Gaviacetus

Gaviacetus Temporal range: Middle Eocene,
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Infraorder:	Cetacea
Family:	†Protocetidae
Genus:	†Gaviacetus Gingerich, Arif, and Clyde, 1995
Species:	†G. razai
Binomial name
†Gaviacetus razai Gingerich, Arif, and Clyde, 1995

Gaviacetus (from Latin Gavia, "loon" and cetus, "whale") is an 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.

Location

The only known Gaviacetus razai specimen was found in Punjab, Pakistan. (30.1°N 70.4°E / 30.1; 70.4, paleocoordinates 11.6°N 65.5°E / 11.6; 65.5)

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 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.

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, 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, 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). Uhen 2009 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.

References

• Bajpai, S.; Thewissen, J. G. M. (1998). "Middle Eocene Cetaceans from the Harudi and Subathu Formations of India". In Thewissen, J. G. M. (ed.). The Emergence of Whales. Advances in vertebrate paleobiology. New York: Plenum Press. pp. 213–233. ISBN 9780306458538. OCLC 300450327.
• Gingerich, Philip D.; Arif, Muhammad; Clyde, William C. (1995). "New Archaeocetes (Mammalia, Cetacea) from the middle Eocene Domanda Formation of the Sulaiman Range, Punjab (Pakistan)". Contributions from Museum of Paleontology, the University of Michigan. 29 (11): 291–330. hdl:2027.42/48650. OCLC 34123868.
• Uhen, Mark D. (2009). "Basilosaurids". In Perrin, William F.; Wursig, Bernd; Thewissen, J.G.M. (eds.). Encyclopedia of Marine Mammals (2nd ed.). Academic Press. ISBN 9780080919935.