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Re: Phylogeny and evolutionary history of tyrannosauroid dinosaurs (free pdf)



John D'Angelo <assuming.dinosaur@gmail.com> wrote:

> This issue was discussed recently on a TetZoo podcast, because some
> homogeneous and morphologically well-defined bird genus was found to be
> paraphyletic with respect to a clearly distinctive species.

I certainly take your point here.  I don't think we need to be
ruthless about this.  For extant taxa, if certain species within a
genus are paraphyletic relative to another genus, it might be better
to preserve the status quo.

I'm not aware of what bird genus you're referring to (I am curious),
but it may not be worthwhile overturning long-standing taxonomic
practices simply based on the topology of a given phylogenetic
analysis.

There is a well-known example in microbiology of convention trumping
phylogeny.  Phylogenetically, the bacterial genus _Shigella_ is nested
inside the genus _Escherichia_ (specifically, the species _E. coli_).
For reasons connected to medicine/epidemiology, _Shigella_ is best
left standing as a distinct genus; and there is no reason to split up
_Escherichia_ just because of _Shigella_.

But these are exceptions.  For fossil genera, there doesn't appear to
be a compelling reason to maintain paraphyletic genera IMHO.  We only
have to look at the way that _Iguanodon_ has been split up into
multiple genera, with _Iguanodon_ (sensu stricto) now comprising only
three or four species.  I think this is helpful to the cause of better
understanding ornithopod evolution.  But one could argue that, for the
sake of stability, _Iguanodon_ should represent a paraphyletic grade
of ornithopods and comprise consecutive outgroups (most of which are
erstwhile _Iguanodon_ species or specimens), with _Kukufeldia_,
_Barilium_, _Proa_, _Hypselospinus_, and _Mantellisaurus_ all sunk
into _Iguanodon_.   However, I don't see a compelling reason to do
this.  The same applies to tyrannosaurids.  Let the topology decide
whether this new tyrannosaurid species belongs in _Daspletosaurus_, or
constitutes a new genus.