Pakicetus is described as an early ancestor to modern whales. These organisms were land mammals, but fossil evidence shows a relation to whales and dolphins based on a number of specializations of the ear related to hearing underwater. The diagram shows three different skulls in the whale fossil record.

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acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.