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Re: paleontolgist, dinosaur and also Re: "Wonderful Life" - repeated.



In a message dated 96-11-14 23:22:18 EST, mrowe@indiana.edu (Mickey P. Rowe)
writes:

<< You could (as George is wont to do) postulate thousands
 of small dinosaurs that have left no discernible traces, or you could
 accept that non-avian dinosaurian diversity may never have been all
 that large. >>

It's not merely a matter of "postulating" these small dinosaurs; the >known<
fossil record demands it. Unless, of course, you imagine that each dinosaur
arose by special creation exactly where it was found at exactly the time its
embedding strata were deposited. Otherwise there >must< have been a certain
number--a >large< number--of intermediate forms lying on or near what some
cladists have taken to calling "ghost lineages." These aren't even
necessarily small (body length <30cm) animals, just hundreds and hundreds of
garden-variety dinosaur genera missing from the fossil record. Among these
are Jurassic marginocephalians, Jurassic-Cretaceous thescelosaurids,
sauropods intermediate between camarasaur-like and diplodocus-like forms,
Jurassic titanosaurs, a host of spinosaurians and megalosaurs,
pre-_Alxasaurus_ segnosaurs, Jurassic bullatosaurs, loads of Jurassic
hypsilophodontians, early Cretaceous tyrannosaurids, Gondwana dinosaurs of
all kinds, you name it. Not to mention about 50 million years of
pre-_Archaeopteryx_ avians.

The entire Aalenian (earliest Middle Jurassic) stage has yielded virtually no
dinosaur fossils whatsoever. There's 5 million years of the dinosaur fossil
record that are just plain gone. Does this mean that dinosaurs became extinct
then, to arise from the dead as Lazarus taxa later in the Middle Jurassic?
No? Then just how many Aalenian dinosaurs were there?

The number of localities (probably more than 500 by now) where the
dinosaurian fauna has been sampled seems large, but it is almost
infinitesimal when compared to the number of possible dinosaur habitats that
probably existed during some 165 million years of dinosaur hegemony. Surely
you don't believe that the only compsognathids that ever existed lived
exclusively on the shores of the Solnhofen and Canjuers lagoons in the Late
Jurassic of central Europe, just where we'd find them 145 million years
later! And what about island endemic forms? There must have been dozens of
archipelagoes during the Mesozoic in which each island evolved its own
indigenous dinosaurian fauna.

Small dinosaurs existed in >droves<; footprint evidence of such forms is
accumulating by leaps and bounds (no pun intended). Dime-size theropod tracks
from Nova Scotia, tiny dino tracks in South Africa and Australia. Just ask
Martin Lockley, Tony Thulborn, or Adrian Hunt.

When it takes a whole field crew working for an entire summer to extract a
single good sauropod skeleton, or a summer's walking over hot desert sands to
find a few theropod bones, it is no wonder that the known dinosaur fossil
record is so sparse. We just don't have the manpower to prospect and excavate
all the known dinosaur localities, still less manpower to do the science of
describing and publishing. The number of new dinosaur genera described each
year presently depends less on Mesozoic dinosaur diversity that it does
simply on the the number of people working in dinosaurology. As long as each
new expedition to a previously unprospected locality brings back half a dozen
previously unknown genera, I think we're far from having plumbed the depths
of dinosaur diversity.