[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Princeton Field Guide



 Let's try this again.  Relative to Anolis and its 300 species .....

Well there are 200+ species of the freshwater antiarch placoderm Bothriolepis. Granted they are not all contemporaneous, but still that is alot of species for one genus of fish. I'm not a placodem guy (although I think they are quite cool animals) but from what I've read of the antiarch literature there seems to be little interest in revising the genus and most species seem to be considered valid. I suppose fish diversity like this can be conveniently ignored through the explanation of "species flocks" (as in chichlids).

Dan


On 9/30/2010 6:06 PM, David Marjanovic wrote:
> And donât get me started with what is going on about all the stuff
 being tossed into Mamenchisaurus and Omeisaurus.

Oh yeah. I'd love to see a phylogenetic analyses of the 10 or so "species" that have ended up, seemingly at random, in these two "genera".

 There are a few properly handled dinosaur genera that include a
 normal, large number of species such as Psittacosaurus, Apatosaurus
 (some species not yet named), Diplodocus (ditto). But dinopaleo has
 gotten into the bad habit of usually making almost every species
 into its own genus. This is illogical considering that many modern
 bird and mammals contain large numbers of species â Varanus (now
 formally includes Megalania), Panthera, Felis, Canis, Vulpes,
 Cervus, Tragelaphus, Cephalophus, Ovis, Gazella, Macropus,
 Balaenoptera, Buteo, Falco, Anas.

*Varanus* is a nightmare with 70 species. The sooner it gets blasted to tiny bits, the better. (We can't simply use the existing subgenera because there's no evidence they're monophyletic.) And this goes triply and quadruply for *Anolis*, the excruciatingly bad joke with 300 species.

*Felis* has been shrinking for decades. *Panthera* contains species that are really hard to tell apart based on bones alone. *Gazella* and *Macropus* should be fragmented, and *Anas* is something of a joke, IIRC; I don't know the others well.

I note you don't mention *Bufo* and *Rana* (they're neither birds nor mammals, but neither is *Varanus*). Both have been blown to pieces recently.

 I see that ceratopsid genera are now actually being defined entirely
 on differences in their cranial adornments â thatâs a mind blowing
 development â when these are of course specific level in nature.

See, this kind of statement is just wrong. There are no such levels in nature. A genus is whatever you want it to be.

 In an SVP abstract it is stated that ceratopsians were evolving lots
 of genera when the degree of variation they are refering to is
 actually the minor specific grade. Many in dinopaleo seem to have
 forgotten that the most prolific level of evolution is SPECIATION,
 not GENUATION, with evolution churning out the minor variants we call
 species in far greater numbers than the larger divergences that are
 gathered into a genus. Matters have gotten out way of out hand, and
 when finishing the book I could not use all the pseudogenera because
 people would presume I actually accepted them (as in âeven Greg Paul
 agrees that Agujaceratops and Corythosaurus are real genera). Someone
 needs to call out the taxonomic madness instead of facilitating it
 (the usual names are of course noted).

First, it should be "generation", not "genuation" (_genus_ belongs to the consonantic declension, not the U declension); second, it doesn't matter, because no such process exists. There is no genus level of evolution. There isn't even a species level of evolution. _The_ level of evolution is the population level. "Macroevolution" is just microevolution seen from afar. There is no evidence for any processes in evolution other than mutation, selection and drift.

OK, "species" has at least been defined, even though the 147 different definitions (as of February 2008) have nothing in common except the word "species" and lead to a stupendous variety of results (depending on the species concept, there are from 101 to 249 endemic extant bird species in Mexico). So, once you have picked a species concept, there is such a thing as speciation, even though that means different processes count as speciation for different people. But genera? The only attempt at a genus concept I've ever seen is "if they can have fertile offspring, they're in the same species; if they can have sterile offspring, they're in different species of the same genus; if they can't have offspring, they're in different genera", but this not only presupposes one of the Biological Species Concepts, it's laughably impractical, for instance completely inapplicable to fossils.

Genera don't exist outside our heads! And don't think I'm singling you out. If that SVP meeting abstract claims to count the genera that evolved, its authors have fallen into that very same trap.

 There are also a number of cases in which what are clearly juveniles
 (perhaps with some sexual variation thrown in) are being assigned
 their own genus distinct from their adults, this is especially true
 of some oviraptors and pachycephalosaurs.

That I'm looking forward to reading about!

 It cannot be overemphasized how the nested classification system is
 virtually useless for a popular field guide, it providing no graded
 structure that the public can latch onto.

For a field guide, why have a classification at all? One that pretends to be relevant to biology, I mean. I like field guides to presume complete ignorance on my part, so when I see a yellow flower and want to look up what it is, I can just look under "yellow" instead of under "Compositae".

 Monophyletic clade only classification is a slap at the public
 already skeptical about scientists whom they see as elitists who
 donât care all that much with communicating with ordinary folks.

So are Linnaean ranks. Do you really believe anyone in "the public" cares whether Ornithischia is an order or a subclass?

Phylogenetic nomenclature is at least useful for _someone_ (biologists, that is).

 In any case the phylogenetic classifications disagree with one
 another so much that I threw up my hands

Rank-based classifications disagree with each other even more. That's because they have two sources of instability: changes in our knowledge of phylogeny, and mood swings on the part of whoever can be bothered to publish a classification. "No, I don't think they're subfamilies of the same family anymore, they're different enough that now I feel they should be different families in a new subfamily" is a perfectly valid argument under rank-based nomenclature. Under phylogenetic nomenclature, it's irrelevant because ranks don't matter.

 and cobbled what I could together (an SVP abstract on how difficult
 it is to place heterodontosaurs relative to other ornithischians
 addresses this problem).

I don't think we should hide our ignorance of phylogeny.