''Ancalecetus'' (from Greek ''ankale'', "bent arm", and ''ketos'', "whale") is an extinct genus of early whale known from the

Late Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', "d ...

(

Priabonian The Priabonian is, in the ICS's geologic timescale, the latest age or the upper stage of the Eocene Epoch or Series. It spans the time between . The Priabonian is preceded by the Bartonian and is followed by the Rupelian, the lowest stage ...

, )

Birket Qarun Formation Birket is a small town in Lolland Municipality, Denmark ) , song = ( en, "King Christian stood by the lofty mast") , song_type = National and royal anthem , image_map = EU-Denmark.svg , map_caption = , subdivision_type = Sovereign ...

(, paleocoordinates ) in

Wadi Al-Hitan ( ar, وادي الحيتان, lit=Valley of the Whales ) is a paleontological site in the Faiyum Governorate of Egypt, some south-west of Cairo. It was designated a UNESCO World Heritage Site in July 2005 for its hundreds of fossils of som ...

, Egypt. The species is named after anthropologist and primate researcher

Elwyn L. Simons Elwyn LaVerne Simons (July 14, 1930 – March 6, 2016) was an American paleontologist, paleozoologist, and a wildlife conservationist for primates. He was known as the father of modern primate paleontology for his discovery of some of humankind' ...

who discovered the type specimen in 1985. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of seve ...

is a partial cranium (the top of the skull was destroyed by erosion), both dentaries, 20 vertebrae and some sternal elements, partial ribs, and most of both forelimbs. ''Ancalecetus'' differs from other archaeocetes and modern whales in having narrow scapulae, very limited mobility in the shoulder joint, and fusion of the humerus, ulna, and radius at the elbow joint. In the wrist, the carpal bones are small like in ''

Zygorhiza ''Zygorhiza'' ("Yoke-Root") is an extinct genus of basilosaurid early whale known from the Late Eocene (Priabonian, 38–34 Ma) of Louisiana, Alabama, and Mississippi, United States, and the Bartonian (43–37 Ma on the New Zealand geologic tim ...

'', but, unlike in this other basilosaurid, the

magnum ''Magnum'' is a Latin word meaning " great". Magnum may also refer to: Businesses and organizations * Magnum Research, a firearms maker * Magnum Semiconductor, a spin-off of Cirrus Logic * Magnum Photos, a photojournalist cooperative * Magnum ...

is fused with the

trapezoid A quadrilateral with at least one pair of parallel sides is called a trapezoid () in American and Canadian English. In British and other forms of English, it is called a trapezium (). A trapezoid is necessarily a convex quadrilateral in Eucli ...

in ''Ancalecetus''.

Forelimbs

The well-preserved forelimbs are the most distinctive parts of ''A. simonsi''. A broad scapula and a ball-and-socket shoulder joint is characteristic of cetaceans, but ''Ancalecetus'' lacks both. The interior surface of the narrow scapula is not broadly curved as in most cetaceans, but tightly curved. The roughened vertebral border suggests the presence of a cartilaginous extension that extends the surface of the scapula like in modern cetaceans. Compared to other cetaceans, the

infraspinous fossa The infraspinous fossa (infraspinatus fossa or infraspinatous fossa) of the scapula is much larger than the supraspinatous fossa; toward its vertebral margin a shallow concavity is seen at its upper part; its center presents a prominent conve ...

is smaller, the caudal border is less curved and not oriented posteriorly. The

glenoid cavity The glenoid fossa of the scapula or the glenoid cavity is a bone part of the shoulder. The word ''glenoid'' is pronounced or (both are common) and is from el, gléne, "socket", reflecting the shoulder joint's ball-and-socket form. It is a sh ...

is very shallow and directed posteriorly, rather than ventrally like in other cetaceans. Likewise, the oddly folded

acromion In human anatomy, the acromion (from Greek: ''akros'', "highest", ''ōmos'', "shoulder", plural: acromia) is a bony process on the scapula (shoulder blade). Together with the coracoid process it extends laterally over the shoulder joint. The ac ...

is pointing ventrally and posteriorly, and not anteriorly as in other cetaceans. Unlike in other basilosaurids, the humerus of ''Ancalecetus'' is flattened and has a relatively small head. The distal end has flat, textured surfaces for the articulation of the radius and ulna; these bones are fused on the left limb and tightly fitting and the right side, and neither permitted motion at the elbow joint.

Dentition

Most of the upper dentition has been eroded away, but the dental formula of ''Ancalecetus'' most likely was . Tooth wear show that ''Ancalecetus'', like other basilosaurids, fed on larger prey, probably fish, that required mastication before swallowing and that the type specimen survived into adulthood. The unfused

mandibular symphysis In human anatomy, the facial skeleton of the skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more p ...

reaches as far posteriorly as P₂. The large mandibular foramina, which contain the auditory fat pad in modern whales, is very well-preserved in ''Ancalecetus''.

Notes

References

* {{Taxonbar, from=Q1062904 Basilosauridae Prehistoric cetacean genera Fossil taxa described in 1996 Eocene mammals of Africa