A Word on ABSRD (long)

["Tim Williams" <twilliams_alpha@hotmail.com>]

I hate to beat my own drum too much, but I?ve been asked (off-list) to 
please-explain what exactly I mean by ABSRD (Anything But a Small Running 
Dinosaurs).  How, for example, does it differ from BAND (Birds Are Not 
Dinosaurs).  Well, as advocated by Feduccia and others, it doesn?t.  At 
least not in my not-so-humble opinion.

There are two schools of thought on the origin of birds.  The first view is 
that birds evolved from small, bipedal theropods.  This is the view favored 
by most paleontologists who have worked with theropods and Mesozoic birds.  
The skeletons of such theropods suggest they were cursorial and 
ground-dwelling animals, although the possibility that some smaller 
theropods spent at least part of their lives in trees cannot be excluded.  
Among non-avian theropods, _Microraptor_ in particular shows good arboreal 
adaptations in its pes.

The other view, supported by Feduccia, Martin, Olson, and Ruben proposes 
that birds evolved from small arboreal diapsids in the Triassic.  On the 
identity of these ancestors, Feduccia and others are a little vague.  What 
is obvious is that Feduccia and others will consider almost any Triassic 
diapsid as possibly ancestral to birds, as long as it is (a) small in size, 
(b) shows arboreal adaptations, and (c) isn?t a dinosaur.  In the absence of 
an explicit proposed ancestor or sister taxon, I have termed this theory on 
bird origins ?Anything But a Small Running Dinosaur? (ABSRD).

If it isn?t clear by now  ;-) , I favor the theory that birds evolved from 
dinosaurs.  I give BAND/ABSRD short shrift.  If anyone is interested, here?s 
why.

As expressed by Feduccia, ?Anything But a Small Running Dinosaur? is poor 
science.  As a professional biologist who dabbles in evolutionary theory, I 
have a lot of problems with the methodology behind ABSRD/BAND.  You see, 
Feduccia have already made up their mind on how birds evolved: Birds evolved 
in trees and their ancestor had feathers, and any similarities between 
theropods and Mesozoic birds is due to convergence.  With this in mind, 
Feduccia and co then examine the fossil record and assess each fossil on the 
basis of how it ?fits? with their theory.

_Caudipteryx_ is a good example of this thinking.  According to recent 
cladistic analyses, _Caudipteryx_ is a basal oviraptorosaur and is 
positioned outside the Aves.  In other words, according to these analyses, 
_Caudipteryx_ is not a bird.  The existence of a feathered, ground-dwelling 
nonavian theropod is the kiss of death for Feduccia?s ABSRD model.  However, 
one DML list member, who happens to agree with Feduccia, told me (off list) 
that Caudipteryx is a bird because Feduccia has shown that the skull of 
_Caudipteryx_ has features in common with the skull of early 
enantiornithines.  Thus, _Caudipteryx_ is a secondarily flightless offshoot 
of volant enantiornithine stock.  Make sense?

Not to me it doesn?t.  After looking at the sum of _Caudipteryx_?s skeletal 
characters, Feduccia has chosen a certain subset of characters that are 
congruent with his theory on bird origins.  These are ?good? characters 
because they fit with his theory.  The other characters (such as the 
oviraptorid and nonavian characters of Caudipteryx) are ?bad? characters 
because they DO NOT fit with his model; they must be ?primitive? or 
convergent characters.  He has assessed characters as ?good? and ?bad? based 
on a preconceived theory and not based on anything resembling an objective 
analysis.  In assessing data, you have to look at ALL the data  ? and take 
the good with the bad.

