Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!elroy.jpl.nasa.gov!jarthur!uunet!tdatirv!sarima
From: sarima@tdatirv.UUCP (Stanley Friesen)
Newsgroups: sci.bio
Subject: Re: What's a monotreme?
Keywords: monotremes
Message-ID: <209@tdatirv.UUCP>
Date: 23 Apr 91 19:39:27 GMT
References: <1991Apr22.111159.29888@kuhub.cc.ukans.edu> <4896@kitty.UUCP>
Reply-To: sarima@tdatirv.UUCP (Stanley Friesen)
Organization: Teradata Corp., Irvine
Lines: 36

In article <4896@kitty.UUCP> larry@kitty.UUCP (Larry Lippman) writes:
>In article <1991Apr22.111159.29888@kuhub.cc.ukans.edu> mcginnis@kuhub.cc.ukans.edu writes:
>>What is a monotreme?  An article on the echidna in the Feb., 1991
>>Scientific American says that the echidna has "a cavity uncommon in
>>mammals, into which all the internal organs empty...".  Now, this
>>is obviously wrong (because the heart doesn't empty into this
>>cavity, nor do the lungs, etc.) so I presume that this single
>>cavity gets the urine and sperm and feces.  Is this correct?

Quite correct, this cavity is called a 'cloaca' and is present in birds
and reptiles, but not in most mammals.
(I suspect that SA was trying to be 'polite' and avoid direct reference
to such things as feces and urine).

>	The only definition I am aware of for "monotreme" is that of an
>egg-laying mammal, such as the duck-bill platypus and spiny anteater.
>The term "monotreme" arises from the order Monotremata, which encompasses
>such animals.

Monotreme is indeed the 'common' form of 'Monotremata'.  The taxon in
question is distinguished from other mammals by several characteristics.

Posession of a cloaca is one, laying yolk-filled eggs is another, as is
incubation of the eggs in a pouch, and lack of nipples (the milk just
oozes out of a general region of the mother's breast, where it is lapped
up by the infant).

In fact they are mammals only in possesing milk (i.e. mammary glands),
insulating hair, and (to some degree) endothermy.

The only known monotremes are the Platypus and the various species of
Spiny Anteater (or Echidna).  There is essentially no fossil record
of monotremes.
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uunet!tdatirv!sarima				(Stanley Friesen)