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Re: Hanson 2006, Mortimer, Baeker response
Mike Taylor wrote:
[In Homer Simpson voice:] Ah, beer! Is there _anything_ it can't do?
The cause of, and solution to, all of life's problems.
Somehow we are still talking past each other here. If a specimen is
morphologically very different from its closest known relative, then that
alone makes it interesting (to me, anyway). So if we mean anything at all
by "family", then surely what we mean is something like "group that is
morphologically similar within itself, but different to other things".
That's the traditional way the term "family" was used. In fact, that's the
traditional way *any* Linnaean group was used: to emphasize morphological
distinctiveness, and try and quantify the level of distinctiveness by
assigning ranks (phylum, class, order, family, etc....).
(And, yes, I know perfectly well that this is not cladistically sound or
any of that stuff. That's fine. I am very fond of clades, and recognise
their utility in discussing evolution, but I see no reason why they should
be the _only_ groups we acknowledge).
Then therein lies the problem of... well, whatever it is we're talking
about. A disciple of cladistics would respond to your statement by saying
"No!!! It's clades or nothing!" Phylogenetic taxonomy defines clades by
shared common ancestry, not by perceived different-ness. If a group is
demonstrated to be polyphyletic or paraphyletic, then it gets thrown on the
The other issue is whether "morphologically distinctive" taxa should be
granted a monotypic family in order to highlight this distinctiveness. Some
authors erect families solely for this reason - such as Tendaguriidae,
Agustiniidae, Huabeisauridae, Velocisauridae, etc. Other authors prefer not
to erect monotype families, even when it is clear that the taxon being
described is quite distinct and/or cannot be accommodated in any existing
family - _Eoraptor_, _Incisivosaurus_, _Bagaaratan_, _Jobaria_,
_Saturnalia_, etc. This appears to be a matter of personal choice. But
phylogenetic taxonomy regards as redundant any clade ("family" or otherwise)
that includes only one genus (=monotypic).
Ah, now I think you've confused yourself by tying together Linnaean and
phylogenetic principles. In suggesting that Tenduguriidae couldn't be
considered a "family" because of orthographical accident of falling inside
another group with a name that ends "-idae", you are taking us down a path
that I'm sure neither of us wants to take!
I'm only confused because the system itself is confused. In the changeover
from Linnaean hierarchy to phylogenetic taxonomy some unattractive Linnaean
features have carried over. We've effectively abandoned ranks, yet the
hierarchial system persists in the way that names with certain suffixes
require a descending level of inclusiveness. For example, we cannot have
one -idae inside another -idae (like Agustiniidae inside Titanosauridae), or
have -inae above -idae (such as Dromaeosauridae inside Microraptorinae).
Other clades can change in content relative to each other, but these
family-level coordinated clades ("family", "subfamily", "tribe" - idae,
-inae, -ini) have to stay in a hierarchial sequence. This is the "baggage"
you are referring to.
In short, I think we bothe know what you and I are talking about, Mike. But
we're both trying to come to grips with the different Linnaean and cladistic
universes. The ICZN and PhyloCode need to get together in a smoke-filled
room and sort this mess out.
No, no, you've gone all ICZN-y on me again :-)
It's not just the ICZN who gets uptight about this. Phylogenetics doesn't
do this either. When one family is sunk into another family (such as
Dryptosauridae into Tyrannosauridae, or Agustiniidae inside Titanosauridae),
the sunken family is history - unless it's kept on as a less inclusive taxon
(like Dryptosaurinae or Agustiniinae, which hasn't happened in these
The reason I don't feel the mandatory surge of outrage whenever I hear the
word "family" is that I want a way to say the following kind of thing,
which is actually pretty common:
Other sauropod remains from the Hastings Beds Group
represent basal Titanosauriformes, Titanosauria and
Diplodocidae; the new taxon brings to four the number
of sauropod 'families' represented in this unit.
I'm totally fine with this. However, while "family" is useful for
categorizing diversity, it does not quantify diversity in any meaningful
way. In the above sentence you could replace 'families' with 'taxa'; this
would convey the same meaning, given that the first clause already clues us
in about the level of phylogenetic diversity.
The knee-jerk reaction seems to be to say "the number of clades", but a
moment's consideration shows that this is nonsense.
Yep, I agree.
Since clades nest, the number of clades can be equally legitimately
considered to be one (Sauropoda), two (Titanosauriformes and
Diplocodoidea), or a dozen (Chordata, Amniota, Reptilia, etc.)
Interestingly, the one number that _does_ seem hard to support is three,
since one of the[snip]
three groups we want to discuss ("basal titanosauriforms") is not a clade
at all, but a paraphyletic assemblage that is nevertheless worth discussing
as it is morphologically distinct.
I suppose the bottom line of what this fragment is trying to say is "brings
to four the number of morphologically distinct sauropod groups represented,
where degree of morphological distinctiveness is understood in the context
of overall sauropod diversity and evaluated as is typical for group". That
is what I am using "family" as shorthand for.
Yes, the term "basal titanosauriform" is useful. But a reviewer might
choose to be pedantic and say, "So four sauropod families are represented in
the Hastings Beds Group? Which families are those? Name them." If your
basal titanosauriform cannot be assigned to any known family, then you've
painted yourself into a corner. This isn't a criticism on my part; I'm just
trying to think what somebody else might say about your choice of wording.