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> The Solnhofen limestone is indeed thought to have
> been deposited in shallow lagoons, with patchy small islands;
> the largest predators on these tiny islands were Archeaopteryx and
> the diminutive Compsognathus, sharing the islands with turtles,
> pterosaurs and thalattosuchian crocodiles.
> Pieter Depuydt
The presence of Archaeopteryx and Compsognathus might be evidence
that the dinosaurs did become diverse. Flying dinosaurs could have
arrived at remote islands like birds and lost flight. Since they still
had the replaceable, socketed teeth, hand claws and tail, they would
evolve but still resemble other theropods. Plant eating descendants
might be toothless such as the ornithomimids (no grinding teeth).
One limitation that mammals might have had in reaching large size
quickly was their dental system. Once the final teeth come in, there was
not a convenient way to continue growing like with the dinosaurs'
In addition, those that did obtain large size on islands probably will
not be preserved as islands tend to be eventually destroyed by oceans.
In water, the first air breathing reptiles that reverted back to the
probably had a big advantage. Warm Sea ways might have been an
advantage for a lower metabolic rate animal as far as the amount of
food required for sustenance. Unlike mammals that had many millions
of years of trying to keep warm because of their small size. Dinosaurs,
even if they were warm-blooded, might have cooled off excessively in
cooler water. Water cools the body much quicker than air at the same
temperature. Animals like Hesperonis might be the dinosaurs best attempt
at a water existence.