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DERIVED THEROPODS



Joseph C. Daniel wrote:
 << One question that I have had with cladistics for a long time was the
 time factor.  As an example, the ceratosaurs at least used to be
 considered "basal" or "primitive" theropods, right?  Yet they didn't
 appear until tens of millions of years after the earlier more derived
 theropods,>>

Which theropods are these?  As far as I know, the earliest theropods are tme
more "primitive" Herrerasaurs etc in the Late Triassic, then Coelophysid
Ceratosaurs later in the Late Triassic, and then Tetanurans in the mid to Late
Jurassic.

Also, terms like primitive and basal are misleading.  In truth, nothing is
more advanced, derived, primitive etc...  Features may be derived or basal
compared to eachother.  Say, Ornithomimosaurs have a hand that is more derived
compared to the basal maniraptoriforme condition that is seen in
ornitholestids, saurornithoidids, dromaeosaurs etc, but to say that an
ornithomomosaur is more derived or advanced than say a dromaeosaur is not
truthful, and in some ways misleading.

Most of the time advanced or derived are used loosely to describe the left or
right side of cladograms....

Peter Buchholz
Tetanurae@aol.com