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RE: Platypuses may be older than we think...
Dann Pigdon wrote:
> Given the limited number of extant montotreme morphotypes (namely two), it's
> not surprising that fossil monotremes have been shoe-horned into 'platypus'
> or 'echidna' camps. Who knows what variations in form extinct monotremes may
> have toyed with? It's like trying to classify fossil placental mammals if
> only primates and antelope still existed (anything with hooves was a
> proto-antelope, anything with fingers a proto-primate!). Our modern points
> of comparison for monotremes are some-what limited.
Good point. Nevertheless, monotremes (both living and extinct) can be broadly
divided into two categories: 'diggers' and 'swimmers'. Modern echidnas are
diggers, and so was _Kryoryctes_ (based on humeral morphology). On the other
hand, the platypus lifestyle has been extrapolated to _Steropodon_ and
_Teinolophos_ based on the inferred presence of platypus-style
electro-reception. The teeth of _Kollikodon_ have been interpreted as being
adapted to crushing shellfish, so this critter has been regarded as an aquatic
predator too. _Obdurodon_ (for which a beautiful skull is known) is certainly
a bona fide platypus. _Monotrematum_ is also regarded as a true
ornithorhynchid (see below). _Monotrematum_ is known from teeth that are so
similar to those of _Obdurodon_ that some researchers even consider the two
genera to be synonymous (or so I've heard - I don't have any references to back
<< Still worse: they got that minimal age by means of assuming that the
Palaeocene *Monotrematum* was a platypodan. Problem is, *M.* is only known
>> from two teeth, and not a single tachyglossan tooth is known, so we can say
>> absolutely nothing about its phylogenetic position with respect to
> I've just had an e-mail from /Monotrematum/, and it demands I correct this
> outrageous libel. 'Two teeth' indeed! Remains are vastly more extensive;
> 50%. A third molar was reported by Pascual R, Archer M, Juareguizar EO, Prado
> JL, Godthelp H, & Hand SJ, 1992. Two is merely the number of lowers.
This same paper also supports the referral of _Monotrematum_ to the
Ornithorhynchidae, saying "...the lower molar morphology of _Monotrematum
sudamericanum_ agrees with previous statements that it is a monotreme closely
allied with _Obdurodon_."
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