Unlike us, our earliest vertebrate ancestors had soft, squishy bodies, meaning they very rarely fossilised. On the exceptional occasions they did, their remains were squashed, often beyond recognition. This makes it incredibly difficult for scientists to interpret fossils of early vertebrates and, as a result, reach an understanding about this enigmatic period of evolution.
However, new fossil imaging techniques are beginning to offer a rare glimpse into this period, allowing us to see the world through the eyes of the early vertebrates that lived during it.
One of these techniques is known as synchrotron X-ray fluorescence imaging and it was just used by a team of scientists from the University of Manchester to reveal some of the oldest evidence of advanced eyes in two tiny jawless fish.
These fish, known as Jamoytius and Lasanius, were found at a site near Lesmahagow, just south of Glasgow, and dated to 443 million years ago. Both are extinct species of primitive, eel-like fish that are understood to be some of the earliest ancestors of two of the strangest fish alive today: hagfish and lamprey.
As part of a study published today in Proceedings of the Royal Society B, flattened fossils of Jamoytius and Lasaniuswere subjected to synchrotron X-ray fluorescence imaging at the Stanford Synchrotron Radiation Lightsource (SSRL) in California, USA. The findings from these X-rays were extraordinary, reshaping our understanding of how the vertebrate body first evolved.
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“What we were able to discover was far beyond our expectations,” said co-author Roy Wogelius. “Not only did we identify early bone structures deep in the geological record, but we also captured images of…camera-type eyes. These eyes preserve even the small notch where the optic nerve connected - features that form the basis of modern vertebrate eyes today.”
This isn’t the first time synchrotron X-ray fluorescence imaging has been used on fossils; it has previously been used on mummified dinosaur skin by several of the same scientists involved in this latest study.
The technique works by focussing an intense X-ray beam at a sample, causing atoms in the sample to emit their own X-rays that a scanner then detects. The properties of these emitted X-rays are specific to the chemical elements they originated from, allowing scientists to identify concentrations of certain chemical elements locked inside fossils.
In the latest study, the University of Manchester-led team found traces of zinc and copper in the eyes of Jamoytius. These chemical elements revealed that the structure of the retina and the pigment layer was surprisingly advanced and camera-like, similar to our own eyes. The team also found evidence of calcium and phosphorus in both Jamoytius and Lasanius - a sign these early vertebrates possessed bone-like tissues.
“It’s been amazing to see just how much new information we can recover from fossils, which are usually too poorly preserved to be useful, using these new technologies,” said lead author Jane Reeves. “Our findings help resolve scientific debates that have been running since the Victorian era. They point to a very early origin of bones and eyes in vertebrate history, probably even predating the group appearing altogether.”
Last week, a study published in Nature presented even older evidence of camera-like eyes, this time in two species of myllokunmingids (ancestors of vertebrates) that lived in China approximately 518 million years ago. This study found these strange animals had four eyes, rather than two, and that these additional eyes may have been able to generate images, as well as just sense light.
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Reeves praised this other study, adding, “I love how our findings fit with work from other groups; when you put our respective research together, they connect to fill in a lot of gaps in our knowledge, creating a really well supported picture of the early evolution of vertebrates.”
As humans, it’s difficult for us to imagine our ancestors beyond the likes of neanderthals, australopithecines, and other primates. The remarkable thing about these recent studies is that they give us an opportunity to look into the eyes of our earliest ancestors and see elements of ourselves staring back. They may look wildly different to us, but the way Jamoytius, Lasanius, and the two Chinese myllokunmingids viewed the world is not so dissimilar from the way we view it today.
“I love these fossil fish. They may have been dead for over 400 million years but they keep on surprising us with new, hidden data about our deep origins,” concluded co-author Robert Sansom.
The study was published in the journal Proceedings of the Royal Society B and conducted by the University of Manchester’s Jane Reeves, Roy Wogelius, Phil Manning, and Robert Sansom, and the SSRL’s Nick Edwards.
Top image: A reconstruction of Jamoytius - one of the oldest known fossil vertebrates and the owner of a pair of particularly advanced eyes. Credit: N. Tamura
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