Australia: The Land Where Time Began

A biography of the Australian continent 

Haikouichthys and Related Forms

Haikouichthys, a small animal that resembled a fish was found in Chengjiang deposits in China, of Early Cambrian age, about 525 Ma. It had a notochord but no bony plates, rays supporting a long dorsal fin, a number of paired gill pouches, and possibly scleral cartilages surrounding the eyes. A subsequently published papers by Shu et al. suggest it may have had a backbone and otic capsules (ear) that were part of the developing braincase. Though the specimen was not preserved well there are smudges that have been interpreted as representing the backbone, that repeated at regular intervals with the same shape, around the notochord. According to Long they could possibly be structures of bone. Haikouichthys, as well as 4 other fish from the Early Cambrian in the same strata, have well-developed sense organs in the head. In vertebrates these structures are derived from neural crest cells in the embryonic stage. Long suggests there is good evidence to show that Haikouichthys had reached an evolutionary level either above or close to that of lampreys, being higher than lampreys on a phylogenetic tree.

Other forms, such as Myllokungmingia from the same deposits have proven more difficult to interpret, with a single specimen having been found at the time of writing. With their position still being debated some believe they should be places a step below lampreys but above hagfishes (M.P.Smith et al., 2001).

Sources & Further reading

1. John A Long The Rise of Fishes - 500 Million years of Evolution, University of New South Wales Press, 2011