In a message dated 2/18/00 11:24:32 AM Pacific Standard Time, ragweed at igc.org
writes:

> I?m curious though about whether the presence of a cloaca
> goes along with nitrogen waste excretion primarily through u
> ric acid. Vicki mentioned that her iguana has droppings similar
> to birds. Do all reptiles excrete primarily uric acid?

Excretion of nitrogenous wastes as uric acid is a derived characteristic of
reptiles (which under modern, descent-based definitions, include turtles,
lizards, snakes, crocodilians, and birds). Excretion of urea is a primitive
characteristic that mammals share with amphibians.

Note also that modern definitions exclude mammals and their ancestors from
the Reptilia.

--Nick Pharris
Olympia, WA
mailto: NJPharris at aol.com