Gaviacetus

Gaviacetus (from Latin Gavia, "loon" and cetus, "whale")^[3] extinct archaeocete whale that lived approximately 45 million years ago. Gaviacetus was named for its characteristic narrow rostrum and the fast pursuit predation suggested by its unfused sacral vertebrae.^[3]

The G. razai specimen was found in Punjab, Pakistan (30°06′N 70°24′E / 30.1°N 70.4°E / 30.1; 70.4, paleocoordinates 11°36′N 65°30′E / 11.6°N 65.5°E / 11.6; 65.5)^[4] and those of G. sahnii in Kutch, India (23°30′N 68°42′E / 23.5°N 68.7°E / 23.5; 68.7, paleocoordinates 5°54′N 61°42′E / 5.9°N 61.7°E / 5.9; 61.7).^[5] The skulls are similar in size in both species, but the teeth of B. sahnii are 150–200% larger.^[6]

Although often represented as having small hind limbs,^[7] 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.^[8][9][10]

Description

The skull of Gaviacetus is characteristic of protocetids, but the rostrum is extremely narrow anterior to P³, suggesting some kind of trophic specialization.^[11]

The well-preserved auditory bulla in Gingerich, Arif & Clyde 1995'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.^[12]

Preserved alveoli (tooth sockets) show that Gaviacetus had double- and tripple-rooted cheek teeth,^[13] but some controversy remains regarding the number of molars. Based on other cranial characters, Gingerich, Arif & Clyde 1995 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, Bajpai & Thewissen 1998, who's 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).^[6] Uhen 2009 argued against this assignment until more solid evidences have been found.^[14]

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.^[11]

Notes

References