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Fam Jansma wrote-
> What is was wondering: why does Segnosaurus have 5
metatarsels when one of the earlier genera, Beipiaosaurus, has only 4?
Metatarsal 4 is rudimentary compared to other Therizinosaurs, but he hasn't lost
it yet, so that the later genera have this bone still. If you look at the
original drawing by Perle (1979) of Segnosaurus galbinensis it contains the 4
metatarsals present in Beipiaosaurus, but a rudimentary fifth one! Beipiaosaurus
is from the early Cretaceous and Segnosaurus from the late Cretaceous, although
Segnosaurus is in morphology more primitive than B. <
Both Beipiaosaurus and Segnosaurus have five metatarsals, like
most theropods (Jibeinia + Ornithothoraces lost mtV, and derived ornithomimids
and Avimimus lost mtI). The fifth metatarsal of Beipiaosaurus isn't
illustrated, but the authors say it is "slender and strap-like", being half the
length of the main metatarsals.
Mickey Mortimer
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