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Re: Carnivore Energetics: Why Are Lions Not As Big As Elephants? .. and why aren't antelopes?
John Bois (firstname.lastname@example.org) wrote:
<[A] combintion of protection from predators (presumably a benefit enjoyed by
mammals but not utilized to the extent of dinosaurs), and a winning strategy in
outcompeting other herbivores, i.e., food processing and fewer calories needed
per gram body weight (also a benefit for mammals).>
Both of these are in fact enjoyed by many OTHER groups of animals, wherein
mammals are ALSO exploitative. Consider the completely absurb body sizes of
sauropods, of several magnitudes of size over ANY theropod that far exceeds
that given by any potential mammalian predator and its prey (not counting
parasites), including the only truly viable case among terrestrial predators,
lions and elephants. In the sea, a whale might find itself attacked by orca,
for example, if sick or small.
The other example given above is also true for reptiles, who indeed need to
eat so much less per body weight that they far exceed most mammals in this
regard, especially in the larger sizes. Small mammals eat more relative to body
weight than larger mammals, while the inverse is true for reptiles. This is, of
course, dependant on them being cold-blooded reptiles. As dinosaurs, it is
likely that for a predator/prey pair, the functional
homeothermy/tachymetabolism of the animals were likely on par to a similar
sized pair of mammals or just under that level, if they were warm-blooded or
functionally active metabolically.
Given the complexity enjoyed by apparently some dinosaurs who did consume
stones and not by accident (say, *Caudipteryx* or
*Jeholornis*/*Shenzhouraptor*), there is a substantially advanced gut that
earlier reptiles likely did not have. Until recently, stomach stones in
sauropods and other herbivorous dinosaurs implied complex stomachs and
intestinal tracts, include ceca, and while this has not been ruled out, it is
largely irrelevant. Having a more simplistic gut may mean its nutritional needs
were met more simplistically, rather than using the ruminant system of
reprocessing food to derive more nutrition from any given bite. This means it
was able to sustain and increase body size over any terrestrial mammal on a
less-efficient diet/metabolism, and over a variety of habitats including
coastal, tidal, riparian, plain, etc. also enjoyed by mammals.
From the sauropod to the hypsilophodont, dinosaurian herbivores were as
varied and derived as mammals, and they managed diversity through so-called
lower efficiency. In short, I see limited comparisons, here.
<The second hypothesis is that fairly large animals cannot hide their nests
easily and are therefore susceptible to nest predation--this sets up an arms
race between dinosaurian pred/prey--this is a protection advantage not needed
by mammals (who can simply run away with baby inside). In this view, large
size in dinosaurs is more of an evil necessity than an unalloyed gee whiz perk
of superior dinosaurian metabolic potential.>
Some large birds or crocs don't hide their nests at all: They either guard
them, or make it difficult for predators to get at the eggs. This includes
ostriches, megapodes, and of course, the crocodile. Some large mammals give
birth in the open (whales and elephants) and defend their young vigorously.
There is limited reason to date to assume that many dinosaur ytoung were simply
abandoned in open clutches, which seems the only actual dichotomy offered in
the hypothesis obove. I would consider it, perhaps, a false comparison, if the
examples I give are correct.
Jaime A. Headden
"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
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