PLESIOSAUR REPRODUCTION ONCE MORE

[darren.naish@port.ac.uk]

Regarding the live birth vs. egg laying debate in plesiosaur science, 
I fwded my (long) message on this subject to Dave Martill. Dave and I 
have had many arguments on this subject, and here is his slightly 
caustic response (don't worry, he doesn't really hate me)...

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BLESSED ARE THEY THAT GO ROUND AND ROUND IN CIRCLES.......
.......FOR THEY SHALL BE KNOWN AS WHEELS

Darren,

Although Mesozoic was full of terrestrial predators, this was not 
necessarily the case for small isolated Mesozoic islands. So, nesting 
on island havens might have been the case, just like large sea birds 
today.

Most compelling negative evidence against giving birth in Sea water 
is lack of baby plesiosaurs in Kimmeridge clay, Oxofrd Clay and Lower 
and Upper Lias. Especiallu the Lower Lias where plesiosaurs are very 
well known from many specimens. So, no pregnant female plseisaurs in 
marine envronment.

This does not mena they laid eggs. They could have had been 
viviparous, but in river systems rather than ouit to sea. 

Need to look for baby plseisoaurs in non marine Jurassic. Perhasp the 
Hugh Miller reptile Bed of Eig in Scotland could help. certainly the 
plesiosaur bones in this deposit are small, but I think dave Brown 
reckons they are from a small species  rather than juvenile.

Perhaps someone could look at thin sections of HMRB to check for egg 
shell fragments..But would the eggs, if any, have been calcified????

To explain lack of baby plsiosaurs one could invoke the 
Metriorhynchid and Steneosairid crocs. If these crocs were truly tied 
to egg laying du to the calcium metabolism of their embryos, then ask 
yourself these questions.

Where are the fossil marine crocodile eggs for the Jurassic? and 
where are the fossil baby Metriorhynchus and Steneosaurus. They 
certainly are not in the Oxford Clay or Kimmeridge clay.

They have not been overlooked either, because both of thse formations 
have yielded remains of smaller fihses and invertebrates.

However, a spanner in my own works....the Oxford Clay has not yielded 
baby ichthyosaurs either.. 


Over to you Darren

Dave



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DARREN NAISH
darren.naish@port.ac.uk