The skulls and isolated tympanics are described for the earliest whales, pakicetids, from the H-GSP Locality 62 in the Ganda Kas area in Northern Pakistan. Currently three pakicetid genera are known: Pakicetus, Ichthyolestes, and Nalacetus. Ichthyolestes is smaller than the two other genera. Nalacetus and Pakicetus are similar in size, but morphologically different. Pakicetids have a nasal opening at the tip of the rostrum. Their palate retains an incisive foramen. This study reveals three characters of the cranial anatomy useful for systematic analyses. In pakicetids the orbits are orientated dorsally, and there is no supraorbital shield. The dorsal orientation of the orbits is diagnostic for the family, and the lack of supraorbital shield distinguishes pakicetids, ambulocetids, and remingtonocetids from the other Eocene archaeocetes. The intertemporal region of the pakicetid skull is very narrow, a feature that also occurs in many other Eocene cetaceans. The tympanic, which is the most abundant cranial bone (more than 30 specimens) in the pakicetid collections from H-GSP Locality 62, can be used to distinguish the species of pakicetids. In Ichthyolestes, the tympanic bulla is of the same absolute size as in Pakicetus, hence relatively larger, and the tympanic bulla of Nalacetus is larger than either of these. Morphologically, the tympanic bullae differ between the genera, and on the basis of these morphologies it is possible to recognize a fourth species of pakicetid at this locality.
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Vol. 26 • No. 3