Talk:Placodermi

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Untitled[edit]

In the "See Also" section, do people think it's best to leave Dunkleosteus terrelli as it is, pointing at a redirect, or change it to Dunkleosteus terrelli, which doesn't redirect but doesn't look as nice. 193.63.43.10 13:32, 26 March 2007 (UTC)

Article doesn't exist[edit]

I'll have to delete this link, the article doesn't work http://www.amonline.net.au/archive.cfm?id=1137

--HoopoeBaijiKite 20:50, 18 June 2007 (UTC)

Taxobox Picture Question[edit]

Why is it so horrible to use this picture [1] in the taxobox?--Mr Fink (talk) 05:18, 21 April 2008 (UTC)

Nothing wrong in terms of accuracy as fas as I can tell, so why not using it either in the taxobox or in the text? ArthurWeasley (talk) 20:15, 21 April 2008 (UTC)
  • Seems like Nicolás10 has an aversion towards strong contours and bright colours, which is a rather silly rationale for removing images. There is room for both. Funkynusayri (talk) 01:54, 29 April 2008 (UTC)

Placoderms and sharks are not sister-groups[edit]

" ...when more fossil specimens were found, especially the exceptionally well-preserved fossils from the Gogo Reef formation in Australia, Stensiö's theory of sharks and placoderms as sister groups became accepted as fact."

This statement is misleading. While Stensiö's work remains highly respected, the idea of a sister-relationship between chondrichthyians and placoderms has been almost universally rejected by vertebrate palaeontologists since the mid-1990s. The current consensus is that placoderms are stem-gnathostomes and are thus no more closely related to sharks than bony fish are. The Gogo fossils provided strong evidence *against* a placoderm-shark relationship (Gogo placoderms show separate bone for the nasal capsules which are incorporated into the braincase of sharks and bony fish). If no one objects, I will rewrite this section ASAP.

REFS = Goujet, Daniel & Young, Gavin (2004). Placoderm anatomy and phylogeny: new insights. (in) Arratia, Wilson and Cloutier (eds) Recent Advances in the Origin and Early Radiation of Vertebrates. Verlag Dr. Friedrich Pfeil, Munchen, Germany.

Young, G.C. & Goujet, D. & Lelievre, H. (2001) Extraocular muscles and cranial segmentation in primitive gnathostomes - fossil evidence. J. Morphology. 248:304.

Phillipe Janvier's page at the tree of life = http://www.tolweb.org/Gnathostomata/14843

John Long - personal communication.

Ozraptor4 (talk) 01:46, 13 June 2008 (UTC)

We should elaborate more on why Stensiö's theory has been rejected in favor of placoderms being stem-gnathostomes, like, listing some more traits that the Gogo reef placoderms have demonstrated to have in common with all/most other gnathostomes.--Mr Fink (talk) 03:30, 13 June 2008 (UTC)
Absolutely - the process which settled the relationships of placoderms to other fish was as intense and complex as the bird-dinosaur ancestry debate. I have most of the key papers on the subject but will take a little while to condense the main points into a succinct and readable account. Note that the Gogo placoderms were probably eclipsed in importance by Taemas-Wee Jasper material in settling the debate. All the Gogo placoderms are highly derived while the older NSW material represents fine preservation of much older/primitive forms. Ozraptor4 (talk) 11:47, 14 June 2008 (UTC)
Like, concerning how Brindabellaspis' braincase anatomy has more in common with various agnathans?--Mr Fink (talk) 18:06, 14 June 2008 (UTC)

Descendants of this group of species?[edit]

This article is well done, but conspicuously omits information that would describe the connections between Placodermi and other lineages of fish. Contextual information of this kind was what I was looking for. Janice Vian, Ph.D. (talk) 16:59, 15 November 2012 (UTC)

