To classify animals and distinguish them
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The remains of a Hadrosaur are an example of a fossil typically structures like bones shells and teeth fossilized more often then things like tissues or plant leaves.
To protect them from ultraviolet rays from the sun.
The early hominid stages can be differentiated from one another based on the complexity of the tools used by these species. The tool evolved along with the evolution of the humans. The more the hominids evolved by more complex their tools became. The tools made by the earliest hominids were used to fish out the termites. These tool developed and became more widely used as the humans evolved.
Hence, the answer is 'by observing the complexity of the tools'.
