Thursday, April 06, 2006

Tiktaalik

[Today's big discovery...]
Tiktaalik (IPA pronunciation: [tikta:lik]) is a genus of extinct sarcopterygian (lobe-finned) fishes from the late Devonian with many tetrapod-like features.[1]

"Tiktaalik", said Dr. Neil Shubin, is "both fish and tetrapod, which we sometimes call a fishapod."[2]

Tiktaalik
Fossil range: Devonian

Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Osteichthyes
Subclass: Sarcopterygii
(unranked) Tetrapodomorpha
Genus: Tiktaalik
Species: T. roseae


Tiktaalik roseae
Daeschler, Shubin & Jenkins, 2006

It crossed the threshold from fish to land animals in the late Devonian period (approximately 375 million years ago). Its name comes from a suggestion of Inuit elders of Canada's Nunavut Territory, where the fossil was discovered:[3] it is an Inuktitut word meaning burbot[4], a shallow water fish. It has been suggested that it was an intermediate form between fishes like Panderichthys, which lived about 385 million years ago, and early tetrapods such as Acanthostega and Ichthyostega that lived about 365 million years ago.

The three fossilized Tiktaalik skeletons were discovered in frozen river sediments in Ellesmere Island, Nunavut, in northern Canada[5]. During the species's heyday, Ellesmere Island was part of the Laurentia continent[3], which, at the time, was centered on the equator and had a warm climate. Neil Shubin and Ted Daeschler, the leaders of the team, had been searching Ellesmere Island for fossils since 1999[6].

The remarkable find was made by a paleontologist who noticed the skull sticking out of a cliff wall. On further inspection the ancient animal was found to be in fantastic shape for a 383 million year old specimen[6].

The discovery was published in the April 6, 2006 issue of Nature.[1]

Tiktaalik generally had the features of a fish, but with front fins featuring arm-like skeletal structures more akin to a crocodile, including a shoulder, elbow, and wrist. It had the sharp teeth of a predator, and its neck was able to move independently of its body, which is not 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, which were used to support its body and aid in breathing via lungs; a long snout suitable for catching prey on land; and a small gill slit that, in more derived animals, became an ear.[7] The discoverers said that in all likelihood, Tiktaalik flexed its proto-limbs primarily on the floors of streams and may have pulled itself on to the shore for brief stretches.[8] Specimens found thus far range from 4 to 9 feet (1.2 to 2.75 meters) in length.

[More...]

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