Everything about Tiktaalik totally explained
Tiktaalik is a
genus of
extinct sarcopterygian (lobe-finned)
fish from the late
Devonian period, with many features akin to those of
tetrapods (four-legged animals). It is an example from several lines of ancient sarcopterygian fish developing adaptations to the oxygen-poor shallow-water habitats of its time, which led to the evolution of
amphibians. Well-preserved fossils were found in 2004 on
Ellesmere Island in
Nunavut,
Canada.
Tiktaalik lived approximately 375 million years ago. Paleontologists suggest that it was an intermediate form between fish such as
Panderichthys, which lived about 380 million years ago, and early tetrapods such as
Acanthostega and
Ichthyostega, which lived about 365 million years ago. Its mixture of fish and tetrapod characteristics led one of its discoverers,
Neil Shubin, to characterize
Tiktaalik as a "
fishapod" .
Description
Tiktaalik appears to be a transitional form between fish and amphibian. Unlike many previous, more fishlike transitional fossils, Tiktaalik's 'fins' have basic wrist bones and simple fingers, showing that they were weight bearing. Close examination of the joints show that although they probably were not used to walk, they were more than likely used to prop up the creature’s body,
push up fashion. The bones of the fore fins show large muscle facets, suggesting that the fin was both muscular and had the ability to flex like a wrist joint. These wrist-like features were speculated to evolve, if not from land excursions, then as a useful adaptation to anchor the creature to the bottom in fast moving current.
A more robust ribcage is also a feature of
Tiktaalik, which would have been very helpful in supporting the animal’s body if it did indeed venture from the water. Tiktaalik also lacked a characteristic that most fishes have - bony plates in the gill area that restrict lateral head movement. This means
Tiktaalik is currently the earliest fish with a neck, which would give it more freedom in hunting prey either on land or in the shallows.
Also notable are the spiracles on the top of the head, which suggest the creature had primitive lungs as well as gills. This would have been useful in shallow water, where higher water temperature would lower oxygen content. This development may have led to the evolution of a more robust
ribcage, a key evolutionary trait of land living creatures.
Tiktaalik is a
transitional fossil; it's to tetrapods what
Archaeopteryx is to birds.
Its mixture of both fish and tetrapod characteristics include these traits:
- Fish
- "Fishapod"
- half-fish, half-tetrapod limb bones and joints, including a functional wrist joint and radiating, fish-like fins instead of toes
- half-fish, half-tetrapod ear region
- Tetrapod
- tetrapod rib bones
- tetrapod mobile neck
- tetrapod lungs
Tiktaalik generally had the characteristics of a lobe-finned fish, but with front fins featuring arm-like skeletal structures more akin to a crocodile, including a shoulder, elbow, and wrist. The rear fins and tail have not yet been found. It had rows of sharp teeth of a predator fish, and its neck was able to move independently of its body, which isn't possible in other fish. The animal also had a flat skull resembling a crocodile's; eyes on top of its head, suggesting it spent a lot of time looking up; a neck and ribs similar to those of tetrapods, with the latter being used to support its body and aid in breathing via lungs; well developed jaws suitable for catching prey; and a small gill slit called a spiracle that, in more derived animals, became an ear .
The fossils were found in the "
Fram Formation", deposits of meandering stream systems near the Devonian equator, suggesting a
benthic animal that lived on the bottom of shallow waters and perhaps even out of the water for short periods, with a skeleton indicating that it could support its body under the force of gravity whether in very shallow water or on land . At that period, for the first time,
deciduous plants were flourishing and annually shedding leaves into the water, attracting small prey into warm oxygen-poor shallows that were difficult for larger fish to swim in..
Neil Shubin and
Ted Daeschler, the leaders of the team, have been searching Ellesmere Island for fossils since 1999. In an interview, Ted Daeschler stated that "we're making the hypothesis that this animal was specialized for living in shallow stream systems, perhaps swampy habitats, perhaps even to some of the ponds. And maybe occasionally, using its very specialized fins, for moving up overland. And that's what is particularly important here. The animal is developing features which will eventually allow animals to exploit land."
The name
Tiktaalik is an
Inuktitut word meaning "
burbot", a freshwater fish related to true
cod. The "fishapod" genus received this name after a suggestion by
Inuit elders of
Canada's
Nunavut Territory, where the fossil was discovered .
Discovery
The three fossilized
Tiktaalik skeletons were discovered in rock formed from late Devonian river sediments on
Ellesmere Island,
Nunavut, in
northern Canada. At the time of the species' existence, Ellesmere Island was part of the
Laurentia continent.
The discovery was published in the
April 6 2006 issue of
Nature
Images: casts of Tiktaalik fossils
Image:Tiktaalik skull full front.jpg|Skull front view
Image:Tiktaalik skull rear.jpg|Skull rear view
Image:Tiktaalik limb.jpg|Limb fin to shoulder
Image:Tiktaalik limb2.jpg|Limb shoulder to fin
Further Information
Get more info on 'Tiktaalik'.
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