''Maiacetus'' ("mother whale") is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of early middle

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'', " ...

(c. 47.5 mya) cetacean from the Habib Rahi Formation of

Pakistan Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's fifth-most populous country, with a population of almost 243 million people, and has the world's second-lar ...

Paleobiology

The genus contains a single species, ''Maiacetus inuus'', first described in 2009 on the basis of two specimens, including a specimen which has been interpreted as a pregnant female and its

fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal dev ...

. This represents the first description of a fetal skeleton of an

archaeocete Archaeoceti ("ancient whales"), or Zeuglodontes in older literature, is a paraphyletic group of primitive cetaceans that lived from the Early Eocene to the late Oligocene (). Representing the earliest cetacean Evolutionary radiation, radiation, t ...

. The position of the fetus (head-first) suggests that the animal gave birth on land."Earliest whales gave birth on land"
'' Science News'', 3 February 2009 Modern whales generally give birth tail first, while land mammals give birth head first. That the ''Maiacetus'' should give birth on land is not so implausible because this whale is semiaquatic or amphibious. ''Maiacetus'' represents the transition of land mammals back to the oceans where these animals were living on the land-sea interface and going back and forth."Ancient Whale Relative Gave Birth on Land"
, "

Science Friday ''Science Friday'' (known as ''SciFri'' for short) is a weekly call-in talk show that broadcasts each Friday on public radio stations, distributed by WNYC Studios, and carried on over 400 public radio stations. ''SciFri'' is hosted by award-wi ...

", 6 February 2009 However,

Hans Thewissen Hans Thewissen is a Dutch-American paleontologist. His field work has discovered fossils for the steps in the transition from land to water in whales: '' Ambulocetus'', '' Pakicetus'', ''Indohyus'' and '' Kutchicetus''. He now studies modern b ...

, discoverer of ''

Ambulocetus ''Ambulocetus'' (Latin ''ambulare'' "to walk" + ''cetus'' "whale") is a genus of early amphibious cetacean from the Kuldana Formation in Pakistan, roughly 48 or 47 million years ago during the Early Eocene (Lutetian). It contains one species, ' ...

'', has questioned these conclusions, suggesting that the smaller skeleton could be a partially digested meal. Even if the small skeleton is a fetus, Thewissen writes that it may not have been preserved in its normal in-vivo position. Authors pointed out in the original article, however, that the fetal skull has no tooth marks. The hip bones were strong, suggesting that ''Maiacetus'' was able to walk on land; however, the short legs and flat digits would've made walking difficult. Looking at the flattened finger and toe bones, scientists have come to the conclusion that ''Maiacetus'' had webbed feet and was most likely amphibious. The teeth of the preserved fossils show similarity to the teeth of ''

Basilosaurus ''Basilosaurus'' (meaning "king lizard") is a genus of large, predatory, prehistoric archaeocete whale from the late Eocene, approximately 41.3 to 33.9 million years ago (mya). First described in 1834, it was the first archaeocete and prehistor ...

'', another genus of prehistoric cetaceans. The incisors are cone-like, linking ''Maiacetus'' to modern toothed whales and other extinct cetaceans. The middle ear bones are also similar to those of ''

'' and modern whales. This species is medium-sized with a skeleton in length and an estimated weight of . Males are slightly larger than females; of the two adult skeletons found, the one interpreted as male was about 12% larger than the one interpreted as female.

References

Protocetidae Fossil taxa described in 2009 Prehistoric cetacean genera Extinct mammals of Asia {{paleo-whale-stub

Paleobiology

See also

References