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. 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 ==