RE: Pegomastax, new heterodontosaurid from South Africa in new Sereno monograph (free pdf!)

[Jaime Headden <qi_leong@hotmail.com>]

  There remains a systemic problem, although not as deep as others, in 
regarding "nomina dubia," either by name or by concept. Primary among them is 
the problem of how one treats taxa one disagrees with as being "important" or 
"distinctive," whether by a suite of "distinctive apomorphies" or by the 
presence of "autapomorphies" (either absolutely unique, or inferred from 
closely-related taxa and a phylogenetic scheme); and there are the problem 
inherent when one declares a taxon "non-useful" when it is comprised of a 
"brevity" of material -- say, just teeth -- without qualifying these examples. 
Indeed, the very problem involved is that qualification never precedes a 
diagnosis of a taxon as "non-useful" or specifically as a "nomen dubium:" The 
argument is made, it is defined in the broad sense, so that the researcher may 
then proceed on, but specific applications always tend to be made "off the 
cuff," when subjective decisions forming the qualification of a taxon as such.

  I may not be extremely articulate about this subject, despite writing posts 
on my blog about it, but think so far that the message is clear _in general_: 
the subjectivity of determining as "not useful" material is never a very good 
one, and it is applied liberally and often. I argue that it should stop, as it 
does not promote information or communication, nor does it promote 
investigation save to have other researchers simply "disagree" -- which is what 
responses usually amount to.

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: Wed, 3 Oct 2012 13:12:38 -0700
> From: mickey_mortimer111@msn.com
> To: dinosaur@usc.edu
> Subject: RE: Pegomastax, new heterodontosaurid from South Africa in new 
> Sereno monograph (free pdf!)
>
>
> And here I thought Butler was redescribing heterodontosaurids...
>
> In general, this is an excellent paper with numerous useful photographs and 
> illustrations (well, besides the bobble-headed Tianyulong- 
> http://www.pensoft.net/J_FILES/1/articles/2840/export.php_files/ZooKeys-226-001-g030.jpg).
>   But I can't wrap my head around Sereno's dismissal of Geranosaurus-
>
> "Geranosaurus atavus, nonetheless, differs in several regards from 
> Heterodontosaurus tucki, which also occurs in the Clarens Formation, and from 
> heterodontosaurids from the underlying Upper Elliot Formation. The dentary 
> tooth row in Geranosaurus atavus appears to be composed of eight subequal 
> postcaniniform teeth arranged along a medially bowed tooth row (Fig. 2B). In 
> Heterodontosaurus, in contrast, there are 11 or 12 dentary teeth that 
> increase in size toward the center of a relatively straight tooth row. 
> Abrictosaurus also has a higher tooth count and size differential along the 
> dentary tooth row, as well as a relatively smaller caniniform tooth. Unlike 
> Heterodontosaurus and Lycorhinus, a postcaniniform diastema is not present in 
> Geranosaurus atavus, as the second tooth positioned adjacent to the 
> caniniform tooth (Fig. 2B). Crompton and Charig (1962) cited the absence of 
> an arched premaxilla-maxillary diastema in Geranosaurus atavus to 
> differentiate Geranosaurus atavus, although this portion of the upper jaw 
> does not appear to have been preserved.
>
> Recently Norman et al. (2011) concluded that Geranosaurus atavus cannot be 
> distinguished by a “unique combination of characters”. Although not adequate 
> to justify taxonomic recognition, the features exhibited by Geranosaurus 
> atavus and discussed above clearly suggest there is a second 
> heterodontosaurid taxon in the Clarens Formation in addition to 
> Heterodontosaurus tucki."
>
> So it's distinctive from other heterodontosaurids and already has a name, yet 
> it is "not adequate to justify taxonomic recognition."  Er...
>
> Mickey Mortimer
>
> ----------------------------------------
> > Date: Wed, 3 Oct 2012 09:19:17 -0700
> > From: bcreisler@gmail.com
> > To: dinosaur@usc.edu
> > Subject: Pegomastax, new heterodontosaurid from South Africa in new Sereno 
> > monograph (free pdf!)
> >
> > From: Ben Creisler
> > bcreisler@gmail.com
> >
> > A new taxon in a new monograph at ZooKeys site. The pdf is free!
> >
> > Paul Sereno (2012)
> > Taxonomy, morphology, masticatory function and phylogeny of
> > heterodontosaurid dinosaurs.
> > ZooKeys 224: 1-225.
> > doi: 10.3897/zookeys.224.2840
> > http://www.pensoft.net/journals/zookeys/article/2840/taxonomy-morphology-masticatory-function-and-phylogeny-of-heterodontosaurid-dinosaurs
> >
> >
> > Heterodontosaurids comprise an important early radiation of
> > small-bodied herbivores that persisted for approximately 100 My from
> > Late Triassic to Early Cretaceous time. Review of available fossils
> > unequivocally establishes Echinodon as a very small-bodied,
> > late-surviving northern heterodontosaurid similar to the other
> > northern genera Fruitadens and Tianyulong. Tianyulong from northern
> > China has unusual skeletal proportions, including a relatively large
> > skull, short forelimb, and long manual digit II. The southern African
> > heterodontosaurid genus Lycorhinus is established as valid, and a new
> > taxon from the same formation is named Pegomastax africanus gen. n.,
> > sp. n. Tooth replacement and tooth-to-tooth wear is more common than
> > previously thought among heterodontosaurids, and in Heterodontosaurus
> > the angle of tooth-to-tooth shear is shown to increase markedly during
> > maturation. Long-axis rotation of the lower jaw during occlusion is
> > identified here as the most likely functional mechanism underlying
> > marked tooth wear in mature specimens of Heterodontosaurus. Extensive
> > tooth wear and other evidence suggests that all heterodontosaurids
> > were predominantly or exclusively herbivores. Basal genera such as
> > Echinodon, Fruitadens and Tianyulong with primitive, subtriangular
> > crowns currently are known only from northern landmasses. All other
> > genera except the enigmatic Pisanosaurus have deeper crown proportions
> > and currently are known only from southern landmasses.
> >
> > new release with video:
> > http://phys.org/news/2012-10-fanged-dwarf-dinosaur-southern-africa.html
> >
> > (NOTE: One glitch in the name : mastax "jaw" is feminine in Greek so
> > the name should be Pegomastax africana to follow the letter of the
> > rules.)
>