228 3 Summative Assessment In 2004, a fossil of roseae. The Tik shown on the pho

Question

228 3 Summative Assessment In 2004, a fossil of roseae. The Tik shown on the photograph of the fossil below an unknown vertebrate was discovered in northern Canada and subsequently called Tiktaalik sil was quite well preserved and many interesting features could be identified. These are taalik fos The shoulder bones are not attached to the skull, allowing its neck to turn independently of the body. Tiklaaliks head is flattened horlzontally like that of a crocodile with the eyes on top, looking up. Rod-like bones that help pump water over gills are present, but th presence of ribs indicates that lungs were also present. The bones of the limbs have a primitive pentadactyl arrangement similar to tetrapods, which allowed it to support its body weight. The fossil of Tiktaalik was covered with scales much like those of fish. Fish-like fins are clearly visible 1. Use the information above to place Tiktaalik on the time line of vertebrate evolution. Discuss the evidence tor your decision Jawless fish Bony lish Amphibians . Reptiles Birds Mammals 150 mya 300 mya 365 mya 400 mya 550 mya Vertebrate ancestor

Explanation / Answer

Since Tiktaalik has fish ( Scales, Fins Gills and lungs) and tetrapod (Neck, Ribs, Fin skeleton, Flat skull , Eyes on top of skull) like features it is considered to have been the ancestor of tetrapods.Hence it is safe to say it predates tetrapods but postdates fishes.

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