Temporal range: Early cambrian
Chen et al., 1995
Yunnanozoon is similar to the form Haikouella which is almost certainly a chordate. Still, there are anatomical differences from Haikouella, including a smaller stomach and much larger (1 mm) pharyngeal teeth. It is by no means certain whether Yunannozoon possessed features such as a heart, gills, etc., which are seen in well-preserved specimens of Haikouella. Yunnanozoon somewhat resembles the Middle Cambrian Pikaia from the Burgess shale of British Columbia in Canada. Thirteen pairs of symmetrically arranged gonads have been identified, as have possible gill slits. However, some authors think that Yunnanozoon is closely related to the chordate Haikouella and that Yunnanozoon is probably a chordate rather than a hemichordate. A close relationship between Yunnanozoon and the phylum Vetulicolia has also been proposed.
- Shu, D., Zhang, X. and Chen, L. 1996. Reinterpretation of Yunnanozoon as the earliest known hemichordate, Nature. 380:428–430 (4 April 1996).  – accessed 3 December 2005
- J. J. Sepkoski. 2002. A compendium of fossil marine animal genera. Bulletins of American Paleontology 363:1–560
- Chen (2009). "The sudden appearance of diverse animal body plansduring the Cambrian explosion". The International journal of developmental biology 53 (5–6): 733–751. doi:10.1387/ijdb.072513cj. PMID 19557680.
- A picture can be found at http://www.gs-rc.org/repo/repoe.htm
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