Thescelosaurus neglectus was a bipedal herbivorous dinosaur that lived in the Late Cretaceous, approximately 70 to 65 million years ago. It lived in North America and fossil specimens have been discovered in locations such as Alberta, Colorado, and Wyoming. When it was alive, this dinosaur reached lengths of approximately 3 m (9 feet) and weighed close to 90 kg (200 lbs) (1). Its body was more heavily built than some of its relatives, meaning that T. neglectus was probably not as gracile and swift as other hypsiolophodontids. T. neglectus was among the last dinosaurs, probably living up until the mass extinction that ended the Mesozoic (2).
Thescelosaurus neglectus is an herbivorous dinosaur that lived approximately 70 to 65 million years ago in the Late Cretaceous. It probably went extinct in the same event that killed the rest of the non-avian dinosaurs. Fossil specimens of T. neglectus have been found at various locations in North America, such as Colorado, South Dakota, Wyoming, and Alberta. It lived in well-watered forested environments (1).
One of the locations where T. neglectus has been found is at the Hell Creek formation (1). The environment represented by the Hell Creek Formation was a subtropical forested floodplain. This area was characterized by high diversity. A wide range of animal groups such as freshwater turtles, mammals, and monitor lizards are represented here and at similar sites. Dinosaur species found at the Hell Creek Formation include Triceratops, Tyrannosaurus rex, and Edmontosaurus. Among these, Thescelosarus is a commonly found fossil, and this species was likely abundant in the ecosystem (2). Juvenile T. rex individuals may have taken advantage of this abundance to prey upon Thescelosaurus (1).
Thescelosaurus neglectus is part of Ornithischia, and is considered a “bird-hipped” dinosaur. This is a broad order and encompasses a diverse range of body plans and species, such as Ankylosaurus, Stegosaurus, Triceratops, and Edmontosaurus (1). T. neglectus is further classified within Ornithopoda, a smaller, but still relatively broad, evolutionary grouping. This group is mainly bipedal and herbivorous and grew to dominate the North American landscape of the Cretaceous (2).
T. neglectus has been shown to be closely related to the dinosaur species Jeholosaurus, Haya, and Changchunsaurus. They are placed together in a group called Thescelosaurinae, which, together with the group Orodrominae, falls within Thescelosauridae (3).
Thescelosaurus neglectus was an herbivorous dinosaur. It walked bipedally on its hind legs and likely used its front limbs to assist in feeding. It was similar to a deer in both size and lifestyle, browsing on mixed vegetation up to a height of approximately one meter (1). Their tooth rows are deeply inset in the skull with a bony ridge extending outward over them. This has been used to infer that Thescelosaurus had muscular cheeks, which could have been used to hold plant material during feeding (2).
In 2000 a very special Thescelosaurus specimen was described. This specimen was found preserved in articulation, with bones in similar positions as when the animal was alive. It was remarkably preserved, showing features such as cartilaginous plates attached to the ribs. These are often lost in less complete specimens. A structure that was interpreted as a four-chambered heart was also discovered, preserved as a hardened iron-rich structure. This was a very important discovery, as it implied that Thescelosaurus and other dinosaurs had the high metabolic rate that a four-chambered heart usually accompanies (1). However, these findings have been disputed by further research (2).
Samples chemically examined from the “heart” structure show no evidence of animal origin. In addition, comparisons between CT scans of the Thescelosaurus “heart” and a modern ostrich heart show significant differences. The Thescelosaurus “heart” instead appears to be a sedimentary concretion, with unconnected chambers of lower-density material (2). Even though this preserved “heart” may be sand and sedimentary accumulations, it is still probable that dinosaurs had four-chambered hearts. Their closest living relatives, crocodiles and birds, both have four-chambered hearts, implying that their shared ancestor likely had this feature and therefore dinosaurs did as well (3).
