Re: [dinosaur] Party like it's 1758!

[Tim Williams <tijawi@gmail.com>]

Jason <pristichampsus@yahoo.com> wrote:

> I get how these taxa can be an issue, but they are also the exceptions to the 
> rule.

I'd say these exceptions *are* the rule.  Major evolutionary
transformations (such as the evolution of powered flight; or return to
fully aquatic/marine habits) are the cumulative result of smaller
transformations over time.  I know you know all this.  :-)   I'm just
trying to convey the notion that traditional 'concept-based' taxonomy,
which would treat artiodactyls separate from cetaceans, or dinosaurs
separate from birds (or pennaraptorans), reinforces the kind of
typology that phylogenetic nomenclature actively avoids.

It is true that whale and bird evolution is very well documented in
the fossil record.  (In contrast to, say, bats or pterosaurs, which
essentially appear from nowhere in the fossil record.)  So deciding
where to put the "imaginary line" (as you phrase it) between
artiodactyl/cetacean or dinosaur/avian becomes challenging.  But
rather than being a challenge, I'd say it reveals how arbitrary these
distinctions are - so we should not  'define' paraphyletic groups at
all.

> Referring to any dinosaur outside of Pennaraptora as dinosaurs in the 
> paraphyletic sense, doesn't hurt the meaning at all or cause any confusion.

I partly agree.  But I think we should refer to any taxon *inside*
Pennaraptora as a dinosaur as well - including birds.  Demoting
'dinosaur' (and Dinosauria) to a paraphyletic grade is potentially
misleading.  In a large part, the confusion is based on a preference
for traditional/ typological concepts over phylogenetic concepts.  The
latter has whales (Cetacea) nested inside Artiodactyla (or
Cetartiodactyla, as it's now called), and birds (Aves) nested inside
Dinosauria, with the nomenclature reflecting this (a good thing, in my
view).

Terms like 'non-pennaraptoran dinosaur' and 'non-avialan theropod' may
be clumsy, but at least they have the benefit of being explicit.

> The addition of a monophyletic
> alternate name also allows those who prefer a strict monophyly to happily 
> have it too. I suspect that this is the main reason why there was never any 
> real arguments about this in herpetology,
> regarding snake taxonomy. It has long been established that snakes evolved 
> from lizards, but only a few herpetologists ever refer to snakes as lizards, 
> instead opting for the monophyletic
> Squamata.

I might be misunderstanding you, but this just highlights the
limitations of common/vernacular names (like 'lizard' or 'snake').

> All that said, whether Archaeopteryx is the "first" bird, a crown bird or a 
> strange dinobird has been argued back and forth for decades even after the 
> advent of a monophyletic
> Dinosauria. Insisting on monophyly hasn't really done anything to make that 
> argument any easier.

I think phylogenetic nomenclature (specifically clade-based taxonomy)
has made this entire argument irrelevant.  Phylogenetically speaking,
it doesn't matter if _Archaeopteryx_ is called a "bird' or not.  What
matters is its place in dinosaur phylogeny.  That's one of the
advantages of this approach: it defuses the entire typological concept
of what (or what is not) a bird.