[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: mammal mystery



> No, this is not my idea.  I say that dinosaurs, inasmuch as they lay eggs
> that were relatively easy to find (relative, that is, to avian dinosaurs,
> mammals, snakes, lizards, and turtles) _always_ suffered intense 
> predation on their eggs  

     So rather being a particularly successful vertebrate group, for 150
million years of global distribution and continuous speciation they were
actually just hanging on by the skin of thier teeth?

> I say this can be viewed independently of marine extinctions.  Not only
> that, marine extinctions may not have been simultaneous as claimed.  Ward
> says data on ammonites are consistent with either a sudden extinction _or_
> a gradual one.

      The point being is that a lot of different groups in all ecosystems
and across the world went extinct about the same time, regardless of if
it was "instantaneous" or more drawn out. A rather remarkable coincidence,
unless you consider that some large scale (as in global) environmental
factor, (such as climate change or an asteroid impact) was involved.  The
egg eater theory runs into the same problem as Bakker's epidemic idea; it
would have to be a localized event, which does not explain a global
extinction.  The evolution of a nasty egg eater could hypothetically cause
extinctions in the area where it evolved, but becoming distributed
worldwide with Pangea broken up and shallow seas still splitting up a lot
of continants would be a nifty trick.  Unless you advocate the
simultaneous development of egg eaters on all the isolated land all over
the world, another remarkable coincidence. 

> plankton are still disputed with some saying that the species that went
> were not key species, that most successful ones survived.

     So what?  The extinction happened, and it happened around the same
time as the dinosaurs.    

> to this question: why were dinosaurs (apart from birds, alright) becoming
> less diverse?  

      Abundance, not diversity, is the issue.  Dinosaurs MAY have had
relatively few species IN NORTH AMERICA at that time, but that doesn't
say anything about the abundance in terms of numbers of individuals at
that time, which is what is really important.  Again, I think (no entirely
positive) that this decline in diversity is only known from North America.
What about the rest of the world?     
      I summary your idea has three problems:
1) It does not account for the geographic isolation of terrestrial
   ecosystems by continental drift and the existence of shallow seaways.
2) It does not account for the marine extinctions that occured about the
   same time.
3) It does not account for the exticntion of other terrestrial
   groups.
      In sum, there is no reason to think that egg eaters were involved in
the K-T extinciton at all.  Your idea is based entirely on assumptions
about the inability of a large, non-arboreal land animal to defend its
eggs, which is not only unfounded, but does not take into account the
success of crocodilians or ratites.  There is no evidence that a
particularly nasty new egg eater evolved at the end of the Maastrichtian,
and the sucess of dinosaurs, both in numbers of species and global
distribution, does not suggest they were constantly on the edge of
disaster at the hands of egg eaters for 150 million years.

LN Jeff 
O-