The fossils date to the Silurian period, an important era for life on earth from 443 million years ago to 419 million years ago.

NEW YORK — A large haul of fish fossils in southern China includes the oldest teeth ever found — and could help scientists learn how our aquatic ancestors got their bite.

The findings provide new clues about a key period of evolution that has been difficult to figure out because scientists haven’t found many fossils from that era until now. In a series of four studies published Wednesday in the journal Natureresearchers detail some of their finds, from ancient teeth to never-before-seen species.

The fossils date to the Silurian period, an important era for life on earth from 443 million years ago to 419 million years ago. Scientists believe that our vertebrate ancestors, who still floated on a watery planet, may have begun to evolve teeth and jaws around this time.

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This allowed the fish to hunt for prey instead of “grabbing” as bottom feeders, filtering food from the mud. It also caused a number of other changes in their anatomy, including different types of fins, said Philip Donoghue of the University of Bristol, a palaeontologist and author on ope from research.

“It’s just at the crossroads between the Old World and the New World,” Donahue said.

But in the past, scientists haven’t found many fossils to show this shift, said Matt Friedman, a paleontologist at the University of Michigan who was not involved in the study. They relied on fragments of that time—a piece of spine here, a piece there.

Fossils from China are expected to fill in some of those gaps as researchers around the world study them.

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A field team discovered the fossil in 2019, Ming Zhu, a paleontologist at the Chinese Academy of Sciences who led the study, said in an email. On a rainy day after a disappointing trip that failed to turn up a single fossil, researchers were examining a pile of rocks near a roadside bluff. When they split open one rock, they discovered fossilized fish heads staring back at them.

After taking more rocks to the lab for study, the research team found a huge number of fossils that were in excellent condition for their age.

The most common species in the group is a small boomerang-shaped fish that probably used its jaws to scoop up worms, said Per Erik Alberg of Uppsala University, Sweden, author one of the studies.

Another fossil shows a shark-like creature with bony armor on its front, an unusual combination. A well-preserved jawless fish shows how ancient fins evolved into arms and legs. While head fossils of these fish are commonly found, this fossil included the entire body, Donahue said.

And then there is teeth. The researchers found bones called dental whorls with several teeth growing on them. The fossils are 14 million years older than any other teeth found in any species and are the earliest hard evidence of jaws to date, Zhu said.

Alice Clement, an evolutionary biologist at Australia’s Flinders University who was not involved in the research, said the fossil find was “remarkable” and could rewrite our understanding of the period.

The wide range of fossils suggests that there were plenty of toothy creatures swimming around during this time, Clement said in an email, even though this is the next evolutionary era, considered the “Age of Fishes.”