Well, the page is a work in progress, and we need to write in (and source) that the Placoderms are an extinct sister taxon of all other jawed vertebrates, i.e., the group was the first to diverge from the ancestral gnathostomes sometime during the start of the Silurian. Having said that, the Placoderms left no descendants, having all died out by the very end of the Devonian.--Mr Fink (talk) 17:08, 15 November 2012 (UTC)

Placoderm Diagram[edit]

This thread has been relocated from User talk:Epipelagic

Shouldn't all of the orders end at the end of the Devonian? I've never heard of any ptyctodontids surviving into Early Carboniferous time.--Mr Fink 05:49, 19 February 2013 (UTC)

Hi Mr Fink. That's some good work you have done on palaeontology articles down through the years. Yes, I think you are right. My initial concern was to faithfully present the data as Michael Benton presented it in Vertebrate Palaeontology 2005. The diagram is based on his chart on page 73. This clearly shows ptyctodontids surviving for a short period into the Carboniferous. I was tempted to treat this as an error, and adjust the chart. But then I noticed that Benton does the same again with another chart on page 35, and again shows the clear survival of a small number of placoderms into the Carboniferous. I used this as a basis for this chart. So now I don't think it is appropriate to adjust the charts without good reason. Benton doesn't seem to mention the matter in his text, but surely he wouldn't have done that unless he had good reason. I haven't made any assertions about the matter in the Wikipedia articles, but have merely said that the charts are based on Benton, which is true. I can't find any references to placoderms or ptyctodontids surviving beyond the Devonian, though page 7 here refers to Carboniferous records for placoderms as being potentially "reworked fossils". So what do you suggest? Maybe we could just comment in a footnote that Benton shows some survival into the Early Carboniferous, though this appears to be an error. Or do you think we should modify the chart, and put a footnote that it has been modified? Or ask Benton whether it was an error or not? --Epipelagic (talk) 07:25, 19 February 2013 (UTC)
I guess to avoid synthesis, we should leave it as is, aside from mentioning that it was based on Benton's notes. But, one of us definetly should contact Benton to ask about those Carboniferous ptyctodonts. From what I've been able to glean of the matter, all "Carboniferous" placoderms have turned out to be either a) reworked fossils/zombie taxa, b) mistaken identification, or c) from strata later reappraised to be (Late) Devonian.--Mr Fink 18:44, 19 February 2013 (UTC)
Pages 18–19 of Douglas Palmer's 1999 The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals has a chart mapping out the evolution of the placoderm orders. It is very much aligned with Benton's chart, and shows the ptyctodontids as progressing clearly into the Carboniferous. However he doesn't mention his source. --Epipelagic (talk) 04:16, 21 February 2013 (UTC)
Oh, if that's the case, then I suspect that Palmer and Benton are using very out of date sources.--Mr Fink 03:09, 22 February 2013 (UTC)
Here's a more recent source from the University of South Dakota claiming placoderms survived to the "end of Permian" (slide 9). On the other hand Janvier, in Early Vertebrates 1995, specifically excludes ptcytodonts on page 291 "A sudden extinction of the major placoderm taxa occurs, however, at the Fammennian-Carboniferous boundary. Although represented by a variety of taxa (antiarhs, arthrodires, ptcytodonts, and phyllolepids) up to the latest level of the Famennian, no placoderm survives into the Carboniferous." --Epipelagic (talk) 04:08, 22 February 2013 (UTC)
I'm inclined to trust what Monsieur Janvier says, as he's a noted specialist of Paleozoic fishes, placoderms and agnathans in particular.--Mr Fink 04:11, 22 February 2013 (UTC)
Yes of course. That's why I pointed to him. But the source to Janvier is the most dated of the lot, and Benton is not to be ignored either. Nelson in his Fishes of the World 2006 says there "is no clear evidence of placoderms surviving a major extinction event into the Lower Mississippian", and cites:
  • Carr, R.K. 1995. Placoderm diversity and evolution. VIIth International Symposium: Studies on Early Vertebrates. Bulletin du Muséum d’Histoire Naturelle, 17: 85–125.
  • Maisey, John G (1996) "Fossil Fishes: So Much Diversity, So Little Change". Natural History, 105 (6).
This is not the same as saying it didn't happen.
The Britannica article states that placoderms "existed throughout the Devonian Period (about 416 million to 359 million years ago), but only two species persisted into the succeeding Carboniferous Period."
This 2010 paper has a chart on page 473 clearly showing some placoderms as crossing the Devonian Carboniferous boundary. --Epipelagic (talk) 07:33, 22 February 2013 (UTC)
I just find it frustrating that no one seems able to put names on who these Carboniferous placoderms were. That, and I would be more to accept the placoderms surviving into the Carboniferous if we were able to find literature more substantial than just tantalizing snippets and graphs.--Mr Fink 16:46, 22 February 2013 (UTC)
There must be more relevant stuff out there somewhere. Kotpal in Modern Text Book Of Zoology Vertebrates 2010 says on page 132 that they "became extinct in Permian" Also, see his chart on page 103. --Epipelagic (talk) 22:59, 22 February 2013 (UTC)
I wonder if Kotpal was confusing placoderms with acanthodians or still thinking that acanthodians were a subgroup when writing that. Plus, it doesn't seem like a very well-researched chapter if it states that there are only two orders of placoderms.--Mr Fink 04:14, 23 February 2013 (UTC)
Yes, I had the same thoughts, I don't think that one's reliable. Other recent Indian texts seem to have similar confusions. Let's keep looking, and ask Janvier and Benton for input if it's too unclear. --Epipelagic (talk) 05:13, 23 February 2013 (UTC)

