Temporal range: Cambrian Stage 3,
Artist's restoration of Haikouella lanceolata.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Infraphylum: Agnatha
Family: Haikouellidae
Genus: Haikouella
Type species
Haikouella lanceolata
Chen, Huang & Li, 1999[2]
Other species
  • H. jianshanensis

Haikouella is an agnathan chordate from the Lower Cambrian Maotianshan Shales of Chengjiang County in Yunnan Province, China. An analysis in 2015 placed Haikouella as a junior synonym of Yunnanozoon, another Maotianshan shale Cambrian chordate.[3][4]

It is similar to the form Yunnanozoon,[5] which is possibly a hemichordate.[6] Still, there are anatomical differences from Yunnanozoon, including a larger stomach and smaller (0.1 mm) pharyngeal teeth. Haikouella does not have bones or a movable jaw, but it otherwise resembles vertebrates. Haikouichthys and Myllokunmingia, which seem to share significant fish-like characters, have been found in the same beds. Suspected hemichordates are also known from these deposits as well as from the Middle Cambrian Burgess Shale of British Columbia. Other than possible fish scales/plates from the Upper Cambrian of Wyoming and conodonts, teeth plates of extinct Agnatha, these Chinese fish-like chordates are one of the only known pre-Ordovician craniates.

Haikouella lanceolata fossil from Chengjiang, China.
Haikouella lanceolata fossil from the Chlupáč Museum, Prague.

Haikouella is known from 305 specimens mostly from a single bed in the Maotianshan Shales. The animal is 20 to 30 mm (40 mm max) in length and has a head, gills, brain, notochord, well developed musculature, heart and circulatory system. It has a bent caudal projection of the notochord that might be a primitive tail fin. It might have a pair of lateral eyes. Very small (0.1 mm) structures that are probably pharyngeal teeth are present in the body cavity. A few specimens display dorsal and ventral fins.

There are two known species, the type species, H. lanceolata, and H. jianshanensis.[7]

  1. ^ Yang, C.; Li, X.-H.; Zhu, M.; Condon, D. J.; Chen, J. (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.
  2. ^ Cite error: The named reference chen was invoked but never defined (see the help page).
  3. ^ Cong, Pei-Yun; Hou, Xian-Guang; Aldridge, Richard J.; Purnell, Mark A.; Li, Yi-Zhen (2015). Smith, Andrew (ed.). "New data on the palaeobiology of the enigmatic yunnanozoans from the Chengjiang Biota, Lower Cambrian, China". Palaeontology. 58 (1): 45–70. doi:10.1111/pala.12117. S2CID 84567733.
  4. ^ Tian, Qingyi; Zhao, Fangchen; Zeng, Han; Zhu, Maoyan; Jiang, Baoyu (2022-07-08). "Ultrastructure reveals ancestral vertebrate pharyngeal skeleton in yunnanozoans". Science. 377 (6602): 218–222. Bibcode:2022Sci...377..218T. doi:10.1126/science.abm2708. ISSN 0036-8075. PMID 35857544. S2CID 250380981.
  5. ^ Cite error: The named reference sudden was invoked but never defined (see the help page).
  6. ^ Shu, D.; X. Zhang; L. Chin (4 April 1996). "Reinterpretation of Yunnanozoon as the earliest known hemichordate". Nature. 380 (6573): 428–430. Bibcode:1996Natur.380..428S. doi:10.1038/380428a0. S2CID 4368647.
  7. ^ Cite error: The named reference shu was invoked but never defined (see the help page).

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