How vision may have driven fishes onto land

March 8, 2017 by John Long, The Conversation 

About 375 million years ago, certain fishes had developed powerfully strong paired fins that were capable of transporting them out of the water and onto land. 

These fishes would eventually evolve into the first truly terrestrial animals, called tetrapods. They had four limbs bearing digits – fingers and toes – to help them when they walked around around on land.

But one of the biggest mysteries for scientists is figuring out what could have driven such fishes out of the water and onto land in the first place. 

Was it availability of new food sources, or perhaps their need to escape from predators in the water?

A new theory says it was improved vision, as shown by dramatic increases in eye size and visual acuity, that enabled fishes peeping upwards at the waterline to spot prey on land. 

This would have motivated them to venture out of the water to hunt for food. The new research is published today by Malcolm MacIver from Northwestern University in the US and colleagues. They have named this the "Buena Vista" hypothesis, from the Spanish for "good view". 

All the better to see you with

The team measured the eye sizes of many kinds of fossil fishes and early tetrapods that lived between 390 million and 250 million years ago to show a dramatic increase in eye size just before the most advanced fishes, called elpistostegalians, left the water to evolve into the first tetrapods.

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Study of jaw mechanics shows tetrapods still fed underwater

4 hours ago by Marie Daniels

A study of the jaws of one of the earliest known limbed vertebrates shows the species still fed underwater, not on land.

Scientists from the University of Lincoln, UK, University of Zurich, Switzerland, University of Cambridge and University of Bristol, developed an innovative new method to infer the feeding mechanism of Acanthostega – one of the earliest and most primitive tetrapods.

Tetrapods - the four-legged limbed vertebrates - evolved from fish and include today's amphibians, reptiles, birds and mammals.

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Tetrapod anatomy: Backbone back-to-front in early animals

Textbooks might have to be re-written when it comes to some of the earliest creatures, a study suggests.

Researchers have found that our understanding of the anatomy of the first four-legged animals is wrong.

New 3D models of fossil remains show that previous renderings of the position of the beasts' backbones were actually back-to-front.

The findings, published in the journal Nature, may even change our thinking on how the spine evolved.

The scientists looked at a group of animals called the tetrapods, examining three creatures called Ichthyostega, Acanthostega and Pederpes.

The textbook examples turn out to be wrong”

Prof John Hutchinson Royal Veterinary College

These primitive four-legged animals are of great interest to palaeontologists: they were the first creatures to haul themselves out of the oceans, paving the way for all future vertebrate life on land.

Studying how these animals are put together is key to understanding how they made this transition.

The researchers from the University of Cambridge and the Royal Veterinary College (RVC) used the European Synchrotron Radiation Facility (ESRF) to bombard the 360-million-year old fossils with high energy X-rays.

This enabled them to create detailed computer reconstructions of the prehistoric animals.

Continued:  http://www.bbc.co.uk/news/science-environment-20987289

Body Armor for Breathing?

Many of the earliest four-legged creatures that ventured onto land were heavily armored beasts, sporting plates of bone beneath their skin. This "dermal bone" might have protected their blood vessels and nerves while keeping these so-called tetrapods warm and hydrated. Now researchers have come up with a possible new function for the material: It may have prevented the animals' blood from turning to acid.

"Nobody's suggested this before, but it certainly seems plausible," says Jennifer Clack, a vertebrate paleontologist at the University of Cambridge in the United Kingdom, who was not involved in the work.

One of the biggest challenges of life on land is getting rid of your carbon dioxide. All we have to do is exhale—but early land dwellers, many of which were semi-aquatic amphibians, had primitive lungs. And unlike us, their ribs were fixed in place, making it hard to breathe in and out. As a result, carbon dioxide could have easily built up in their blood, acidifying it—especially after they chased prey or escaped predators.

Dermal bone may have solved this problem. For instance, when turtles spend a long time underwater holding their breath, there's no intake of oxygen to displace the carbon dioxide that slowly builds in their blood. To compensate, the dermal bone in their shell leaches calcium and magnesium ions into their bloodstream, replacing the acidic hydrogen ions that have built up there.

Read more:  http://news.sciencemag.org/sciencenow/2012/04/body-armor-for-breathing.html