by (opens in new tab)
Researchers in China have discovered the remains of a 439-million-year-old shark-like fish with unusual features that “set it apart from any known vertebrate,” or animal with a backbone. The strange creature, which is covered in spines and “bony armour”, is the oldest undisputed vertebrate ever discovered, according to a new study.
Scientists discovered the remains of the newly identified, extinct species in the Rongxi Formation, a famous fossil site in Guizhou Province, southern China. The researchers named the species Fanjingshania renovataafter a nearby mountain known as Fanjingshan.
The team collected thousands of fossilized skeletal fragments, scales and teeth from the site and then painstakingly recreated what the ancient fish might have looked like. Their findings were published online Sept. 28 in the journal Nature (opens in new tab).
F. renovata belongs to an extinct group shark-like creatures known as echinoderms, also called “spiny sharks”, which have spiny fins and bony plates surrounding their shoulder areas. In the fish family tree, echinoderms lie somewhere between the chondrichthyans, which include modern sharks and rays, and the osteichthyans, or bony fishes. Acanthodians have shark-like body designs, but their bony plates and skeletons are similar to those of bony fish. Researchers suspect that F. renovata may be a close relative of the undiscovered common ancestor of the two groups.
Related: Great ancient fish the size of a great white shark discovered by chance from a fossilized lung
The newly discovered species dates back to Silurian periodbetween 443.8 and 419.2 million years ago, and is about 15 million years older than the oldest known jawed fish, making it the oldest jawed vertebrate to date, the researchers said in a statement (opens in new tab).
Scientists are particularly interested in the appearance of jawed fish because their development was an important point in the diversification of vertebrates. The discovery will help researchers “gain necessary information about the evolutionary steps leading to the origin of important vertebrate adaptations such as jaws, sensory systems and paired appendages,” study co-author Min Zhu, a paleontologist with the Chinese Academy of Sciences, the statement said.
Unique specimen
Although F. renovata shares many features with other echinoderms, the researchers said it also had features that set it apart from others in the group.
One of the main differences is in the fish’s shoulder armor, which covers a larger area than that of other acanthodians and is fused with multiple spines, the researchers wrote.
Picture 1 of 3
The creature’s spiny fins were also covered in unusual tooth-like scales, which the team suspected would fall off in clumps and regrow. Similar scales are seen in modern sharks, but are not replaced in this way, according to the statement.
His petrified bones F. renovata they also show evidence of a process known as resorption, when parts of bone or teeth are destroyed and later replaced, often during the development of the organism.
“This level of hard tissue modification is unprecedented in chondrichthyans,” study lead author Plamen Andreev, a paleontologist at Qujing Normal University in China, said in the statement. It shows a “greater than understood plasticity” of how early mineralized skeletons developed and points to the evolutionary origins of modern skeletons, including those in humans, he added.
Redefining fish evolution
F. renovata is just one of many fossils discovered by researchers at the site of the Rongxi Formation.
In a separate study, also published Sept. 28 in the journal Nature (opens in new tab)researchers have discovered another new species of extinct jawed fish, Qianodus duplicis. This species also dates back to about 439 million years ago. However, it was only described from fossilized teeth and scales, meaning researchers are more uncertain about exactly which group it might have belonged to.
(opens in new tab)
The same team also described three more extinct fish species from fossils discovered at the site, citing them in additional papers published on the same day. Xiushanosteus mirabilis it was an armored fish in a group known as placoderms. Shenacanthus vermiforis It may have been a placoderm but it also has similarities to some jawless fish. and Tujiaaspis vividus belongs to a group of jawless fish called galeaspids, which are known for having helmet-like shields on their heads, according to Chinese Academy of Sciences (opens in new tab). None of these samples were as old as F. renovata the Q. duplicisbut X. mirabilis and S. vermiforis they are still older than any other known species of early jawed fish.
Together, these newly described species completely change what scientists know about the evolution of jawed fishes. Previous discoveries had shown that the appearance and diversification of jawed fish did not actually begin until about 420 million years ago, according to the study. But the new fossils show that a variety of jawed fish were already swimming in Earth’s seas about 20 million years before that.
Related: Sharks are older than dinosaurs. What is the secret of their success?
“Up until this point, we’ve picked up hints from fossil scales that the evolution of jawed fish occurred much earlier in the fossil record, but we haven’t uncovered anything definitive,” study co-author Ivan Sansom, a vertebrate paleobiologist at the University of Birmingham in United Kingdom, he told a statement (opens in new tab). “These are the first creatures we would recognize today as fish.”
Furthermore, researchers suspect that jawed fish actually originated even earlier.
Based on the similarities between F. renovata and modern sharks, rays and bony fishes, the team estimated that a putative common ancestor – also a jawed fish – of chondrichthyans and teleosts could date back to about 455 million years ago.
Originally published in Live Science.
