New Fossils Of Extremely Primitive 4-Legged Creatures Close The Gap Between Fish And Land Animals
ScienceDaily (June 27, 2008) — 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 researcher Per Ahlberg from Uppsala University and colleagues 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.
In 2006 the situation changed dramatically with the discovery of an almost perfectly intermediate fish-tetrapod, Tiktaalik, but even so a gap remained between this animal and the earliest true tetrapods (animals with limbs rather than paired fins). Now, new fossils of the extremely primitive tetrapod Ventastega from the Devonian of Latvia cast light on this key phase of the transition.
"Ventastega was first described from fragmentary material in 1994; since then, excavations have produced lots of new superbly preserved fossils, allowing us to reconstruct the whole head, shoulder girdle and part of the pelvis", says Professor Per Ahlberg at the Department of Physiology and Developmental Biology, Uppsala University.
The recontructions made by Professor Ahlberg and Assistant Professor Henning Blom together with British and Latvian colleagues show that Ventastega was more fish-like than any of its contemporaries, such as Acanthostega. The shape of its skull, and the pattern of teeth in its jaws, are neatly intermediate between those of Tiktaalik and Acanthostega.
"However, the shoulder girdle and pelvis are almost identical to those of Acanthostega, and the shoulder girdle is quite different from that of Tiktaalik (the pelvis of Tiktaalik is unknown), suggesting that the transformation from paired fins to limbs had already occurred. It appears that different parts of the body evolved at different speeds during the transition from water to land", says Per Ahlberg.
Above: This lower jaw with teeth is one of the new fossils of Ventastega found in Latvia. Photo: Ivars Zupins, Latvian Museum of Natural History. Below: Reconstruction of Ventastega in side view. With the help of new, superbly preserved fossils, Per Ahlberg and his colleagues have been able to reconstruct the whole head, shoulder girdle and part of the pelvis. The silhouette is based on fossils of one of its contemporaries, Acanthostega, Scale bar 10 cm. Picture: Per Ahlberg. (Credit: Image courtesy of Uppsala University)
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.
In 2006 the situation changed dramatically with the discovery of an almost perfectly intermediate fish-tetrapod, Tiktaalik, but even so a gap remained between this animal and the earliest true tetrapods (animals with limbs rather than paired fins). Now, new fossils of the extremely primitive tetrapod Ventastega from the Devonian of Latvia cast light on this key phase of the transition.
"Ventastega was first described from fragmentary material in 1994; since then, excavations have produced lots of new superbly preserved fossils, allowing us to reconstruct the whole head, shoulder girdle and part of the pelvis", says Professor Per Ahlberg at the Department of Physiology and Developmental Biology, Uppsala University.
The recontructions made by Professor Ahlberg and Assistant Professor Henning Blom together with British and Latvian colleagues show that Ventastega was more fish-like than any of its contemporaries, such as Acanthostega. The shape of its skull, and the pattern of teeth in its jaws, are neatly intermediate between those of Tiktaalik and Acanthostega.
"However, the shoulder girdle and pelvis are almost identical to those of Acanthostega, and the shoulder girdle is quite different from that of Tiktaalik (the pelvis of Tiktaalik is unknown), suggesting that the transformation from paired fins to limbs had already occurred. It appears that different parts of the body evolved at different speeds during the transition from water to land", says Per Ahlberg.
Above: This lower jaw with teeth is one of the new fossils of Ventastega found in Latvia. Photo: Ivars Zupins, Latvian Museum of Natural History. Below: Reconstruction of Ventastega in side view. With the help of new, superbly preserved fossils, Per Ahlberg and his colleagues have been able to reconstruct the whole head, shoulder girdle and part of the pelvis. The silhouette is based on fossils of one of its contemporaries, Acanthostega, Scale bar 10 cm. Picture: Per Ahlberg. (Credit: Image courtesy of Uppsala University)
4 comments:
New discoveries of intermediate fossil forms close gaps in human knowledge of how life evolved. Where will theism hide its gangrenous god as our ignorance shrinks?
Two new gaps in the fossil record!
Per is discussing the finds on TalkRational, here. He is good at answering questions, too.
Discoveries such as these, make an absolute mockery of creationists such as Ray Comfort and Kent Hovind who continue to claim that there are no transitional fossils.
We have an excellent fossil sequence for the evolution of ancient tetrapods, and it just keeps getting better and better.
As PZ Myers said to creationist Geoffrey Simmons during their recent radio debate, when Simmons claimed that we have no transitional whale fossils; "Your ignorance about the state of the fossil record is not evidence that there are holes in evolutionary theory."
Soon there will be nowhere for creationists to hide, except in their own shadows. Oh wait, that's where they're already hiding!
It's only by keeping themselves deliberately ignorant about such discoveries, that they can continue to make ridiculous statements such as Simmons did during his debate with Myers. I can't understand how they are not embarrassed to publicly flaunt such ignorance.
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