AP BIOLOGY

Detailed explanation-1: -Like a fish, the fossil of Tiktaalik shows evidence of scales, gills, and fins. But inside the fins, Tiktaalik contains limb bones that are characteristic of an early tetrapod.

Detailed explanation-2: -Tiktaalik retained both fish and tetrapod characteristics. Its fish characteristics include scales, fins, and gills, and its tetrapod characteristics include a neck, ribs capable of bearing weight, a flat head, dorsally positioned eyes, a fin skeleton, and ear notches (The University of Chicago, 2006).

Detailed explanation-3: -Tiktaalik roseae has features of the skull, neck, ribs and appendages that are shared with the earliest limbed animals (tetrapods), as well as fishlike features such as scales and fin rays. This mosaic of features makes it a textbook example of a transitional fossil, say paleontologists.

Detailed explanation-4: -The Four-Legged Vertebrates The word “Tetrapoda” means “four legs” in Greek. Amphibians, reptiles (including dinosaurs and birds) and mammals are the major groups of the Tetrapoda. Tetrapods include all land-living vertebrates, such as frogs, turtles, hawks, and lions.

Detailed explanation-5: -With a broad flat head and sharp teeth, Tiktaalik looked like a cross between a fish and a crocodile, growing up to a length of nine feet as it hunted in shallow freshwater environments. It had gills, scales and fins, but also a mobile neck, robust rib cage and primitive lungs.