RE: WHEN THE FISH CRAWLED OUT OF THE SEA (was Re: An end to miracles

["Curtis B. Olson" <olson_c@mediasoft.net>]

On Wednesday, April 08, 1998 5:45 AM, Pieter.Depuydt@rug.ac.be 
[SMTP:Pieter.Depuydt@rug.ac.be] wrote:
> Betty wrote:
> >   Furthermore, the amphibians (supposedly very similar to the first land
> > dwelling vertbrates) of today seem rather intolerant of salt exposures
> > on their sensitive skins (and I don't believe they will lay eggs in
> > alkaline pools of water in deserty areas either).

> The Andreyevka fauna, where the primitive tetrapod Tulerpeton occurs
> together with antiarchs, groenlandaspids, osteolepiforms, dipnoi
> (lungfishes) has been interpreted, based on the sedimentology, as
> been laid down in an estuarine and even occasionally marine
> environment: i.e. probably a large tidal flat, with large deltas and
> frequent marine incursions.

> Ichthyostega and Acantostega are accepted as being preserved in
> fluvial sediments, but with tidal flats, lagoons and deltas nearby
> (Janvier 1997. Early Vertebrates, Oxford University Press).
> So it seems that at least some of the early vertebrates had their
> habitat in at least partially marine (estuarine, tidal)
> circumstances.

Actually, there is at least one extant amphibian, Rana cancrivora ("the 
crab-eating frog") that lives and breed around brackish estuaries.  Some 
tadpoles can even survive sea water.  It's ability to deal with the osmotic 
pressures of a saline environment is of some importance to science, but even 
more so to the frog who, after all, eats marine crabs.  Another, Bufo viridis 
from Sweden, is also know to have larvae that is capable of development in 
somewhat brackish water.  Then there is Bufo marinus which, well, you get the 
idea.  It is a misconception that amphibians cannot tolerate salt.

It should also be noted that amphibians sometimes lay their eggs out of water, 
up on stream banks, even up in trees, thereby escaping harsh water chemistries, 
and quite probably representative of a trend towards terrestriality.