More than eight decades ago, pioneering Museum of Northern Arizona geologist Major L.F. Brady made a surprising find in sedimentary rocks high up on the east flank of Mt. Elden, outside Flagstaff. These outcrops are far older than the rest of Mt. Elden, having been lifted high up and tipped over by the emerging lava dome that created the mountain about half a million years ago.
Major Brady was excited to find fossilized remains of fish in Martin Formation limestone strata from the late Devonian Period. Over 360 million years old, these fossils were the first Devonian fossil fish ever found in Arizona, and they were Placoderms, long-extinct armored fish.
Placoderm means “plate-skinned” in Greek. They had bony armor plates covering their heads and upper bodies. Placoderms were the first vertebrates to evolve jaws, and they were the dominant fish of the Devonian. Their jaws had no teeth, but they had tooth-like structures that extended into the mouth, a continuation of bony plates of the head.
Most Placoderms were predators. They varied in size from only a few inches to the huge apex predator Dunkleosteus, which must’ve been the terror of Devonian seas- up to 30 feet long, with enormous jaws!
The Mt Elden Placoderm fossils weren’t so large- only a few inches long. Notwithstanding their small size, they’re still considered among the most important vertebrate fossils in the Museum of Northern Arizona’s collection, and a prized part of Major Brady’s legacy.
This Earth Note was written by Steve Schwartz and produced by KNAU and the Sustainable Communities Program at Northern Arizona University.
