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RE: tiny-armed theropods



  ANSP 9259 has a peculiar morphology relative to other known troodontid taxa's 
dentition. In this, it is unique. It is, however, not unique to other known 
shed troodontid teeth for which no associated cranial remains are known, 
included dentaries with _in situ_ teeth. In named taxa for which teeth are 
known along with jaws, we have *Saurornithoides mongoliensis*, *Zanabazar 
junior*, *Sinornithoides youngi*, *Byronosaurus jaffei*, *Mei long*, 
*Sinovenator changii*, *Sinusonasus magnodens*, *Xixiasaurus henanensis* & 
*Talos sampsoni* (two loose teeth associated, but not _in situ_). In all of 
these taxa, the mesial margins of all teeth are smooth and nondenticulate. 
Aside from *Zanabazar junior* and *Saurornithoides mongoliensis*, the dentition 
for these taxa are also "high" in having an Fore-Aft Basal Length < Apico-Basal 
Height, while the aspect in these two taxa and in ANSP 9259 is much shallower 
(thus the tooth is closer to as evenly high as "long", or are "short").

  However, isolated teeth from the Dinosaur Park Formation are known with 
mesial denticulation, while a dentary with teeth from the Formation also bears 
mesial denticulation. The teeth in this jaw bear very rounded denticles, and 
this differs strongly from ANSP 9259, while the loose teeth do in fact bear 
some stronger resemblances to ANSP 9259, raising the plausibility of finding 
the same species (or close taxon) in both the Judith River Formation and the 
Dinosaur Park Formation. Despite this, differences in nondental remains make it 
difficult to infer precisely which of these remains the teeth belong to, and 
even Phil Currie (in his 1995 review of DPF teeth) admits this and uses the 
referral provisionally, which is how anyone else should (at the most) use it.

  So, if we were to regard *Troodon formosus* on the sole basis of whether it 
has an autapomorphy, then it is "valid." If we were to regard the value of 
isolated teeth as being useful for taxonomy, then it is "valid." If we were to 
regard the utility of referring skeletal remains to tooth-based taxa (TBT) 
without any form of overlap (a subject I go on at length in several posts: 
http://qilong.wordpress.com/tag/tooth-based-taxa/ [but especially the last 
one]) as problematic, however, as you cannot ensure or even qualify the remains 
in the same animal, then one should stop using *Troodon formosus* for the 
skeletal remains.

  As I said, and as Tim said, there is an "out:" Name a neotype. I do not think 
Mickey's "solution" (keep using it, disregard the quality of the argument of 
referral as material to the referral) is useful, although this is also the 
utility others have made (such as Julia Sankey), and it is largely 
conventional: Everyone else is still doing it, why can't I just trudge along in 
their footsteps? Because "everyone else" hasn't figured out that virtually all 
tooth-based taxa eventually die or are discarded: *Deinodon*, *Trachodon*, 
*Diclonius*, *Asiatosaurus*, *Astrodon* (although there's an attempt on 
Carpenter et al.'s part to re-use it), *Altispinax*, *Sinosaurus* (attempts to 
keep using it because it's one of them new-fangled "spinosaurs" seem to be 
cropping up), and so forth. *Troodon formosus* is a mystery, especially as it 
was heavily confused at a time when "saurornithoidids" were known with 
pachycephalosaur crania.

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)


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> Date: Sun, 16 Oct 2011 01:26:22 +0000
> From: keenir@hotmail.com
> To: tijawi@gmail.com; dinosaur@usc.edu
> Subject: RE: tiny-armed theropods
>
>
>
>
>
> > Date: Sun, 16 Oct 2011 12:13:00 +1100
> > From: tijawi@gmail.com
> > To: dinosaur@usc.edu
> > Subject: Re: tiny-armed theropods
> >
> > Mickey Mortimer <mickey_mortimer111@msn.com> wrote:
> >
> >
> > > I don't know where you got the idea that nomina dubia aren't taxa or 
> > > organisms. Troodon formosus is a real animal, diagnostic
> > > holotype or not. There was a living organism which the type tooth of 
> > > Troodon belonged to, and this individual can be included in a
> > > phlogenetic analysis, regardless of whether additional individuals could 
> > > be assigned to its species.
> >
> >
> > Of course the tooth of _Troodon formosus_ came from a real animal.
> > I'm not suggesting it was carved out of stone by Cretaceous trolls.
> >
> >
> > But if a genus is declared a nomen dubium, then it no longer denotes a
> > real taxon. For example, the teeth named _Deinodon horridus_ (a nomen
> > dubium) could belong to any number of tyrannosaurid species. So
> > although the teeth came from a real individual, that individual does
> > not represent a distinct taxon. Thus, it would serve no purpose to
> > code the teeth and put them into a phylogenetic analysis. Yes, you
> > *could* put _Deinodon_ into a phylogenetic analysis. But it's like a
> > dog chasing a car: it can be done - but what's the point?
>
> Let me make sure I understand this: the type tooth _Troodon formosus_ is not 
> the same as other known Troodon teeth (while being a likely member of the 
> Troodont group)...
>
> ...yet despite its differentness, we shouldn't call it distinct? Or we 
> shouldn't pay it any attention? (and if we're not going to bother with it, 
> why not just sell it and the other nomia dubia - we already know there's a 
> market)
>
> I think I lost track of the thrust of the argument a few posts back.
>
>
>