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AMPHIBIOUS DINOSAURS



Nick Longrich said..

>         Is it possible, then, that some of these things spent a lot of
> time in water? Something like a hippo, perhaps?

No doubt all kinds of non-avian dinosaurs went swimming, in cases even quite
frequently. Some lived in habitats where there were permanent or near-permanent
large bodies of water, and some dinosaurs also have nice adaptations for
swimming. _Ceratosaurus_, with a deep flexible tail where the caudifemoralis
longus goes all the way down to caudal vert no. 30 or so, is a prime example.
It's possible, at least according to what Jack Horner says, that the hadrosaur
_Gryposaurus_ was amphibious. In _Hunting Dinosaurs_ he cites several characters
of this genus that suggest an amphibious lifestyle. As all of them occur in
other hadrosaurs, though, I would reckon that palaeoenvironmental data would be
more telling. A number of hadrosaur taxa are known to have occurred in lowland
swamps.

Like some modern animals (e.g. bovids), the design of, say, hadrosaurs, may be
generalised enough to allow very similar animals to thrive in very different
habitats. Some swamp-dwelling antelopes (perhaps analogous to _Gryposaurus_) are
very similar to savannah-dwelling forms (perhaps analogous to, say,
_Maiasaura_).

As for the ankylosaurs, Coombs has repeatedly stated that their presence in
marine palaeoenvironments does not represent autochthonous preservation. He's
said that (paraphrased): 'Ankylosaurs were wide ranging animals with broader
habitat preferences that most dinosaurs'. As noted previously here on the list,
preservation in marine strata does not by any means indicate mode of life.

> Yes, I know, hydrophilic
> dinosaurs are very unfashionable, but there's supposed to be an aquatic
> ground sloth, too.

The 'marine sloth', _Thalassonectes_ (that may be spelt wrong), is a rather
controversial form. De Muizon et al suggested that it was truly adapted for a
life in the sea - it's tibia is longer than its femur for example ('classic
marine adaptation' in mammals). While I'm pretty certain that it could swim if
it had to, and it did eat kelp (it lived on a coastal desert plain), I don't see
why it couldn't just wander out at low tide to browse on the kelp, like some
populations of deer and sheep do in the Scottish islands. No real evidence that
it was out there swimming around like a giant sea otter. In fact, with
_Carcharocles megalodon_ out there, this may have been a tad risky.

My colleague Colin McHenry inspired me on the sloth, so I have to acknowledge
his input.

I've just checked out Janvier's new book, _Early Vertebrates_. It is awesome.

".. we should warn them that they may catch the anti-nuclear bug which is said
to be reaching epidemic proportions in this region."

DARREN NAISH