More than a century ago, scientists were puzzled by the discovery of an unusual fossil discovered by a Scottish quarry. The remains suggest an toothless eel-like creature with a potentially cartilaginous skeleton and for 130 years after the mysterious creature – named Palaeospondylus gunni – was discovered, he continued to oppose the classification. Now, with the use of high-resolution images, a research team has finally discovered that this mysterious fish may have been one of our earliest ancestors.
“To put it down Paleospondyl in the evolutionary tree, the identification of each skeletal element is a prerequisite, “said Tatsuya Hirasawa, an associate professor of paleontology at the University of Tokyo in Japan and lead author of a new study on fossils. its size, with a body only 2.4 inches (6 centimeters) long and the unfortunate fact that fossilization dramatically compresses its skeleton, pressing individual bones into a distorted mass that was a paleontological nightmare to discover, Hirasawa told Live Science in an email.
Before the new study, scientists knew this Paleospondyl lived in the Middle Ages of Devon, about 398 million to 385 million years ago. The fish had well-developed fins, but no limbs. Curiously, it lacked teeth, unlike most vertebrates of the time.
Repeated attempts to place the fish on the evolutionary tree have fixed it throughout the map. In 2004, researchers confidently reported in the journal American scientist (opens in a new section) that Paleospondyl it was a primitive lung fish. However, a 2016 study published by Hirasawa in the journal Zoological letters (opens in a new section), suggested that he was a relative of Mexico instead. A year later, a team from the Australian National University questioned the status of Mexico’s fish, suggesting instead that it was cartilaginous fish like modern sharks.
Connected: Fish germinate their fingers before they dare to go ashore, fossils show
Nor is this taxonomic tennis match a recent phenomenon. “This strange animal has puzzled scientists since its discovery in 1890 as a puzzle that was impossible to solve,” said study co-author Yu (Daisy) Hu, a researcher in the Department of Materials Physics at the Australian National University in Canberra. said in a statement (opens in a new section).
Indeed, it seems that the only thing that paleontologists can agree with is that no one really knew the identity of this animal.
Recently, Hirasawa and Hu, armed with microcomputer tomography (CT) scanning technology, were able to create digital images with the highest resolution. Paleospondyl to date. In order to gather the most accurate data, they had to choose the best fossils. Since 1890 a lot Paleospondyl specimens have been found, but most have been damaged in some way – either by fossils or excavations – which may have contributed to previous classification errors. To circumvent this problem, the authors of the new study chose specimens with heads that were completely wrapped in rock. “I looked for specimens showing only tails, and finally found two specimens that revealed only the tail of the surface,” Hirasawa said.
Scanning these specimens revealed several key features. One was that the inner ear consisted of several semicircular canals, similar to the ears of modern fish, birds and mammals. This is important, the authors note, because it puts some evolutionary distance between them Paleospondyl and more primitive jawless fish like Mexico that lack this feature. Researchers have also been able to identify cranial features at the site Paleospondyl in a group called tetrapodomorphs, which includes all four-legged creatures and their closest relatives. Most importantly, phylogenetic analysis of these exceptional characteristics suggests that Paleospondyl it may not be just a garden tetrapodomorph; may be the ancestor of all tetrapods.
“Our analysis concluded that Paleospondyl is a close relative of vertebrates that have limbs (with toes) and those that have limb-like fins, also known as “fishponds,” Hirasawa said. According to the researchers, Paleospondyl it is probably more closely related to limb-bearing tetrapods than to older species such as lungs and coelacanths that would make Paleospondyl a close aquatic ancestor of the first animals to crawl on land.
Even if this phylogenetic mystery is already solved, a number of open questions still remain. Tetrapodomorphs usually have teeth, but Paleospondyl they did not have – or if there were, they failed to petrify. In addition, he lacked obvious appendages, while his closest relatives usually had them.
What can explain these anomalies? One possibility, Hirasawa suggested, is that teeth and limbs may have been evolutionarily lost in Paleospondyl. Another possibility is known Paleospondyl fossils can be larval or juvenile forms of the animal.
“Whether these characteristics have been evolutionarily lost or normal development is half-frozen in fossils may never be known,” Hirasawa said. said in a statement.
While now we have a better idea of where Paleospondyl sitting on the evolutionary tree, there is still a lot of work to do. At the moment, as at the time of its discovery, this fish keeps many of its ancient secrets.
This study was published May 25 in the journal nature (opens in a new section).
Originally published in Live Science.