Path: news.ucalgary.ca!news
From: macrae@geo.ucalgary.ca (Andrew MacRae)
Newsgroups: talk.origins
Subject: new "transitional fossil" brachiopod
Date: 23 Aug 1996 05:15:22 GMT
Organization: The University of Calgary
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Reply-To: macrae@geo.ucalgary.ca
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	I know, I know.  Brachiopods just are not as sexy as vertebrates,  
but bear with me for a moment.

	For many years, I have been familiar with an usual brachiopod from  
the Permian that is particularly common at localities in the fossil reefs  
of the Glass Mountains of Texas.  This area is famous for its silicified  
fossils in limestone.  This preservation mode allows the extraction of  
perfect, delicate specimens of invertebrate fossils by dissolving away the  
limestone with hydrochloric acid.  It is really beautiful stuff.  The  
brachiopod found at this location is unusual because it is so atypical in  
morphology.  Instead of having two approximately equal valves (i.e. the  
two halves of the shell, superficially like a clam) hinged together, with  
an attachment point (the pedicle) at one end, these brachiopods have  
developed into a bizarre, elongated, cylindrical or cone shape.  The  
lower, cone-shaped valve is encrusted on other reef material by elaborate  
spines, and the upper valve is much reduced, and forms a lid for the  
"cone".  Inside the lower valve, there are a variety of other strange  
spines that seem to be related to filtering water currents.  If I handed  
you a specimen, you would probably think it was a solitary coral before  
thinking it could be a brachiopod.  They are as weird as an example of  
brachiopods as bats or whales are as examples of mammals.

	This group of brachiopods is known as the superfamily  
Richthofenoidea.  They are most diverse in the Permian, and a few are  
known earlier, from the late part of the Late Carboniferous (i.e. Late  
Pennsylvanian).  They have clear similarities to a large group of  
brachiopods known as the productids, currently the Suborder Productidina,  
which is within the Order Strophomenida.  Historically, the origins of the  
richthofenoids has been cryptic, and no "transitional forms" to the  
immediate ancestor of the group were known, although several authors  
placed the ancestry within the relatively "normal-productid-looking"  
family Aulostegidae based upon certain morphological similarities.  The  
problem with that proposal was that the Aulostegidae occurred a bit  
younger than the first appearance of the first of the true  
richthofenoideans (gasp!).  This problem was solved in 1988, when older,  
late *Early* Carboniferous (i.e. Late Mississippian) genera of  
Aulostegidae were discovered, but this left the problem of documenting the  
transition itself.

	Enter the new discovery:

Sutherland, P.K., 1996.  _Ardmosteges_orchamus_ new genus, new species, in  
the Early Pennsylvianian of Oklahoma -- possible ancestor to the  
richthofenoid brachiopods.  Journal of Paleontology, v.70, Supplement to  
no.2, part 2.  The Paleontological Society, Memoir 46, p.1-25.

	This thing is *so* cool.  Sunderland describes a new genus which  
occurs, temporally, between (early Late Carboniferous/Early Pennsylvanian)  
the older known Aulostegidae and the first appearance of the true  
richthofenoids.  It *combines* features of the conical shape of the  
richthofenoids with more ancient productids that have a more "normal"  
brachiopod shape.  In its early growth stages, _Ardmosteges_orchamus_  
looks just like an ordinary productid brachiopod with close similarities  
to the Aulostegidae.  Looking at the illustrations of the juveniles, you  
would never know how weird this thing was going to turn out.  It looks  
like a "normal" productid.  As growth proceeds, the characteristic conical  
shape of the richthofenoids develops, right on top of the more  
unspecialized productid morphology! It is a "transitional fossil" even in  
a single specimen :-), and it also shows the importance of developmental  
clues (i.e. ontogeny) in fossils for sorting out evolutionary history.  I  
have simplified the explanation a bit (particularly the taxonomy), so I  
recommend taking a look at the paper if you are interested in the details  
and pictures.

	Okay, so maybe this isn't as familiar as land mammals to whales,  
but this *is* a major morphological change, and this new species documents  
a transition at approximately family or suprafamily grade (in current  
classifications, at least).  The richthofenoids are truely bizarre as  
brachiopods go, and they were a major, diverse group in the Permian.  No  
one could claim that this is a trivial morphological change, even if it is  
still "just a brachiopod" :-)  Are these things two different "kinds" in  
the sense that some creationists attempt to use the term?  You got me.   
But it is evidence for evolution, and evolution did predict, by a few  
years, a connection between the richthofenoids and older productids,  
specifically productids in the family Aulostegidae.

--

	-Andrew
	macrae@geo.ucalgary.ca
	home page: http://www.geo.ucalgary.ca/~macrae