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Re: Dinosaurs vs. mammals: a hypothetical scenario



2011/4/8 Raptorial Talon <raptorialtalon@gmail.com>:
>
> Yet the Miocene saw the
> replacement of nearly all the archaic lumberers with much more
> fleet-footed forms - even in forests, the traditional stronghold of
> the more graviportal-ish critters. Not that there weren't holdouts (or
> aren't today, for that matter). But as a general trend, the various
> horses, rhinos, tylopods, and pecorans that constituted the greater
> share of the large-herbivore biota of the day were pretty well-adapted
> to swift and/or efficient locomotion.
>
Even in forests? Is there a source stating this? (of course, I do not
require it for just now). In South America at least, there was still
plenty of non-cursorial beasts in the Miocene, especially among
xenarthrans, marsupials, toxodonts, etc. In North America, you still
have slow oreodonts by the time. Rodents, generally speaking, never
were too fast either, yet they form, today and likely then, great part
of the prey of predators. Velocity is mostly important regarding
predation, and I do not see that the Miocene presented faster
carnivores than today. Today, most terrestrial carnivores which are
not canids, felids or hyenids are not cursorial, and they amount to
less than half of the diversity of carnivorous mammals, surpassed in
number by slower carnivores as mustelids, ursids, viverrids,
procyonids, herpestids, etc. It seems difficult that in the Miocene,
with more forests than today as David indicates, and with African
creodonts, South American borhyaenoids, and Holarctic amphycyonids,
the pressure for velocity on herbivores was any stronger than today.
It seems to me that another advantage for cursoriality is stride
increase and thus energy-saving locomotion, not only velocity.