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Re: Equid feet



In a message dated 96-02-08 09:37:32 EST, Thomas_R_HOLTZ@umail.umd.edu (th81)
writes:

>Basal four toed equids, which used to be included under the name
>'Hyracotherium' (which properly belongs to the paleothere lineage) ARE
>included in Equidae in most classifications.  Furthermore, three-toed equids
>are, to my knowledge, *universally* included in Equidae (the one-toed
>condition being evolved more than once).
>
>So, differences in the feet as great as the number of toes are not regarded
>as sufficient to separate genera out of a single family in well-studied
>clades.

The problem, of course, rests with how conservative a group might be with
respect to a particular anatomical feature. Horse feet changed quite a bit
from hyracotheres to _Equus_, and the change is well documented in the fossil
record. But among theropods the feet were almost incredibly conservative: the
feet of modern avialan birds differ only in detail from the feet of
ceratosaurian theropods. So a change in pedal anatomy to the
arctometatarsalian form could be considered radical enough to  warrant
erecting new families (or, as Tom H., did, a higher-level taxon).