Thescelosaurus: Beast of the Week

 This week we will be looking at a little dinosaur that definitely deserves more attention.  Check out Thescelosaurus!

Thescelosaurus was a relatively small plant-eating dinosaur that lived in what is now North America, during the latest part of the Cretaceous period, between 68 and 66 million years ago.  From beak to tail the largest specimens were almost 15 feet (4.5 meters) long.  The genus name translates to "godlike lizard/reptile" in reference to how surprised scientists were at how well preserved and complete the first studied specimen's bones were.  Thescelosaurus and its closest relatives were long thought to be part of the ornithopod group of dinosaurs. (includes more famous members like Iguanodon) More recently, however, paleontologists have found that Thescelosaurus' lineage branched off earlier than the oldest true ornithopods, despite being physically similar in appearance to them. (that being said as more information is learned about dinosaurs, this part of the family tree could change again for all we know.)

Watercolor reconstruction of Thescelosaurus neglectus by Christopher DiPiazza.

Thescelosaurus is currently known from three species, Thescelosaurus neglectus, which was the first named and lived in the United States, named after the fact that the specimen was kept in a box for years until it was formerly examined for the first time. Thescelosaurus garbanii was also from the United States but was slightly larger and more robust.  Thescelosaurus assiniboiensis was the smallest of the three species and lived in what is now Western Canada.  When alive, Thescelosaurus would have shared its environment with famous dinosaurs, like Tyrannosaurus, Triceratops, Pachycephalosaurus, Acheroraptor, and Edmontosaurus.

In general Thescelosaurus is characterized by being a pretty robust dinosaur, despite the fact that it wasn't overall a very large.  It would have walked on its hind legs, but some suggest it could have possibly moved or rested on all fours at least some of the time.  Its front limbs were relatively long and strong, and tipped with five fingers on each hand.  It had a flexible neck and a proportionally small skull with a narrow beak in the front of its jaws and teeth lining the sides ideal for shredding plants once inside the mouth. This dinosaur also had teeth at the tip of its snout, where the beak was, which may have helped it strip leaves off of stems and shoots as it ate.

Thescelosaurus skeleton on display at the Canadian Museum of Nature in Ottowa, Ontario, Canada.

Some Thescelosaurus also had overlapping bony plate-like structures on their ribs.  At first some believed these were to aid in breathing but they lack the sort of surface texture that normally would imply there were muscles attached in life.  Thanks to specimens of Thescelosaurus that weren't quite mature when they died, we know these plates may have started as cartilage and would have solidified into bone as the animal aged.  Perhaps they provided extra protection in some sort of intraspecies combat only mature individuals engaged in?  

Thescelosaurus skeletal mount on display at the Smithsonian National Museum of Natural History.  Note the bony rib plates. 

Most recently, research led by paleontologist, Clint Boyd, uncovers more than one Thescelosaurus specimens had a pair of bony, knob-like spurs growing out of each of their forearms.  These features have only been found in mature individuals so far, and therefore imply they may have been used in some sort of display or combat between rivals within a species.  This connects really nicely with the rib plates previously mentioned and it is easy to imagine two rival males squaring up and using their arms like studded maces to smash each other in the flanks, or even bear-hugging each other, over territory or mating rights.  

Watercolor reconstruction of two rival Thescelosaurus using arm spurs in combat by Christopher DiPiazza.

We also have Thescelosaurus specimens that preserved skin patches thanks to being naturally mummified after death.  Thanks to this find we know that Thescelosaurus had scaly skin on at least some of its body!  

That is all for this week!  As always feel free to comment below!

References

Boyd, Clint A.; Cleland, Timothy P. (2008). "The morphology and histology of thoracic plates on neornithischian dinosaurs". Abstract with Programs - Geological Society of America; Southeast Section, 57th Annual Meeting. 40 (2): 2.Boyd, Clint A.; Brown, Caleb M.; Scheetz, Rodney D.; Clarke, Julia A. (2009). "Taxonomic revision of the basal neornithischian taxa Thescelosaurus and Bugenasaura". Journal of Vertebrate Paleontology. 29 (3): 758–770. 

Brown; Caleb M.; Boyd, Clint A.; and Russell, Anthony P. (2011). "A new basal ornithopod dinosaur (Frenchman Formation, Saskatchewan, Canada), and implications for late Maastrichtian ornithischian diversity in North America". Zoological Journal of the Linnean Society. 163 (4): 1157–1198. 

Brown, Caleb Marshall; Evans, David C.; Ryan, Michael J.; Russell, Anthony P. (2013). "New data on the diversity and abundance of small-bodied ornithopods (Dinosauria, Ornithischia) from the Belly River Group (Campanian) of Alberta". Journal of Vertebrate Paleontology. 33 (3): 495–520. 

Galton, Peter M. (1995). "The species of the basal hypsilophodontid dinosaur Thescelosaurus Gilmore (Ornithischia: Ornithopoda) from the Late Cretaceous of North America". Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 198 (3): 297–311. 

Galton, Peter M. (1997). "Cranial anatomy of the basal hypsilophodontid dinosaur Thescelosaurus neglectus Gilmore (Ornithischia; Ornithopoda) from the Upper Cretaceous of North America". Revue Paléobiologie, Genève. 16 (1): 231–258.

Stein, Walter W. “The Paleontology, Geology and Taphonomy of the Tooth Draw Deposit; Hell Creek Formation (Maastrictian), Butte County, South Dakota. .” The Journal of Paleontological Sciences, Apr. 2021, pp. 1–108.