re: Ptero embryo, PS

["Jaime A. Headden" <qilongia@yahoo.com>]

David Peters (davidrpeters@earthlink.net) wrote:

<Just checked the minimum egg diameter (41mm) with the pelvis of
Haopterus.
 
The egg is twice as deep as the pelvic opening.>

  The current diameter of the eggshell is a function of crushing: it is
likely the "living" embryo would have a diameter of much less than 4cm.
The pelvis of *Haopterus* also suffers from crushing, and reconstructions
should not be used to imply maximum depth, especially when the ischia in
most pterosaurs do not touch, possibly increasing the size of the cloaca
or anus. In fact, this has been suggested (at least onlist) as a relation
to laying large eggs or giviung large babies a push out. However ... there
are also eggshell fragments associated, which would seem to contradict the
finding of neonates (especially since no one else has been able to). The
organism is a embryonic pterosaur with ossified bones, as would be
apparent, also known in other fossil embryos of sauropsidan nature,
including ichthyosaurs, dinosaurs (hadrosaurs, oviraptorids, troodontids
apparently, and one referred to *Lourinhanosaurus,* an allosauroid or
"megalosaurid"), suggesting that any neonate will begin to ossify their
bones. This occurs in the bracketing species, as turtles, snakes, and
crocs also have ossification occur in their neonates, largely due to fact
(I am sure) that their young are precocial. Hadrosaur embryos, on the
other hand, while having ossified bones, typically lack ossified
epipophyses, indicative of altriciality, as occurs in some birds, but not
all. They still have ossified bones. There would be no reason, based on
the multitude of preservation of sauropsidans in the fossil record for
embryos, for the young not to have ossified bones. This would seem to
speak against the finding of neonates and a preponderance of females in
the fossil record of pterosaurs preserved in various lagerstätten.

  A perspective on viviparity:

  Among living amniotes today, only mammals consistently give live birth;
and in that, only _therian_ mammals give live birth, whereas monotremes
lay soft-shelled eggs. In sauropsids, rather than synapsids, the case is
narrower, as live bith has been observed in SOME snakes, but certainly not
a majority of them, including some booids, viperids, elapids, etc. Though
the latter two belong to a single monophyletic clade, along with colubrids
(Elapoidea), the basal members and the universality of them do no give
live birth. No crocodile, turtle or bird gives live birth. This would seem
to argue that if Pterosauria is part of any clade of Archosauromorpha, it
should not be prone to live birth.

  The finding of IVPP V13758 provides several adequate tests to the
discovery of neonates in the Bavarian and Jehol lagerstätten:

  1) it preserves ossified bone structure - none of Dave Peters' specimens
     preserve any identifiable ossification.
  2) it preserves eggshell - none of Dave Peters' identifications are
     considered to have been hatched, but rather to have been "born" or
     "expelled" post-mortem.

  The fact that after so many specimens have been recovered and this is
the first identified embryo with eggshell can offer that the event of
embryos being put into the fossiliferous beds is rare enough, arguing
against Peters' finding of neonates associated with so many specimens,
many of these specimens the only ones of their species identified. While
Wang and Zhou (2004) do not refer the embryo to any species -- they only
suggest that it is most similar to *Haopterus,* but not _why_, as much as
they also offer features that suggest it can be referred to
Ornithocheiridae ("relatively short metatarsals [less than 25% of the
length of the humerus] and the rounded, flange-shaped deltopectoral crest
of the humerus") -- it is important nonetheless without identification to
any particular species. It is also unlikely that, as was implied for
*"Pterodactylus" elegans* (which I think is what Wang & Zhou are
indicating as the smallest *Pterodactylus* juvenile), this animal could
fly, and that it reflects the logical absence or extreme rarity of such
small individuals from the fossil record.

  Based on this, I would offer that the embryos of pterosaurs would most
likely be ossified, and hatched, rather than would have been born live.
The absence of a skull in the specimen is indicative of it's fragility, as
parts may be present, yet unindentified, and that the specimen may have
been broken open prior to burial, causing loss of elements. OR ... the
material was unossified, which is unlikely, but possible (skulls and limb
bones usually ossify at the same time, or the skull prior to the limbs, in
most amniotes).

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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


        
                
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