Your Daily Fossil

Haikouichthys

When: Early Cambrian (~530 million years ago) 

Where: China

What: Haikouichthys is one of the oldest fish known. Though first described from a single specimen in 1999, it is now one of the most well understood Cambrian chordates, as a spectacular find in China unearthed over five hundred individual specimens.   Haikouichthys was primarily soft bodied, and so most of these fossils are impressions. There is a limited amount of information one can glean from a squished fossil, but when you have literally hundreds of individuals of a single species, all squished in a slightly different way, most of the morphology of an animal can be determined.  This ancient fish was tiny, at only about 1.2 inches (~3 cm) long on average. It had well developed anteriorly placed eyes, a notocord, and rudimentary fins along the midline of its body. It was not an armored fish, but several specimens suggest it had a cartilaginous head shield in life, a precursor to the ossified dermal armor of the later placoderms. 

Haikouichthys was closely related to the ancestor of all later fish, not just the placoderms, and as fish gave rise to tetrapods, it is also one of the first representatives of our own lineage. Phylogenetic analysis place Haikouichthys near the base of all vertebrates, with some minor ambiguity as to its placement relative to the living jawless fishes, the hagfish and lamprey. These two forms are not commonly mentioned when ‘living fossils’ are highlighted, but they are the only living examples of a once diverse assemblage of jawless and mostly finless fish.  

Reconstruction from Talifero  via wikimedia.