Parksosaurus

Taxobox
name = "Parksosaurus"
fossil_range = Upper Cretaceous

---

image_width = 250px
image_caption = life restoration of "Parksosaurus warreni"
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Ornithischia
subordo = Cerapoda
infraordo = Ornithopoda
familia = Hypsilophodontidae
subfamilia = ?Thescelosaurinae
genus = "Parksosaurus"
genus_authority = C. M. Sternberg, 1937
subdivision_ranks=Species
subdivision=
*"P. warreni" (Parks, 1926 [originally "Thescelosaurus"] ) (type)

"Parksosaurus" (meaning "William Parks's lizard") was a genus of hypsilophodont ornithopod dinosaur from the early Maastrichtian-age Upper Cretaceous Horseshoe Canyon Formation of Alberta, Canada. It is based on most of a partially articulated skeleton and partial skull, showing it to have been a small, bipedal, herbivorous dinosaur. It is one of the few described non-hadrosaurid ornithopods from the end of the Cretaceous in North America, existing around 70 million years ago.

Description

Explicit estimates of the entire size of the animal have not been done, but William Parks found the hindlimb of his "T. warreni" to be about the same length overall as that of "Thescelosaurus neglectus" (93.0 centimeters (3.05 ft) for "T. warreni" versus 95.5 centimeters (3.13 ft) for "T. neglectus"), even though the shin was shorter than the thigh in "T. neglectus", the opposite of "T. warreni".cite journal |last=Parks |first=William A |authorlink=William Parks |year=1926 |title="Thescelosaurus warreni", a new species of orthopodous dinosaur from the Edmonton Formation of Alberta |journal=University of Toronto Studies (Geological Series) |volume=21 |pages=1–42 ] Thus, the animal would have been comparable to the better-known "Thescelosaurus" in linear dimensions, despite proportional differences (around 1 meter (3.3 ft) tall at the hips, 2-2.5 meters (6.56-8.2 ft) long). The proportional differences probably would have made it lighter, though, as less weight was concentrated near the thigh. Like "Thescelosaurus", it had thin cartilaginous plates along the ribs.cite journal |last=Butler |first=Richard J. |coauthors=and Galton, Peter M. |date=2008 |title=The 'dermal armour' of the ornithopod dinosaur "Hypsilophodon" from the Wealden (Early Cretaceous: Barremian) of the Isle of Wight: a reappraisal |journal=Cretaceous Research |volume=29 |issue=4 |pages=636-642 |doi=10.1016/j.cretres.2008.02.002]

Classification

"Parksosaurus" has been considered to be a hypsilophodont since its description. Recent reviews have dealt with it with little comment,cite book |last=Sues |first=Hans-Dieter |coauthors=and Norman, David B. |editor= Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=1st |year=1990 |publisher=University of California Press |location=Berkeley |isbn=0-520-06727-4 |pages=498–509 |chapter=Hypsilophodontidae, "Tenontosaurus", Dryosauridae] cite book |last=Norman |first=David B. |authorlink=David B. Norman |coauthors=Sues, Hans-Dieter; Witmer, Larry M.; and Coria, Rodolfo A. |editor=Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=2nd |year= 2004|publisher=University of California Press |location=Berkeley |isbn=0-520-24209-2 |pages=393–412 |chapter=Basal Ornithopoda] cite journal |last=Butler |first=Richard J. |coauthors=Upchurch, Paul; and Norman, David B. |title=The phylogeny of the ornithischian dinosaurs|journal=Journal of Systematic Palaeontology |volume=6 |issue=1 |year=2008 |pages=1–40 |doi=10.1017/S1477201907002271] although David B. Norman and colleagues (2004), in the framework of a paraphyletic Hypsilophodontidae, found it to be the sister taxon to "Thescelosaurus", and Richard Butler and colleagues (2008) found that it may be close to the South American genus "Gasparinisaura". However, basal ornithopod phylogeny is poorly known at this point, albeit under study. Like "Thescelosaurus", "Parksosaurus" had a relatively robust hindlimb, and an elongate skull without as much of an arched shape to the forehead compared to other hypsilophodonts.

Discovery and history

Paleontologist William Parks described skeleton ROM 804 in 1926 as "Thescelosaurus warreni", which had been discovered in what was then called the Edmonton Formation near Rumsey Ferry on the Red Deer River. When found, it consisted of a partial skull missing the beak region, most of the left pectoral girdle (including a suprascapula, a bone more commonly found in lizards, but which is believed to have been present in cartilaginous form in some ornithopods due to the roughened ends of their scapulae),cite journal |last=Gilmore |first=Charles W. |authorlink=Charles W. Gilmore |year=1915 |title=Osteology of "Thescelosaurus", an orthopodus dinosaur from the Lance Formation of Wyoming |journal=Proceedings of the U.S. National Museum |volume=49 |issue=2127 |pages=591–616 ] the left arm except the hand, ribs and sternal elements, a damaged left pelvis, right ischium, the left leg except for some toe bones, articulated vertebrae from the back, hip, and tail, and a number of ossified tendons that sheathed the end of the tail. The body of the animal had fallen on its left side, and most of the right side had been destroyed before burial; in addition, the head had been separated from the body, and the neck lost. Parks differentiated the new species from "T. neglectus" by leg proportions; "T. warreni" had a longer tibia than femur, and longer toes.

