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Here's an idea that's been running through my head.  It is often claimed that
dinosaurs had sub-standard running abilities comared to mammals and birds
because they had disproportionately short metatarsals, but a thought occured
to me.  Perhaps the unusually long metatarsals of modern birds and mammals
are an evolutionary response to the reduction of the primitively huge
caudofemoralis muscle seen in dinos and therapsids.

In other words, the femur powered by the caudofemoralis was where most of the
power in dinos and therapsids came from, but as each lineage progressed into
birds and mammals respectively, the caudofemoralis was reduced, thus making
the femur a much less powerful part of the leg movement.  In response to
that, each lineage greatly increased the size of its gastrocnemeus muscles
and the length of its metatarsals, thus forcing those parts to become the
major power generater in the movement of the legs.

What I'm getting at, is that when people claim that dinosa couldn't run
because their metatarsals were too short, are ignoring the fact that the
modern analogues HAVE to have long metatarsals in order to run, and that
dinosaurs had perfectly powerful leg muscles to move their femora and thus
their whole legs, whereas the modern analogues just have big calf muscles and
move only their metatarsals (well, they move the rest of their legs, but not
a great deal) when they run.

It is my position, that because of this, dinosaurs could run just as fast, if
not faster than a similarly sized modern bird or mammal, and that the
elongation of the metatarsals in modern representatives of the ornithodiran
and synapsid lineages is an evolutionary response to the reduction of the
caudofemoralis muscle, and not a true indicator of greater running ability.


Peter Buchholz

Los Angeles loves love