Sinoceratops: Beast of the Week

This week we'll be checking out a large ceratopsian that truly stands out from its relatives.  Enter Sinoceratops zhuchengensis!

Sinoceratops was a ceratopsian dinosaur that lived in what is now China during the late Cretaceous, between 72 and 66 million years ago.  From beak to tail tip it measured just under twenty feet long and like all its relatives, it would have eaten plants when alive.  The genus name translates to "Chinese Horned Face" and the species name is in reference to Zhucheng, the city its remains were discovered in.

Sinoceratops reconstruction in watercolors by Christopher DiPiazza

There were lots of ceratopsian dinosaurs that flourished throughout the Cretaceous.  Sinoceratops is particularly special because it is so far the only known ceratopsid, the family that includes the large kinds of ceratopsians with prominent horns and frill ornamentation, that lived in what is now Asia.  All other known ceratopsids lived in North America.  There are lots of small ceratopsian species known from China from the early Cretaceous, and even the late Jurassic.  It is possible most ceratopsians migrated into North America via a land bridge that existed at the time, called Beringia, and a few stayed back to give rise to Sinoceratops. However, it is also possible, given Sinoceratops' similarities to North American taxa, that some large ceratopsids could have migrated back to China, reslutling in Sinoceratops.

Within ceratopsids there are two major varieties.  The chasmosaurines, are the ones with long frills, and generally have long brow horns and short nose horns. (although exceptions exist).  Triceratops, Chasmosaurus, and Pentaceratops are all examples of chasmosaurines.  Sinoceratops belongs to the other group, the centrosaurines.  Centrosaurines had proportionally taller snouts and generally had large nose horns and small brow horns.  Styracosaurus and Pachyrhinosaurus are both examples from this group.  That being said some older forms of this group had long brow horns and short nosehorns, like Nasutoceratops and Machairoceratops, suggesting that long brow horns were ancestral to ceratopsids before chasmosaurines and centrosaurines split. Sinoceratops is more similar to the later centrosaurines, with a long nose horn and short brow horns, supporting the idea that it shared a more recent common ancestor with the later forms, and therefore was more likely a result of migration back to Asia from North America, instead of being from a lineage that just stayed in Asia the whole time.

Very rough info-graph I put together showing how Sinoceratops ended up in China from North American centrosaurine ancestors.

Sinoceratops is known from a few skulls that show us really interesting horn ornamentation.  The long nose horn and small, basically nonexistent, brow horns are not unheard of in this kind of dinosaur.  However, Sinoceratops had what appears to be knobby structures above its nostrils just in front of the nose horn on either side.  Unfortunately the fossilized skull that has these isn't that well preserved and as far as I know, the texture of the fossil doesn't tell us if these were smaller horn structures, or just the shape of the underlying skull.  This leads to some variation in reconstructions by paleoartists.

Section of Sinoceratops' snout, showing the unusual bony knob just infront of the nose horn.  Photo courtesy of Dr. Andy Farke.

The frill sported a series of narrow horns at its top that grew forwards and curved downwards at the tips.  In addition, the frill, itself, had a series of bumpy knobs along the top and down its center which may have had a layer of keratin, forming shallow horns, in life.   

Close up of the top of Sinoceratops' frill.  In addition to the forward facing horns on the top, you can also see the raised areas on the frame of the frill that may have been shallow horns in life.  Photo courtesy of Dr. Andy Farke.

As usual, the exact purpose of these horns is unknown, but it is possible they were for display within the species, maybe for attracting mates and/or intimidating rivals.  The nose horn could have been a stabbing weapon against predators and the frill horns could possibly have helped by deterring hungry jaws away from the neck. That being said, if defense was the primary purpose for ceratopsid horns, we'd see more uniformity over the millions of years that this branch of dinosaurs evolved.  Display adaptations, however, evolve and change more rapidly.

Portion of Sinoceratops' skull, featuring the eye socket, nose horn, and the little bony knobs over the nostrils.  Photo courtesy of Dr. Andy Farke.

Sinoceratops is featured in the newest installment of the Jurassic Park franchise, Jurassic World Fallen Kingdom.  In the movie it is depicted with two holes in its frill.  Let it be known this isn't backed up by any evidence and almost certainly wasn't the case for the  real animal.  While there were two holes in the skull, like there are in most ceratopsians, they were almost certainly covered up by skin in life.

That is all for this week!  As always feel free to comment below or on the  facebook page.  Special thank you to Dr. Andy Farke for kindly providing the amazing photographs of Sinoceratops' fossil material used in this post.

References

Xu, X., Wang, K., Zhao, X. & Li, D. (2010). "First ceratopsid dinosaur from China and its biogeographical implications". Chinese Science Bulletin. 55 (16): 1631–1635.