Another great milestone in the history of science . The classification of a 390-million-year-old fish-like creature found in Scotland 130 years ago places it at the bottom of the vertebrate family tree. It is one of the earliest ancestors of four-limbed animals, including us humans.
Your place on the evolutionary tree
Its name is Palaeospondylus gunni and it has become one of the most enigmatic fossil vertebrates; its phylogenetic position has been unclear since its discovery in Scotland in 1890. Despite its age, its position on the evolutionary tree has been unclear until now.
“This strange animal has puzzled scientists since its discovery in 1890 like a puzzle that has been impossible to solve,” says Daisy (Yuzhi) Hu, researcher and PhD graduate of the Australian National University (ANU).
Research led by the University of Tokyo in conjunction with ANU and the RIKEN Evolutionary Morphology Laboratory has found that the specimen was likely one of the earliest ancestors of four-limbed animals.
“Recent improvements in high-resolution 3D visualization and segmentation have made this previously impossible task possible. Finding a specimen as well preserved as the ones we use is like winning the lottery , or even better!” say the authors in their paper published in the journal Nature.
Difficulties in cataloging
There are several reasons why classifying this animal has been so problematic. Fossils of this creature are abundant, but because Palaeospondylus was so small and its fossils so damaged, reconstructing its cranial anatomy was enormously difficult.
The researchers analyzed the fossils with synchrotron radiation X-ray microcomputer tomography , which allowed them to image the fossils at very good resolution without destroying them, for extensive examination and reconstruction.
“The strange morphology of Palaeospondylus , which is comparable to that of tetrapod larvae, is very interesting from a developmental genetic point of view,” says Hirasawa. “With this in mind, we will continue to study the developmental genetics that caused this and other morphological changes that occurred at the transition from water to land in vertebrate history.”
The creature had a flat head, an eel-like body, and lived in a freshwater lake bed in the far northeast of the Highlands. It had a strange basket-shaped apparatus on its snout and a well-developed cartilaginous spine, but no apparent fins. It fed on leaves, animal remains, and other organic debris that fell to the bottom of the lake from the surrounding land. At the time, the Scottish landmass was south of the equator, where central Africa is today, so the environment was hot and semi-arid.
It’s a crucial evolutionary finding, as Palaeopondylus dates back to a point in history when the first vertebrates began to emerge from the water.
“Despite the investigation, it is still difficult to determine which animal it was with 100% accuracy,” Hu said. “Even with this new information, long- term research with the joint effort of scientists from around the world is needed to give us the perfect answer of what Palaeospondylus gunni really is.”
Referencia: Tatsuya Hirasawa, Yuzhi Hu, Kentaro Uesugi, Masato Hoshino, Makoto Manabe, Shigeru Kuratani. Morphology of Palaeospondylus shows affinity to tetrapod ancestors. Nature, 2022; DOI: 10.1038 / s41586-022-04781-3
