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Re: Hanson 2006, Mortimer, Baeker response
Mickey Mortimer wrote:
Tendaguria seems to have gotten its own family largely because Bonaparte
was being more phyletic than cladistic.
I would say more "phenetic" than "phyletic", but I get what you mean.
In regard to the theme of this thread, finding 'new' categories of
dinosaurs is impossible in a way.
I don't know what DP meant (his emails have a tendency to make my head
spin), but I was not so much referring to new categories of dinosaurs as
filling in the phylogenetic gaps. The gaps in dinosaur phylogeny are not so
nearly as large (or as numerous) as they once appeared to be. I gave two
examples in a previous message: segnosaurs (therizinosaurs) and
_Opisthocoelicaudia_. Back when segnosaurs were regarded as some sort of
ornithischian-prosauropod transitional group, this required an enormous
ghost lineage stretching back from the Late Cretaceous to the Late Triassic
or Early Jurassic. When _Opisthocoelicaudia_ was regarded as a weird Late
Cretaceous camarasaur, this also required a lengthy ghost lineage (though
not as long as the segnosaur one). Now that segnosaurs and _O_ are
comfortable in the Maniraptora and Titanosauridae, respectively, this
drastically reduces two big gaps in dinosaur evolution.
What tended to happen in the past is that oddball dinosaurs were assumed to
represent the culmination of very long, unknown lineages. Nowadays, these
oddballs are usually recovered as autapomorphy-rich taxa that have a closely
related known sister taxon.
And the gaps are sometimes huge. So there's still plenty of work to do.
That's true. But cladistics has helped sort out some of these weird taxa,
by showing that the 'weirdness' is usually concentrated in a relative few
anatomical characters, and the rest of the anatomy does a better job in
resolving the relationships of these 'weird' taxa. _Agustinia_ looks weird
courtesy of its strange body armor, and that's why Bonaparte gave it it's
own family. _Opsithocoelicaudia_ seems to be an atypical titanosaur,
because of the forked neural spines and opisthocoelous caudals; but the
majority of its anatomical characters redaily identify it as a titanosaur,
fairly close to _Saltasaurus_.