Chordate


Chordates
Temporal range: Cambrian Stage 3Present, (Possible Ediacaran record, 555 Ma[2])
Branchiostoma lanceolatumPolycarpa aurataTiger sharkSiberian tigerChordata.png
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Example of chordates: Branchiostoma lanceolatum (Cephalochordata), Polycarpa aurata (Tunicata), as well as a Tiger shark and a Siberian tiger (Vertebrata).
Scientific classification e
Kingdom: Animalia
Subkingdom: Eumetazoa
Clade: ParaHoxozoa
Clade: Bilateria
Clade: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Haeckel, 1874[3][4]
Subgroups

And see text

A chordate (/ˈkɔːrdt/) is an animal of the phylum Chordata (/kɔːrˈdtə/). All chordates possess, at some point during their larval or adulthood stages, five synapomorphies, or primary characteristics, that distinguish them from all the other taxa. These five synapomorphies include a notochord, dorsal hollow nerve cord, endostyle or thyroid, pharyngeal slits, and a post-anal tail. The name “chordate” comes from the first of these synapomorphies, the notochord, which plays a significant role in chordate structure and movement. Chordates are also bilaterally symmetric, have a coelom, possess a circulatory system, and exhibit metameric segmentation.

In addition to the morphological characteristics used to define chordates, analysis of genome sequences has identified two conserved signature indels (CSIs) in the proteins cyclophilin-like protein and mitochondrial inner membrane protease ATP23, which are exclusively shared by all vertebrates, tunicates and cephalochordates.[5] These CSIs provide molecular means to reliably distinguish chordates from all other metazoan.

Chordates are divided into three subphyla: Craniata (fish, amphibians, reptiles, birds, and mammals); Tunicata or Urochordata (sea squirts, salps); and Cephalochordata (which includes lancelets). The Craniata and Tunicata compose the clade Olfactores, which is sister to Cephalochordata. (See diagram under Phylogeny.) Extinct taxa such as Vetulicolia and Conodonta are Chordata, 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: hemichordates and Echinodermata form the Ambulacraria, the sister phylum of the Chordates. The Chordata and Ambulacraria, together and possibly with the Xenacoelomorpha, form the superphylum Deuterostomia.

Chordate fossils have been found from as early as the Cambrian explosion, 539 million years ago.[6] Cladistically (phylogenetically), vertebrates – chordates with the notochord replaced by a vertebral column during development – are a subgroup of the clade Craniata, which consists of chordates with a skull. Of the more than 65,000 living species of chordates, about half are ray-finned fishes that are members of the class Actinopterygii and the vast majority of the rest are tetrapods (mostly birds and mammals).

  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: 1–11. 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. ^ 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. doi:10.1016/j.ympev.2015.09.019. ISSN 1055-7903. PMID 26419477.
  6. ^ "Stratigraphic Chart 2022" (PDF). International Stratigraphic Commission. February 2022. Archived (PDF) from the original on 9 October 2022. Retrieved 25 April 2022.

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