Re: Tanystropheus egg question (long but perhaps a bit explanatory)

["silvio.renesto" <silvio.renesto@uninsubria.it>]

Dear all,

 having actually seen most specimens, I dare to put my two cents to this 
interesting thread:

to my knowledge, no Tanystropheus specimen can be considered an hatchling.
Even the smaller among the so-called "juveniles" show fully ossified tarsal 
bones, stiffened necks and rather large size for an hatchling .
It is quite feasible, however,  that very young prolacertiformes had 
proportionally much shorter and less rigid necks, than adults and semi 
adults.There is a very probably  juvenile  Macrocnemus (see my website for 
a line drawing and a photo)  but as far as it can be judged by body size, 
proportions etc., it is not a newborn. Its neck is shorter with 
proportionally shorter vertebrae  than in larger specimens.

Cosesaurus might also be a juvenile, but its preservation is not good 
enough to allow too much speculations.

If I am not wrong, there is a very small Langobardisaurus, 
unpublished,  which could represent a very early growth stage, I have seen 
a photo, Fabio dalla Vecchia has seen the specimen. He can comment about 
neck morphology if he wants.

Some comparative and bio mechanical study has been made by Karl Tschanz for 
his PhD thesis, but are substantially unpublished apart an excerpt in 
Palaeontology (1988) dealing only with neck allometry.  A rather in depth 
study  on osteology has been published by Wild in 1973. I have seen some 
small Tanytrachelos (courtesy of Nick Fraser) and I am amazed about the 
neck morphology, with  those large plowshare shaped ribs forming two big 
rods at each side of the neck.



There is no "evidence"  for or against possible viviparity among 
Tanystropheus and, to my knowledge, other prolacertiforms (but see below) 
.  Even if Tanystropheus was fully aquatic (perhaps another speculation), 
its limbs allowed him to walk on land to lay egg, and much better than 
turtles. As for reptiles in general, oviparity could be the  more usual 
strategy and viviparity an exception, however, who knows.
On the other hand, there are  the odd bones of Tanystropheus and 
Tanytrachelos quoted in this thread as epipubic. They are not epipubic, 
since they do not lie on, or close to, the pubis. They are ETEROTOPIC 
perhaps postcloacal and lie posterior to the very base of the tail. In 
Tanystropheus they are present only in some of the larger specimens 
and  possibly a sexual character,  Wild considered it a support for a 
lizard-like double penis, thus present in males. In Tanytrachelos,  again 
they are present only in some specimens and Olsen suggested they could have 
acted as a support for an egg pouch, thus borne by females.  To me, these 
bones seem too big to support penis (also because it had to be even bigger, 
and because I don't know of similar structures in lizards) , but (wild 
speculation, OK, I am aware of it) if an egg pouch was indeed present, thus 
Tanytrachelos/Tanystropheus may have kept their eggs  until hatchling (were 
they ovoviviparous)??

To my knowledge no Tanystropheus egg has been found so far. Thus any 
discussion about the egg shape etc. is inconsistent. In the same sites a 
putative neusticosaur embryo has been collected (Sander,  Science, 1988) 
but no eggs of any kind.

All the best,

                                                                                           Silvio 
Renesto







" Men take in great consideration what falls within their sphere of 
knowledge, but they don't realize how much it depends from what is beyond 
that""
                                                        (Zhuang Zhi)


Prof. Silvio Renesto
Department of Structural and Functional Biology
Università degli Studi dell Insubria
via Dunant 3
21100 Varese
Italy
phone +39-0332-421560
e-mail: silvio.renesto@uninsubria.it
see my Triassic website at http://dipbsf.uninsubria.it/paleo/