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Re: Four-toed theropods



In a message dated 96-09-11 13:08:45 EDT, nclark@museum.gla.ac.uk (Neil
Clark) writes:

> I too have a problem with a four toed possible theropod .... but not
> from the Cretaceous.  I found mine in the Middle Jurassic of
> Northern England.
>  The toes are elongate and pointed and slightly curved.  At first I
> thought it may have been the track of a croc or similar, but I
> showed it to Bill Sargeant who said it wasn't.  It remains a mystery
> and undescribed.  At least mine was not a segnosaur, perhaps a late
> surviving prosauropod? .... perhaps there is a group of theropods
> with four toes for which no ossified remains have been found???
> Tracks are notoriously difficult to assign to any group unless you
> find the animal that made them collapsed at the end of the trackway!

If the well-known theropod groups are indeed descendants of groups of small,
arboreal, narrow-metatarsal dino-birds in which the hallux was large and
retroverted (as I imagine), then the tetradactyl theropod foot could easily
be an intermediate evolutionary stage between the large-retroverted-hallux
foot and the typical theropod foot, in which the reduced hallux points
medially inward and no longer contacts the substrate. The rarity of
tetradactyl theropods may indicate the rapidity of this evolutionary trend.