Question

The Tikataalik was an organism that lived at least 375 million years ago. It is catagorized as a fish with scales, but had a head that was similar to a crocodile. In 3–5 sentences, describe why it is considered a transition fossil and how it is evidence of a correlation between the limbs of land animals and fish.

Answer 1

Tiktaalik is considered a transitional fossil because it combines clearly fish-like features (scales, gills, and fin rays) with tetrapod-like traits (a flat, crocodile-like skull with eyes on top, a mobile neck, robust ribs, and weight-supporting shoulder bones). Crucially, its pectoral fins contain internal bones — including structures homologous to a humerus, radius and ulna and primitive wrist elements — that are intermediate in form between lobe-finned fish fins and the limbs of early land vertebrates. That mosaic of characters documents an evolutionary step from swimming to bearing weight on shallow water or land, demonstrating the anatomical correlation between fish fins and the limbs of terrestrial animals.