Cedarpelta

Taxobox|
name = "Cedarpelta"|
fossil_range = Early Cretaceous


image_width = 200px
image_caption = Holotype skull of "Cedarpelta bilbeyhallorum"
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Ornithischia
subordo = Thyreophora
infraordo = Ankylosauria
familia = Ankylosauridae
genus = "Cedarpelta"
species = "C. bilbeyhallorum"
binomial = "Cedarpelta bilbeyhallorum"
binomial_authority = Carpenter "et al.", 2001

"Cedarpelta" is the most basal known ankylosaurid ankylosaur (Ankylosauridae; Ankylosauria), based on material recovered from the Lower Cretaceous of North America. The skull lacks extensive cranial ornamentation, a trait which has been interpreted as plesiomorphic for ankylosaurs. Carpenter "et al." (2001) diagnose "Cedarpelta" by the presence of a rostrocaudally elongate pterygoid with a caudolaterally oriented, trochlear-like process, a premaxilla with six conical teeth, and a straight ischium. The presence of premaxillary teeth is a plesiomorphic character because it is present in other, primitive ornithischians. In contrast, closure of the opening on the side of the skull behind the orbit, the lateral temporal fenestra, is an advanced (apomorphic) character only known in ankylosaurid ankylosaurs.

Two skulls are known, and the skull length for "Cedarpelta" is estimated to have been roughly 60 cm. Significantly, one of the "Cedarpelta" skulls was found disarticulated, a first for an ankylosaur skull, allowing paleontologists a unique opportunity to examine the individual bones instead of being limited to a cossified unit. The etymology of this binomen may be read as "Bilbey and Hall's Cedar (Mountain) shield," with the genus named for the Cedar Mountain Formation and the animal's armored plates and the species named for Sue Ann Bilbey and Evan Hall, discoverers of the type locality.

All material referrable to "Cedarpelta" has been recovered from the Ruby Ranch Member of the Cedar Mountain Formation. Radiometric dates place the site the specimen was collected in the (Albian) of eastern Utah.

Holotype

Carpenter "et al." (2001) designated CEUM 12360 as the holotype specimen of "Cedarpelta bilbeyhallorum" (CEUM is the acronym of the College of Eastern Utah Prehistoric Museum in Price, Utah). CEUM 12360 consists of an articulated, incomplete skull lacking the snout and mandibles. Carpenter "et al." (2001) also designated a long list of paratype material, mostly isolated bones that could be referred to "Cedarpelta bilbeyhallorum".

Phylogenetics

"Cedarpelta bilbeyhallorum" was believed by Carpenter "et al." (2001) to be closely related to "Gobisaurus domoculus" of north-central China and "Shamosaurus scutatus" of Mongolia, and they placed the taxon within the Family Ankylosauridae. Vickaryous "et al." (2004), however, interpreted the genus as the basalmost member of the Family Nodosauridae, most closely related to the nodosaurids "Pawpawsaurus campbelli", "Silvisaurus condrayi", and "Sauropelta edwardsorum". However, new material of the skeleton confirms the original identification of Carpenter "et al." of "Cedarpelta" being the most primitive ankylosaurid.

References

* Carpenter, K., Kirkland, J. I., Birge, D., and Bird, J. 2001. Disarticulated skull of a new primitive ankylosaurid from the Lower Cretaceous of Utah. in Carpenter, K. (editor) 2001. The Armored Dinosaurs. Indiana University Press
* Vickaryous, Maryanska, and Weishampel 2004. Chapter Seventeen: Ankylosauria. in The Dinosauria (2nd edition), Weishampel, D. B., Dodson, P., and Osmólska, H., editors. University of California Press.

External links

* [http://www.users.qwest.net/~jstweet1/ankylosauridae.htm Ankylosauridae]
* [http://dino.lm.com/images/display.php?id=1472 "Cedarpelta" at the Dinosauricon]