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Re: Antarctic Elasmosaur



Larry Febo wrote:

> One wonders then, (well,...I wonder then), if a case couldn`t
> be made for elasmosaurs being somewhat warm-blooded to be
> living in a Polar region?

The 'Polar' oceans of the Cretaceous were much warmer than today (there
were no ice caps in either the Artic or Antarctic), so I don't think
it's necessary to make a case for 'warm-blooded' plesiosaurs on that
account... they probably did have some 'reptilian' mechanism for
maintaining their body temperature, but it's a bit difficult to envision
what that was.  From the increased number of plesiosaur remains found in
deposits laid down in cooler waters, it seems apparent that they
preferred lower temperatures. 

Steve Brusatte wrote:

> Perhaps...or, maybe they seasonally migrated (like some modern
> whales, which are endothermic, but that's beyond the point).

>From trying to locate sources of gastroliths found in Kansas plesiosaurs
(late Cretaceous), it is apparent that plesiosaurs migrated (or at least
swam) long distances occasionally to replenish their 'grinding
stones'.... The nearest source of pink quartzite is in northwester
Iowa... a distance of several hundred miles from where the plesiosaur
remains were found in western Kansas.
    < http://www.oceansofkansas.com/Gastro2.html >
    < http://www.oceansofkansas.com/plesio2.html >
Plesiosaurs are relatively rare in Kansas... and almost non-existant in
Gulf Coast deposits.... but are fairly common in Canadian localities.

Rutger Jansma wrote:

> First of all, I don't see any reason that Elasmosaurs,
> Ichtyosaurs or Mosasaurs being warmblooded. Alright, you can't
> base an argument on a bad feeling in the stomach, but these type
> of animals are related to basal diapsids and not to the lineage
> that will eventually produce archosaurs.

I see all sorts of reasons that all marine reptiles must have had some
sort of thermo-regulation..... even if water temperatures averaged 80
degrees F., this is quite a ways below most reptiles required / desired
body temperature to be active... Marine reptiles didn't have the luxury
of laying out in the sun to warm their body temps.... they were in the
water all the time.. and presumedly losing body heat 24 hours per day...
swimming more or less constantly generates a considerable amount of body
heat....some sharks, tuna, other game fishes, and some marine turtles
(all cold-blooded animals, right?) have mechanisms to conserve body heat
around the vital organs, esp. the brain and eyes in some fishes.

> The climate should have been warm at the time, possibly with small > lakes in 
> which this Elasmosaur could live.

So far as we know, plesiosaurs were open-water, marine animals...
although a few specimens have been found in fresh water (near-shore?)
deposits.

Dann Pigdon wrote:

> Except that whales only migrate to breed in warmer waters.
> Plesiosaurs and Pliosaurs in southern Australia (inside the
> Antarctic circle in the Cretaceous) appear to have bred in the
> colder waters.

As noted above, nothern hemisphere plesiosaurs also appear to have lived
(including bearing their young - alive) in cooler waters. Lots of energy
apparently available in a diet high in fish oil :-)

Steve Brusatte wrote:

> And, as Rutger said, mosasaurs weren't very closely related to the
> dinosaur/avian stock.  Perhaps they evolved endothermy or another
> type of elevated metabolism separately, but maybe the new
> elasmosaurs could live and breed in the colder waters just fine.

Ichthyosaurs and plesiosaurs were around a long, long time.. about the
same length of time as the dinosaurs... they were very well adapted to
the oceans of the Jurassic and early Cretaceous, and had evolved
whatever physiological mechanisms were necessary to survive in the
ocean, including live birth. I doubt if thermal regulation was much of a
hurdle to overcome in that period of time... Mosasaurs were a bit
different, evolving from a shore dwelling lizard to an ocean dominating
sea monster / predator in just a few million years at the end of the
Cretaceous... They also were very active animals.. and lived just about
everywhere including the oceans of the Artic and Antarctic.... 

Whatever they did to return to the sea, they were very successful at
it.... 

Just my humble opinion... :-)

Mike Everhart  < http://www.oceansofkansas.com>
Adjunct Curator of Paleontology
Sternberg Museum of Natural History
Fort Hays State University, Hays, KS