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Article states: "The gills of osrtacoderms were used not for feeding, but for respiration." Isn't this the normal use for gills? What am I missing? Jeffrey L. Whitledge 22:09, 2004 Oct 20 (UTC)
This is the first time "gills" were used solely for respiration. Previously they were part of the feeding apparatus. At least that is what's meant. If I'm wrong, please LMK.--DanielCD 12:12, 21 Oct 2004 (UTC)
- That's a lot clearer now, thanks. (I just hope that it's true! :) ) Jeffrey L. Whitledge 21:06, 2004 Oct 22 (UTC)
I'm going to look for some refs. If you would like to nominate this for deletion on those grounds, please message me first. --SpencerTC 03:31, 25 February 2006 (UTC)
- What, nominate for deletion on the grounds that you're looking for refs? :) --M1ss1ontomars2k4 | T | C | @ 03:58, 16 May 2006 (UTC)
Ostracoderms are not a good evolutionary taxon.
"There is a number of taxa of fossil jawless vertebrates which were formerly referred to as the "ostracoderms" ("shell-skinned") because most of them possess an extensive, bony endo- and exoskeleton. The "ostracoderms" lived from the Early ordovician (about 480 million years ago) to the Late Devonian (about 370 million years ago). The relationships of the various groups of "ostracoderms" has been the subject of considerable debate since the mid-nineteenth Century, and the theory of relationship proposed here is far from definitive, yet the best supported by the currently available data. The "ostracoderms" are represented by five major groups, four of which are almost certainly clades: the Heterostraci, Osteostraci, Galeaspida, Anaspida, and Thelodonti (the monophyly of the latter being debated, Thelodonti page). In addition, there are minor groups which only include a few species: the Arandaspida, Astraspida, Eriptychiida, and Pituriaspida. The Arandaspida, Astraspida, Eriptychiida, and Heterostraci are regarded as forming a clade, the Pteraspidomorphi. Some monospecific genera, Jamoytius, Endeiolepis, and Euphanerops, formerly referred to the Anaspida, are now removed from that clade and may be more closely related to lampreys (see Hyperoartia)."
- Yes, it is an excellent evolutionary taxon, but it is not a phylogenetic taxon. The grpup is most certainly ancestral to the jawed vertebrates, and thus form an evolutionary grade of advanced jawless fishes. Petter Bøckman (talk) 08:47, 12 October 2011 (UTC)
- Yes, it seems to be so. I tried to clear this question; the best prooflink that I found is this. Stas000D (talk) 14:09, 9 November 2012 (UTC)
- (update): the best candidate is Pterichthyodes, an antiarch placoderm. Stas000D (talk) 19:32, 9 November 2012 (UTC)
There seem to be two contradictory statements on whether we will find ostracoderms as a group in the classification system:
The term does not often appear in classifications today because it is paraphyletic or polyphyletic, and has no phylogenetic meaning.
The Subclass Ostracodermi has been placed in the division Agnatha along with the extant Subclass Cyclostomata, which includes lampreys and hagfishes.