Chordate

Not to be confused with Caudata, a group of amphibians.
Not to be confused with Cordate (disambiguation), Cordata (disambiguation), or Caudate (disambiguation).

Chordates
Temporal range: Cambrian Stage 3–Present, 525–0 Ma[1] (Possible Ediacaran record, 555 Ma[2])
LanceletChondrichthyesTunicateTetrapod
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Subkingdom: Eumetazoa
Clade: ParaHoxozoa
Clade: Bilateria
Clade: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Haeckel, 1874[3][4]
Subgroups

And see text

A chordate (/ˈkɔːrdeɪt/ KOR-dayt) is a deuterostomal bilaterian animal belonging to the phylum Chordata (/kɔːrˈdeɪtə/ kor-DAY-tə). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics (synapomorphies) that distinguish them from other taxa. These five synapomorphies are a notochord, a hollow dorsal nerve cord, an endostyle or thyroid, pharyngeal slits, and a post-anal tail.[8]

In addition to the morphological characteristics used to define chordates, analysis of genome sequences has identified two conserved signature indels (CSIs) in their proteins: cyclophilin-like protein and inner mitochondrial membrane protease ATP23, which are exclusively shared by all vertebrates, tunicates and cephalochordates.[9] These CSIs provide molecular means to reliably distinguish chordates from all other animals.

Chordates are divided into three subphyla: Vertebrata (fish, amphibians, reptiles, birds and mammals), whose notochords are replaced by a cartilaginous/bony axial endoskeleton (spine) and are cladistically and phylogenetically a subgroup of the clade Craniata (i.e. chordates with a skull); Tunicata or Urochordata (sea squirts, salps, and larvaceans), which only retain the synapomorphies during their larval stage; and Cephalochordata (lancelets), which resemble jawless fish but have no gills or a distinct head. The vertebrates and tunicates compose the clade Olfactores, which is sister to Cephalochordata (see diagram under Phylogeny). Extinct taxa such as the conodonts are chordates, but their internal placement is less certain. Hemichordata (which includes the acorn worms) was previously considered a fourth chordate subphylum, but now is treated as a separate phylum which are now thought to be closer to the echinoderms, and together they form the clade Ambulacraria, the sister phylum of the chordates. Chordata, Ambulacraria, and possibly Xenacoelomorpha are believed to form the superphylum Deuterostomia, although this has recently been called into doubt.[10]

Chordata is the third-largest phylum of the animal kingdom (behind only the protostomal phyla Arthropoda and Mollusca) and is also one of the most ancient taxons. Chordate fossils have been found from as early as the Cambrian explosion over 539 million years ago.[11] Of the more than 81,000[12] living species of chordates, about half are ray-finned fishes (class Actinopterygii) and the vast majority of the rest are tetrapods, a terrestrial clade of lobe-finned fishes (Sarcopterygii) who evolved air-breathing using lungs.

  1. ^ Yang, Chuan; Li, Xian-Hua; Zhu, Maoyan; Condon, Daniel J.; Chen, Junyuan (2018). "Geochronological constraint on the Cambrian Chengjiang biota, South China" (PDF). Journal of the Geological Society. 175 (4): 659–666. Bibcode:2018JGSoc.175..659Y. doi:10.1144/jgs2017-103. ISSN 0016-7649. S2CID 135091168. Archived (PDF) from the original on 9 October 2022.
  2. ^ Fedonkin, M. A.; Vickers-Rich, P.; Swalla, B. J.; Trusler, P.; Hall, M. (2012). "A new metazoan from the Vendian of the White Sea, Russia, with possible affinities to the ascidians". Paleontological Journal. 46 (1): 1–11. Bibcode:2012PalJ...46....1F. doi:10.1134/S0031030112010042. S2CID 128415270.
  3. ^ Haeckel, E. (1874). Anthropogenie oder Entwicklungsgeschichte des Menschen. Leipzig: Engelmann.
  4. ^ Cite error: The named reference Nielsen2012 was invoked but never defined (see the help page).
  5. ^ a b He, K.; Liu, J.; Han, J.; Ou, Q.; Chen, A.; Zhang, Z.; Fu, D.; Hua, H.; Zhang, X.; Shu, D. (2023). "Comment on "Ultrastructure reveals ancestral vertebrate pharyngeal skeleton in yunnanozoans"". Science. 381 (6656). doi:10.1126/science.ade9707.
  6. ^ Mussini, G.; Smith, M. P.; Vinther, J.; Rahman, I. A.; Murdock, D. J. E.; Harper, D. A. T.; Dunn, F. S. (2024). "A new interpretation of Pikaia reveals the origins of the chordate body plan". Current Biology. 34 (13): 2980–2989.e2. doi:10.1016/j.cub.2024.05.026. PMID 38866005.
  7. ^ a b Lerosey-Aubril, R.; Ortega-Hernández, J. (2024). "A long-headed Cambrian soft-bodied vertebrate from the American Great Basin region". Royal Society Open Science. 11 (7). doi:10.1098/rsos.240350. PMC 11267725. PMID 39050723.
  8. ^ Freeborn, Michelle (1 January 2015). Roberts, Clive Douglas; Stewart, Andrew L.; Struthers, Carl D. (eds.). The fishes of New Zealand. Vol. Two. Te Papa Press. p. 6. ISBN 978-0-9941041-6-8.
  9. ^ Gupta, Radhey S. (January 2016). "Molecular signatures that are distinctive characteristics of the vertebrates and chordates and supporting a grouping of vertebrates with the tunicates". Molecular Phylogenetics and Evolution. 94 (Pt A): 383–391. Bibcode:2016MolPE..94..383G. doi:10.1016/j.ympev.2015.09.019. ISSN 1055-7903. PMID 26419477.
  10. ^ Kapli, Paschalia; Natsidis, Paschalis; Leite, Daniel J.; Fursman, Maximilian; Jeffrie, Nadia; Rahman, Imran A.; Philippe, Hervé; Copley, Richard R.; Telford, Maximilian J. (19 March 2021). "Lack of support for Deuterostomia prompts reinterpretation of the first Bilateria". Science Advances. 7 (12): eabe2741. Bibcode:2021SciA....7.2741K. doi:10.1126/sciadv.abe2741. ISSN 2375-2548. PMC 7978419. PMID 33741592.
  11. ^ "Stratigraphic Chart 2022" (PDF). International Stratigraphic Commission. February 2022. Archived (PDF) from the original on 9 October 2022. Retrieved 25 April 2022.
  12. ^ "Chordates". eol.