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Tiktaalik was thus inserted below Acanthostega and Ichthyostega, acting as a transitional form between limbless fish and limbed vertebrates ("tetrapods"). [1] Some press coverage also used the term " missing link ", implying that Tiktaalik filled an evolutionary gap between fish and tetrapods. [ 34 ]
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. It was among the earliest four-limbed vertebrates ever in the fossil record and was one of the first with weight-bearing adaptations for terrestrial locomotion.
In the tetrapod and higher clades from the lower-middle Famennian there are several defining changes on the basis of anatomy of Ichthyostega, Tulerpeton, and Acanthostega. In the cranium, there is a stapes derived from the hyomandibular of fishes; a single bilateral pair of nasal bones, and a fenestra ovalis in the otic capsule of the braincase ...
In Late Devonian vertebrate speciation, descendants of pelagic lobe-finned fish such as Eusthenopteron exhibited a sequence of adaptations: Panderichthys, suited to muddy shallows; Tiktaalik with limb-like fins that could take it onto land; early tetrapods in weed-filled swamps, such as Acanthostega, which had feet with eight digits, and Ichthyostega, which had limbs.
The order Ichthyostegalia was erected for Ichthyostega, and contained until the 1980s only three genera (Ichthyostega, Acanthostega and Tulerpeton).While Ichthyostegalia in principle contain the most basal of animals with toes rather than fins, Clack and Ahlberg uses it for all finds more advanced than Tiktaalik (the closest relative of tetrapods known to have retained paired fins rather than ...
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
The result is the appearance of the neck. This feature appears only in tetrapods and Tiktaalik, not other tetrapodomorph fishes. Tiktaalik also had a pattern of bones in the skull roof (upper half of the skull) that is similar to the end-Devonian tetrapod Ichthyostega. The two also shared a semi-rigid ribcage of overlapping ribs, which may have ...
Tiktaalik lived approximately 375 million years ago. Paleontologists suggest that it is representative of the transition between non-tetrapod vertebrates such as Panderichthys , known from fossils 380 million years old, and early tetrapods such as Acanthostega and Ichthyostega , known from fossils about 365 million years old.