Weird species of lizard that walked the Earth 49 million years ago had FOUR eyes that doubled up as a ‘biological clock’
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03:08 2018-04-04

An extinct monitor lizard that walked the Earth 49 million years ago had four eyes.
A new analysis of fossils unearthed in the 1870s suggests the metre-long lizard species ‘Saniwa ensidens’ had two light-sensing organs in the top of its skull.
The creature used these ‘third and fourth eyes’ as and a biological clock and internal compass that helped it orient itself, scientists said.

The research, from experts at the Senckenberg Research Institute in Frankfurt, Germany, provides the first example of a jawed vertebrate with these extra organs.
Known as the pineal and parapineal organs, the eye-like structures played key roles in the animals’ sleep and mating cycles, as well as orientation.
The photosensitive pineal organ is found in a number of small vertebrates such as fishes and frogs, the researchers said.

It’s often referred to as the ‘third eye’ and was widespread in primitive vertebrates.
Scientists had previously suggested the pineal evolved from the parapineal organ, another photosensitive organ found in primitive creatures such as lampreys.
The fact that a single creature had both of the organs sheds new light on the history of their evolution, researchers said.

Study lead author Dr Krister Smith said: ‘On the one hand, there was this idea that the third eye was simply reduced independently in many different vertebrate groups such as mammals and birds and is retained only in lizards among fully land-dwelling vertebrates.

‘On the other hand, there was this idea that the lizard third eye developed from a different organ, called the parapineal, which is well developed in lampreys.

‘These two ideas didn’t really cohere.
‘By discovering a four-eyed lizard – in which both pineal and parapineal organs formed an eye on the top of the head – we could confirm that the lizard third eye really is different from the third eye of other jawed vertebrates.’

Saniwa ensidens, a close relative of the modern monitor lizard, was the first extinct lizard fossil discovered in North America, though the species also lived in Europe.

Growing to around 4.3 feet (1.3m), the reptile lived during the Eocene epoch around 50 million years ago, hunting everything from other lizards to mammals and birds.

Dr Smith and his colleagues got the idea that the lizards had a fourth eye after other experts could not agree on where the species’ third eye was located.

They studied several 50 million-year-old specimens collected nearly 150 years ago at Grizzly Buttes as part of a Yale College expedition to the Bridger Basin, Wyoming.

CT scans showed that two different individuals had spaces where a fourth eye would have been, which Dr Smith said the team ‘certainly did not expect’.

Their evidence confirms that the pineal and parapineal glands weren’t a pair of organs in the way that vertebrate eyes are.

They also suggest that the third eye of lizards evolved independently of the third eye in other vertebrate groups.

Dr Smith said that while there’s ‘nothing mystical’ about the pineal and parapineal organs, they do enable extraordinary abilities.

For instance, they allow some lower vertebrates to sense the polarisation of light and use that information to orient themselves geographically.

Scientists still have much to learn about the evolution of these organs and their functions in living animals, the researchers said.

The new findings are a reminder of the hidden value within fossils left lying around in museums for more than a century.

‘The fossils that we studied were collected in 1871, and they are quite scrappy – really banged up,’ Dr Smith said.
‘One would be forgiven for looking at them and thinking that they must be useless. Our work shows that even small, fragmentary fossils can be enormously useful.’

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