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Re: definition of dinosaur
In a message dated 96-02-22 10:57:09 EST, email@example.com (King, Norm)
>I believe I read somewhere (I think it was here) that we should define
>dinosaurs as all the descendants of the most recent common ancestor of
>_Megalosaurus_ and _Iguanodon_.
>I can provide that definition to my students (but I will have to follow
>up with an explanation as to how they can recognize a dinosaur when they
>see one). I predict that these questions will be asked about the
>Why are those two genera singled out? Isn't it true that after all these
>years we still do not have even one complete composite skeleton of
>_Megalosaurus_? Why not choose _Allosaurus_, instead?
That suggestion was mine. _Megalosaurus_ and _Iguanodon_ were the first two
dinosaur genera to be scientifically described, and by coincidence they
happen to represent the two clades of Dinosauria (in the taxonomy proposed by
Michael Cooper  and, probably independently, by Bob Bakker , and
supported by my own investigations, such as they are): Phytodinosauria
Bakker, 1986 (= Ornithischiformes Cooper, 1985) and Aves _sensu lato_,
including all theropod-like archosaurs from _Longisquama_ to extant birds.
All we need at this level of definition is to have _Iguanodon_ be a
certifiable phytodinosaur (it is, more specifically, an ornithopod) and
_Megalosaurus_ to be a certifiable avian (it is, more specifically, a
Define Phytodinosauria to be all dinosaurs closer to _Iguanodon_ than to
_Megalosaurus_, and Aves to be all dinosaurs closer to _Megalosaurus_ than to
_Iguanodon_, and you're done. This classification, not entirely by
coincidence, separates the plant-eating dinosaurs from the meat-eating
dinosaurs (not counting, of course, those avians that evolved herbivory
secondarily much later in the evolution of Aves).
I'll have more details in _Mesozoic Meanderings_ #2, which I'm still
rewriting. Lots of text, lots of cladograms, lots of characters discussed.
(Too much work.)