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In a message dated 96-12-22 17:51:31 EST, steve.cole@genie.com writes:

<< Stephen Throop noted in a recent message that the switch from
 Stegosaurs to Nodosaurs might have been linked to
 the switch from allosaurian grab-hunters to tyrannosaur impact-hunters. >>

Trouble is, there was no switch from stegosaurs to nodosaurs. Nodosaurs are
now being found in the Jurassic, and Early Cretaceous stegosaurs have been
known since the 19th century. Contrary to current popular belief in a clade
Thyreophora, stegosaurs and nodosaurs/ankylosaurs were not particularly
closely related; the pelvic structure of stegosaurs is much closer to that of
heterodontosaurids and marginocephalians, and of ornithopods, than it is to
that of nodosaurs and ankylosaurs; and the hind foot structure of stegosaurs
strongly suggests a lengthy stint as swift bipedal runners for the earliest
members of that clade, quite different from the lifestyle of the earliest
nodosaurs and ankylosaurs. Stegosaurs represent a distinct radiation of
rather lightly armored ornithischians that originated before the Early
Jurassic (earliest known member: _Emausaurus ernsti_ from northern Germany),
coeval with the well-known basal ankylosaurs _Scutellosaurus_ and
_Scelidosaurus_. Details will appear in _Historical Dinosaurology_ #1, though
some details were originally published in my articles for _Dino-Frontline_ on
stegosaurs and ankylosaurs.