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RE: 2 questions: "horizon" in anatomy, and the absurd Nyctosaurus



Only chiming in on the distinction of some "crests" in pterosaurs.

Unfortunately, *Ornithocheirus simus* lacks an occiuput, though obviously Mark 
is referring here to *Tropeognathus mesembrinus* which is treated by some 
authors as being *Ornithocheirus mesembrinus* -- even if those same authors 
treat *Barsbosania gracilirostris* as distinct from *Brasileodactylus 
araripensis* despite they having even fewer differences.

The nubbin that extendes from the caudal margin of the occiput in 
*Tropeognathus mesembrinus* -- and some other skulls -- is not a crest like 
structure, but a nubbin that lies below the margin of the occipital rim or is 
flush with it, and in *Tropeognathus mesembrinus* especially involves a folding 
caudally of the dorsal part of the supraoccipital forming a sort of caudal 
fossa that was curtainly distinct from the dorsal margin of the skull. That is, 
it doesn't involve the parietals or frontals at all. This is very different 
from the morphology seen in the KJ1/KJ2 specimens, or *Ludodactylus sibbicki*, 
or indeed any dsungaripterid or azhdarchoid/tapejaroid you might consider, in 
which the supraoccipital only forms a ventral brace for the caudally and 
dorsally expanded frontoparietal.

The function of such a nubbin, rather than a crest, is likely associated with 
epaxial muscles, especially the splenialis and trapezius muscle complexes, as 
the nubbin is confluent ventrally with a median ridge that descends towards the 
foramen magnum even in very high occiputs (e.g., *Tapejaridae*), and the 
function of the muscles associated (including some portions of the M rectis 
capitis complex) are in pulling the head back relative to the body, and lifting 
the head relative to the axis. The purpose of the nubbin would then to increase 
the surface area of the muscle attachment without interfering in the surface 
area of adjacent muscles, while decreasing the lever arm and thus increasing 
force generated relative to energy required.

>From the appearance of *Pteranodontidae* and the nyctosaur skulls, the crest 
>and t
tle on the function of head to neck; but with "ornithocheirids" (bearing in 
mind that Rodrigues & Kellner have recently leveled a serious review that 
disfavors this term) this crest has more intimate relationship to these 
muscles, but almost no dorsal expression. Though only preserved in lateral 
view, the crest in *Ludodactylus sibbicki* doesn't appear to have much of a 
ventral component that one would associate with epaxial musculature, though 
*Pteranodon longiceps* does.

This suggests a far more complex arrangement of crest to occiput and thus the 
muscular relationships of the base of the skull, than has previously been 
noted. Functionality of these muscles in living animals, where larger 
components of epaxial musculature relative to hypaxial musculature exist, have 
suggested that head-lifting and manipulation with the head and a mobile neck 
are related to feeding (Snively et al., 2013: 
http://palaeo-electronica.org/content/2013/389-allosaurus-feeding; Habib & 
Godfrey, 2010) by the reduction of lever arms and increasing surface area for 
attachment, increasing mechanical advantage.

Habib, M. & Godfrey, S. 2010. On the hypertrophied opisthotic processes in 
*Dsungaripterus weii* Young (Pterodactyloidea, Pterosauria). Acta Geoscientica 
Sinica 31 (S1): 26-26. (Abstract)

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, 24 Nov 2013 10:41:11 +0000
> From: mark.witton@port.ac.uk
> To: dinosaur@usc.edu
> Subject: Re: 2 questions: "horizon" in anatomy, and the absurd Nyctosaurus
>
> "I would like to see intermediates as well."
>
> I guess we see variably developed supraoccipit
> ornithocheiroids (Ornithocheirus, Ludodactylus, Pteranodon). In some
> respects, the crest of Nyctosaurus is just a crazy version of the things we
> see in these animals. I agree with Mike about the weight. We don't often
> show pterosaur crests in anterior view in papers and documentaries, but
> they're mere millimetres wide and almost completely hollow. The weight of
> even a big crest would be pretty unsubstantial.
>
> Mark
>
>
> On 24 November 2013 10:32, Renato Santos <dracontes@gmail.com> wrote:
>
>> On 11/24/13, Hammer <hammeris1@att.net> wrote:
>>> Wiki? Really? I tend to avoid it (even though I edit many articles in
>> it)
>>> as it is thoroughly unreliable minute-by-minute.
>>
>> Really. The extinct archosaur articles tend to have good curation and
>> they usually list references you can obtain from the authors. You know
>> there's an edit history, right?
>> Failing that there are also previous discussions in mailing list
>> archives, http://dml.cmnh.org/ , say:
>> http://dml.cmnh.org/2003Aug/threads.html#00217 . Note that in this
>> area of science where it relates to the reconstruction of extinct
>> organisms answers may be a bit thin on the ground and when they exist
>> not particularly satisfactory depending on your mileage.
>>
>>> As far as the whydah bird,
>>> that's a tail, not a tree branch growing out of its head! :-) Thanks
>> for
>>> the clarification on the horizon term.
>>
>> All the same it's a structure that creates a handicap by its
>> proportional unwieldiness. Here's a recent review on sexual
>> selection:
>> http://www.rug.nl/research/theoretical-biology/_pdf/ku_eaarees12.pdf
>> . And you'll likely be able to obtain
>> http://www.sciencedirect.com/science/article/pii/S0169534712001875
>> from the authors.
>>
>> --
>> Renato Santos
>> http://dracontes.deviantart.com
>>
>
>
>
> --
> Dr. Mark Witton
> www.markwitton.com
> Palaeobiology Research Group
> School of Earth and Environmental Sciences
> University of Portsmouth
> Burnaby Building
> Burnaby Road
> Portsmouth
> PO1 3QL
> Tel: (
> If pterosaurs are your thing, be sure to check out:
>
> - Pterosaur.Net: www.pterosaur.net
> - The Pterosaur.Net blog: http://pterosaur-net.blogspot.com/
> - My palaeontological artwork: http://markwitton-com.blogspot.co.uk/          
>