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Re: Ankylosaurs, Stegosaurs, and other fun things..



In a message dated 7/2/02 6:04:16 PM EST, TiJaWi@agron.iastate.edu writes:

<< However, there are folks (including two or more on the DML) who hold strong
 views to the contrary, and do not regard stegosaurs and ankylosaurs as
 especially closely related, and regard the Thyreophora as polyphyletic. >>

Not only that, but I see no close relationship between Hesperosaurus and 
Huayangosaurus. Rather, Hesperosaurus and Stegosaurus are sister genera in 
the family Stegosauridae, and indeed Hesperosaurus may in time prove to be 
merely a distinct, short-skulled basal species of Stegosaurus, once the genus 
Stegosaurus itself is taxonomically described. They share alternating, thin 
dorsal plates, for example, and both lack shoulder spines. Likewise they 
share a number of features of the skull and mandible, such as the dentary 
ridge. If Hesperosaurus and Huayangosaurus were sister genera, then the 
alternating, thin dorsal plates would have evolved twice and the shoulder 
spines would have been lost twice, independently in Hesperosaurus and in 
Stegosaurus. Thin, alternating plates are quite absent in Huayangosaurus and 
any other known Jurassic Chinese stegosaur (the Early Cretaceous Wuerhosaurus 
is a sister taxon to Hesperosaurus-Stegosaurus in Stegosauridae), whereas all 
known Jurassic Chinese stegosaurs have shoulder spines.

I outed Emausaurus as a primitive stegosaur way back in the 1994 article on 
ankylosaurs for Dino Frontline. The skull is juvenile or subadult, and it is 
a ringer for the skull of Huayangosaurus in many ways. There is also a very 
un-ankylosaur-like cervical plate associated with the skull. It's the 
earliest known true stegosaur, and in no way is it closely related to 
Scutellosaurus or to Scelidosaurus.