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Re: kellner's ankle abstract
3) limited, but well-expressed development in a digit can cause distal
condensation to cease, in which the more proximal elements take up the
role of the distal most elements, usually unguals. This occurs in mammal
digits, and why even carnivorans have claws despite thier 2-3-3-3-3
Paleontology disagrees. Various Permian therapsids show how the extra
phalanges became disklike -- like in the feet of *Pterodactylus* -- and then
fused to their neighbors, turning 2-3-4-5-3 into 2-3-3-3-3 without any loss
In the absence of evidence to the contrary, however, I think that the actual
loss of the ungual on the 5th toes of pterosaurs is the most parsimonious
interpretation for its apparent absence.
5) duplication events can cause the identity of a bone to be repeated in
series, say for an interruption then later re-expression of the control
genes on the growth plate, but only in series, hence the polydactyly of
some amphibians, ichthyosaurs, etc.
The praepollex and praehallux of some living amphibians is not a duplication
of anything. It's a genuine digit that comes from the radiale instead of the
ulnare. -- Usual cases of pathological polydactyly, and of polydactyly in
ichthyosaurs, involve Y-shaped metacarpals, indicating the split of a
digital ray by a mechanism that is IIRC known but I have forgotten.
<And there are better matches in the protorosaurs than anywhere in the
archosaurs -- at present. They just haven't been input that often.>
This is based on a biased opinion no one else has yet supported in print
since 2000, either the interpretation of pterosaurs or the relationship
with "prolacertiforms" or "protorosaurs."
They should be put in. Of course they should be put into any cladistic
analysis that wants to find the sistergroup of Pterosauria. I'm waiting for
an analysis that does this -- and doesn't include characters that are
size-related, ontogeny-related, or just plain unconfirmable in the fossils,
plus doesn't code "inapplicable" as one more state of an unordered
multistate character. Don't get me wrong. The long lists of apomorphies
which pterosaurs and progressively larger groups of "prolacertiforms" share
are quite impressive; I wouldn't be surprised at all if more analyses found
pterosaurs as prolacertiforms. I'm just waiting for an analysis that
_really_ tests this.