It is hard to not think of jaws when you mention the ocean. There are many mouths in the deep waters, including the bear-trap maws of sharks and dolphins. Jawed fish crawled out of the sea millions of years ago and gave rise to the jawboning animals we are today.
But when did the invention come about? The answer may lie tens of millions of years deeper into the past than previously thought after two fossil beds were found in Southern China. The findings, which include beautifully preserved new species of early fish, the oldest- known vertebrate teeth and a lot of fish with armor, were published Wednesday across four papers in Nature.
Matt Friedman, a paleontologist at the University of Michigan who was not involved in the research, wrote a perspective article that accompanied the Nature papers.
A period known as the age of fish, or the Devonian, took place during which jawed fish exploded into the fossil record. According to a paleobiologist at the University of Chicago who was not involved in the new papers, fish of this era have their identities written on their bodies. They include ancient groups like jawless fish and the first fishes to hop on land.
The sudden diversity of jawed fish, also called gnathostomes, has led scientists to suspect that their origins must lie deeper in the fossil record. The number of Silurian gnathostome fossils used to be counted on one hand.
A decade ago, researchers set out to systematically survey the rocks of the late Silurian period in China. They were given complete fossils of early fish.
They were encouraged to dig into the rocks. There were two deposits outside of Chongqing in 2020.
Each of the fossil beds has a different complement of species.
The oldest complete jawed fish, which is only a few centimeters long, can be found in the bed. Most of them are of a placoderm species that lived on the ocean floor. Shenacanthus vermiformis is a cartilaginous fish that is related to sharks and rays and has armor plates that are similar to those of placoderms.
The most remarkable specimen from the site is a jawless fish, according to Philip Donoghue, a paleontologist at the University of Bristol. Thousands of head shields from the species' family are known from the fossil record, but the first body is not. There is a set of fins jutting out from the skull that is thought to be from the gnathostomes. The two sets of fins were thought to be separate.
Dr. Donoghue said that it overturns conventional wisdom.
More important fossils can be found at the second site. A paper describes a collection of dead-ringers for later examples of cartilaginous fish from an animal called Fanjingshania renovata. A whirl of connected teeth from a fish is recorded by another. The chondrichthyans are a group of fish that include sharks, rays and ratfish. Humans andbony fish are the other branches.
The presence of shark relatives at the site suggests that the split between cartilaginous and bony fish happened before the Silurian. The two sites push the origin of jaws and teeth back 14 million years.
Dr. Friedman said that it was a big change from the consensus chronology.
Jawed fish are thought to have started as early as 485 million to 450 million years ago when the marine world ruled. There are few known fish from that time period. He said they looked like armor- plated tadpoles. Proto-sharks and Proto-bony fish are not supposed to be at the same place at the same time.
More fish species have been found in the Silurian rocks in China. Researchers may need a bigger boat to study the earliest jawed fish.
There will be more discoveries according to Dr. Ahlberg. This will change our understanding of the earliest phase of jawed vertebrate evolution.
All Rights Reserved © 2024
