Fish got their jaws millions of years earlier than previously thought

Without its scary rows and rows of razor sharp teeth, your average great white shark (Carcharodon carcharias) wouldn’t be quite as terrifying. Their ancient ancestors (known as acanthodians) were even more prickly, with bristly spines along their fins. Now, a new fossilized fish skeleton found in China is older than the next-oldest specimen by a whopping 15 million years and is the, “oldest undisputed jawed fish.”

In a paper published in the journal Nature, the team of researchers from the Chinese Academy of Sciences, Qujing Normal University, and the University of Birmingham in the United Kingdom write that the new species Fanjingshania renovatais (F. renovata for short) has a body is similar to a spiny acanthodian. They lie somewhere between the class chondrichthyans (modern sharks and rays) and the group osteichthyans (bony fish). They lived in the the Paleozoic period, and F. renovata may be the close relative of a yet-to-be discovered common ancestor of both modern class and group of fish.

The team thousands of tiny skeletal fragments to reconstruct F. renovata, which show that it is a is a funky fish with an external bony “armor” and multiple pairs of fin spines. These spines set it apart from current jawed fish as well as cartilage containing sharks and rays and bony ray- and lobe-finned fish. The new species was uncovered in the bone bed samples of the Rongxi Formation in South China and named after the UNESCO World Heritage Site Fanjingshan.

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“This is the oldest jawed fish with known anatomy,” ZHU Min from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences said in a press release. “The new data allowed us to place Fanjingshania in the phylogenetic tree of early vertebrates and gain much needed information about the evolutionary steps leading to the origin of important vertebrate adaptations such as jaws, sensory systems, and paired appendages.”

This discovery shows evidence that major vertebrate groups began to diversify tens of millions of years before the beginning of the Devonian period, or the Age of Fishes, about 419.2 million and 358.9 million years ago when many different kinds of fishes began to swim Earth’s oceans.

According to the study, there are several features that set apart F. renovata from any known modern or ancient vertebrate. Its has armor along its shoulders that fuse together as a unit that covers more area than other known acanthodians.

Its spiny fins were covered in unusual teeth-like scales, that possibly would fall out in clumps and regrow. Sharks living today also shed and regrow teeth, but aren’t replaced in this way. F. renovata‘s fossilized bones show evidence of resorption, or when parts of bones or teeth break down and are later replaced. This process usually occurs during the organism’s development.

[Related: This whale fossil could reveal evidence of a 15-million-year-old megalodon attack.]

“This level of hard tissue modification is unprecedented in chondrichthyans, a group that includes modern cartilaginous fish and their extinct ancestors,” lead author Plamen Andreev, a researcher at Qujing Normal University, said in a statement. “It speaks about greater than currently understood developmental plasticity of the mineralized skeleton at the onset of jawed fish diversification.”

F. renovata is one of several fossils that this same team uncovered at the Rongxi Formation site. The team describes another species of extinct jawed fish (Qianodus duplicis or Q. duplicis) published in a separate study in Nature. This species is also about 439 million years old, but it was described only from fossilized scales and teeth, so the researchers are more uncertain about exactly which fish group it may have been a member of.

Three other extinct fish species unearthed at the site include Xiushanosteus mirabilis, Shenacanthus vermiforis, and Tujiaaspis vividus. While none of them were quite as old as F. renovata or Q. duplicis, X. mirabilis and S. vermiforis are still older than any other known species of early jawed fish.

The newly discovered species are changing what scientists already knew about the evolution of jawed fishes. While researchers first estimated this evolution took place about 420 million years ago, now we can place its jump 20 million years earlier than that.

“The new discovery puts into question existing models of vertebrate evolution by significantly condensing the timeframe for the emergence of jawed fish from their closest jawless ancestors,” said Ivan J. Sansom from the University of Birmingham, in a statement. “This will have profound impact on how we assess evolutionary rates in early vertebrates and the relationship between morphological and molecular change in these groups.”