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

RE: Ah ha! That's where therizinosaurs came from

Jason Brougham wrote:

<But cladograms don't tell us the actual ancestors. They tell us the
 sister groups, and if you found an actual ancestor, as improbable as 
that is, it would show up in a cladogram as a basal sister group. So, I 
guess, this debate is outside science. There is no rigorous or empirical
 scientific method that can demonstrate if an animal had a flying 
ancestor or not.>

  It has been argued, although I cannot exactly recall where, but Paul may 
actually have said this (_DotA_?), that we should be able to extrapolate an 
"ancestor" on the basis of inferences from the two sister taxa and the most 
restrictive node they share (because Paul eschews cladisitic terminology, I'm 
actually using my own words for the generalized concept here, which essentially 
argues that two relatives can present an ancestor by the fea6tures they share 
in common -- we would expect their ancestor to have them). Moreover, however, 
we can also take their next sister taxon and infer the features our two initial 
forms have that that ancestor lacks. This is essentially cladistics, an 
algorithm performed at each potential taxon+taxon<taxon junction. So it is in 
general part of the predictive element of Science to determine how we can know, 
even if we should not infer a true ancestor when considering phylogeny in 

  This becomes more complicated and less theorietical ancestral finding when 
one takes this practice to the hereditary level and looks at individuals or 
very small time scales, and has been adapted by workers looking at human 
ancestors. There is a tendency, as in the question of the origin and relations 
of *Australopithecus africanus*, *afarensis* and *anamensis* and the arising of 
*Homo*, to treat the taxa as parts of anagenetic lineages rather than sister 
taxa, and that many of these forms are segments along these lineages. This has 
been most extreme in attempting to determine exactly how one identifies *Homo* 
in the fossil record. In short, this is a conflict between cladistic methology 
(which removes the assumption of true ancestors) and heredity (which assumes 
they must actually exists and that we recover fossils of them). Both can be 
true, but the methodology of Science cannot easily distinguish them. This has 
recently been of some issue among the dinosaur community due to the work of 
Scannella and Horner, as they argue *Triceratops* includes all [or most] Hell 
Creek and equivalent (Lancian) ceratopsids from North America.

  Phylogeny reconstruction is actually very complicated, but 
ancestor-descendant relationships are not: one must be controlled by objective 
processes, while the other is based on subjective inferences. The relation 
between the two, evident no less in the *Triceratops* Lumping Event of 2010 
[and ridiculously overblown by some certain vociferous DML writer] is what I 
call "The *Homo* Problem" and I will eventually get back to this.

  Nonetheless, I must actually say the problem is (or can be) within Science, 
but that the situation has to be looked at in different ways. A position may be 
selected from among them, but it must be congruent with the data and be arrived 
at independently using the same methodology employed in the first case (or by 
the application of better predictive inferences). I do not think Paul's 
inference of flightlessness in taxa basal to the rise of birds (as recovered by 
cladistic analysis) is usefully scientific, simply because there is no way to 
distinguish the criteria employed, as I have said before and Jason (below) 

<It helped me realize that there is no single feature that is 
unambiguously associated with volant taxa. Not a furcula, not a 
triosseal canal, nothing. Rather it is more a matter of proportions 
between the elements: long arms, big pectoral girdles, etc.

Therefore we cannot prove that ratites had flying ancestors based on 
their skeletal morphology. Nothing in their skeleton proves that they 
don't retain the primitive condition of the avian lineage before they 
attained flight.>


  Jaime A. Headden
  The Bite Stuff (site v2)

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion