Some 375 million years ago, during the Devonian period, our ancestors emerged from the sea and walked on land for the first time. The evolutionary link between primitive fish and modern land dwellers gained key evidence in 2006, when Neil Shubin, the Robert R. Bensley Distinguished Service Professor of Organismal Biology and Anatomy, discovered a fossil of the transitional “fishapod” Tiktaalik, with features of both fish and four-limbed animals.
How fins and their bony rays evolved into limbs and digits has remained a puzzle. The two kinds of appendages have been thought to be distinct both structurally and developmentally. Notably, they are composed of different types of bone tissue—one type of bone formed directly for fin rays, a different type of bone preformed in cartilage for finger and toe bones.
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