[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

BIRD STUFF AND CLADISTICS




<<I think Ax or something very shortly before gave rise to all birds 
plus the troods, ornithos, tyranns., ovis, droms, avimimids & 
alvarezissississids.>>

Must I emphasize again that _Archaeopteryx_ is too apomorphic to give 
rise to all of these creatures?  Now, I am not a strict cladist (though 
I may be using cladistics in a bird paper in prep), and I am aware that 
there are some things that cladistics cannot account for.  Hell, 
EVERYTHING has its weaknesses.  I would be the first person to tell you 
that a given opinion is full of horse feces because it clashes with 
something physiological, anatomical, or biomechanical in a certain 
group, but these instances are few and sometimes non-existent.  Let me 
use an example of the usefullness of cladistics in anseriform 
(waterfowl) evolution:

In the field of avian systematics there are two groups: the intuitive 
school spear-headed by Storrs Olson and Alan Feduccia and the cladist 
school led by most everyone else.  The intuitive school denounces 
cladistics because they view that certain fossils cause fundamental 
problems (the old 'fossil-mosaic' buga-boo).  As listed by Livezey 
(1997) the intuitive school is characterized by: "a) failure to provide 
a phylogenetic tree with explicit documentation of supportive 
characters, most failing even to provide an intuitive tree or a complete 
compilation of the characters for the taxa compared; b) comparatively 
heavy reliance on a few characters, typically predicated on assumptions 
of function and convergence, as opposed to a phylogenetic consideration 
of the totality of evidence; c) variable reliance on antiquity of 
fossils as indicative of primitiveness and time of divergence; and d) 
phenetic assignment of fossils to an existing or a new, phenetically 
sequenced, higher taxon" Livezey; 394.  Sounds oddly familiar, does it 
not?  

As Livezey ably shows, the intuitive school with their approach failed 
on many points on the classification of the weird anseriform (not so 
weird anymore!) _Presbyornis_.  Olson and Feduccia considered 
_Presbyornis_ to be a primitive anseriform because it shares many 
characters with shorebirds (Chradriiformes).  As Livezey (and later in 
the same issue, Ericson) show, _Presbyornis_ is almost certainly not a 
basal anseriform but a sister-group of the Anatidae!  (To those who 
don't know much about anseriform evolution, the widely held arrangement 
goes: (Anhimidae (Anseranatidae (Anatidae))).  This conflicts with the 
intuitive approach and shows rather convincingly that phylogenetic 
systematics is more reliable in producing phylogenies.  

Also related to this issue, Presbyornithidae and Anseranatidae (magpie 
goose) are to the first two anseriform to appear in the fossil record 
(around 70 million years; I think that there may be some Anatidae 
material from late K too) while the more basal Anhimidae (screamers; 
very similiar to fowl) doesn't appear until the Eocene!  That's one hell 
of a gap.  (I think that Thomas Stidham is working on fossil anseriforms 
and has produced phylogenetic results similiar to Ericson and Livezey).  
Galliforms (fowl) appear in the Cretaceous but are rather fragmentary so 
you can dispute this the way that John Jackson does and argue that more 
derived anseriforms (Anatidae, Presbyornithidae, Anseranatidae) appeared 
first and led to Anhimidae which led to Galliformes (which I think are 
the nearest relatives to anseriform now).  So it goes like this:

Rather than Galliformes->Anhimidae 
(+Diatrymidae?)->Anseranatidae->Presbyornithidae->Anatidae

...the phylogeny based on morphology and most widely accepted...  (And 
remember, Presbyornithidae and Anseranatidae, which are related to 
Anatidae, are late K while Anhimidae and Diatrymidae, which are very 
galliform-like, are late Paleocene and early Eocene, and galliforms, 
which may or may not appear in the late K are found undisputedly in the 
early Eocene.)  

...the approach that is used by John Jackson makes this cladogram (which 
is concordant with the fossil record)...

?Charadriiformes->Presbyornithidae+Anatidae->Anseranatidae->Anhim-idae?+Diatrymidae->Galliformes

...but is less likely based on nearly all neontological evidence.  

  (True, this isn't exactly the same as what Jackson proposes, but it is 
a similiar argument based on similiar priniciples such as time, many 
reversals based on behavior, etc.  Care to answer John?)

<<This group minus obvious birds I will refer to as the K2FP's 
(Cretaceous secondarily flightless pinnants).>>

Must we march into another debate on this issue?  _Archaeopteryx_ is too 
apomorphic and similiar to later birds to be ancestral to the 'K 
theropods'.  I don't care whether or not all things are related to 
function or not, the K2FP scenario requires too many reversals.  Look at 
giant birds; some are extremely apomorphic in matters of diet and 
behavior, but there are no huge reversals regarding large complexies of 
characters.  

<<What is indisputable is that the stratigraphy is circumstantial 
evidencepointing just one way.  People who love money pay others to take 
polls you know, so statistics must have something going for it!>>

Use your statistics on my scenario above.  

<<It depends which bird-like theropods you mean.  The ones you mention 
here are quite bird-like and I would agree they are the sister taxa to 
birds, but the ones I'm refering to are the K2FP's (see above).>>

Some of these taxa are considered members of some of you 'K2FP's.  There 
really are no great differences between these groups and the 'K 
theropods'.  

<<I've made that abundantly clear in the past and it's spelt out in my 
website.>>

Whether I agree with your viewpoints or not, the website is very good!

<<As for the drom. teeth, Chris Brochu told us that the croc. lines, 
which are much less disputed than theropods, allow us to say with some 
confidence that teeth are not particularly reliable as diagnostics, at 
least for crocs.>>

Croc lines are less disputed than theropods?!  OK, maybe not to the same 
extent, but there are many issues that are in dispute.  

Well, here's my two cents.  In hopes of an open-scientific debate, fire 
away and tackle my anseriform problem!

Matt Troutman 
m_troutman@hotmail.com


______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com