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Natural Science Forum / Biology / Paleontology / September 2004Largest extinct clade?
Can anyone think of the largest extinct clade? Fine print: By "largest" I mean greatest number of known species. And by "extinct clade" I mean a monophyletic group none of whose members have survived to the present. Thus Dinosauria is not an extinct clade, but Ornithischia is. You may if you like consider the potential taphonomic biases at work too. The extent of a group's fossil record may not be a reliable measure of its past diversity. The candidates I came up with immediately were Paleodictyoptera (which may be a clade) and Trilobita (which certainly is, though there may be a somewhat more inclusive, and thus even bigger, clade to consider if we had a good handle on what it included). This was prompted by consideration of some bizarre, relict distributions in living birds. We now know that grebes are the living sister group of flamingos, and that the kagu (home: New Caledonia) and sunbittern (South America) are sister groups. Both of these, to me at least, imply a much larger radiation about which we currently know nothing at all. Which led by a chain of free-association to musings about what we can know about past biotas, and eventually to the present question. >The candidates I came up with immediately were Paleodictyoptera (which >may be a clade) and Trilobita (which certainly is, though there may be a >somewhat more inclusive, and thus even bigger, clade to consider if we >had a good handle on what it included). If one is talking about known species ... then you've probably got a better idea than me of clade sizes (and formal names), but ammonites were a speciose clade. Also graptolites and conodonts, tho' I'd expect these to smaller (graptolites being pelagic, IIRC). Otherwise, one might imagine that some extinct clade of beetles, perhaps scarcely known or unknown in the fossil record, is the largest extinct clade.  SignatureStewart Robert Hinsley >>The candidates I came up with immediately were Paleodictyoptera (which >>may be a clade) and Trilobita (which certainly is, though there may be a [quoted text clipped - 5 lines] > were a speciose clade. Also graptolites and conodonts, tho' I'd expect > these to smaller (graptolites being pelagic, IIRC). I thought of those (and Ammonoidea would be much larger than ammonites), but I think both Trilobita and Paleodictyoptera would be larger still. > Otherwise, one might imagine that some extinct clade of beetles, perhaps > scarcely known or unknown in the fossil record, is the largest extinct > clade. I don't know of any extinct families (or larger group) of beetles. Then again I haven't looked. Does anyone have that information? It has to be a monophyletic family too. Paleodictyoptera is an order of insects, but of course we know little of its actual diversity. > If one is talking about known species ... then you've probably got a > better idea than me of clade sizes (and formal names), but ammonites > were a speciose clade. Also graptolites and conodonts, tho' I'd expect > these to smaller (graptolites being pelagic, IIRC). Well, graptolites don't really have to be supposed to be extinct. Beklemishew (1951, 1970) erected Graptolithoidea to encompass extinct Graptolithina (Stolonoidea + Camaroidea + Tuboidea + Dendroidea + Graptoloidea) and recent Pterobranchia (Rhabdopleuroidea + Cephalodiscoidea). More recently Dilly (1993) suggested that the extant Cephalodiscus graptolitoides Dilly, 1993 can be in fact classified as a graptolite. Recent investigations (eg. Urbanek and Dilly, 2000; Mierzejewski and Kulicki, 2001) not only confirms the idea of Beklemishew's Graptolithoidea, but also shows that Pterobranchia, or pterobranchs, should be used only as a common, non-taxonomic, name for extant orders of graptolites (Graptolithoidea). I encourage You to read the following, especially the Introduction, which I used writing my answer: Mierzejewski, P. and Kulicki, C. 2002. Discovery of Pterobranchia (Graptolithoidea) in the Permian. Acta Palaeontologica Polonica 47 (1): 169-175. Downloadable from: http://app.pan.pl/acta47/app47?169.pdf Cheers, and like always sorry for my poor English, Dawid. >>If one is talking about known species ... then you've probably got a >>better idea than me of clade sizes (and formal names), but ammonites [quoted text clipped - 13 lines] > graptolites (Graptolithoidea). I encourage You to read the following, > especially the Introduction, which I used writing my answer: Does that mean that known extinct graptolites do not form a clade unless you include extant pterobranchs? Otherwise they would count. > Mierzejewski, P. and Kulicki, C. 2002. Discovery of Pterobranchia > (Graptolithoidea) in the Permian. Acta Palaeontologica Polonica 47 (1): > 169-175. > > Downloadable from: http://app.pan.pl/acta47/app47?169.pdf I tried that, and I downloaded a file of some weird type that Acrobat won't recognize, and which I therefore can't read. Hello. > Does that mean that known extinct graptolites do not form a clade unless > you include extant pterobranchs? Otherwise they would count. Yes. You have to include extant pterobranchs. > I tried that, and I downloaded a file of some weird type that Acrobat > won't recognize, and which I therefore can't read. http://app.pan.pl/acta47/app47-169.pdf That's the proper link. I don't know why You cannot read it. Cheers, Dawid. > Hello. > >>Does that mean that known extinct graptolites do not form a clade unless >>you include extant pterobranchs? Otherwise they would count. > > Yes. You have to include extant pterobranchs. I see no such claim in the paper. >>I tried that, and I downloaded a file of some weird type that Acrobat >>won't recognize, and which I therefore can't read. > > http://app.pan.pl/acta47/app47-169.pdf > That's the proper link. I don't know why You cannot read it. It worked that time. But I don't see anything that makes the claim of graptolite paraphyly, much less presents evidence for it. All I see is this sentence: "It is remarkable that morphological differences between some living and fossil sessile Graptolithoidea are less pronounced than the differences between the sessile and the planktic orders within this class (Urbanek 1986)." But the degree of morphological difference doesn't make a clade or non-clade. This paper doesn't say whether the extinct or extant groups are or are not clades. Perhaps some of the references do, e.g. Urbanek and Dilly 2000? |
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