''Gaviacetus'' (from Latin ''Gavia'', "

loon Loons (North American English) or divers (British English, British / Irish English) are a group of aquatic birds found in much of North America and northern Eurasia. All living species of loons are members of the genus ''Gavia'', family (biolog ...

" and ''cetus'', "whale") is an extinct archaeocete

whale Whales are a widely distributed and diverse group of fully Aquatic animal, aquatic placental mammal, placental marine mammals. As an informal and Colloquialism, colloquial grouping, they correspond to large members of the infraorder Cetacea ...

that lived approximately . ''Gaviacetus'' was named for its characteristic narrow

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit ** podium * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ...

and the fast

pursuit predation Pursuit predation is a form of predation in which predators actively give chase to their prey, either solitarily or pack hunter, as a group. It is an alternate hunting strategy, predation strategy to ambush predation — pursuit predators rely o ...

suggested by its unfused sacral vertebrae.

Location

The only known ''Gaviacetus razai'' specimen was found in

Punjab Punjab (; ; also romanised as Panjāb or Panj-Āb) is a geopolitical, cultural, and historical region in South Asia. It is located in the northwestern part of the Indian subcontinent, comprising areas of modern-day eastern Pakistan and no ...

Pakistan Pakistan, officially the Islamic Republic of Pakistan, is a country in South Asia. It is the List of countries and dependencies by population, fifth-most populous country, with a population of over 241.5 million, having the Islam by country# ...

. (, paleocoordinates )

Description

The skull of ''Gaviacetus'' is characteristic of protocetids, but the rostrum is extremely narrow anterior to P³, suggesting some kind of

trophic Trophic, from Ancient Greek τροφικός (''trophikos'') "pertaining to food or nourishment", may refer to: * Trophic cascade * Trophic coherence * Trophic egg * Trophic function * Trophic hormone * Trophic level index * Trophic level * ...

specialization. The well-preserved

auditory bulla The tympanic part of the temporal bone is a curved plate of bone lying below the squamous part of the temporal bone, in front of the mastoid process, and surrounding the external part of the ear canal. It originates as a separate bone (tympanic b ...

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 Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * M ...

(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 Basilosauridae is a family of extinct cetaceans that lived during the middle to late Eocene. Basilosaurids are known from all continents including Antarctica, and are probably the first fully aquatic cetaceans.Buono M, Fordyce R.E., Marx F.G., F ...

(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 ''Protocetus atavus'' ("first whale") is an extinct species of primitive cetacean from Egypt. It lived during the middle Eocene period 45 million years ago. The first discovered protocetid, ''Protocetus atavus'' was described by based on a cran ...

'', better adapted to pursuit predation than ''

Rodhocetus ''Rodhocetus'' (from ''Rodho'', the geological anticline at the type locality, and ''cetus'', Latin for whale) is an extinct genus of protocetid early whale known from the Lutetian of Pakistan. The best-known protocetid, ''Rodhocetus'' is known ...

''. 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''.Donald Prothero (2007). ''Evolution: What the Fossils Say and Why it Matters''Richard Dawkins (2009). '' The Greatest Show on Earth''

Taxonomic history

The

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

''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.

Notes

References

* * * {{Taxonbar, from=Q5528061 Extinct mammals of Asia Protocetidae Fossil taxa described in 1995 Monotypic prehistoric cetacean genera