Bivalves-first molluscs (my cladogram)
barry_roth at YAHOO.COM
Tue Aug 27 20:37:33 CDT 2002
In his post below, Ken Kinman selectively quotes from a post by David R. Lindberg to the Mollusca list. In the spirit of full disclosure, I here pass along Dr. Lindberg's message in its entirety, for which I trust David will forgive me:
Kinmans bivalve-first hypothesis of molluscan origins fails not because malacologists have been mislead by convergence or are unwilling to consider alternative phylogenies, but rather for the most basic of reasons - it is overwhelmingly contradicted by scientific evidence as both Haszprunar and Giribet have alluded to. Kinmans postings are riddled with special pleadings "look to me", "could have been preceded by", "could have later evolved", "And doesn't it make sense", "thus explaining", "probably also had", "would have forced", "there are also perhaps", "probably gave rise to", "Therefore, in my opinion." Yes, one can imagine all kinds what if and just so scenarios for molluscan origins, as well as the extinction of the dinosaurs and the creation of the Cobb Salad, but thats not science folks (see OHara 1988, Systematic Zoology 37:142-155). Science requires a specific model that can be tested, and ALL of the tests that have been performed up to now (morphological, molecular, stratigraphic) falsify a bivalve-first hypothesis of molluscan origins.
It has taken the better part of 2400 years for classification to move from the alchemy of Aristotelian essentialism to the organizing principal of modification with descent. There also exists today the methodologies to rigorously quantify characters states and examine their distributions algorithmically, and it is this paradigm shift that has moved systematics from an arcane Greek art to a modern science. Moreover, the power of this methodology to examine alternative hypotheses is readily demonstrated by testing Kinmans what if scenarios.
Kinman has proposed that Sacoglossa may be more closely related to bivalves than other gastropods or are the first (semi-torted) gastropods and maintain the plesiomorphic bivalved-shell. To test the Kinman hypothesis take the bivalve and gastropod character states from the Ponder & Lindberg (1997) analysis, score your favorite sacoglossan taxon for the same characters, enter the matrix, and hit return. I look forward to seeing any tree that has a Sacoglossa + Bivalve clade or the Sacoglossa at the base of a gastropod clade. If such a tree cannot be found, we must reject the Kinman hypothesis and move on to another topic - How about that Sowerby dynasty?
I also observe that at this juncture in the discussion, the epithet "'strict' cladists" has reared its head.
Ken Kinman wrote:
The debate over my "bivalves-first" hypothesis continues on the
molluscalist newsgroup. Below is a cladogram with synapomorphies for my
proposed subclades of Mollusca according to my tree topology (upside down from the way it has long been taught).
> I hope that someone will indeed run the test which Dr. Lindberg
>suggested (I don't have the necessary literature yet). And perhaps also
>plug in the MESENTOBLAST data as well (which is one of the newest
>phylogenetic characters now being used). Thus I am putting sacoglossans in
>a clade with their euthyneuran descendants, and then streptoneurans alone
>("real torsion" clade) splitting off next----a few primitive streptoneurans
>might still develop the mesentoblast at the 24-cell stage, but the vast
>majority apparently delay such "4d formation" until about 40 or 63 cells.
>Polyplacophora apparently delay even longer (72-cell stage).
> The big question in my mind is whether protobranch bivalves develop
>their mesentoblast at the 24-cell stage (I haven't been able to find out
>yet). I have added this character to the synapomorphy list below. Anyway,
>perhaps the new popularity of "mesentoblast timing" as a character will
>make the skeptics at least a bit less skeptical of my hypothesis? The
>dinosaur researchers laughed their heads off (on DML) when I proposed
>oviraptorosaurs were closely related to confuciusornithid birds, but then
>Maryanska et al., 2002, published a cladistic analysis which independently
>came up with the same conclusion. Will I be that lucky with molluscs?
>We'll just have to wait and see. I am thus accustomed to having my methods
>branded as "unscientific", especially by "strict" cladists. :-)
> ----- Cheers, Ken Kinman
>Dr. Lindberg wrote (on molluscalist):
>>Kinman has proposed that Sacoglossa may be more closely related to
>>bivalves than other gastropods or are the first (semi-torted) gastropods
>>and maintain the plesiomorphic bivalved-shell. To test the Kinman
>>hypothesis take the bivalve and gastropod character states from the Ponder
>>& Lindberg (1997) analysis, score your favorite sacoglossan taxon for the
>>same characters, enter the matrix, and hit return. I look forward to
>>seeing any tree that has a Sacoglossa + Bivalve clade or the Sacoglossa at
>>the base of a gastropod clade. If such a tree cannot be found, we must
>>reject the Kinman hypothesis and move on to another topic.
Do You Yahoo!?
Yahoo! Finance - Get real-time stock quotes
More information about the Taxacom