how many species

[Nick Longrich <longrich@alumni.princeton.edu>]

>  >>I don't believe _Wellnhoferia grandis_ is a valid genus - just a large
> specimen of _A. lithographica_.  Elzanowski is of the opinion that multiple
> archaeopterygid species inhabited the Solnhofen.<<
>
> And why not? There are different types of gulls and terns in the same area.
> Also, not all the Solnhofen specimens come from the same beds.

	A good point. Where i live, we've got the northwest crow, 
raven, and the magpie; I wonder if modern paleontologists would just 
throw them all in one species as a "growth series". Looking at modern 
ecosystems one would expect to get several or many different species 
which would be subtly different if not almost indistinguishable.
	For that matter, would you expect that in the length and 
breadth of the entire Morrison Formation you would have just one 
species of Allosaurus and one species of Ceratosaurus? Admittedly 
species diversity decreases with size, but if you look at North 
America's carnivore diversity before humans arrived:

FELIDAE: bobcat, cougar, jaguar, Panthera leo atrox(extinct) and 
Smilodon(extinct).

CANIDAE: red fox, grey fox, arctic fox, kit fox, coyote, wolf, dire 
wolf(extinct)

URSIDAE: black bear, brown bear, polar bear, short-faced bear(extinct)

Now I REALLY don't want to get into another debate over the 
biological reality or otherwise of species, BUT-

	It might be expected that you'd have a couple of species of 
theropod per family running around at any given point, furthermore if 
you sampled over time, as ranges expanded and retreated, you might 
detect even more species, say three or four in deposit, even though 
only one or two lived there at any given time. Furtherfurthermore, 
you'd have extinction and origination of species every however many 
million years, so the longer you sample the more species you're going 
to get.
	Looking at the fossils, you've got a bunch of Ceratosaurus 
specimens which do show real differences. I suppose this could be 
individual variation, but wouldn't between-species differences be 
pretty subtle? I haven't personally tried, but I suspect that sorting 
out, say Corvus corax, Corvus brachyrhynchos and corvus caurinus 
would be a real bitch. How many paleontologists would just knowingly 
say, "Individual and sexual variation, yep." I doubt Ceratosaurus' 
differences are sexual since the type and the two animals illustrated 
by Madsen are all robust, and furthermore C. magnicornis is pretty 
darn big but as illustrated by Marsh, the sutures in the skull of the 
smaller holotype are pretty well fused up, seemingly indicating that 
this was a fairly mature animal. We're not really sure what the 
patterns of fusion are in individual theropod species though, let 
alone how they vary across species.
	As for Allosaurus, Britt has noted that the stuff in the Dry 
Mesa quarry is much more robust for the same length of element than 
the stuff in the Cleveland-Lloyd Quarry; also he notes that all the 
CLDQ stuff has blunt apices to the lacrimal horns, whereas the Dry 
Mesa critter has acutely pointed orbital horns.
	These are admittedly trivial variations. So is it just 
variation in a species? If you try field-identifying birds the 
differences are pretty trivial- a hoarser, croaking call sets the 
raven apart from the other birds, along with its larger size, its 
preference for soaring,  its spade-shaped tail, and its more solitary 
habits, Corvus caurinus likes to forage in tidepools and around the 
water for food, is smaller, flaps instead of soars, has a 
wedge-shaped tail and tends to be highly gregarious...
	similarly, if you sort salmon species the characteristics are 
equally trivial. Reds have a deep turqoise-blueish back (in the ocean 
phase), more hexagonal scales, a clear tail. Pinks have green backs 
and spots on the back and tail. Kings have silver and spots on the 
tail, besides getting huge (50+ lbs). Silvers and dogs are both 
large, both lack spots, both have silver on the tail, and are 
indistinguishable to the novice fisherman, but dogs have smaller 
pupils than silvers, and silvers have more silver on the tail and a 
fatter tailstock... I'm sure there are osteological differences too 
(average number of vertebrae, number of fin rays, number and size of 
gill rakers and teeth) but you see that separating species from 
species is a pretty tedious job which can take some experience (say, 
handling a few dozen each of silvers and dogs)  even with lots of the 
animal on hand- let alone with a few fragments of the skeletons of 
each.
	Then apparently some researchers have separated Sphenodon 
into two species, S. punctatus and S. guentheri, and although their 
morphologies overlap the mean morphology is significantly different 
and so are the genomes... also the question of how many species of 
Coelacanth there were was decided in a molecular lab, not by 
morphologists.

	Anyways, I'm beginning to think that if two dinosaurs come 
from widely separated areas and/or times, we should expect them to be 
different species. We should also expect to see multiple species 
within a family for a given deposit, and furthermore this should 
(following the general trend) increase with smaller body size. I'm 
not arguing to make every find a new species, but I don't think that 
a single species should be our working assumption for animals which 
come from different places and times and show different morphology. 
Looking at modern diversity patterns, three or four species each of 
Ceratosaurus, Archaeopteryx and Allosaurus seems perfectly possible 
to me; while a single species of Troodon (T. formosus) throughout the 
Late Cretaceous of North America seems just impossible- it'd be like 
having all the cats or canids in North America from the Miocene on, 
all in one species.