Friday, 15 January 2016

Look at the little baby dinosaur!

Finally, the baby Chasmosaurus paper is out! This specimen is by no means new to the media or public, being highly publicised since it was first discussed at the Society of Vertebrate Paleontology meeting in 2013, and has been on display in Edmonton, Canada for a period (at least a cast has). However, the highly anticipated description of this specimen is finally out, which is very exciting for several reasons. Not only is this a truly beautiful dinosaur fossil (nearly complete, skin impressions, may the list go on), but it's also very significant (it's a little baby!).

I remember when this specimen was found, as I was still at the University of Alberta then. If I remember correctly, the story goes something like this: In 2010, Phil Currie was wandering through Dinosaur Provincial Park (as he normally does in the summer), when he saw something sticking out of the sediment. He thought it was a turtle shell (which are fairly common in the area), but he thought he'd investigate. Once he started uncovering it, he realised he had found something truly special, but just how special wasn't clear until the animal was uncovered - a nearly complete baby Chasmosaurus, the smallest baby ceratopsid, missing just it's front limbs and part of the pectoral girdles, and a few tail vertebrae. This specimen was so special that it was hidden in the lead preparator's office (Clive Coy), and I remember them taking off the blanket that constantly covered it so I could see. The specimen was recently published by Currie and colleagues in the Journal of Vertebrate Paleontology. And here it is:
Baby Chasmosaurus from Currie et al. (2016)
Isn't it cute! While adult Chasmosaurus are typically 4-5m in length, this little one was just 1.5m long, making it the smallest ceratopsid ever found. It can be hard to determine what species juvenile fossils belong to due to the change in morphology throughout an animal's life (ontogeny), but several features of the skull tell us this was a Chasmosaurus. Juvenile dinosaurs are important because they show us how animal's grew, and can give us ideas into what features were important for adults. For example, there is virtually no evidence of the nasal horncore in this specimen, and only very small orbital horns, showing that these features grew later on in the animal's life, possibly relating to sexual maturity. Another cool feature of this specimen is that it had skin impressions preserved, which is not very common, and the reason for blocks of matrix still present on the specimen that have not been removed.
Baby's skull - look at the tiny orbital horns! From Currie et al. (2016).
Skin impressions from Currie et al. (2016)

Aside from the obvious awesomeness of the preservation and completeness of this specimen, it's also significant for what it shows about determining species in juvenile animals, and using juveniles in phylogenetic analyses. Using 2 different phylogenetic analyses made the animal move around quite a bit in the ceratopsid tree. When doing the analysis using all features, including characters that are very clearly juvenile or immature features/states, this little dinosaur comes out at the base of the ceratopsid tree, close to a juvenile Triceratops and along with centrosaurine ceratopsids. This isn't really surprising as centrosaurines are known for having shorter, wider frills, and this is obviously a feature of this juvenile, but this is also known to change throughout ontogeny. Centrosaurines also have smaller orbital horns, a feature seen in this specimen, but which is not common in chasmosaurines. When these immature features are coded as unknown (?), the specimen ends up in the right place, nestled with Chasmosaurus belli and Chasmosaurus russelli. This shows the importance of how careful you need to be when using immature specimens in a phylogenetic analysis of any kind.

If you want to hear a bit more about this find and other dinosaurs from Alberta, check out my Palaeocast interview with Phil Currie.

This specimen has been CT scanned (yay!) and we can expect more studies on this awesome little dude in the future. Until then, imagine this little guy running around, about the size of a golden retriever (credit to Andy Farke for that comparison!) and just try not to go "awwwwww!".

Currie P.J., Holmes R.B., Ryan M.J., and Coy C. 2016. A juvenile chasmosaurine ceratopsid (Dinosauria, Ornithischia) from the Dinosaur Park Formation, Alberta, Canada. Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2015.1048348.