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>> H. sapiens has become the top predator elsehwere (due to migration), but
>> there has been a continuing presence of hominines in Africa for a couple of
>> million years.
>It has been written that, as humans spread to new lands, meeting species not
>adapted to the threat posed by humans, they eliminated megafaunal elements.
>disappearance of megafauna coincides with 'invasion time' of humans. Yet in
>Africa, megafauna have remained because the animals there had evolved with an
>ever-present human threat. Hence the more or less unique, surviving African
>I have my doubts about this. Firstly, it might already have been proved that
>many megafaunal elements were in trouble before humans began preying on them.

While this is true, it would make the species that much more susceptible to
extinction.  As Raup and others point out, it is probably multiple causes
which are responsible for most extinctions of once-common animals.

>Secondly, many species supposedly wiped out by human invaders seem about as
>adapted to the danger as the African animals that survived. Consider the big
>elephants, for example. 

Since the Plesitocene "mass extinctions" do not occur in parallel with
marine invertebrate extinctions, floral extinctions, or even sever
micromammal extinctions, there are reasons to suspect a non-standard agent
in the loss of the megamammals.  Humans are certainly suspects, although
climate change etc. may have contributed.

>To swing this around to dinosaurs, this rather mundane hypothesis (kind of
>'survival of the fittest', with deadly, new species wiping away the old order)
>is advanced with ingenious subtlety by Uncle Bob Bakker in his _Utahraptor_
>rantings. Not that there isn't at least a small grain of truth there, of

Especially since there is no evidence that Utahraptor is an Asian immigrant,
and that Utahraptor was probably extinct before the other taxa described

Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661