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Tiktaalik: Iconic fossil's rear parts described

Scientists have finally managed to describe the back end of one of the key fossil finds of the past 10 years.
Known as Tiktaalik, the 375-million-year-old creature is considered pivotal because it has many features that look half-way between fish and land animals.

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Ichthyostega
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 3D whole body reconstruction of Ichthyostega



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 Ancient walking mystery deepens

One of the first creatures to step on land could not have walked on four legs, 3D computer models show.
Textbook pictures of the 360-million-year-old animal moving like a salamander are incorrect, say scientists.
Instead, it would have hauled itself from the water using its front limbs as crutches, research in Nature suggests.

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Oldest land-walkers
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The oldest evidence of four-legged animals walking on land has been discovered in southeast Poland.
Rocks from a disused quarry record the "footprints" of unknown creatures that lived about 397 million years ago.
Scientists tell the journal Nature that the fossil trackways even retain the impressions left by the "toes" on the animals' feet.
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Acanthostega
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New evidence gleaned from CT scans of fossils locked inside rocks may flip the order in which two kinds of four-limbed animals with backbones were known to have moved from fish to landlubber.
Both extinct species, known as Ichthyostega and Acanthostega, lived an estimated 360-370 million years ago in what is now Greenland. Acanthostega was thought to have been the most primitive tetrapod, that is, the first vertebrate animal to possess limbs with digits rather than fish fins.

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Newly exposed parts of Tiktaalik roseae--the intermediate fossil between fish and the first animals to walk out of water onto land 375 million years ago--are revealing how this major evolutionary event happened. A new study, published this week in Nature, provides a detailed look at the internal head skeleton of Tiktaalik roseae and reveals a key intermediate step in the transformation of the skull that accompanied the shift to life on land by our distant ancestors.
A predator, up to nine feet long, with sharp teeth, a crocodile-like head and a flattened body, Tiktaalik's anatomy and way of life straddle the divide between fish and land-living animals. First described in 2006, and quickly dubbed the "fishapod," it had fish-like features such as a primitive jaw, fins and scales, as well as a skull, neck, ribs and parts of the limbs that are similar to tetrapods, four-legged animals.

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Tetrapods
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New exquisitely preserved fossils from Latvia cast light on a key event in our own evolutionary history, when our ancestors left the water and ventured onto land. Swedish researchers Per Ahlberg and Henning Blom from Uppsala University have reconstructed parts of the animal and explain the transformation in the new issue of Nature.
It has long been known that the first backboned land animals or "tetrapods" - the ancestors of amphibians, reptiles, birds and mammals, including ourselves - evolved from a group of fishes about 370 million years ago during the Devonian period. However, even though scientists had discovered fossils of tetrapod-like fishes and fish-like tetrapods from this period, these were still rather different from each other and did not give a complete picture of the intermediate steps in the transition.

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RE: Tiktaalik roseae
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Neil Shubin, a University of Chicago professor of biology and anatomy and internationally renowned palaeontologist, will deliver a free public lecture at the University of Utah on his discovery of a fossil that has been dubbed the "missing link" between fish and land animals.
The fossil, Tiktaalik roseae, better known as the "fishapod," is a 375-million-year-old fish that was discovered in the Canadian Arctic in 2004 by Shubin and colleagues. Its discovery highlights a pivotal point in the history of life on Earth: when the first fish ventured onto land. Tiktaalik (which means "large freshwater fish" in Inuit) lived about 12 million years before the first tetrapods, or four-legged animals, so the existence of tetrapod features in a fish like Tiktaalik marks the earliest appearance of shoulders, necks, limbs, elbows and wrist-joints in the fossil record.

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Humans could be closer to pond life than had been realised. Researchers have linked a raft of our anatomical and genetic features with fishy ancestors that lived hundreds of millions of years ago.
They have found that the origin of human hands and fingers could lie in the emergence of a finned fish 365m years ago. Similarly, the sophisticated joints that give us the ability to run, grip and turn may owe their existence to a sea creature known as the tiktaalik that lived in the Arctic 375m years ago.

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Fins to limbs
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U.S. scientists have determined the transition from fins to limbs occurred much earlier than thought, shedding new light on the evolution of life on Earth.
University of Florida researchers studying shark embryo development identified a spurt of genetic activity that's required for digit development in limbed animals.
The finding shows what was thought to be a relatively recent evolutionary innovation existed eons earlier than previously believed. The researchers said their finding also potentially provides insight for scientists seeking ways to cure human birth defects.

Genetic processes were not simple in early aquatic vertebrates, only to become more complex as the animals adapted to terrestrial living. They were complex from the outset. Some major evolutionary innovations, like digits at the end of limbs, may have been achieved by prolonging the activity of a genetic program that existed in a common ancestor of sharks and bony fishes  -Associate Professor Martin Cohn of the university's Genetics Institute

The research is reported in the online journal PLoS One.

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