|MadSci Network: Zoology|
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!
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