More than a century ago, scientists discovered a mysterious fossil found in a Scottish quarry.. The remains belonged to a toothless, eel-like creature with a cartilaginous skeleton.. 130 years have passed since the discovery of Palaeospondylus gunni, but it has not been possible to unequivocally classify it.. Now, a team of scientists have determined that this mysterious ancient fish could be the earliest human ancestor, Live Science reports..

According to study lead author Tatsuya Hirasawa of the University of Tokyo, in order to place a creature on the evolutionary tree, it is necessary to identify every element of its skeleton.. The small fish is accompanied by riddles due to two factors: its tiny size (its body is only six centimeters long) and the fact that the petrification sharply compressed the skeleton, turning the bones into a distorted mass.. According to Hirashiva, "

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Previous research has shown that Palaeospondylus gunni lived during the Middle Devonian, approximately 398 to 385 million years ago.. This fish had well developed fins but no limbs.. Unlike most vertebrates of that time, the "

Repeated attempts to place fish on the evolutionary tree have fixed it on all " In 2004, researchers confidently reported in American Scientist that Palaeospondylus was a primitive lungfish.. However, a 2016 study published by Hirasawa in the journal Zoological Letters suggested that it was a relative of hagfish (a class of jawless fish - ed.. A year later, an Australian National University team questioned the hagfish's status, suggesting instead that it was a cartilaginous fish like modern sharks..

This " Scientists have been trying to solve the mystery of the creature since 1890. The only thing that paleontologists agreed on was that no one knows what the mysterious fossil actually was..

In a new study, scientists were able to obtain the highest resolution digital images of Palaeospondylus to date.. To get the most accurate data, the researchers collected the best fossils. Many Palaeospondylus specimens have been discovered since 1890, but most have been damaged in some way, either by fossilization or excavation, which may have contributed to previous misclassifications.. The researchers chose fossils in which only the head was encased in stone, and the tail was left free..

Sample scans reveal several key features. First, the inner ear of the creature consisted of several semicircular canals, very similar to the ears of modern fish, birds and mammals.. The authors noted that this is important because it establishes some evolutionary distance? between Palaeospondylus and more primitive jawless fish such as hagfish, which lack this feature. The researchers were also able to identify skull features that place the creature in a group called tetrapodomorphs, which includes all four-limbed creatures and their closest relatives.. Most importantly, a phylogenetic analysis of these prominent features suggests that Palaeospondylus may be the ancestor of all tetrapods..

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The researchers concluded that Palaeospondylus was likely more closely related to limb-bearing tetrapods than to older species such as lungfish and coelacanths, making Palaeospondylus a close aquatic precursor to the first animals to land on land..

But even if scientists have managed to solve this phylogenetic mystery, there are still a number of open questions.. Tetrapodomorphs usually have teeth, but Palaeospondylus did not have them, and if they did, they were not fossilized..

He also didn't have any obvious appendages, while his immediate family usually did..

One possible explanation for these anomalies could be that teeth and appendages were lost during evolution.. It is also likely that Palaeospondylus fossils may represent larval forms of creatures.

Previously, scientists discovered the remains of a dinosaur that was probably the largest land predator ever to have lived in Europe.. Fossils have been found on the coast of England.