Charles M. Sternberg, upon the discovery of the specimen he named "Thescelosaurus edmontonensis", revisited "T. warreni" and found that it warranted its own genus (it was named in an abstract, which is not typical, but the specimen had already been thoroughly described).cite journal |last=Sternberg |first=Charles M. |year=1937 |title=Classification of "Thescelosaurus", with a description of a new species. |journal=Geological Society of America Proceedings for 1936 |pages=365] In 1940, he presented a more thorough comparison and found a number of differences between the two genera throughout the body. He assigned "Parksosaurus" to the Hypsilophodontinae with "Hypsilophodon" and "Dysalotosaurus", and "Thescelosaurus" to the Thescelosaurinae.cite journal |last=Sternberg |first=Charles M. |authorlink=Charles Mortram Sternberg |year=1940 |title="Thescelosaurus edmontonensis", n. sp., and classification of the Hypsilophodontidae |journal=Journal of Paleontology |volume=14 |issue=5 |pages=481–494 ] The genus attracted little attention until Peter Galton began his revision of hypsilophodonts in the 1970s. "Parksosaurus" received a redescription in 1973, wherein it was considered to be related to a "Hypsilophodon""Laosaurus""L. minimus" lineage.cite journal |last=Galton |first=Peter M. |authorlink=Peter Galton |year=1973 |title=Redescription of the skull and mandible of "Parksosaurus" from the Late Cretaceous with comments on the family Hypsilophodontidae (Ornithischia) |journal=Life Sciences Contribution, Royal Ontario Museum |volume=89 |pages=1–21] After this, it once again returned to obscurity.

George Olshevsky [http://dml.cmnh.org/2001Jan/msg00151.html emended the species name] to "P. warrenae" in 1992,cite book |author=Olshevsky, G. |title=A Revision of the Parainfraclass Archosauria Cope, 1869, Excluding the Advanced Crocodylia |series=Mesozoic Meanderings No. 2 |year=1991 |publisher=Publications Requiring Research |location=San Diego |pages=268] because the species name honors a woman (Mrs. H. D. Warren), but outside of Internet sites, the original spelling has been preferred.

Paleoecology and paleobiology

"Parksosaurus" shared the Horseshoe Canyon Formation with flat-headed hadrosaurid "Edmontosaurus", spike-crested "Saurolophus", and hollow-crested "Hypacrosaurus", ankylosaurid "Euoplocephalus", nodosaurid "Edmontonia", horned dinosaurs "Montanoceratops", "Anchiceratops", "Arrhinoceratops", and "Pachyrhinosaurus", pachycephalosaurid "Stegoceras", ostrich-mimics "Ornithomimus" and "Struthiomimus", a variety of poorly-known small theropods including troodontids and dromaeosaurids, and the tyrannosaurids "Albertosaurus" and "Daspletosaurus".cite book |last=Weishampel |first=David B. |authorlink=David B. Weishampel |coauthors=Barrett, Paul M.; Coria, Rodolfo A.; Le Loueff, Jean; Xu Xing; Zhao Xijin; Sahni, Ashok; Gomani, Elizabeth M.P.; and Noto, Christopher N. |editor=Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=2nd |year= 2004|publisher=University of California Press |location=Berkeley |isbn=0-520-24209-2 |pages=517-606 |chapter=Dinosaur distribution ] The dinosaurs from this formation are sometimes known as Edmontonian, after a land mammal age, and are distinct from those in the formations above and below.cite book|last=Dodson |first=Peter |authorlink=Peter Dodson |title=The Horned Dinosaurs: A Natural History|publisher = Princeton University Press |year=1996 |location=Princeton |pages=14-15 |isbn=0-691-05900-4] The Horseshoe Canyon Formation is interpreted as having a significant marine influence, due to an encroaching Western Interior Seaway, the shallow sea that covered the midsection of North America through much of the Cretaceous.

In life, "Parksosaurus", as a hypsilophodont, would have been a small, swift bipedal herbivore. It would have had a moderately long neck and small head with a horny beak, short but strong forelimbs, and long powerful hindlimbs.

References

External links

* [http://www.users.qwest.net/~jstweet1/ornithopoda.htm Ornithopoda] at "Thescelosaurus"!
* [http://internt.nhm.ac.uk/jdsml/nature-online/dino-directory/detail.dsml?identifier=parkso&showTaxonomy=yes&section=home&Genus=Parksosaurus&&beginIndex= "Parksosaurus"] in the Natural History Museum's Dino Directory