Gaviacetus
Introduction '''''Gaviacetus''''' (from Latin ''Gavia'', "loon" and ''cetus'', "whale") is an extinct archaeocete whale that lived approximately . ''Gaviacetus'' was named for its characteristic narrow rostrum and the fast pursuit predation suggested by its unfused sacral vertebrae.
Location The only known ''Gaviacetus razai'' specimen was found in Punjab, Pakistan. (, paleocoordinates )
Description The skull of ''Gaviacetus'' is characteristic of protocetids, but the rostrum is extremely narrow anterior to P3, suggesting some kind of trophic specialization.The well-preserved auditory bulla in 's specimen is dense like in other archaeocetes, is equipped with a prominent sigmoid process, but has 3-5 contacts with the rest of the cranium.Preserved alveoli (tooth sockets) show that ''Gaviacetus'' had double- and triple-rooted cheek teeth, but some controversy remains regarding the number of molars. Based on other cranial characters,  concluded that ''Gaviacetus'' is a protocetid (more primitive archeocetes with a third upper molar) and therefore assumed the presence of M3 though no traces thereof are preserved in their specimen. In opposition to this, , whose specimen is also lacking the essential maxillar part, thought the cranium above the very small M2 to be to narrow for the presence of M3, hence indicating ''Gaviacetus'' is a basilosaurid (a more derived archaeocetes lacking a third upper molar). argued against this assignment until more solid evidence has been found.The preserved sacral vertebra was not fused with its posterior neighbour, indicating that ''Gaviacetus'' was a tail-powered swimmer like ''Protocetus'', better adapted to pursuit predation than ''Rodhocetus''. The preserved transverse process of the sacral vertebra is distally expanded, suggesting a synchondrosal joint between the vertebral column and pelvis.Although often represented as having small hind limbs, this is an inference from the general progression of other fossil species towards limb loss; the only postcranial remains found for ''Gaviacetus'' are a rib and several vertebrae. At least three popular science books misspell this genus as ''Gaviocetus''.
Taxonomic history The genus ''Gaviacetus'' was established in 1995 with the description of ''G. razai''. A second species,'' G. sahnii'', was described in 1998, but'' ''transferred to its own genus,'' Kharodacetus'' in 2014 based on newly discovered remains.
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