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Re: Hyacotherium/Eohippus



>>>In a message dated 96-02-07 09:32:08 EST, Thomas_R_HOLTZ@umail.umd.edu (th81)
>>>writes:
>>>
>>>>>This makes me _seriously_ doubt the proposed relationship between
>>>>_Mononykus_
>>>>>and _Alvarezsaurus_. If they're going to be confamilial, they should at
>>>>least
>>>>>have the same pedal structure, for Heaven's sake.
>>>>
>>>>Such as Hyracotherium and Equus?
>>>>
>>>>
>>>
>>>I couldn't care less about _Hyracotherium_ and _Equus_.
>>>
>>>But--don't tell me they're in the _same family_?!
>>
>>Actually they are not.  Hyracotherium is a basal paleothere while the North
>>American forms (usually called Hyracotherium or Eohippus or Protorohippus or
>>???) are equids (so they probably aren't in the same "family")
>
>That's right: I had heard about this "hyracothere plexus problem" (i.e.,
>almost all basal perissodactyls are called "Hyracotherium", so it is a
>paraphyletic genus.
>
>Any chance that the type of Eohippus will turn out to be a basal equid?
>Wouldn't that be nice!

Unfortunately Eohippus is a nomen dubium.  Marsh's original material consisted
of a maxillary frag with about five very worn teeth.  The specimen is from
New Mexico (San Jose fm.) and from my experience in that unit, it is either
attributable to Xenicohippus (a somewhat derived equid) or to Systemodon
(a basal tapiromorph).  In either case it is not a basal equid (sorry).

The really unfortunate part is that the type is currently missing (apparently
Bob Bakker had it last???) and Yale doesn't know where it went.
David J. Froehlich                              Phone: 512-471-6088   
Vertebrate Paleontology Laboratory                Fax: 512-471-5973
J.J. Pickle Research Campus
The University of Texas, Austin, Texas 78712