Re: post from Holloway
chris brochu (firstname.lastname@example.org)
18 Oct 1995 00:42:26 GMT
In article <email@example.com> H. M. Hubey,
>>Every last one of these can be explained as a direct adaptation for
>>swimming. The deep tail acts as a scull - remember, these things are
>>still using side-to-side tail sweeps for propulsion.
>OK. I guess what you're saying is a matter of difference of degree
>and not a difference of kind.
>Or are you saying that some animals have tails which are wider
>than they are deeper? In other words are there land lizards now
>which have flat tails ?
By "deeper," I mean "laterally compressed." Most nonavian reptiles have
compressed tails to some degree, but not like in crocodylians, sea
snakes, or mosasaurs. The distinction is actually quite sharp.
>The elongate snouts
>>present less resistance in the water as they capture fish.
>ARe there any lands lizards which do not have elongated
>snouts? Isn't elongation something which we expect in
>lower life forms and something that gets shorter and shorter
>up the evolutionary scale? Is this relative elongation
>between land and water versions?
1. Flush the "lower vs. higher" misconception down the commode. There
ain't such a thing.
2. Compare the snout of an iguana or varanid with that of a 'gator - or,
better yet, a gavial - and you'll see what I mean. In fact, most
squamates have preorbital rostra about as elongate as in most mammals
relative to body size; since their braincases aren't quite as big, it
gives them a longer appearance. Semiaquatic herps - including those
fossil taxa surmised to be semiaquatic - show a positively allometric
relationship of snout length relative to their terrestrial relatives.
This relationship shows up not only in crocodyloforms but in phytosaurs,
several lineages of lepidosauroform (mosasaurs, Hovasaurus, Jurassic
aquatic sphenodontids), ichthyosaurs, and mesosaurs. The only exceptions
are sea turtles and some plesiosaurs, but the feeding mechanisms are very
different from those of more conventional swimmers in both cases.