Answer: The correct option is B. Vertebrates appeared in the oceans before they moved on to land.
Vertebrate paleontology involves study of fossils of the vertebrates starting from the earliest fishes to the ancestors of modern day mammals. The spreading up of life from water to land needed modifications and adaptations such as protection from drying and support against the gravity. The tetrapod vertebrates evolved and started to live on land from oceans during the Devonian period. The succession of the Devonian period showed fossil evidences towards terrestrialization
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A major factor in determining the mode of nitrogen excretion is the availability of water in the environment. Generally, aquatic animals excrete mostly ammonia, whereas terrestrial animals excrete either urea or uric acid.
