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





----Original Message Follows----
From: "Jaime A. Headden" <qilongia@yahoo.com>
Reply-To: qilongia@yahoo.com
To: dinosaur@usc.edu
Subject: Re: taxonomy is not stratigraphy (was Re: JVP 25(2): New Dinos, Birds, Discoveries)
Date: Fri, 15 Jul 2005 22:45:04 -0700 (PDT)


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

If you're talking about the Arctic tundra, that is. Elk are restricted largely to forests and woodlands, it seems. Otherwise the largest herbivore the grey wolf interacts with would be the American bison. In Eurasia it'd be the European bison, or the Megaloceros, aurochs, woolly rhinoceros, woolly mammoth and steppe bison in the good ol' days of the Pleistocene (plus all the miscellaneous Stephanorhinus and Palaeoloxodon/Elephas species hanging around during the interglacials).


And besides, it's important to take note that the wolf may be considered a 'top' predator now, but what about in the Late Pleistocene? I wouldn't be surprised if in North America, the grey wolf and puma were much lower and had to defer to the dire wolf, American lion, sabertooth, scimitar cat and short-faced bear...

And in Eurasia, the wolf probably would be competing with cave lion and spotted/cave hyena, as well as the tiger in the Asiatic parts of its range.

Bobcat vs. Moose?
Lion/Tiger vs. Elephant/Water buffalo
Orca vs. well ... any mysticete

You could throw in brown bear/grizzly as the largest carnivore for the Eurasian and North American ecosystems, but I don't think it really counts as a "super-predator"


As for the big cats, lions would be taking on African elephant, cape buffalo (water buffalo are exclusively Asian), white rhinoceros, black rhinoceros and common hippopotamus, while the largest tigers (if we're talking about Indian tigers) would be facing off against Asian elephant, Indian rhinoceros, (plus Sumatran and Javan rhinoceros which once ranged into eastern India as well), and water buffalo. Siberian tigers would be up against moose, steppe bison, woolly rhinoceros and woolly mammoth (provided these were sympatric with Siberian tigers in the Pleistocene).

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.

Not too sure if we have any real data on that, since there do seem to be lion prides that specialise in killing Cape buffalo, even adult cows and bulls. Desperation and hunger may play an important role in that as well, plus the fact that hunting buffalo must be infinitely more rewarding than scuffling over warthog piglets during the dry season. (Think this must be some prerequisite for almost any documentary featuring lions - insert long drawn-out battle between buffalo and lions)


In any case, the idea that theropods evolved gigantism in response to the ever-increasing size of sauropods is a tantalising idea, but unfortunately one that I'm afraid is difficult to test, due to the imperfection of the fossil record. However, at the moment, at least, I think we do have evidence that it was the herbivores that first 'developed' the tendency to grow to much larger sizes, case in point being the prosauropods/basal sauropodomorphs. Unless there are actually some 20-foot long coelophysians/herrerasaurs/avepods that I've forgotten about.

Ivan

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