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Re: Leapin' Mosasaurs, Batman!



Nick L. wrote:

>I have a piece of mail from Mr. Parris of the NJ state museum
>referring to a "Mother Mosasaur" w "unborn youngsters." 
>What?! Ms Kiernan, I believe this is your forte. Enlighten us >all, and for
the moment we'll pardon the unforgivable sin of >being interested in
something other than dinosaurs

Since at *least* the early 1980's, evidence for live birth in mosasaurs,
either ovoviviparity or true viviparity, has been accumulating steadily. It
began while I was at the Red Mtn. Museum in Birmingham, AL, with the
recognition of fairly common subadult mosasaur remains (primarily _Clidastes_
and _Tylosaurus_) from the Mooreville Chalk (early-late early Campanian) of
Alabama. Eventually, as we learned better ways of recovering microvertebrates
from the chalk (we were getting lots of disarticulated _Ichthyornis_), a
couple of specimens were found that we were fairly certain were foetal (based
on degree of ossification and size). I think it was one of those cases where
it's just a matter of knowing what to look for, because soon we were coming
across Niobrara and Pierre mosasaurs, in the field and in collections, that
had been overlooked, sometimes mistaken for fish or even ichthyornithid and
hesperornithid birds. In the case of _Clidastes_, some of these remains were
remarkably tiny, and superbly well-preserved (unlike the Niobrara, there's
very little crushing of fossil bone in the Mooreville, and unlike so much of
the Pierre, virtually no marcasite or selenite encrusting the bone).

At the time, I was working primarily on mosasaur systematics, and the little
mosasaurs were taken on by Gorden Bell and Amy Sheldon. In 1986, Gorden
designed and carried out experiments (which he reported on at SVP in
Philadelphia that year) which demonstrated that it would have been impossible
for adult mosasaurs to have left the water to lay eggs. Even the most
primitive mosaurs known at that time (the halisaurines) would have almost
certainly have died trying. Their bodies were too big, their sternums and
limbs too weak.

But, to my knowledge, the first direct evidence for mosasaur live birth came
a couple of years back, when Gorden (now at the School of Mines in Rapid
City, SD) recovered a _Plioplatecarpus_ specimen from the Pierre Shale and
the remains of foetal _Plioplatecarpus_ in the region of the abdominal
cavity. Though the site was carefully screened, no evidence of eggshell was
recovered, and the bone showed no evidence of having been damaged by gastric
acids, so cannibalism can probably be ruled out. 

We'd seen smaller mosasaurs inside bigger ones before. Jim Martin (SDSM)
described the intestinal contents of a big Pierre tylosaur that had
cannibalised other mosasaurs (when I looked at the specimen in '85, it was
quite clear that the material iniside the tylosaur was _Platecarpus_, along
with misc. fish and bird remains).

This is *probably* the specimen Dave Parris was speaking of in his letter,
unless new material has come to light that I'm unaware of. Most of my own
research continues to focus on mosasaur biostratigraphy/biogeography and
systematics, and I have spoken with Gorden since '93 or so.

Hope that answers some questions. 

Caitlin R. Kiernan