Thescelosaurus

Thescelosaurus Temporal range: Late Cretaceous (late Maastrichtian), 69.42–66.04 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Reconstructed skeleton
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	†Ornithischia
Family:	†Thescelosauridae
Subfamily:	†Thescelosaurinae
Genus:	†Thescelosaurus Gilmore, 1913[1]
Type species
†Thescelosaurus neglectus Gilmore, 1913
Other species
†T. edmontonensis Sternberg, 1940[2] (nomen dubium) †T. garbanii Morris, 1976[3] †T. infernalis (Galton, 1995)[4] (nomen dubium) †T. assiniboiensis Brown et al., 2011[5]
Synonyms
Bugenasaura Galton, 1995[4]

Thescelosaurus (/ˌθɛsɪləˈsɔːrəs/ THESS-el-oh-sore-us^[6]) is a genus of ornithischian dinosaur that lived during the Late Cretaceous period in western North America. It was named and described in 1913 by the paleontologist Charles W. Gilmore; the type species is T. neglectus. Two other species, T. garbanii and T. assiniboiensis, were named in 1976 and 2011, respectively. Additional species have been suggested but are currently not accepted. Thescelosaurus is the eponymous member of its family, the Thescelosauridae. Thescelosaurids are either considered to be basal ("primitive") ornithopods, or are placed outside of this group within the broader group Neornithischia.

Adult Thescelosaurus would have measured roughly 3–4 m (10–13 ft) long and probably weighed 200 to 300 kg (440 to 660 lb). It moved on two legs, and its body was counter-balanced by its long tail, which made up half of the body length and was stiffened by rod-like ossified tendons. The animal had a long, low snout that ended in a toothless beak. It had more teeth than related genera, and the teeth were of different types. The hand bore five fingers, and the foot four toes. Thin plates are found next to the ribs' sides, the function of which is unclear. Scale impressions are known from the leg of one specimen. An herbivore, Thescelosaurus was likely a selective feeder, as indicated by its teeth and narrow snout. Its limbs were robust, and its femur (upper thigh bone) was longer than its tibia (shin bone), suggesting that it was not adapted to running. Its brain was comparatively small, possibly indicating small group sizes of two to three individuals. The senses of smell and balance were acute, but hearing was poor. It might have been burrowing, as acute smell and poor hearing are typical for modern burrowing animals. Burrowing has been confirmed for the closely related Oryctodromeus, and might have been widespread in thescelosaurids. The genus attracted media attention in 2000, when a specimen unearthed in 1999 was interpreted as including a fossilized heart, but scientists now doubt the identification of the object.

Thescelosaurus has been found across a wide geographic range across western North America. The first specimens were discovered in the Lance Formation of Wyoming, but subsequent discoveries have been made in North Dakota, South Dakota, Montana, Alberta, and Saskatchewan, in geological formations including the Frenchman Formation, Hell Creek Formation, and Scollard Formation. It was relatively common, and may have been the most common dinosaur in the Frenchman Formation. Living during the late Maastrichtian age, it was among the last of the non-avian dinosaurs before the entire group went extinct during the Cretaceous–Paleogene extinction event around 66 million years ago.