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Re: Alternative origins of birds (humor) ... and Prum's feathers

Tom Holtz wrote:

Some of us have joked about a comic symposium for SVP called "Anything But
Dinosaurs: Alternative Hypotheses to Bird Origins". The goal was to come up
with the most outrageous alternatives to the dinosaurian origin, the weirder
the better.

I have heard on the grapevine that some Feducciary/ABSRD/BAND folk are taking another look at lagosuchians. Not all that weird though (at least when compared to frogs or _Lingula_... or _Megalancosaurus_). In fact, the rabbit-crocs are ominously close to dinosaurs (and ARE dinosaurs according to Greg Paul.)


Darren Naish wrote:

I think I agree with Tim as goes the evolution of flight and flight-
related structures.

Thanks; but after Primal Dude's cogent response, I now have second thoughts...

One of the most interesting things about the recent
Richard Prum work on feather evolution is that the morphology of his
earliest proto-feathers are not dependent on a functional framework -
viz., the earliest proto-feathers sensu Prum are not hypothesised with
either flight or insulation in mind. They could have had advantages to
either.

Prum has emphasized that his model is functionally neutral; but it is also most consistent with aerodynamic properties (which demand the most refined structure) appearing at the *end* of the evolutionary/developmental trajectory (contra Feduccia).

However... Prum does believe that the plumules (down feathers) of *modern birds* are simplified versions of the more complex flight feathers. (This is something Feduccia has used to argue in favor of flight coming *before* insulation as the function of feathers.)

With respect to down vs flight feathers of modern birds, Prum's model implies that insulatory feathers evolved twice:

(1) neormorphic(?) hairlike structures (later branched) in proavian theropods;
(2) flight feathers --> insulatory feathers in the line leading to modern birds

This second transformation represents an exaptive reversal. In other words, the down-like feathers of Liaoning non-avian theropods and the down of modern birds have different origins (though undoubtedly homologous in structure and probably analogous in function). This bamboozles me. Before reading Prum's paper I had thought that the down-like "fuzz" first evolved in non-avian theropods were retained by modern birds for the same purpose (insulation).

If Prum is correct, my guess is that some time on the direct line beween proavian theropods and Neornithes, insulatory feathers were lost and then re-evolved again. In this second time round, rather than being "re-born", the insulatory feathers were produced by "trimming-down" the contour (flight) feathers. This happened in the ancestor of all modern birds.



Tim


Mike's would have won by a longshot!! Other alternatives were 
turtles (present in the Late Triassic, and thus older than birds; have
modified cervicals; have toothless beaks; not dinosaurs), frogs (live in
trees; present in the Late Triassic; have synsacra; not dinosaurs), and the
inarticulate brachiopod Lingula (found in lagoonal sediments, like
Archaeopteryx; present in the fossil record much earlier than birds; has
long tail-like pedicle; maybe sprang out of the water and spin
helicopter-like to settle back down; not dinosaur).

The other comic symposium I came up with this year is "You Can't Handle The
Truth: Alternative Ecologies of Famous Fossil Forms".  The two talks
suggested so far is the reality that hadrosaurids were voracious predators,
from which the herbivorous tyrannosaurs had to run in terror; and the fact
that trilobites were NOT really marine bottom feeders but were in fact
flying terrestrial ravenous carnivores.  In fact, it turns out that
vertebrates had colonized the land very early in the Cambrian, but the
piranha-like feeding habits of the trilobites prevented from any of their
skeletons from making it into the fossil record.  Only after the decline of
trilobite diversity in the Frasnian-Fammenian extinctions (Late Devonian)
was the depredations of these forms reduced enough that we start to pick up
a better terrestrial vertebrate fossil record...

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796



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