This suggests tetrapod evolution is older than the dated fossils of " Panderichthys " through to " Ichthyostega ".
12.
Trackway impressions made by something that resembles " Ichthyostega "'s limbs were formed 390 Ma in Polish marine tidal sediments.
13.
These events of extinctions led to the disappearance of primitive tetrapods with fish-like features like Ichthyostega and their primary more aquatic relatives.
14.
Ichthyostega, on the other hand, is considered to be a fully terrestrial tetrapod that perhaps depended on water for its aquatic young.
15.
Acanthostega is likely exclusive to an aquatic environment, while Ichthyostega is progressed in the aquatic to terrestrial transition by living dominantly on the shores.
16.
But the discoveries of " Acanthostega " and " Ichthyostega " confirm that the pentyldactyl ancestor came later in the development of tetrapods.
17.
Tiktaalik also had a pattern of bones in the skull roof ( upper half of the skull ) that bears similarity to the end-Devonian tetrapod Ichthyostega.
18.
He brought back fossils of " Ichthyostega, " by then the earliest known tetrapod, and published an extensive preliminary report on it in 1932.
19.
The feet are only known from " Ichthyostega ", Acanthostega, and Tulerpeton, but appear to be fin rays like those found in fish.
20.
For most of this century, in fact, only one primitive specimen was known in any detail : a bulky, dog-size beast from Greenland named Ichthyostega.
