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Re: External mandibular fenestra in basal pterosaurs



To clarify:

Bennett _argues_ that *Tawa hallae* and *Dromomeron* spp. are
synonyms. The perceived differences are chalked up to preservational
and implied ontogenetic variation in ossification. Bennett does not
actually cite works to affirm the ossification pattern in the femora
are explainable via ontogenetic variation, and this is a problem;
instead, he contradicts Nesbitt and Hone on the one hand, and Nesbitt
et al. (two works) on the other, regarding the three considered named
taxa.

To back this claim up, Bennett merely mentions the morphology of the
smaller femora seem more incomplete than that of the larger, but
placing these femora in series requires a more extensive analysis than
assertion. This is not going to be the end of it. Differences between
the femora include the holotype of *Tawa hallae* in the presence of a
basined "scar" around the insertion of the mCF on the femur, and a
distinct acuminate crest in all other considered femora. Some of these
ridges are in femora referred to *Tawa hallae*, but not part of the
holotype. One may be cautious by considering that referral of other
femoral to *Tawa hallae* is questionable, without assuming certain
other taxa are synonyms.

Solutions to this may include removal of femora and other material
from the hypodigm of *Tawa hallae* (consisting of paratypes) and
considering them in ontogenetic studies of greater depth, including
assessing properly features of histology. These things should be dealt
with prior to conflating issues of preservation, wear, with that of
lack of ossification due to immaturity.

On Tue, Jul 7, 2015 at 6:18 PM, Tim Williams <tijawi@gmail.com> wrote:
> Although this study is principally concerned with the phylogenetic
> position of pterosaurs, it also discusses the non-pterosaurian taxa
> _Tawa_ and _Dromomeron_.  According to Bennett:
>
> * _Dromomeron romeri_ and _Tawa hallae_ are conspecific, with the
> femora representing an ontogenetic series.  (The apparent absence of a
> fourth trochanter in the _Dromomeron romeri_ holotype is attributed to
> both its juvenile age and crushing.)  This taxon is a theropod.
>
> * _Dromomeron gregorii_ is a small basal dinosauriform, and is not
> congeneric with _Dromomeron romeri_.
>
>
>
>
> On Wed, Jul 8, 2015 at 1:23 AM, Ben Creisler <bcreisler@gmail.com> wrote:
>> Ben Creisler
>> bcreisler@gmail.com
>>
>> A new paper:
>>
>> S. Christopher Bennett (2015)
>> An external mandibular fenestra and other archosauriform characters in
>> basal pterosaurs re-examined.
>> Historical Biology 27(6): 796-814
>> DOI:10.1080/08912963.2015.1036257
>> http://www.tandfonline.com/doi/full/10.1080/08912963.2015.1036257#abstract
>>
>> It was claimed that pterosaurs had external mandibular fenestrae,
>> antorbital fossae and muscle scars homologous with the femoral fourth
>> trochanter of archosauriforms, and that those characters suggested
>> that the Pterosauria were within the clade Erythrosuchus +
>> Archosauria. Pertinent parts of available specimens are described to
>> confirm that one pterosaur had external mandibular fenestrae and one
>> had antorbital fossae. However, arguments are presented that
>> possession of external mandibular fenestrae does not support inclusion
>> of the Pterosauria within the clade Erythrosuchus + Archosauria and
>> that the antorbital fossae in the one pterosaur are not homologous
>> with those of the clade Erythrosuchus + Archosauria. Arguments are
>> also presented that the possession of a m. caudofemoralis scar by some
>> pterosaurs does not support inclusion of the Pterosauria within the
>> clade Erythrosuchus + Archosauria, whereas the lack of homologous
>> antorbital fossae and a mound-like or aliform fourth trochanter
>> supports exclusion of the Pterosauria from that clade.



-- 
Jaime A. Headden
The Bite Stuff: http://qilong.wordpress.com/


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