Thescelosaurus
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| Thescelosaurus neglectus Gilmore, 1913 |
Thescelosaurus (from the Greek meaning 'wonderful', 'marvelous', or 'surprising' 'lizard') was a small herbivorous dinosaur that appeared at the very end of the Cretaceous period in North America, and was a member of the last dinosaurian fauna before the extinction at the Cretaceous-Tertiary boundary at around 65.5 million years ago. It is known from several partial skeletons and skulls that show it to have been around 8-12 feet (2.4-3.7 m) long on average, with sturdy hind limbs, small wide hands, a head with an elongate pointed snout, and possibly small armor scutes along the midline of the back.
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[edit] Discovery and Species
Thescelosaurus was first discovered in 1890 by the great paleontologist John Bell Hatcher, from beds of the Lance Formation of Wyoming, but the skeleton remained in its shipping crates, undescribed, until Charles Gilmore of the National Museum of Natural History (Smithsonian Institution) had it prepared and described it, first naming it as T. neglectus ("Neglected wonderful, surprising, or marvelous lizard") in a short paper in 1913, then providing a detailed monograph in 1915 of what was an excellent skeleton in natural articulation, missing only the head and neck. The name comes from the surprise Gilmore felt at finding such a good specimen that had been unattended to for so long.
Other remains of similar animals were found throughout the late 1800s and 1900s, although they didn't receive much attention, giving the false impression that thescelosaur-like animals were very rare. Another very good skeleton from slightly older beds in Alberta was named T. warreni by William Parks in 1926, but this animal had notable differences from T. neglectus, and so Charles M. Sternberg renamed it Parksosaurus in 1937. Sternberg also named another skeleton T. edmontonensis in 1940, but it has generally been considered a more robust individual of T. neglectus since Peter Galton's 1974 review.
William Morris in 1976 named a new species on the basis of limb remains: T. garbanii. This species scaled up would have been about 16 feet (4.9 m), much larger than average T. neglectus. He also described a partial skull with heavy ridges on the lower jaw and cheek as T. sp. Galton in 1995 renamed the skull Bugenasaura infernalis and suggested that T. garbanii belonged to the same genus (although it could also be the leg of similarly sized pachycephalosauridStygimoloch). Only one valid species of Thescelosaurus is currently recognized: T. neglectus.
[edit] Relatives
It has often been allied to Hypsilophodon and other small ornithopods (Gilmore, 1915; Sternberg, 1940; Galton, 1974; most reviews) as a hypsilophodontid, although this area of the dinosaur family tree is complicated by a lack of research. Because of its distinctive skull and unusual hind limbs (the femur is longer than the tibia, the opposite of Hypsilophodon and running animals in general), it probably was an offshoot not connected to other major ornithopod groups.
Today, it is generally thought, although untested, that Bugenasaura and Thescelosaurus are closely related, and/or that Thescelosaurus belongs in its own family, Thescelosauridae.
[edit] Paleobiology
Recently, a skeleton known as "Willo" has been described as including the remnants of a four-chambered heart, and aorta (Fisher et al., 2000; Russell et al., 2001). This has been disputed; some researchers think that the heart is really a concretion (Rowe et al. 2001). Regardless, because both crocodilians and birds, the closest living relatives of dinosaurs, have four-chambered hearts, dinosaurs probably did too.
Thescelosaurs appear to have been heavily-built bipedal animals that were probably mostly herbivorous, but their pointed beaks and front teeth could have allowed them to ingest some animal matter. They may have been able to move on all fours a bit, given fairly long arms and wide hands, but this is uncertain. Large thin flat bony plates have been found next to the sides of the ribs, similar to those in Talenkauen, with an unknown function.
[edit] References
- Fisher, Paul E.; Russell, Dale A.; Stoskopf, Michael K.; Barrick, Reese E.; Hammer, Michael; and Kuzmitz, Andrew A. 2000. "Cardiovascular evidence for an intermediate or higher metabolic rate in an ornithischian dinosaur." Science 288(April): 503-505.
- Galton, Peter M. 1974. "Notes on Thescelosaurus, a conservative ornithopod dinosaur from the Upper Cretaceous of North America, with comments on ornithopod classification." Journal of Paleontology 48(5): 1048-1067.
- Galton, Peter M. 1995. "The species of the basal hypsilophodontid dinosaur Thescelosaurus Gilmore (Ornithischia: Ornithopoda) from the Late Cretaceous of North America." Neues Jahrbuch fèur Geologie und Palèaontologie Abhandlungen 198(3): 297-311.
- Gilmore, Charles W. 1913. "A new dinosaur from the Lance Formation of Wyoming." Smithsonian Miscellaneous Collections 61(5): 1-5.
- Gilmore, Charles W. 1915. "Osteology of Thescelosaurus, an orthopodus dinosaur from the Lance Formation of Wyoming." Proceedings of the U.S. National Museum 49(2127): 591-616
- Morris, William J. 1976. "Hypsilophodont dinosaurs: a new species and comments on their systematics." In: Churcher, C.S. (ed) Athlon. Royal Ontario Museum: Toronto, Canada, pp. 93-113.
- Parks, William A. "Thescelosaurus warreni, a new species of orthopodous dinosaur from the Edmonton Formation of Alberta." University of Toronto Studies (Geological Series) 21: 1-42.
- Rowe, Timothy; McBride, Earle F.; and Sereno, Paul C. 2001. "Technical comment: dinosaur with a heart of stone." Science 291(February): 783a.
- Russell, Dale A.; Fisher, Paul E.; Barrick, Reese E.; and Stoskopf, Michael K. 2001. "Reply: dinosaur with a heart of stone." Science 291(February): 783a.
- Sternberg, C.M. 1937. "Classification of Thescelosaurus, with a description of a new species." Geological Society of America Proceedings for 1936, 365.
- Sternberg, Charles M. 1940. "Thescelosaurus edmontonensis, n. sp., and classification of the Hypsilophodontidae." Journal of Paleontology 14(5): 481-494.
