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Re: Hanson 2006, Mortimer, Baeker response
Mike Taylor wrote:
I now find I don't need to reply to Tim because Mickey said _exactly_ what
I was going to say. I think any disagreement between Tim and me here is
And nothing a few pints couldn't solve. :-)
Of course in saying that _Tendaguruia_ and _Agustinia_ don't "fit at all
convincingly into any of the
established clades less inclusive than Neosauropoda" I wasn't proposing
that there must be other Neosauropod clades besides Diplocodoidea and
Macronaria :-) Just they they are morphologically
so freaky that they're not "a good fit" anywhere.
Yep, that's how I interpreted it. But what I was driving at is that
"morphologically freaky" is usually not the same as "not a good fit
anywhere". Weird oddball taxa that are given their own "families" because
they are so different (morphologically speaking) usually end up being sunk
into a pre-existing family.
So that if we accept that the notion of "families" is a useful one (on
which see below), then it does indeed make sense to accept Bonaparte's
erection of Tendaguriidae and Agustiniidae.
But if both _Agustinia_ and _Tendaguria_ turn out to be titanosaurids, then
Tendaguriidae and Agustinidae cannot be used. Otherwise, Titanosauridae
becomes paraphyletic. The idea behind phylogenetic taxonomy is that common
ancestry is used to define clades, not characters or degrees of
'different-ness', which was the basis for Linnaean ranks.
Yes indeed. But I don't have a problem with that. Just because we
(mostly) all agree that families are not objectively real, it doesn't
follow that they have no utility.
The utility and validity of families should depend on the relationships of
the taxon is question. Agustiniidae and Tendaguriidae are only valid if
_Agustinia_ and _Tendaguria_ are not contained within another "family-level"
taxon, like Titanosauridae. But if _Agustinia_ and _Tengaguria_ are each
demonstrated to be nested within the Titanosauridae, then the family-level
distinction is no longer necessary (and is also misleading, from a
This kind of thing happens all the time - especially in the world of
invertebrates. There are some truly bizarre worms were once given in their
own "phylum", because they appeared to be so weird and different that were
considered to have "earned" their own phylum. Many of these phyla have been
shown to be nested within other clades. Like the phyla Pogonophora and
Vestimentifera, which evolved from within a group of annelids and so were
subsequently sunk within the "family" Siboglinidae. This reminds me of how
birds used to be considered a "class" separate from theropods. Keeping
_Agustinia_ out of Titanosauridae because it's so "morphologically
different" from other titanosaurids follows this same rationale.
So to go back to my original point concerning _Tendaguruia_,_Agustinia_ and
the unnamed third example, rather than claiming that they fall into clades
that no-one knew existed, the thing that excites me is how morphologically
distinct they are from all the well-known taxa that you see on all
Upchurch's and Wilson's cladograms. Afte all, if you're prepared to write
_Agustinia_ off as "just a
titanosaur", then you also have write _T. rex_ off as "just a coelurosaur"
I think we can appreciate the distinctiveness of a genus (like _Agustinia_
or _Tendaguria_) without having to emphasize this distinctiveness by
erecting (or maintaining) monotypic families. The latter sounds rather
Linnean and typological to me. There's nothing bad about being a titanosaur
- _Agustinia_ is weird AND it's a titanosaur. Similarly, _T. rex_ is cool
AND it's a tyrannosaurid AND it's a coelurosaur.