Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!spool.mu.edu!uunet!bu.edu!transfer!lectroid!jjmhome!smds!rh
From: rh@smds.UUCP (Richard Harter)
Newsgroups: sci.bio
Subject: Re: Platypus bones (was Re: What's a monotreme?)
Summary: Not silly at all
Keywords: monotremes
Message-ID: <420@smds.UUCP>
Date: 26 Apr 91 07:54:44 GMT
References: <1991Apr22.111159.29888@kuhub.cc.ukans.edu> <4896@kitty.UUCP> <1991Apr25.182824.18628@hollie.rdg.dec.com>
Organization: SMDS Inc., Concord, MA
Lines: 35

In article <1991Apr25.182824.18628@hollie.rdg.dec.com>, winalski@psw.enet.dec.com (Paul S. Winalski) writes:

	--- re classification of platypus ---

> I assume that you and the good Dr. Asimov mean hatching, not birth.

	Yes.
> Reclassifying Platypus on this basis seems on the surface as silly as
> arguing that human beings should be reclassified because the ductus
> arteriosus and the fetal hole in the ventricular septum don't close
> until after birth.

The cases are quite different.  The dividing line between the threrapsid
reptiles and the mammals is the jaw bone.  I.e. fossils in that lineage
are classified as one or the other based on whether certain bones are
fused or not.

> What is the common name for the Theraspids?

None that I know of.  They've been gone for a long time.  Therapsids
were the dominant branch of reptiles before they displaced by the 
dinosaurs (circa 200,000,000 BC?).  One branch evolved into mammals.

There is an interesting issue here.  Asimov's proposal is really a
bit of sentimentality, sort of saying "See, the therapsids aren't
really extinct."  However one can take the view that this sentiment
is rooted in the notion that the monotremes (and Platypus in particular)
are more "primitive" than other mammals.  However they are just as
modern as any other animal living today -- they are just in a different
lineage.
-- 
Richard Harter, Software Maintenance and Development Systems, Inc.
Net address: jjmhome!smds!rh Phone: 508-369-7398 
US Mail: SMDS Inc., PO Box 555, Concord MA 01742
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