Re: What do platypus excrete

Wow.  This is a really interesting question.  It was also quite a challenge
to answer!

I was only able to find one reference of much help.  This sources indicates
that the platypus excretes urine.

 http://animaldiversity.ummz.umich.edu/site/accounts/information/Ornithorhynchus_anatinus.html


This implies that the playpus excretes its nitrogenous wastes primarily in
the form of urea (fish typically exrete ammonia, reptiles & birds typically
excrete uric acid, while mammals and amphibians typically excrete urea).

There are some studies out there that have evaluated the structure of the
platypus kidney, and these indicate that the kidney structure, while not
quite as advanced as other mammals, is essentially mammalian in its nature.
 Thus, it is not surprising that the platypus would excrete urine.

 http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1443663&dopt=Abstract


Now, one interesting characterisitc of the platypus is that it has only one
opening for the purposes of excretion & laying eggs - the cloaca.  This is
similar to what we see in amphibians, reptiles, and birds.  In fact, the
platypus is thought to be one of the earlier mammals to evolve, so that it
retains some vestiges of these older vertebrate lineages is not
particularly surprising.
 http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1443663&dopt=Abstract


Thanks for the question!