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RE: Cleveland Lloyd - predator trap?



On Thu, 3 Mar 2005, lzanno wrote:
> There are a mimimum of 47 Allosaurus individuals, approximately 80%
> juvenile.  The main idea seems to be that drought congregated allosaurs

Sort of a temporary or transient predator trap, or concentrator - not like
a tar pit or anything more "permanent". Is this from one drought event or
many?

> around a diminishing water source.  Animals are reluctant to leave a
> water source in times of drought and may use up available food resources
> within the perimeter of the water hole and still not leave the water
> source.  Thus they may either starve, or succumb to disease etc.. hence
> the death assemblage is mainly the more suseptable young.  In terms of
> the large number of predators, similar assemblages have been documented
> in Africa where predators will dominate a water source because a
> herbivore would have to been either stupid or on it's last leg to walk
> over to a watering hole surrounded by hungry carnivores.  Further, at
> least two events of deposition can be identified in the quarry.
> Hope that helps.

I knew this reminded me of something related. A short article on La Brea

 http://www.sciencenews.org/articles/20040124/bob9.asp

from early last year.
 
Now this assemblage IS from over an extended period of time. What they've
found so far broke down like so:

 ...
 Between 1913 and 1915, work at more than 100 pitssome hidden beneath
 shallow pondsyielded more than 1 million bones from animals such as
 mastodons, mammoths, North American lions, and saber-toothed cats.
 ...
 In 1969, when scientists resumed digging at the site specified as Pit 91,
 they began rinsing the gunky tar from the excavated soil and looking
 carefully at what was left. More than 40,000 specimens unearthed at Pit
 91 between 1969 and 1980 have been identified and cataloged in an
 electronic database. Of those remains, 18,498 itemsnearly half of the
 entire take are individual bones of mammals that weighed more than 5
 kilograms.
 ...
 In a result that counters intuition, bones of predators were almost seven
 times as common in Pit 91 as were those of prey. Overall, an estimated 80
 percent of the mammals were carnivores, and 60 percent of the birds were
 birds of prey. That's a surprise, says Harris, since the number of
 herbivores in a stable ecosystem always outnumbers the predators by a
 wide margin.
 ...

 
> Quoting "Richard W. Travsky" <rtravsky@uwyo.edu>:
> > Three quarters from Allosaurus? One individual or several? If several
> > (and
> > dated the same) it would be an interesting (but probably
> > unwarranted)
> > speculation that it was the result of a pack of some sort
> > involved...