Athena Review Image Archive ™
Haikouichthys ercaicunensis, head
Head of Haikouichthys ercaicunensis (after Shu et al. 2003 )
Haikouichthys ercaicunensis
was an Early to Middle Cambrian, fish-like chordate dating from 535-520
mya, found in Yunnan, China. The name Haikouichthys means "fish from Haikou", a
town near the find site, with - ichthys "fish" [Gk], and ercaicunensis for the find site. The type specimen was reported by Luo et al. in 1999 as found in
the Ercaicun beds, near Haikou in the Yuansshan member of the
Qiongzhusi Formation in Yunnan Province. It is in the phylum
Chordata, the clade Craniata, the superclass Agnatha ("jawless"), and
the family Myllokunmingiidae.
Haikouichthys had a defined skull and other characteristics indicating it was a true craniate, and possibly one of the earliest fishes. Cladistic analysis indicates that the animal is probably a basal chordate or a basal craniate. There is a prominent dorsal fin with fin radials similar, but not comparable, to those of hagfish and lampreys.
The body length is 2.5 cm (1 inch), with a distinct head and tail. Haikouichthys is narrower than the related Myllokunmingia, another putative chordate from the same Cambrian beds. It has a distinct head and tail, with the head showing at least six and perhaps nine probable gills. There are a number of muscle segments (myomeres) with rear directed chevrons in the tail. There is probably a notochord, with a short segment preserved in one specimen.
In the figure, a-b and c-d show details of the heads of two Haikouichthys specimens, emphasizing
their anterior structures. Figure b identifies possible otic or
ear capsules.
References:
Luo et al. 1999
Shu et al. 2003. Head and backbone of the Early Cambrian vertebrate Haikouichthys. Nature 421; pp. 526-529
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