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Re: taxonomy is not stratigraphy (was Re: JVP 25(2): New Dinos, Birds, Discoveries)

Perhaps I misinterpret a couple of recent posts, but--

I was taught that the largest herbivore is always
larger than the largest predator. The quantitative
size differential may be affected by various
strategies (e.g., in predators; pack vs solitary
hunting, and in prey; defensive herding behavior,
armor), but the general trend is intact through time.
I am also under the impression that when graphed such
that the y axis = kg, and the x axis = geologic time,
there is a strong positive correlation between largest
herbivore and largest predator.

Surely the fact that the herbivores sometimes (or even
usually) "win" doesn't falsify the hypothesis that
there is a mutual selection for size operating within
the "top" predator/prey relationship? After all, if
the prey doesn't "win" the size race, swift extinction
is a likely result for both, in which case they might
not appear in your data base.

Sauropods may have "won", and packhunting tyrannosaurs
may have turned to smaller prey. After morphing into
solitary hunter/scavengers, intra-specific competition
for food and the implications of a solitary hunting
technique might have dealt the final cards relative to
the size of tyrannosaurs. This doesn't de-couple the
more general evolutionary relationship between
sauropods/therapods relative to size. Details may
never be available, but isn't safe to assume that
sauropods were subject to predation at all times, and
were affected in the evolutionary sense?

--- "Jaime A. Headden" <qilongia@yahoo.com> wrote:

>   While the argument of massive herbivores being the
> selective pressure for
> massive carnivores is a wonderful story, it doesn't
> seem to play out in, at
> least, any modern ecosystem. All super carnivores
> today are many times smaller
> than half that of the largest herbivore in the same
> ecosystem.
> Wolf vs. Carribou/Elk
> Bobcat vs. Moose?
> Lion/Tiger vs. Elephant/Water buffalo
> Orca vs. well ... any mysticete
>   etc.
>   None of these "superpredators" are capable of
> taking on the "prey" without
> inconventience of the latter or assistance of
> numbers of the former. To
> determine in the past whether such behaviors occured
> requires extraordinary
> evidence. 
>   In the Serengeti, lions will not take on a water
> buffalo unless its disabled,
> stuck in mud, or sick. Smaller (read: weaker) and
> seldom full size and
> full-health animals fall to either lion or wolf,
> because even in numbers, the
> mass of the animal is prohibitive and not conducive
> to continuing-health.
>   We have, at Cleveland-Lloyd Dinosaur Quarry, a
> "predator trap" with a massive
> concentration of carnivores but with -- by numbers
> -- much fewer herbivores.
> This seems exemplative of such weakened, disabled
> animals as to be picked on by
> groups or phases of predators.
>   To be big, perhaps, as Nick said, is to prevent
> predators from killing you.
> Herding permits animals to grow bigger with less
> reduction of the population.
> So it seems Mesozoic dinosaur herbivores were either
> tiny, armored, huge, or
> bore offensive anatomy. This seems a response that
> was rather effective. Of
> course, just so stories can explain either herbivore
> preventive size-gain, or
> theropod offensive size-gain, but in the end ... the
> only way to determine an
> animal killed another is with something like the
> Fighting Dinosaurs (and even
> _that_ is ambiguous).
>   Cheers,
> Jaime A. Headden
> "Innocent, unbiased observation is a myth." --- P.B.
> Medawar (1969)
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