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Re: Defining clades like a REAL man (Was: New PaleoBios pa
Mike Taylor wrote:
>> Ye-es. I think it's a matter of philosophy whether you like such
>> magic disappearing clades or not. I am not personally wild about
> Why on earth not?
Warning: high subjective opinions follow. To me, such a self-destructing
clade definition seems like a coward's way out. It encourages people to go
ahead and name the clade irrespective of the support for the topology in
which is was conceived, because the magic will make it vanish if it goes
wrong. But I think it's better to wait until all the phylogenetic ducks
are in a row before naming the clade in the first place.
In an ideal world, all clades would be well-supported and stable in content.
In the real world, a change in the polarity of a relatively small number
of characters can drastically alter the topology of a phylogeny. If you're
waiting for every clade to be rock-solid in content and position, then I
think you'll be waiting till the cows come home. The monophyly of
Diplodocoidea looks set in stone, but I wouldn't hold my breath when it
comes to resolving the relationships of many Chinese taxa (_Euhelopus_,
_Mamenchisaurus_, _Omeisaurus_, _Shunosaurus_, etc). It isn't the lack of
will or hard work on the part of sauropod workers that precludes the
recovery a stable phylogeny; it's that some of these sauropods just won't
'play ball'. Ditto for _Haplocanthosaurus_ and some of those basal
For example, it doesn't take much to convert two sister taxa into two
successive paraphyletic taxa. This can have huge ramifications for a clade
that has these two taxa as specifiers. The _Mamenchisaurus_+_Omeisaurus_
clade is a good example. If these two taxa switch from being sister taxa to
paraphyletic, then a Mamenchisauridae that is defined with _M_ and _O_ as
specifiers can go from a clade that includes two genera to a clade that
contains most of the Eusauropoda. And this could happen without changing
the fact that _Mamenchisaurus_ and _Omeisaurus_ are closely related to one
There are many traditional family-level groups that contain genera that we
can be fairly sure are closely related, but which are now regarded as
paraphyletic: Megalosauridae, Andesauridae, Brachiosauridae,
Hypsilophodontidae, Iguanodontidae, Protoceratopsidae. Some of these
families can be utilized and defined for less inclusive clades. Yet, the
internal relationships of these paraphyletic arrays are prone to rampant
flip-flopping, and so it would be hard to pin down two genera that could be
used as specifiers. How do you define a monophyletic Protoceratopsidae, for
example, when the closest relative(s) of _Protoceratops_ change from one
analysis to the next?
It encourages people to go ahead and name the clade irrespective of the
support for the topology in which is was conceived, because the magic will
make it vanish if it goes wrong.
I don't thing it encourages bad or sloppy definitions. I think these
"coward's definitions" recognize that topologies are prone to revision, and
allows such changes to be accommodated. Again, minor changes of topology
can result in dramatic changes in content for a given clade. Internal
clauses ensure that clades do not become too inclusive.