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Is *Amargasaurus sattleri* a Parent Clade for Dicraeosaurines?



  I feel rather put down by those who feel that
revising whole phylogenies based on such a perspective
of the natural occurrence of paraphyletic parent
groups and the apparent nature of genera that are
ancestral to other ?genera,? would be so difficult or
time consuming, or mind-bogglingly immense, that we
should just not do it.

  Okay, whatever way we look at it, it would appear
that S[attleri] is a more plesiomorphic form than
C[azaui] or H[ansemanni]. In reference to the recent
posts on identifying parent groups as paraphyletic in
incorporating descendents, it would be clear to me (at
least) that ancestors are paraphyletic as a whole, but
individuals may be distinguished. We put names on end
products we perceive as unique biological organisms
(UBEs). Linnaeus coined the usage of binominal
taxonomy as a way of distinguishing forms and
variations of forms. Perhaps we should dump species,
and keep genera. Name supra-generic groups, and name a
?species? or subgroup of ?genus? when it appears there
are two forms within the UBE we?ve given a name to.
*Tyrannosaurus* is a widely recognized UBE with two
apparent subtypes, a North American *T. rex* form, and
a Mongolian *T. bataar* form. If the Mongolian form
does not represent a type of the group that the North
American form represents, then it gets its distinctive
nomen, *Tarbosaurus*. We could refer to ?monospecific?
?genera? by the original name, and if a subtype has
been referred, but is not recognizable due to lack of
another subtype, it can be referred only in reference
to other forms. So, an example:

  ?Tarbosaurus is a Mongolian form of tyrannosaurid
that is distinguished from the North American forms by
? blah, blah, blah ? Analyses by Maleyev (1951, 1952)
and Rozhdestvensky (1963, 1964, 1965) have suggested
that either the Mongolian form is a UBE, or that both
the Mongolian and North American forms represent an
Asiamerican form, which is called Tyrannosaurus by
default (see Osborn, 1903). Subsequently, the two
subtypes can be distinguished by referring to
additional names: rex for the North American form, and
bataar for the Mongolian form; these names represent
means of referring to both forms as UBEs.
Additionally, should any additional form be found to
be closer in ancestry (sharing a more recent common
ancestor) with either the rex or bataar forms, the
single-type form can be removed and referred solely by
its type name (Tyrannosaurus or Tarbosaurus), and the
new sub-type (lancensis, novojilovi, efremovi, etc.)
can be added.?

  So, using a simple bivariate system, forms that hold
common ancestry can be referred to using the
?binomial.?  Forms that are UBEs but cannot be
distinguished using subtypes, can be referred to using
a uninomial. Forms that cannot be distinguished by
common ancestry, that are three or more subtypes to a
form without resolution, can then be further referred
to by a binomial. It might be problematic to then
realize that further variations on a type (subspecies,
variants, races, etc.) that have been used would be
excessive terminology for stages that could be
simplified. Therefore, the term ?species? would refer
to a subtype, and the term ?genus? could be defined as
a UBE.

  Paraphyletic groups could be recognized as all
higher taxa, noting that any ancestral group would be
necessarily paraphyletic. Every taxon would be either
a node or a stem, because there would in fact be
common ancestry. Convergent evolution would remove the
need for apomorphy-defined nodes.

  Tell me what you think.

  As to the title of the post, is it quite possible
that that form of S is ancestral to both H and C,
which expresses itself as plesiomorphies?

=====
Jaime "James" A. Headden

  Dinosaurs are horrible, terrible creatures! Even the
  fluffy ones, the snuggle-up-at-night-with ones. You think
  they're fun and sweet, but watch out for that stray tail
  spike! Down, gaston, down, boy! No, not on top of Momma!

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