The Discovery of Fossil Fish Pushes Back the Origin of Jaws and Teeth

Our jaws and teeth are extraordinarily ancient structures. Adaptations that paleontologists have followed back to our distant fishy ancestors who thrived in the waters, some 425 million years ago, are older than dinosaurs, older than arms and legs, and older than trees. However, the discovery of a cache of vertebrates in China that had been painstakingly preserved has led to the establishment of a new date for the first record of jaws and teeth. Early vertebrates found in the aquarium include some of the earliest fossil fish with paired appendages.

436 Million Years Old Fossil Fish

The fossils are approximately 436 million years old and were found in the tank. Researchers have argued about when the first bites appeared. Molecular studies based on genetic change estimates suggest that the first jaws and teeth emerged around 450 million years ago. Until previously, the oldest fossil fish of jawed vertebrates—or gnathostomes—dated to around 425 million years ago, representing a huge gap. The new fossils from South China, as described by the Institute of Vertebrate Paleontology and Paleoanthropology researcher Min Zhu, sit in the heart of this gap and offer a surprising look at a pivotal period in evolutionary history.

The discovered fossil fish constitute a “Konservat-Lagerstätte,” or a fossil location that records intricate features of ancient organisms that are typically lost in other settings, according to paleontologists. The fish discovered in this case, according to Zhu and co-authors, were minuscule and had delicate bones. That means these fish were unlikely to become fossils unless they were buried soon and protected from scavengers who would otherwise eat them.

The fact that such fish required a rare stroke of luck, likely explains the disparity between the molecular estimate and the fossil record. Having such complete fossils also allows paleontologists to determine to whom all the weird parts and pieces from such old waters belonged.

Galeaspid, Xiushanosteus, and More

The collection described by Zhu and colleagues represents a variety of extremely early fish, not all of which possessed jaws. One of the most well-preserved fossil fish is that of a jawless fish called a galeaspid, which is essentially a biological Roomba with a tail. The bones of this animal’s robust skull shield have long been known, but new South China fossils reveal the shape of the soft flesh beneath those bones. The most frequent armored fish in the collection is the Xiushanosteus, an armored fish with jaws only about an inch long. Even more shocking is the discovery of Fanjingshania Renovata, a new, ancient relative of sharks and cartilaginous fish that challenges paleontologists’ understanding of how sharks, bony fish, and extinct groups like placoderms developed.