The Oldest Meat

From 430 to 360 million years ago, the oceans, rivers and lakes were dominated by aquatic monsters called placoderms, primitive fishes covered by a bone armor. "On the evolutionary tree, they're the first jawed animal, and we're the last. So they're our first jawed ancestors," said Kate Trinajstic, a paleontologist at the University of Western Australia.

Her team discovered - using recent electron microscope scans - the oldest pieces of fossilized muscle and the oldest vertebrate tissue ever known in a 380 to 384 million years old placoid fish, discovered 20 years ago in the Gogo formation, Western Australia. Unearthed in western Australia 20 years ago, the specimens belong to two species of an extinct group of primitive, armored fish known as placoderms.

The remarkably well-preserved soft tissues compassed muscle cells, blood vessels, and nerve cells. "Fossilized muscle is quite rare, and the new finds are even more exceptional, because they weren't flattened but rather preserved with their three-dimensional shape intact," said Trinajstic.

The fossil's muscle has a W-shaped blocks structure, which in current organisms is seen only in lampreys, a living fossil jawless "fish" (thus even more primitive than placoderms). "There has been some discussion as to whether or not placoderms were the most primitive fish or whether sharks were more primitive," Trinajstic said.

[IMG=2]"These muscles show us that placoderms were the most primitive fishes and the most primitive jawed fishes."

Placoderms, which reached lengths from 6 inches to 33 feet (15 cm to 10 m), had a cartilaginous internal skeleton, like sharks do, but with their heavy bony jaws inflicted a strong rigid bite.

The Gogo formation is the site of one of the oldest barrier reef, and 25 marine placoderm species fossils were found here.

In 1986, researchers found the 380-million-year-old placoderm fish Gogonasus (photo), which showed remarkable similar features to land vertebrates. "The Gogonasus fish fossils "changed and revolutionized" our understanding of evolution", said paleontologist John Long of Museum Victoria. "Most people have the "Hollywood view of evolution," in which a fish morphs into an amphibian, followed by a reptile, then a mammal, then a primate, and finally a human," he said.

"But when we look at the Gogo fish, we see that so much of the human body plan is pushed back into the fishes. So that the origin of all our anatomical systems-90 % of it-happened within fishes. After the fishes left the sea and invaded the land, the rest was really fine-tuning of an existing pattern."