Anatomy diagram[edit]

Here's another issue. Should the drawing of Coccosteus decipiens, used as the basis for the anatomy diagram, have an anal fin? --Epipelagic (talk) 08:01, 23 February 2013 (UTC)

Yes, as fossils of C. decipiens clearly show an anal fin. [2] (i.e., the spot underneath the posterior end of the dorsal fin)--Mr Fink 14:04, 23 February 2013 (UTC)
The drawing of a Coccosteus on page 32 of Palmer's Dinosaurs and Prehistoric Animals has no anal fin. Nor do these depictions show an anal fin: [3] (Fig. 271), [4] and [5]. If you search on "anal fin" in this rather dated book you will find comments such as: "Agassiz in his restored figure has represented... a dorsal and anal fin situated opposite each other... there is no anal fin in Coccosteus... It is this peculiar lengthening of the haemapophyses under the dorsal... which has evidently given rise to the old idea of the presence of an anal fin... though M'Coy had previously strongly doubted the existence of an anal fin in Coccosteics, Pander's figure has been copied into almost every text-book... the anal fin is also mentioned as present by Zittel in his handbook. M'Coy was, however, correct — there is no anal fin in Coccosteus". --Epipelagic (talk) 08:51, 25 February 2013 (UTC)
You're right: After checking Denison's book, I realize I keep confusing the postanal plate with the anal fin. How embarrassing. Should we modify the picture, then?--Mr Fink 15:19, 25 February 2013 (UTC)
I've modified it. Don't be embarrassed, I get thing wrong too. --Epipelagic (talk) 05:35, 26 February 2013 (UTC)

Claspers[edit]

The deleted part says "The males reproduced by inserting a long clasper, the basipterygium that was fused to part of the pelvic girdle." This is no longer correct, as the new link explains in the article: "Unlike the claspers of modern sharks and rays that are a part of the paired pelvic fins, the claspers and female basal plates in placoderms were not at all connected to that fin."

Neither are they no longer considered the sister group to all jawed vertebrates, but their direct ancestors, as mentioned in the article about Gnathostomata. 84.210.10.52 (talk) 13:07, 29 June 2014 (UTC)

Technically speaking, a taxon can be regarded as the sister taxon to its direct descendant daughter taxa.--Mr Fink (talk) 20:01, 29 June 2014 (UTC)