Atomic Mass or Atomic Number.
Beavers are descendants of land-dwelling rodents similar to rats. The beavers however have adapted their body shape to live in water bodies like ponds and lakes. This can be hypothesised by saying that the early rodents or the ancestors of beavers were forced to find food in the waters. They lacked the flat tail and the webbed feet. With time the need to increase their ability to catch fishes and floating insects, the rodents with flatter tail and a bigger flat webbed feet gradually evolved. The rodents with flatter tails and webbed feet became adjusted to the life on water and became the modern day beavers.
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) Sea Floor Spreading <span>a process by which molten material erupts at mid-ocean ridges and is split and spread by later erupting molten material</span>
