Priscomyzon riniensis

Name: Priscomyzon riniensis [Ancient sucker of Rini (Grahamstown, South Africa)]

When: Late Devonian Period, about 365 million years ago

Where: Near Grahamstown, South Africa

Claim to fame: Priscomyzon is the oldest fossil lamprey. Unlike living lampreys it is tiny - a large one approaches only five centimeters, but like them, it was a parasite that ate by using a sucker-mouth to attach to a fish, rasp a hole in their skin, and suck their juices. Lampreys have no bone, so their fossil record is very poor. So, being the oldest lamprey, by itself, is a big deal. But there is more.

Really to appreciate Priscomyzon's significance, we need to nerd out a little.

Individual lampreys don't start out evil. As larvae, they live by suspension feeding - filtering digestible particles from suspension in the water. This makes them similar to close invertebrate relatives of vertebrates, like Branchiostoma, that live the same way. For generations, paleontologists viewed the life-cycle of lampreys as confirmation of the notion that ontogeny recapitulates phylogeny. That is, the lamprey in its life cycle relives the evolutionary pathway from Branchiostoma-like suspension-feeding ancestors to vertebrates with complex feeding methods.

But now the cool part: Priscomyzon is known from many specimens representing all growth stage from hatchling onward, so we can see that Priscomyzon actually hatches out of its egg as a tiny blood-sucker, not a suspension-feeding larva! That means that the larval stage seen in later lampreys is secondarily derived, not an ancestral feature. Thus, whatever lampreys are telling us with their life-cycle, their ontogeny definitely does not recapitulate their phylogeny!