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	Yunnanozoon lividum     Yunnanozoon lividum A1,B: whole fossils; A2 interpretative drawing (after Chen & Huang 2008).
	Yunnanozoon lividum was an early chordate from the Early and Middle Cambrian period in Yunnan, China, dating from 535-520 mya. First discovered in the late 1980s, Yunnanozoon is now known from about 60 fossil specimens found in the Chengjiang fauna in the  Maotianshan shales, a Lagerstätten (fine grained shale)  at Ercaicun in southern China. It is named Yunnan- for the Chinese province, and -zoon for "animal". It is now classified in the phylum Chordata, and the subphylum Cephalocordate (chordates with heads).   Yunnanozoon fossils have been subject to ongoing reinterpretation. Chu (1991) classified Y. lividum as a problematic taxon. Chen et al. 1995 reclassified it as a notochord. Shu et. al (1996) and Chen and Li (1997) reclassified Y. livida as an early, tunicate-like hemichordate (which only have notochords as larvae).    Chen, Huang, and Li (1999) proposed Yunnanozoon to be closely related to Haikouella, the earliest craniate-like chordate. Based on evidence of gill rays found in 2004, Chen and Huang 2008 reinterpreted Yunnanozoon as a chordate.    The body length is 1.6 - 2.2 cm. The best preserved fossils of Y. livida show a notochord, along with paired muscle segments or myomeres, branchial or gill arches,  gill slits, sensors or tendrils near the mouth, and a pharygeal cavity or digestive tract. These characteristics are notably similar to those of the slighly later Cambrian taxa Pikaia gracilens described from the Burgess shale by Conway Morris and Caron (2012).  Some Y. livida fossils show gill rays or filaments near the mouth. These resembled the tentacles of Haikouella which must have been used for filter feeding, as well as those of both the modern lancet and hagfish.  This has led to a reinterpretation of Y. livida as a chordate.                        References: Chen et al 1995. Chen and Li 1997. Chen, Huang, and Li 1999. Nature 402, pp.518-522. Chen and Huang 2008. Conway Morris and Caron 2012 Chu 1991. Shu et al. 1996.
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