Talk:Trilobita

From Palaeos

Building From The Bottom of the Seafloor Up

I'm building trilobita bottom up, using Gon, Mikko, wikispecies, Fortey, the Treatise, and a plethora of other references. This will take some time, and the effort will spill over into "early" arthropods.RogerPerkins 15:33, 24 November 2006 (PST)

Were the trilobites, or their elder cousins the "proarthropods" the basal arthopods?--Stanton 15:49, 24 November 2006 (PST)

I guess early is a better term than basal, given the great arthro diversity in the lower C, and the zip pre-C fossil record. I tend to favor Fortey's argument to include Trilobita in Chelicerata, but there are several competing phylogenies out there. I think trilobitamorpha is a decreasingly used catch all.RogerPerkins 16:31, 24 November 2006 (PST)

Hmmm... In that case, then, should we include the proarthropods, like Sprigginia and Parvacorina, with the trilobites' article, or should we have a separate page?--Stanton 21:03, 24 November 2006 (PST)

You mean Parvancorina ;-) Even if they are arthropods (which I don't think they are - personally i'm quite partial to Seilacher's Vendozoa/Vendobionta hypothesis - but anyway) they aren't trilobites, so they would go in a different category M alan kazlev 00:56, 25 November 2006 (PST)

Shoehorning And Other Fun Stuffs

Where should we put Nectaspida?--Stanton 13:09, 24 February 2007 (PST)

My own view is not with trilobites, in spite of their nickname "soft bodied trilobites". As you know, trilobite phylogeny is confounded despite >10K described bugs and a myriad of papers. The understanding of arthropod descendency is many fold worse. I would favor a category "trilobites relatives" (with a redirect from Nectaspida, etc.) to discuss possibilities. Or just have a section on the trilobites page covering this. Everything would be easier if we knew trilobites belonged with Chelicerata aka Arachnomorpha. Wikipedia, wikispecies and TOL all throw up their hands and use trilobitomorpha -- maybe we should capitulate and do the same. Anyway, I'm dredging the more recent literature. RogerPerkins 15:39, 24 February 2007 (PST)

What is the recommended reading on trilobites? My biggest problem is that I never know what research documents to search for, nevermind where to find them localy.--Theburk 08:25, 22 March 2007 (PDT)

By the way, in looking at the trilobites bytes in wikipedia, I'm finding a number of errors, caused by people using search engines, as opposed to going to the literature, e.g., "trilobite had the first true eyes " - yea, right! RogerPerkins 15:39, 24 February 2007 (PST)

I've seen that, too... Who's saying that?--Stanton 16:46, 24 February 2007 (PST)

Ya but this is Wikipedia we are talking about, I'm a member of a satrical wiki called Encyclopedia Dramatica and we constantly have conflicts with them, their mods are insane. This little bit of information from that page confuses me: " Based on the size, location, and shape of the horns, Rob Knell, a biologist at Queen Mary, University of London and Richard Fortey of London's Natural History Museum, concluded that the most likely use of the horns was combat for mates, making trilobites the earliest exemplars of this behavior." i find this strange considering that with the exception of those odd specimins with the flower shaped apperatus on its head, few of them have foreward faceing spines, and most of the horns curve backwards, most likely foiling predators, and with so many legs id love to see one try to acheive ramming speed, nevermind that healed cephalon cracks arent suddenly more common in that time period. they also link sharks to the extinction of trilobites, but, sharks would only be a real threat to free swimming trilobites (if that, sharks dont have crushing teeth), there are plenty of gnathostome fish that would be threatening to them however. im also surprised they didnt mention isopods, because to me isopods are the crustacean answer to the trilobites they also appear right after the trilobites died out dominating most of the trilobites neiches, i do however believe (hope) that there may be 1 or 2 modern trilobite species somewhere in the vast unexplored sea floor plains.--Theburk 08:23, 22 March 2007 (PDT)

I propose we give the "trilobitomorphs" their own page(s), though we should first mention them on this page.--Stanton 16:46, 24 February 2007 (PST)

It might be possible to use "Trilobitomorpha" for the larger trilobite clade - i. e. anything more closely related to trilobites than any living arthropods (I believe I have seen this done in recent publications, but unfortunately I can't recall the references). Seeing as Naraoia and cronies are probably the closest known relatives of "true" trilobites, it's largely a matter of personal taste whether to include them in Trilobita or not--Christopher Taylor 09:58, 25 February 2007 (Perth)

In one senseit's like "how many angels can dance on the head of a pin". On the other hand, including Naraoia to the exclusion of many other lower cambrian arthropods (> 150 from Chengjiang alone) just means a line has been moved a bit. BTW, Fortey seems to prefer Arachnomorpha, though I don't remember why. RogerPerkins 15:10, 25 February 2007 (PST)

Arachnomorpha is a larger clade, containing chelicerates and all taxa closer to them than other living arthropods. The phylogeny of the Cambrian arthropods tends to shift a fair bit, so Fortey may be avoiding anything too fine-tuned.--Christopher Taylor 09:34, 26 February 2007 (Perth)

I've just put up phylogenies for Arthropoda and Arachnomorpha to hopefully help a little--Christopher Taylor 09:56, 26 February 2007 (Perth)

Where do these come from Christopher - I've wondered for quite awhile now? I just went back and read: Fortey RA A. 2001. Trilobite systematics: The last 75 years. Journal of Paleontology 75:1141–1151.; it had been a few years. What I like about Fortey is that he delineates between fact, fiction and speculation; apparently, when you reach his level of stature, you can adhere to the scientific cautionary principle. All his statements have appropriate caveats. I recommend we collectively use this 2001 paper as the trilobite / arthropoda guiding light. I’m unaware of any startling cladistics studies that would render his review dated. Also note his differentiation between trilobites and soft-bodied trilobites, i.e., the lack of a calcareous exoskeleton in the latter. Given the many other lower Cambrian arthropods with cuticles, I vote for not making the softies a 10th Order. RogerPerkins 08:46, 26 February 2007 (PST)

Good point... Plus, I always thought that the Naraoiids were included with the trilobites because their leg-anatomies were so similar.--Stanton 08:50, 26 February 2007 (PST)

The basis for the basalmost Arthropoda tree comes from Budd (2002), which includes a cladistic analysis and a review of the difficult question of identifying segment homologies in early arthropods (but like all Nature papers, it's annoyingly brief). The Arachnomorpha phylogeny comes from Bousfield (1995) which is a little dated, and presents an intuitive phylogeny rather than a proper analysis - hopefully I get something more recent there eventually. Now if I could just decide where to put those damn pycnogonids... If you mean where do any of the dendrograms I put up come from, I've been compiling them for a few years now from the literature. Needless to say, because the number of sources I've been through to date is only the minutest fraction of what is out there, and because my methods of selecting what to go through next are largely random, anything I put up is woefully incomplete--Christopher Taylor 10:14, 27 February 2007 (Perth)