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RE: Stegosaur Questions




Andrew Simpson wrote:

Is there a direct link between Stegosaurs and
Nodosaurs / Ankylosaurs?

Yes. Or at least, that's the hypothesis that has the most support from phylogenetic analyses. Although stegosaurs were not directly ancestral to ankylosaurs, the two are considered sister groups, with the Stegosauria and Ankylosauria sharing a common ancestor that is not shared by any other group.


Stegosauria and Ankylosauria together make up the clade Eurypoda, meaning "broad feet". Eurypods belong to the larger clade Thyreophora ("armor bearers"), which also includes primitive forms like _Scutellosaurus_ and _Scelidosaurus_.

Do all stegosaurs really disappear from the fossil
record mid cretaceous?

That's not entirely clear at the moment. There is one alleged stegosaur of Late Cretaceous age, named _Dravidosaurus_, from India; but some researchers claim that it's not even a dinosaur. Hopefully the identity of _Dravidosaurus_ will one day be resolved.


Stegosaurs certainly go into a steep decline after the mid-Cretaceous. One hypothesis is that stegosaurs, with their unprotected flanks, were especially vulnerable to dromaeosaur attacks.

Thyreophorans as a whole are exceedingly uncommon in the Southern Hemisphere. Maybe they were nudged out by small sauropods. Forms like _Brachytrachelopan_, _Nigersaurus_ and small titanosaurs show some convergence with thyreophorans, at least in terms of the possession of body armor (titanosaurs) and overall morphology.

Could a stegosaurus swim?

Not sure about that.

Cheers

Tim