On a completely different note

Very nice stuff on Precambrian and Cambrian beasts in the newest issue (vol. 45, no. 1; January 2002) of the journal _Palaeontology_. I'm still reading the articles, but

John, Horseshoe crab diversity was actually highest during the Paleozoic, and they just barely made it through the Permian extinction. In fact, it seems rather remarkable that they made it through to the Mesozoic and that the once extremely common trilobites did not. Horseshoe crabs (Class Xiphosurea) go all the way back to the Cambrian. The living Order Limulida alone goes back to the Devonian, and the closely related Order Pseudoniscida is known from Cambrian to Devonian. Order Synziphosurida (Silurian -Devonian) branches out a little further, and Chasmataspida would go from Ordovician to Devonian (if Diploaspida is included in it rather than as a separate Order). Don't be too surprised if we someday find primitive soft-shelled horseshoe crabs in the Upper Precambrian.

I seriously doubt that. You must be envisioning different lineages of soft bodied Precambrian proto-arthropods evolving external skeletons independently and thus transforming themselves into different lineages of Cambrian arthropods. That sounds about as likely as Simpson's parallelophyletic origin of mammals.

I think I know what Kinman means when he said that the Cambrian explosion is a 'myth' and that it is really an explosion of hard parts. He probably thinks that most, if not all, of the arthropod lineages were already in existence prior to the Cambrian, and that these lineages somehow independently acquired their exoskeletons. They were not preserved before the Cambrian because they lack the easily preserved hard body parts, not because they were not around.

Ben, I also took into account the views of Starobogatov, and my Class Xiphosurea is basically the same as his Subclass Limuliones. He regarded it as a holophyletic group, but I think it is probably paraphyletic. Of course, paraphyletic taxa don't bother me, so I will continue to include Chasmataspids in Class Xiphosurea anyway. Whether Strabopids should remain in there is very uncertain. Aglaspids, Cheloniellids, and other 'protrilobite' groups really muck up the big picture (not to mention pycnogonids). By the way, have you seen anything published on the theory that pycnogonids (pantopods) are related to mites (and therefore arachnids)? Sounds a little 'far out', but who knows. Would be nice to get their affinities narrowed down, and some workers don't even think they are real chelicerates.

OK

Ben, Actually Dunlop and Selden place Chasmataspids as sister to the clade Eurypterida-Scorpiones-other arachnids. But that was before Braddy et al.'s 1999 paper in Lethaia (Lamellate book-gills in a late Ordovician eurypterid from the Soom Shale: Support for a eurypterid-scorpion clade). The latter paper supports my Class Scorpionea (for eurypterids and scorpions) and Class Arachnidea sensu stricto (without scorpions). The question now is whether Chasmataspids are sister group to: (1) Scorpionea alone; (2) Arachnidea alone; or (3) a Scorpionea-Arachnidea clade. In any case, it contradicts the 1990 cladistic analysis in Cladistics (by Shultz) which showed scorpions nested well within the arachnids. Needless to say, I am glad I didn't follow that cladistic analysis. The Starobogatov paper was 1990, Paleontol. Zh., 1990(1):4-17, entitled 'The Systematics and Phylogeny of the Lower Chelicerates'. Well, I've got to get back to theropods.

I went to the library to look at this one, and, yeah, super weird. What would it have been living on mostly buried like that? I don't suppose the margins of the vanes are preserved well enough to say anything about that, are they?

But the big question is: why is _Pteridinium_ as a freaky-weird unicellular organism more plausible than _Pteridinium_ as a freaky-weird multicellular one? I really don't see it.

Kinman is disingenuous. It bothers him so much that he will not, as a rule, recognize multiply paraphyletic taxa. It bothers him so much that he will stigmatize paraphyletic taxa with markers. It bothers him so much that he tried to dismantle the paraphyletic colubrid snake genus Elaphe. It bothers him so much that he brings up the possibility that Chondrichthyes may be degenerate bony fishes, and thus making Osteichthyes paraphyletic. OTOH, paraphyletic taxa really do not bother the Darwinians, since the Darwinians treat these taxa the same as holophyletic taxa, and recognize them without any conditions.

That is clear illustration of the instability of cladifications, including Kinman's version. As Mayr and Ashlock (1991) point out, different cladists often disagree on branching order since their character sets are different, and slight differences in branching order can have major differences in the subsequent cladificaiton. Simpson is right. Classification should not attempt to reproduce every detail of phylogeny, since phylogenetic history cannot be directly observed and therefore there will always be uncertainties in the inference of branching order. There is still no better way to depict phylogeny than a tree. The cladists' attempt to reproduce trees with classifications is