This is where cladistics comes in.  Admittedly, cladistics is not perfect.  
Every time you crunch a matrix through PAUP (or whatever program you use) 
there?s no guarantee that it will spit out The One True Tree.  The fossil 
record has enormous gaps, so the data set is going to be very incomplete.  
And, of course, cladistics relies upon the principle of parsimony: the 
shortest route between two character states is assumed to be the most 
likely.  Nevertheless, it?s a good start.  Cladistics is a method by which 
we can attempt to determine which characters shared by a given group of taxa 
are due to shared ancestry and which are not (i.e. due to convergence).  
It?s a way of examining ALL the available data, and has as its basic 
principle the not unreasonable assumption that the more closely related two 
taxa are, the more characters they will have in common.  Assessing which 
features are primitive and which are derived, and which shared characters 
are due to shared ancestry and which are convergent, comes after the 
analysis has been carried out.

Proponents of ABRSD/BAND do not like cladistics.  ?Garbage in, garbage out? 
as Feduccia has described it.  But if a method gives you a result that 
conflicts with your theory, it may just be that the theory is flawed, not 
the method.  In the 25 years since Jacques Gauthier carried out a cladistic 
analysis of the Saurischia, cladograms of the Theropoda have not changed all 
that much.  There are a few differences of opinion among current theropod 
phylogenies (the position of the tyrannosaurids, alvarezsaurids, etc), but 
the overall topology of the Theropoda is still very much the same.  And how 
many new genera of theropods and Mesozoic birds have been described during 
that time??!!

Most published cladograms, such as those of Holtz, Sereno, Chiappe, Norell 
(and many others), have dromaeosaurids as closest to the origin of birds 
(Aves).  But, if a new specimen is discovered which results in, say, 
oviraptorosaurs being placed closer to the origin of birds than 
dromaeosaurids, then so be it.  Holtz and Sereno will not commit hari kari 
in shame nor be fired from their jobs (or at least I hope not, on both 
accounts).  It is just that an expanded data set, upon analysis, is 
producing a different signal.  Theropod paleontologists will not say ?We 
KNOW dromaeosaurids are closer to birds than oviraptorosaurs, so we can 
ignore characters in the oviraptorosaurs that show otherwise.?

Then there are the purely intuitive phylogenies, like the model proposed by 
Feduccia and others for the origin of birds.  The facts must fit the theory, 
not contrariwise as it should be.  This is why Feduccia has had so much 
difficulty finding a group that might be ancestral to birds.  In the quest 
for Anything But a Small Running Dinosaur as the ancestor of birds, some 
pretty unlikely critters have been proposed as ?relevant? to the ancestry of 
birds.  _Longisquama_ has recently been associated with bird origins on 
account of its putative furcula and superficially feather-like dorsal 
appendages (which are more likely to be unusual scales or skin membranes).  
This is despite the fact that there is no good evidence that _Longisquama_ 
is even an archosaur.  _Megalancosaurus_ was similarly proposed as a taxon 
close to the origin of birds because of its bird-like head, strap-like 
scapula and other superficially bird-like features.  But, again, this 
?analysis? of _Megalancosaurus_ simply plucked the superficially bird-like 
characters out of this taxon and ignored all the rest.  Feduccia?s ABSRD 
theory expects to find a small, arboreal non-dinosaurian proavian in the 
Triassic, so fossils of small, arboreal, non-dinosaurian animals from the 
Triassic are viewed accordingly to whether they might possibly be bird 
ancestors.  To me, this is like ramming square pegs into round sockets.

More seriously, ABSRD reminds me of those awful 18th and 19th century 
pseudosciences.  Phrenology is a perfect example.  As John van Wyhe recently 
said of phrenology ?? like so many popular sciences, Gall [Franz Joseph 
Gall, father of the ?science? of phrenology] and the phrenologists sought 
only confirmations for their preconceived hypotheses and did not apply the 
same standard to contradictory evidence.  Any evidence or anecdote which 
seemed to confirm the science was readily and vociferously accepted as 
"proof" of the "truth" of phrenology.  At the same time, contradictory 
findings, such as a very selfish and disagreeable person having a 
well-developed organ of Benevolence were always explained away.?

Pseudoscience, alas, is still with us.  The ABSRD origin of the birds is 
just another manifestation, one that has trickled into the realms of 
paleontology.

Thanks for tuning in.


Tim



------------------------------------------------------------

Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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