【Paragraph 3】The fossil consists of a complete skull of an archaeocyte, an
extinct group of ancestors of modern cetaceans. Although limited to a skull,
the Pakicetus fossil provides precious details on the origins of cetaceans.
The skull is cetacean-like but its jawbones lack the enlarged space that is
filled with fat or oil and used for receiving underwater sound in modern whales.
Pakicetus probably detected sound through the ear opening as in land
mammals. The skull also lacks a blowhole, another cetacean adaptation for
diving. Other features, however, show experts that Pakicetus is a transitional
form between a group of extinct flesh-eating mammals, the mesonychids, and
cetaceans. It has been suggested that Pakicetus fed on fish in shallow water and
was not yet adapted for life in the open ocean. It probably bred and gave birth
on land.(The Origins of Cetaceans)
The word “precious” in the passage is closest in meaning to