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Ancient Fish



This story just came out. I am reminded of Spore, and it's really quite interesting to see how small tiny changes here and there are actually quite important. Here's the abstract and last paragraph from the Nature article concerning Tiktaalik.

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Abstract: Among the morphological changes that occurred during the 'fish-to-tetrapod' transition was a marked reorganization of the cranial endoskeleton. Details of this transition, including the sequence of character acquisition, have not been evident from the fossil record. Here we describe the braincase, palatoquadrate and branchial skeleton of Tiktaalik roseae, the Late Devonian sarcopterygian fish most closely related to tetrapods. Although retaining a primitive configuration in many respects, the cranial endoskeleton of T. roseae shares derived features with tetrapods such as a large basal articulation and a flat, horizontally oriented entopterygoid. Other features in T. roseae, like the short, straight hyomandibula, show morphology intermediate between the condition observed in more primitive fish and that observed in tetrapods. The combination of characters in T. roseae helps to resolve the relative timing of modifications in the cranial endoskeleton. The sequence of modifications suggests changes in head mobility and intracranial kinesis that have ramifications for the origin of vertebrate terrestriality.

Last paragraph: With appendages able to support the weight of the body, a more consolidated skull, ribs capable of sustaining the trunk under a gravitational load, a respiratory system less reliant on water breathing, a head capable of independent motion, and cranial proportions approaching those of tetrapods, Tiktaalik reveals an important stage in the origin of terrestrial vertebrates5,6. T. roseae probably inhabited the benthos, shallows, and mudflats of freshwater floodplains while supporting itself on a solid substrate. In the Late Devonian, marginal freshwater environments were an important locus of the evolutionary
changes that led to the origin of amphibious lifestyles among tetrapodomorphs.
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