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Olfactores; Temporal range: ; Cambrian Stage 3–Present,; 518–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N (Possible Ediacaran record, 557 Ma)
	Example of Olfactores
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Subkingdom:	Eumetazoa
Clade:	ParaHoxozoa
Clade:	Bilateria
Clade:	Nephrozoa
Superphylum:	Deuterostomia
Phylum:	Chordata
Clade:	Olfactores; Jefferies, 1991
Subphyla
	Tunicata; Vertebrata (Craniata);

Olfactores is a clade within the Chordata that comprises the Tunicata (Urochordata) and the Vertebrata (sometimes referred to as Craniata). Olfactores represent the overwhelming majority of the phylum Chordata, as the Cephalochordata are the only chordates not included in the clade. This clade is defined by a more advanced olfactory system which, in the immediate vertebrate generation, gave rise to nostrils.

Etymology

The name Olfactores comes from Latin *olfactores ("smellers," from purposive supine olfactum of olfacio, "to smell," with plural masculine agentive nominalizing suffix -tores), due to the development of pharyngeal respiratory and sensory functions, in contrast with cephalochordates such as the lancelet which lack a respiratory system and specialized sense organs.^[3]

Olfactores hypothesis

The long-standing Euchordata hypothesis that Cephalochordata is a sister taxon to Craniata was once widely accepted,^[4] likely influenced by significant tunicate morphological apomorphies from other chordates, with cephalochordates even being nicknamed ‘honorary vertebrates.’^[5]

The name Olfactores was originally introduced in 1991 as part of the now-disproven calcichordate hypothesis.^[6] However, studies since 2006 analyzing large sequencing datasets strongly support Olfactores as a clade.^[7]^[8]

Studies suggest that the ancestors of Appendicularia and Vertebrata were possibly sedentary-pelagic.^[9]^[10]^[11] A rudimentary neural crest is present in tunicates, implying its presence in the olfactores ancestor also, as vertebrates have a true neural crest.^[12]

Works cited

Ax, P. (2001). Das System der Metazoa: ein Lehrbuch der phylogenetischen Systematik. Spektrum Akademischer Verlag. ISBN 9783437308031.
Benton, M.J. (14 April 2000). Vertebrate Palaeontology: Biology and Evolution. Blackwell Publishing.
Delsuc, F (2006). "Tunicates and not cephalochordates are the closest living relatives of vertebrates" (PDF). Nature. 439 (7079): 965–968. Bibcode:2006Natur.439..965D. doi:10.1038/nature04336. PMID 16495997. S2CID 4382758.
Delsuc, Frédéric; Philippe, Hervé; Tsagkogeorga, Georgia; Simion, Paul; Tilak, Marie-Ka; Turon, Xavier; López-Legentil, Susanna; Piette, Jacques; Lemaire, Patrick (2018-04-13). "A phylogenomic framework and timescale for comparative studies of tunicates". BMC Biology. 16 (39). doi:10.1186/s12915-018-0499-2. hdl:10261/163664.
Dunn, C.W. (2008). "Broad phylogenetic sampling improves resolution of the animal tree of life". Nature. 452 (7188): 745–749. Bibcode:2008Natur.452..745D. doi:10.1038/nature06614. PMID 18322464. S2CID 4397099.
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.
Jeffries, R. P. S. "Two types of bilateral symmetry in the Metazoa: chordate and bilaterian". In Bock, Gregory R.; Marsh, Joan (eds.). Biological Asymmetry and Handedness. Ciba Foundation Symposium. John Wiley and Sons. doi:10.1002/9780470514160.ch7.
Martynov, Alexander V.; Korshunova, Tatiana A. (2022-08-11). "Renewed perspectives on the sedentary-pelagic last common bilaterian ancestor". Contributions to Zoology. 91 (4–5): 285–352. doi:10.1163/18759866-bja10034. ISSN 1875-9866.
Nanglu, Karma; Lerosey-Aubril, Rudy; Weaver, James C.; Ortega-Hernández, Javier (2023-07-06). "A mid-Cambrian tunicate and the deep origin of the ascidiacean body plan". Nature Communications. 14 (1): 3832. doi:10.1038/s41467-023-39012-4. ISSN 2041-1723. PMC 10325964.
Stach, Thomas (2008). "Chordate phylogeny and evolution: a not so simple three‐taxon problem". Journal of Zoology. 276 (2): 117–141. doi:10.1111/j.1469-7998.2008.00497.x.
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.
York, Joshua R.; McCauley, David W. (2020). "The origin and evolution of vertebrate neural crest cells". Open Biology. 10 (1): 190285. doi:10.1098/rsob.190285. PMC 7014683. PMID 31992146.