[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Hanson 2006, Mortimer, Baeker response
Tim Williams writes:
>> (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!"
But I don't _care_ what such a person would say. I thought I'd made
that clear. I love a good, solid clade as much as the next man --
just as I love a good real ale as much as the next man. But just as
I'd not want to have to commit to never drinnking anything else except
beer, so neither do I want to sign the no-non-monophyletic-taxa
> 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.
Yes. Although _Tendaguria_ and _Agustinia_ are (to my eyes at least)
a LOT more way out and freaky than something as relatively pedestrian
as _Jobaria_, which seems to be merely a late-surviving but otherwise
well-behaved "cetiosaurid". (Ha! Paraphylylicious! :-)
> But phylogenetic taxonomy regards as redundant any clade ("family"
> or otherwise) that includes only one genus (=monotypic).
It's stronger than that, of course: it's _impossible_ to define a
node-based taxon based on a single member. Of course you _could_
define Tendaguriidae = (_Tendaguria_ not _Diplodocus_,
_Dicraeosaurus_, _Rebbachisaurus_, _Haplocanthosaurus_,
_Camarasaurus_, _Brachiosaurus_, _Andesaurus_, _Saltasaurus_,
_Mamenchisaurus_) ... but I don't think any of us wants to go down
>> 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).
There's that claim again. Where is this "rule" stated?
> 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.
And it that doesn't work, fifteen rounds in a boxing ring should do it
>> 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 particular cases.)
I flatly contradict this assertion. Given phylogenetic definitions of
Titanosauridae as (_Saltasaurus_ not _Andesaurus_) and Tendaguriidae
as (_Tendaguria_ not _Opisthocoelicaudia_), if we recovered the
then those two "families" would remain, one inside the other, their
names unmodified, according to every set of phylogenetic nomenclatural
principles I've ever seen.
>> 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.
I nearly agree. Saying "family" does not quantify diversity in any
objective, measurable way; but it does quantify diversity in a
subjective way which is nevertheless useful in that it will be
understood in more or less the same way by anyone who's familiar with
Maybe just keeping the word "family" in quotes is the answer.
>> 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."
Ah, well, if that happens I'll just chicken out and say
/o ) \/ Mike Taylor <email@example.com> http://www.miketaylor.org.uk
)_v__/\ "Only two things are infinite: the universe and human stupidity.
And I'm not sure about the former" -- Albert Einstein.