Talk:Chordate

Pigment & Differential Biology
There are some soft constraints that separate Chordata from other biological lineages, but have not yet been made part of the formal definition.
 * Pigmentation : Chordata are not capable of blue pigmentation, that is to say blue skin pigmentation. Blue skin pigmentation is not to be confused with the biological alteration of (for example) feathers in birds -- that appear blue via an evolved prism mechanism in the feather structure.

There still is a lot of differential (DNA sequence based) comparison research going on that is trying to separate out the simplest forms of chordata. As around 90% of the species on Earth don't have a backbone like chordata. Some of these species may have lost their chordata like structures over time and this complication continues to complicate the complete definition of Chordata. Eyreland (talk) 03:04, 10 September 2016 (UTC)

What about blue skinned frogs, blue skinned monkeys like mandrills, blue skinned wattles on turkeys and cassowaries and blue fish? Are none of those pigmented? — Preceding unsigned comment added by 51.6.66.130 (talk) 09:14, 6 February 2017 (UTC)


 * Good point, I have removed it as unsourced, and contradicted by many creatures. --Jules  (Mrjulesd) 02:20, 13 March 2017 (UTC)

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Cladogram
The cladogram under phylogeny is so full of problems that it should be edited or removed: Condrychthyes is missing! Sarcopterygii appears to be a synonym of Tetrapods! — Preceding unsigned comment added by Gabe Lemag (talk • contribs) 17:33, 5 March 2018 (UTC)
 * I agree that is could be improved, but I oppose removal. The Chondrichthyes could be included; the Sarcopterygii gave rise to the tetrapods (plus a few odd fish such as the coelacanths and lung-fish) and this is consistent with the cladogram. --Jules  (Mrjulesd) 17:46, 5 March 2018 (UTC)

Rank of Tetrapoda and Sarcopterygii
This sentence doesn't make sense:
 * Benton included the Superclass Tetrapoda in the Subclass Sarcopterygii

You can't have a superclass within a subclass - should it be the other way round? 31.50.203.97 (talk) 11:48, 15 September 2019 (UTC)
 * Some of Benton's rank usage is rather ideoscncratic. He can use the same rank several times in a taxonomic heirarchy and he does use higher ranks for groups like Tetrapoda and Aves. If you look at the Appendix in the 4th edition of his Vertebrate Palaeontology, you can see on p436 that he does list Superclass Tetrapoda under Subclass Sarcopterygii. The online classification for the third edition has the same, but I can't find it online now. Below is the listing:
 * Subclass Sarcopterygii
 * Order Dipnoi
 * Infraclass Crossopterygii
 * †Order Porolepiformes
 * Superorder unnamed
 * †Order Onychodontida
 * Order Actinistia
 * Infraclass Tetrapodomorpha
 * †Order Rhizodontida
 * Superorder Osteolepidida
 * †Order Osteolepiformes
 * †Family Tristichopteridae
 * †Order Panderichthyida
 * Superclass Tetrapoda
 * I know it is confusing, but that is correctly quoting the source. It might be better to omit his ranks and just state that Tetrapoda are placed within Sarcopterygii.
 * An example of repeating the same rank occurs within Reptilia. He uses Division Archosauriformes under Infraclass Archosauromorpha and later uses Division Mesoeucrocodylia under Order Crocodylia and Division Coelurosauria under Infraorder Tetanurae. Division is used at three different levels within the same taxonomic hierarchy.  Jts1882 &#124; talk 15:01, 15 September 2019 (UTC)

Cephalochordata: (Acrania) or (Acraniata) or nix the lot?
In the classification section, Cephalochordata is listed with Acraniata in brackets behind it. Haeckel's 1866 Acrania is considered synonymous with Cephalochordata according to its page (though it is also shown on a specific internal branch of the tree of that page, which is a problem all of its own), but I am not sure of the taxonomic history of Acraniata. The Acraniata page is a redirect to Invertebrate, whereas Acrania page is for the developmental defect by the same name (not linked here to spare the reader some pretty graphic imagery). There seems to be some chaos here that needs to be straightened out. Can we remove the piece in brackets, as Cephalochordata is simply the most accepted name right now? Or does it have some greater historical significance of which I am unaware? Dr Mark D. Scherz 08:31, 9 April 2021 (UTC)
 * My understanding is that Acraniata is a historic group of organisms without a distinct cranium. As such it would include Cephalochordata, Hemichordata and Urochordata, which makes it paraphyletic with respect to Craniata. I don't think it should be used as a synonym of Cephalochordata. —  Jts1882 &#124; talk 09:02, 9 April 2021 (UTC)
 * However, Benton's Vertebrate Palaeontology does list "Cephalochordata (Acraniata)" (p433) and is the source cited for the listing. Nelson's Fishes of the World has a section "Subphylum Cephalochordata (Acrania, in part)" (p16). —  Jts1882 &#124; talk 09:31, 9 April 2021 (UTC)