Sacabambaspis janvieri

Sacabambaspis janvieri from Wikipedia

Name: Sacabambaspis janvieri [Janvier's shield of Sacabamba]

When: Middle to Late Ordovician Period, about 470 - 450 million years ago

Where: Sacabamba, Bolivia

Claim to fame: Sacabambaspis is the oldest vertebrate that is known from a mostly complete skeleton - a major distinction. Despite its age, it is among the best-preserved members of a very primitive vertebrate group - the arandaspids. These creatures would seem very alien were you to see one alive - jawless and with no fins other than their tail fin. Beyond a series of heavy scales on their tails, their front ends were covered by two bony shields, one on top and one underneath, separated by a row of gill openings.

Strangest of all were their jawless mouths, opened an closed by a series of splint-like oral plates that opened and closed like a bamboo fan. What did they eat? They probably filtered digestible particles from the water. Not a terribly interesting life. Indeed, judging from their shape, they probably spent their days resting on the bottom of shallow ocean environments, suspension-feeding in the manner of modern lamprey larvae, swimming around when disturbed, but quickly settling down.