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Discovery sheds light on how vertebrates see

New research led by Professor Sarah Gabbott from the Department of Geology has overturned a long-standing theory on how vertebrates evolved their eyes by identifying remarkable details of the retina in the eyes of 300 million year-old lamprey and hagfish fossils.

The study, published in the journal Proceedings of the Royal Society B, shows that fossil hagfish eyes were well-developed, indicating that the ancient animal could see, whereas their living counterparts are completely blind after millions of years of eye degeneration – a kind of reverse evolution.

The researchers examined the eye tissue in two fossil jawless fish species - Mayomyzon (a lamprey) and Myxinikela (a hagfish) found in the Carboniferous age Mazon Creek fossil bed, Illinois.

Using a high-powered scanning electron microscope to magnify the eye 5,000 times they could see that the fossil retina is composed of minute structures called melanosomes - the same structures that occur in human eyes and prevent stray light bouncing around in the eye allowing us to form a clear visual image.

This is the first time that such details in fossil vertebrate eyes have been brought to bear on the tricky problem of how their eyes evolved.

The team also found the earliest evidence of skin pigment patterning in a fossil.

Professor Gabbott said: “Sight is perhaps our most cherished sense but its evolution in vertebrates is enigmatic and a cause célèbre for creationists. We bring new fossil evidence to bear on an iconic evolutionary problem: the early evolution of the vertebrate eye. We will now scrutinize the eyes of other ancient vertebrate fossils to see if we can finally build a picture of the sequence of events that took place in early vertebrate eye evolution.” 

LampreySmall.jpg
The fossil of a 300 million year old primitive jawless fish - a lamprey - about 6 cm in length. The eyes are the two dark circles on the right-hand side and are so well-preserved the retina and lens can be seen in high magnification.

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