After more than 130 years of its discovery, the mysterious fish-like creature that puzzled scientists may have finally found its place in the tree of life. The extinct fish named Palaeospondylus gunni was first discovered in Scotland in 1890, wherein scientists estimated it to have lived 390 million years back during the Middle Devonian.
Dr. Daisy (Yuzhi) Hu, a researcher from The Australian National University (ANU), said that its fossils were one of the most mysterious vertebrates ever found and have been impossible to solve until now. Researchers have finally been able to classify it, increasing the possible understanding of the first animals to crawl on Earth.
Life restoration of Palaeospondylus gunni
Unmasking the Mysterious Fish-Like Creature
According to SciTech Daily, Palaeospondylus gunni was a small fish-like creature that measures 2 inches (5 centimeters long) and has an eel-like body. Their small body size and poor quality of cranial reconstruction through CT scans and wax models have prevented scientists from placing them on the evolutionary tree despite the abundance of the fossils found in 1890.
Experts believe that the fish-like creature shares some features with jawed and jawless fish, while its body has baffled evolutionary scientists for many years. There were also unusual features, such as the absence of teeth or dermal bones. In order to resolve this century-long mystery, researchers from the University of Tokyo, in conjunction with ANU, utilized the powerful RIKEN SPring-8 synchrotron that generated high-resolution micro-CT scans on the fossils using synchrotron radiation X-rays.
They carefully selected the fossils with remaining heads that are completely embedded in the rock, unlike previous studies that have used excavated fossil heads. Study lead author Tatsuya Hirasawa said that choosing the best specimen for micro-CT scans allowed them to improve the resolution of the scans. These preparations have played key roles in achieving the results of their study.
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Earliest Ancestors of Humans
The high-resolution micro-CT scans revealed multiple important features of the mysterious creature that surprised researchers. Science Alert reported that researchers claim that it could be the earliest ancestor of tetrapods, animals with four limbs, including humans.
The fossils may not have teeth and dermal bones, but the results were quite impressive. It has three curved canals in its skull, similar to the inner ears of jawed vertebrates. More so, its skull resembled those of two other ancient fish: Eusthenopteron and Panderichthys.
Both species belong and have similar traits to the taxon of Sarcopterygians or lobe-finned fishes. All tetrapods have evolved from some of the Sarcopterygians, also known as tetrapodomorphs.
However, the lack of teeth and dermal bones of the fossils presents a problem since tetrapodomorphs usually have these features. Researchers wrote in their study that Palaeospondylus seems to resemble a juvenile tetrapodomorph that has not yet developed the characteristics of the adult version. Whether they were slower to develop or were lost entirely, the team believes it is an evolutionary quirk.
The team plans to conduct further study to confirm the mystery fish-like creature's imposition in the family tree. Hirasawa said in a statement that the strange morphology of Palaeospondylus is very interesting from the developmental genetic point of view.
The researchers described their findings in full in the study titled, "Morphology of Palaeospondylus Shows Affinity to Tetrapod Ancestors," published in Nature.
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