The world's first-known teeth showed up in fish that lived long before the dinosaurs, say paleontologists studying a fossil 410 million years old.

The finding of a tiny tooth plate from a fossil fish that sat unnoticed in a box for 40 years suggest all teeth — including those of humans — originally evolved from fish scales, the researchers say.

Paleontologists from the Netherlands and the United Kingdom used high energy X-rays at a research institute in Switzerland to reveal the structure and development of teeth and bones, a study appearing in Biology Letters explains.

Thousands of X-rays from multiple angles were combined in a computer using specialized software that could recreate the plate in a manner that could show it may have evolved over time, the researchers wrote.

The long-ignored tooth plate in a museum box came from a Romundina stellina, a member of an extinct class of armored fish.

It was an upper plate possessing many tiny teeth, which the fish probably used to crush food it caught swimming near the surface, the researchers suggest.

"Jaws and teeth are needed to process larger food items, and Romundina represents a predator that was able to swim actively in the water column hunting," says study lead author Martin Rücklin from the Naturalis Biodiversity Center in The Netherlands.

Fossils of Romundina from earlier than the 410-million-year-old example don't show evidence of teeth, providing a good estimate of when they first began to evolve, they say.

The teeth in the analyzed fossil had materials — dentine and enameloid — very similar to what is found in modern teeth, the researchers reported.

Other experts were quick to appreciate the findings.

"This is a really significant discovery that [either] proves the origins of true teeth are deeper down the vertebrate tree, or another mystery of evolution still to be solved," says John Long, a professor at Flinders University in Adelaide, South Australia.

Jaws and teeth are considered important advances in the evolution of vertebrate animals, and jaws are found in more the 98 percent of vertebrate animals.

In R. stellina, the multiple tiny teeth on a tooth plate were present in the absence of a jawbone, suggesting theories that teeth and jaws evolved separately and came together later are correct.

This fits with studies that have determined teeth and jaws evolved from separate components; while teeth evolved from scales, jaws probably evolved from fish bones, the researchers say.