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Re: cladistics and names



>My point is really this:  When attempting to precisely define a concept
>that needs to be precisely defined, we should not borrow a name that
>already has an imprecise definition, and hope we can clean it up.  I
>believe it was Chris Campbell who pointed out that "Diapsida" has always
>had a precise meaning


I'm not sure it always has.  You see both "diapsid condition" and
"Diapsida" in the older literature; one refers to a morphology, the other
to a taxon of varying membership.  When "diapsid" was used, was the author
referring to temporal morphology or group membership?  Context was often
the only way to tell.



and does not seem to be in danger of exploding into
>chaos, because when it was coined nothing else had that label.


Actually, we do face some real problems, as (a) euryapsid reptiles are
almost certainly within Diapsida (either closer to lepidosaurs or to
archosaurs, depending on the tree you prefer; see works by Olivier Rieppel,
John Merck, Mike Caldwell, and many others) and (b) an increasing number of
data sets, INCLUDING MORPHOLOGICAL, place turtles WITHIN Diapsida.  The
name will still mean the same thing (last common ancestor of lepidosaurs
and archosaurs and all of its descendents) even if two very prominent
member lineages - Testudines and Euryapsida - no longer have diapsid
skulls.

(And before you complain about how unfair this is - most living squamates
no longer have "diapsid" skulls in the strictest sense, and it's very clear
that living Sphenodon has one secondarily - its complete infratemporal
fenestra is a reversal. )

chris


Christopher Brochu
Department of Geology
Field Museum of Natural History
Roosevelt Road at Lake Shore Drive
Chicago, IL 60605

312-922-9410 x469