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RE: Greg Paul is right (again) - observational analysis and phylogenetics



  Just as an aside, only one of the mandibles of AMNH FR 619, holotype of 
*Ornitholestes hermanni*, is downcurved, and even then it's partially crushed; 
the other is intact and straight normally, and lacks Paul's hypothesized radial 
array of rostral teeth. It also lacks the "conical" teeth inferred to it by 
Paul, although the mesial dentition is broader across than distal dentition (so 
too are most dromaeosaurid premaxillary teeth!). *Ornitholestes hermanni* is 
currently under study by Norell (comm. to Carpenter, in Carpenter et al. 2005), 
so I hope the details will be more forthcoming later.

Carpenter, K., Miles, C., Ostrom, J. H. & Cloward, K. 2005. Redescription of 
the small maniraptoran theropods Ornitholestes and Coelurus. pp.49-71 in 
Carpenter (ed.) _The Carnivorous Dinosaurs_. Indiana University Press 
(Bloomington, Indiana, USA).

  The AMNH's digital specimen photographs include images of both mandibles, so 
it is easy to compare them, although my understand is that the material has 
been further cleaned since they were taken, almost 10 years ago. These images 
can be accessed at: 
http://research.amnh.org/paleontology/search.php?action=image_detail&specimen_id=147302#

Cheers,

  Jaime A. Headden
  The Bite Stuff (site v2)
  http://qilong.wordpress.com/

"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 
Backs)


----------------------------------------
> Date: Sun, 18 Sep 2011 16:56:14 +1000
> From: tijawi@gmail.com
> To: dinosaur@usc.edu
> Subject: Re: Greg Paul is right (again) - observational analysis and 
> phylogenetics
>
> (Sorry, I wrote this message a while back, but never sent it... so the
> thread is a little "stale".)
>
>
> Jason Brougham <jaseb@amnh.org> wrote:
>
> > In my mind cladistics is an effort to develop a system that is as explicit, 
> > quantitative, rigorous, revisable, and repeatable as possible. In my 
> > opinion the criticisms of cladistics - such as the assertion that
> > cladistics is vulnerable to errors caused by homoplasy - goes double for 
> > other methodologies, which usually resort to the best judgment of the 
> > worker, rather than anything repeatable or revisable by
> > better methods. Rigorous methods rescue us from the days when one 
> > paleontologist says that Archaeopteryx's femoral head is rotated 
> > anteriorly, and another expert says it isn't, and then that's that.
>
>
> It also rescues us from the days when purely intuition-driven
> evolutionary scenarios ruled. This was particularly prevalent when it
> came to reconstructing the evolution of birds. GSP still essentially
> adopts this approach, in (for example) deriving therizinosaurs from
> _Jeholornis_-like ancestors, oviraptorosaurs from _Sapeornis_-like
> ancestors, and deinonychosaurs from _Archaeopteryx_-like ancestors.
> That one phylogenetic analysis (Xu et al., 2011) recovered
> _Archaeopteryx_ as a basal deinonychosaur does not actually vindicate
> this wholly intuitive approach.
>
>
> Personally, I suspect therizinosaurs evolved from forms very similar
> to _Ornitholestes_: small head, downcurved mandible, weakly heterodont
> dentition, short metatarsus (leading to rather poor cursorial
> abilities). In fact, one day in the future _Ornitholestes_ may well
> be recovered as a basal therizinosaur. Similarly, compsognathids may
> well turn out to be basal alvarezsaurs (or to put it another way,
> alvarezsaurs will turn out to be derived compsognathians), which is
> another hunch of mine. However, current phylogenies do not back up
> either hypothesis. So although I might think my hunches are correct,
> phylogenetic analysis remains the final arbiter. If future analyses
> do in fact show _Ornitholestes_ to be closest to therizinosaurs, or
> compsognathids to be closest to alvarezsaurs, then it's not for me to
> claim credit on either score.
>
>
>
>
>
> Cheers
>
> Tim