[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]


 My response to Matt Troutman (my original quotes >>)

>>How would you account for the "pneumatic foramina", the hollow bones
>>that are virtually identical in both birds and pterosaurs? And the
>>braincase being "avian" in character? I suppose you think that these
>>also were the result of convergence?

>As Terry Jones pointed out to me long ago, pterosaurs, unlike birds,
>seemed to not have pneumatopores in the limb bones but only in the
>elongate finger bones.

Not according to Seeley, as noted in his book "Dragons of the Air".He notes
that unlike the Dinosaurs, where pneumatization only occurs in the spinal
column, ..." while Birds and Pterodactyles have the pneumatic condition more
conspicuously developed in the limb bones."
He goes on to say..."The holes by which air enters the bones are usually
much larger in Pterodactyles than in Birds, but the entrance to the air cell
prolonged into the bones is the same in form and position in both groups. So
far as can be judged by this character, there is no difference between them.
The importance of the comparison can only be appreciated by examining the
bones side by side. In the upper arm bone of a bird, on what is known as the
ulnar border, near the shoulder joint, and on the side nearest to it, is the
entrance to the air cell in the humerous. In the Pterodactyle the
corresponding foramen has the same position, form, and size, and is not one
large hole, but a reticulation of small perforations, one beyond another,
exactly such as are seen in the entrsance to the air cell in the bone of a
bird, in which the pneumatic character is found."

>This is rather unlike the avian system of
>pneumatization and suggests that pterosaurs did not hollow out bones
>through their respiratory system, but rather some other way.

"Seeley showed that these holes in the bones of pterosaurs were not merely
air spaces, but pneumatic foramina, structurally inseparable from those of
birds;and he drew the (then) logical inference that they were for admission
of respiratory surface into the limb bones...." (K. Padian-"A functional
analysis of flying and walking in pterosaurs" Paleobiology 1983)

>even if true, it can be considered a flight adaptation because it can
>obviously lighten weight to a point. Interestingly, early birds seem
>not to excavated their limb bones with pneumatopores, this development
>seems to be a strict ornithurine or even neornithine character.

Even among modern birds, this feature is exhibited to less extent in some
groups,...(could be a secondary loss of function).

>Pterosaur braincases have never to my knowledge been considered "avian".
>The only obvious avian character is the inflation of the braincase, but
>this is not as well developed as in theropods. Pterosaurs seem to lack
>the characteristic three tympanic recesses of birds and theropods and
>convergently crocodylomorphs. This is not to say that the recesses were
>a later development, but it seems likely that these are primitive avian
>characteristics since they are present in _Archaeopteryx_.

I`m a bit vague on how comparisons are made via braincase structure, or what
about behavior can be determined from such evidence. I`ll just reiterate the
position of Tilly Edinger on this subject (as quoted from Wellnhofer`s
"Prehistoric Flying Reptiles"). "Tilly Edinger`s research showed that, even
in the upper Jurassic, pterosaurs had developed brains that were more like
those of birds than the brain of their contemporary, the 'primordial bird'
Archaeopteryx. Thus the pterosaur brain was by no means reptile-like and
small, as in modern crocodyles and lizards, but closer to that of a bird in
shape and size. This was an important prerequisite for flight control and

>Yes, I do think that these characters do not link pterosaurs and birds
>any more than they can link any other two disparate groups. These two
>characters are poorly described and do not show a distribution that
>makes them likely as synapomorphies of the pterosaur-bird clade. Hell,
>even Haematothermia has more osteological characters of greater weight
>than these.

There are other structural characteristics in common involving posture and
the advanced mesotarsal ankle joint (which I believe only evolved once).
These I didn`t mention because it could be argued that they were primative
to the Theropod group that allegedly gave rise to both birds and pterosaurs,
..except that I believe it started in the Pterosaurs and was passed down to
both avian and theropod descendants. If you need to view even more
characters that show the closeness between Pterosaurs and Birds, you can
check out K. Padian`s paper "The Origen of Pterosaurs" (1984), where even he
makes the statment..."The detail of many resemblances between pterosaurs and
modern birds is uncanny..."  (Although I don`t doubt that from his position,
he would argue that what couldn`t be derived from early theropods, would
have to be a convergent development of some sort, and in this I wouldn`t

>>That birds hit on the same idea,... to hollow out the bones and make
>>them part of the respiratory system? ( to me...also a somewhat complex
>>development). The more points you claim are convergent, the less likely
>>I am to believe it

>Convergence happens. As Darren Naish (actually Michael Lee) pointed out
>a few days ago, snakes and amphisbaenians and dibamids converged on each
>other because limblessness and burrowing habits. Amphisbaenians could
>be the sister group to snakes, they do show some scolecophidian
>characters, but this relationship is far outweighed by the 40 odd
>characters linking snakes and mosasaurs in Pythonomorpha. To avoid this
>convergence, all we know about scincomorphs, thecoglossids, platynoans,
>and varanoids we have to be turned around. Convergence happens.

I`m sure Feduccia would agree....He`d say that all "avian" traits in
Dinosaurs are convergent!
Seems to me that we had better come up with definative answers as to what
exactly constitutes "Convergence", so that it`s not used as a "catchbasin"
for whatever we cannot fit into our Phylogenetic sequences!

>>I believe the common ancestor was small, insectivorous (small
>>cranium), had furcula as well as acrocoracoid process (enabaling rapid
>>wingbeat allowing for controlled perched landing), typical pterosaurian
>>flight membrane along with (of course) integumentary fibres

>Early birds (_Archaeopteryx_) and avian relatives (dromaeosaurs,
>_Protarchaeopteryx_, _Caudipteryx_) lack a true acrocoracoid process
>(they had the precursor, the biceps tubercle of Walker).

Archaeopteryx also had no keeled sternum, and only some seemed to have a
furcula, this could mean that Archie was on the road to becoming secondarily
flightless....others have said as much.

>In fact, early birds do not have the elongate coracoid in the manner of
>pterosaurs. Your character of the elongate coracoid shared between the
>two groups is more likely a convergent adaptation since basal birds lack
>this character (unless they lost it convergently). The elongation of
>the coracoid, as shown ably by Tarsitano in the Archae. Conf. Volume
>(1985) is a character related to the deepening of the thorax for various
>reasons related to flight. The supracoracoideus wing abductor system
>(which is rather different in the two groups) is related to the
>elongation of the coracoid according to Tarsitano.
>Matt Troutman

Again,...could be related to degree of flight ability in general, becoming
secondarily less adept at flight in these species.
Larry Febo