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RE: Progress schmogress (was Re: competition)



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\uc1\pard\plain\deftab360 \f0\fs20\cf0 On the same subject, I've always wondered why Parasuchians disappeared to be replaced by real crocs in the same habitats, apparently sharing the same global body construction. Was it competition, progress, specializations or something else? Or am I mistaken in my assumptions?\par
Jean-Michel\par
\par
-----Original Message-----\par
From: Thomas R. Holtz, Jr. [mailto:tholtz@geol.umd.edu]\par
Sent: mercredi 1 ao\'fbt 2001 14:58\par
To: edels@email.msn.com; dinosaur@usc.edu\par
Subject: RE: Progress schmogress (was Re: competition)\par
\par
\par
> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of\par
> Edels\par
>\par
> Tim, etc:\par
>\par
> In case you haven't checked cranial capacities lately,\par
> _Homo sapiens neanderthalensis_ actually had an average braincase size\par
> that was 7-10% larger than _Homo sapiens sapiens_ (average).\par
\par
This MAY have to do with Neanderthalers generally more massive proportions,\par
but there is indeed a larger endocranial volume in those guys then us.\par
\par
Incidentally, almost all paleoanthropologists now regard Neanderthalers as a\par
distinct species _H. neanderthalensis_ rather than a subspecies of modern\par
humans.  There are a number of anatomical features found in Neanderthalers\par
that are not present in us, and vice versa.\par
\par
As many evolutionary biologists have shown, it is VERY hard to test\par
hypotheses of competitive exclusion in the fossil record.  It is an\par
appealing story, and it is quite likely the case in many instances, but it\par
is very difficult to demonstrate.  Furthermore, there might be some\par
attributes involved in competitive exclusion (for example, physiological or\par
behavioral features) which would not be obvious in the osteological or shell\par
or hard plant tissue remains that make up most fossils.\par
\par
Finally, the "progressive" state is sometimes hard to establish.  In come\par
cases it is more clear: a fully marine whale without external hindlimbs vs.\par
one with them.  In other cases, though, it seems that people tend to assume\par
"current = progressive".  Okay, but that is not the same as "specialized =\par
progressive", another possible formulation.  For example, sphenodontians\par
today are represented by only a relatively unspecialized (and possibly\par
recidivist!) form, compared to a much higher ecomorphological diversity in\par
the past.  Similarly, crocodylomorphs in the Cretaceous and Tertiary\par
represented a wider range of ecomorphotypes than at present.  Same with\par
horses and rhinos and proboscideans of the Tertiary (much greater diversity\par
of ecological habit in a given time slice than at present).\par
\par
So, as always, be cautious with "why" statements in evolutionary biology\par
(i.e., this is why this happened).  Our first order of business is\par
establishing the "what" statements: describing the details and patterns that\par
are out there.  "Why" statements are often more speculative, and are harder\par
to test against alternative "why" statements.\par
\par
Hope this helps.\par
\par
\tab \tab Thomas R. Holtz, Jr.\par
\tab \tab Vertebrate Paleontologist\par
Department of Geology\tab \tab Director, Earth, Life & Time Program\par
University of Maryland\tab \tab College Park Scholars\par
\tab \tab College Park, MD  20742\par
http://www.geol.umd.edu/~tholtz/tholtz.htm\par
http://www.geol.umd.edu/~jmerck/eltsite\par
Phone:\tab 301-405-4084\tab Email:\tab tholtz@geol.umd.edu\par
Fax (Geol):  301-314-9661\tab Fax (CPS-ELT): 301-405-0796\par
\par
}