), and the armored thyreophroans (like Stegosaurus and Ankylosaurus).  More recently it was suggested that heterodontosaurids were more closely related to marginocephalian dinosaurs (group that includes more ceratopsians and pachycephalosaurs) than other ornithiscians.

We know more about what Tianyulong looked like in life, compared to most prehistoric animals, because there are more than one full skeletons on the fossil record.  Tianyulong had a proportionally large skull and short neck.  It also had very long legs with long foot bones, implying it was a fast runner in life.  The tail was more than double the length of the rest of the body.   

Cast of the holotype of Tianyulong on display at the American Museum of Natural History in New York in the temporary Dinosaurs Among Us exhibit.

In its skull, Tianyulong had small flattened teeth in the back of its jaws that appear to have been ideal for shearing plants.  In the front of its mouth, just behind its beak, it had two pairs of long canine-like teeth, a trait present in all known heterodontosaurids.  It is still unclear as to exactly why this unusual trait evolved, especially in small plant-eating dinosaurs.  It is also worth noting that individuals that appear to have been not fully mature still have these long teeth, so they may not have been an adaptation for sexual selection.  There is also no evidence they were only present in one sex and not the other.  Some have suggested they had something to do with the dinosaur's diet.  Others have suggested that both males and females could have used these teeth to participate in intraspecies combat or display over territory.   

Tianyulong skeleton, including the outline of feathers, currently at the Beijing Museum of Natural History.  Note how most of the body is covered in feathers.  Also check out that cute tail tuft!

Possibly the most amazing thing that we know about Tianyulong is the fact that many of the skeletons found preserved feathers! The exact arrangements of these feathers varies slightly among the known individuals, but they all at least appear to have had long bristle-like structures growing from their backs.  One individual also shows a shorter, but extensive coat of feathers over most of the rest of the body with a tuft of longer feathers at the tip of the tail.  Another still undescribed individual (mentioned by paleontologist, Dr. David Hone) had what appears to be the long bristles in a mohawk arrangement running from the head down almost the entire length of the animal's body.   It is possible these variations could be based on the sex or maturity of the animals. It's also possible they all looked the same in life but fossilized in different stages of decomposition, resulting in some with more feathers than others. Regardless, the presence of these feathers on Tianyulong, an ornithiscian dinosaur and not a theropod (dinosaur group that includes birds), strengthens the argument that feathers may have been more extensive among dinosaurs than originally thought.  

References

Butler, Richard J.; Smith, Roger M.H.; Norman, David B.(2007). "A primitive ornithischian dinosaur from the Late Triassic of South Africa, and the early evolution and diversification of Ornithischia". Proceedings of the Royal Society B: Biological Sciences. 274 (published online): 2041–6.

Butler, Richard J.; Upchurch, Paul; Norman, David B. (2008). "The phylogeny of the ornithischian dinosaurs". Journal of Systematic Palaeontology. 6 (1): 1–40. 

Liu Y.-Q. Kuang H.-W., Jiang X.-J., Peng N., Xu H. & Sun H.-Y. (2012). "Timing of the earliest known feathered dinosaurs and transitional pterosaurs older than the Jehol Biota." Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication).

Zheng, Xiao-Ting; You, Hai-Lu; Xu, Xing; Dong, Zhi-Ming (19 March 2009). "An Early Cretaceous heterodontosaurid dinosaur with filamentous integumentary structures". Nature. 458 (7236): 333–336.