doubtful rodent paraphyly
kinman at HOTMAIL.COM
Sun Oct 17 08:27:01 CDT 1999
The goal is indeed to find if there are any "excluded descendants" (as
Dr. Singh alluded to). However, just simply including these descendants in
Rodentia is only a viable option if the excluded group is relatively small
(e.g., a family of insectivores, or a small order such as the aardvark).
If the excluded group were a medium-sized taxon, such as Lagomorpha
(which seems to me the most likely scenario for rodent paraphyly, if it is
paraphyletic at all), I would be inclined to recognize rodents as a
semi-paraphyletic group, with a marker to show the cladistic placement of
lagomorphs within it (but formally retain Lagomorpha as a separate order, at
least for the time being). It would then be up to the lagomorph specialists
whether they would rather stay with that arrangement or taxonomically "dump"
them in with the rodents. However, I still have seen no strong evidence to
counter the prevailing view that rodents and lagomorphs are sister groups.
The only kind of scenario that might induce me into splitting Rodentia
(into two separate orders) would be the one proposed in the 1996 Nature
article, in which Rodentia paraphyletically gives rise to a very large group
(in this case, lagomorphs + carnivores + most ungulates + primates + by
inference the bats and other "archonts" as well). If this were indeed the
case, the only logical remedy would be to split the rodents into two orders
(sciurognaths and hystricognaths).
However, all of this is probably academic. My initial study of the
actual gene sequences (upon which the 1996 Nature article is based) seems to
show no really hard evidence for rodent paraphyly (although statistically
suggestive enough that it merits a little closer look). The morphological
and genetic evidence still strongly indicates rodent holophyly (i.e. strict
Hennigian monophyly), and it would take much stronger evidence to convince
me of rodent paraphyly. If rodents are paraphyletic at all, I am still
inclined to believe that it would probably only be with respect to
>From: Gurcharan Singh <singhg at SATYAM.NET.IN>
>I think we are going wrong somwhere. If group is a paraphyletic, the
>problem won't be corrected by its splitting it. It would be more logical to
>find the excluded descendents and include them within the group. Splitting
>would simply aggravate the problem of paraphylly.
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