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Tiktaalik is a transitional fossil; it is to tetrapods what Archaeopteryx is to birds, troodonts and dromaeosaurids. While it may be that neither is ancestor to any living animal, they serve as evidence that intermediates between very different types of vertebrates did once exist.
[30] [31] Unlike many previous, more fish-like transitional fossils, the "fins" of Tiktaalik have basic wrist bones and simple rays reminiscent of fingers. They may have been weight-bearing . Like all modern tetrapods, it had rib bones, a mobile neck with a separate pectoral girdle, and lungs, though it had the gills, scales, and fins of a fish ...
Transitional forms prior to fully developed terrestrial tetrapods such as Acanthostega, are thought to have captured prey in the water. [13] Large coronoid fangs are present in the fishes Eusthenopteron, Panderichthys, and Tiktaalik, and the early tetrapod, Ventasega. In Acanthostega, which is more derived, the large teeth are absent.
The evolution of tetrapods began about 400 million years ago in the Devonian Period with the earliest tetrapods evolved from lobe-finned fishes. [1] Tetrapods (under the apomorphy-based definition used on this page) are categorized as animals in the biological superclass Tetrapoda, which includes all living and extinct amphibians, reptiles, birds, and mammals.
[1] [2] [3] He is the discoverer of the transitional fossil tetrapod Hynerpeton bassetti, [4] and a Devonian fish-like specimen of Sauripterus taylori with fingerlike appendages, [5] and was also part of a team of researchers that discovered the transitional fossil Tiktaalik. He received a Ph.D. from the University of Pennsylvania in 1998. [6]
A particularly important transitional species is one known as Tiktaalik. It has a fin, but the fin has bones within it that are similar to mammalian tetrapods. It has an upper arm bone, a lower arm bone, forearm bones, a wrist, and fingerlike projections. Essentially, it is a fin that can support the animal.
Ichthyostega (from Greek: ἰχθῦς ikhthûs, 'fish' and Greek: στέγη stégē, 'roof') is an extinct genus of limbed tetrapodomorphs from the Late Devonian of what is now Greenland.
A cladogram of the evolution of tetrapods showing some of the best-known transitional fossils. It starts with Eusthenopteron at the bottom, indisputably still a fish, through Panderichthys , Tiktaalik , Acanthostega and Ichthyostega to Pederpes at the top, indisputably a tetrapod