Heads and Tails

Nobu Tamura

The fact that basal chordates like Haikouichthys and Myllokunmigia (a contemporary of our animal this week) had crania and tails that are visibly differentiated and identifiable by anyone, even those with very little anatomical experience. The head is not extremely noticeable, as with a giraffe, for example, but in most illustrations and fossil slabs the small animal can be seen to have a head-like end with small eyes on the end of that small head. To be certain, Haikouichthys was a small animal with a minuscule head, but it is certainly a head. The notochord is not as apparent in the illustrations but is apparent in many of the known fossils. The cord is simple and as basic as a noticeable spinal cord could possibly be while still being called a notochord. The first spinal cord was still a ways off, evolutionarily speaking, but this simple hollow dorsal nerve tube, one of the first we know of for certain, was an enormous step on the way to every living vertebrate, not to mention countless fossil species, that we see and interact with every single day.