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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.
Ichthyostegalia is an order of extinct amphibians, representing the earliest landliving vertebrates.The group is thus an evolutionary grade rather than a clade. [1] While the group are recognized as having feet rather than fins, most, if not all, had internal gills in adulthood and lived primarily as shallow water fish and spent minimal time on land.
Until finds of other early tetrapods and closely related fishes in the late 20th century, Ichthyostega stood alone as the transitional fossil between fish and tetrapods, combining a fishlike tail and gills with an amphibian skull and limbs. It possessed lungs and limbs with seven digits that helped it navigate through shallow water in swamps.
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 ]
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 oldest near-complete tetrapod fossils, Acanthostega and Ichthyostega, date from the second half of the Fammennian. [56] [57] Although both were essentially four-footed fish, Ichthyostega is the earliest known tetrapod that may have had the ability to pull itself onto land and drag itself forward with its forelimbs. There is no evidence that ...
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Meaning: fish. The suffix "-ichthys" is used for fish, while the prefix "ichthyo-", while used for fish, is also used for fish-like creatures. Examples: Ichthyosaurus ("fish lizard"); Leedsichthys ("fish from Leeds"); Haikouichthys ("fish from Haikou"); Ichthyostega ("fish roof")