New Fossil Reveals Insights into the Evolution of Vertebrate Skulls
A recent study published in the journal Nature has unveiled new information about the evolution of vertebrate skulls. Researchers have analyzed a 455 million-year-old fossil skull of the jawless fish Eriptychius americanus, providing valuable insights into the ancient ancestors of modern vertebrates.
Jawless fishes were the first animals with backbones and swam Earth’s seas hundreds of millions of years ago. These fish had their brains protected by armored skin and plates made of cartilage. The skull arrangement of E. americanus, however, is unlike anything seen in living vertebrates or in the fish’s extinct relatives. The fossilized head cartilage shows sections of unfused cartilage, some symmetrical and some not, at the front of the head, surrounding the mouth, olfactory organs, and eyes.
Lead study author Dr. Richard Dearden, a postdoctoral research fellow at the Naturalis Biodiversity Center in the Netherlands, described the uniqueness of the cartilage arrangements as “exciting”. He explained that no other creatures possess such a combination of unpaired and paired cartilages.
The fossilized head cartilage of E. americanus was discovered in the Harding Sandstone formation in Colorado. It was initially excavated in 1949 and described in 1967 by paleontologist Robert Denison, a curator of fossil fishes at Chicago’s Field Museum of Natural History. However, due to limitations in technology at the time, scientists were unable to look deeper into the fossil without destroying it.
Using modern CT scans, the researchers were able to visualize and reconstruct the 3D model of the fish’s cranium. This breakthrough allowed them to identify ten cartilage skull pieces in the specimen, along with scales and canals that may have housed sensory or vascular structures.
Despite the new findings, questions about skull evolution and the appearance of jaws in fish still remain. Researchers are uncertain of the purpose of the canals seen in the fossil and why the cartilage appears to be concentrated at the front of the skull. However, this fossil discovery fills a significant gap in our understanding of the evolution of the vertebrate head.
Paleobiologist Lauren Sallan, an assistant professor at the Okinawa Institute of Science and Technology Graduate University in Japan, lauded the discovery, stating that it is a major step forward. The Ordovician ancestors of jawed fishes, like E. americanus, were rare and mostly found in shallow marine waters. Preserving the internal material of these ancient fishes is a remarkable achievement that sheds light on the origins of marine biodiversity.
This new research is a testament to the importance of continually exploring and analyzing ancient fossils. It provides valuable insights into the early stages of vertebrate evolution and deepens our understanding of the intricate development of skulls in modern organisms.