''Protocetus atavus'' ("first whale") is an extinct species of primitive cetacean from

Egypt Egypt ( , ), officially the Arab Republic of Egypt, is a country spanning the Northeast Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via the Sinai Peninsula. It is bordered by the Mediterranean Sea to northe ...

. It lived during the middle

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

period 45 million years ago. The first discovered protocetid, ''Protocetus atavus'' was described by based on a cranium and a number of associated vertebrae and ribs found in middle

Lutetian The Lutetian is, in the geologic timescale, a stage (stratigraphy), stage or age (geology), age in the Eocene. It spans the time between . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it ...

Tethyan marine limestone from the Mokattam Formation at Gebel Mokattam near Cairo, Egypt.

Description

''Protocetus'' are believed to have had a streamlined, whale-like body around long, but was probably primitive in some respects.Palmer D (ed.) (1999). ''The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals''. London: Marshall Editions. p. 230. . Many protocetids (like '' Maiacetus'', ''

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 ...

'') possessed well developed innominates and hind limbs, often attached to the backbone with a

sacrum The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...

. ''Protocetus'' are known to have had at least one sacral vertebrate,Gingerich P.D. (2010). "Cetacea". In Werdelin L & Sanders W.J. (eds.). ''Cenozoic mammals of africa''. Berkeley: University of California Press, p. 873–899 and likely possessed hind limbs and webbed toes. Despite previous proposals to the contrary, the current general consensus is that ''Protocetus'' and other protocetids lacked tail flukes.Thewissen, J.G.M., Cooper, L.N., George, J.C. et al. "From Land to Water: the Origin of Whales, Dolphins, and Porpoises." ''Evo Edu Outreach'' 2 (1): p. 272–288 (2009) The head of ''Protocetus'' measured about 0.6 meters long.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): p. 291–330 The jaws were long and lined with sharp

teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

. While it did not have a true blowhole, the nostrils were placed further back on the head than in most land mammals. Unlike the more primitive ''

Pakicetus ''Pakicetus'' (meaning 'whale from Pakistan') is an extinct genus of amphibious cetacean of the family Pakicetidae, which was endemic to the Indian Subcontinent during the Ypresian (early Eocene) period, about 50 million years ago. It was a w ...

'', the structure of the ears suggests that ''Protocetus'' was able to hear properly underwater, although it is unlikely that it could echolocate. Similarly, it retained sufficient olfactory apparatus to have a good

sense of smell The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, it ...

, although it probably relied more on its eyesight to find prey.

Skull

Recent high-resolution

CT scans A computed tomography scan (CT scan), formerly called computed axial tomography scan (CAT scan), is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or ...

of the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

skull of ''Protocetus atavus'' (SMNS-P-11084) have provided the first detailed reconstruction of its endocranial anatomy, offering significant insights into the evolution of sensory systems in early

cetaceans Cetacea (; , ) is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively c ...

. The study revealed that ''Protocetus'' had a relatively high encephalization quotient (EQ) compared to other

middle Eocene The Eocene ( ) is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''Ēṓs'', ' Dawn') a ...

cetaceans such as ''

'' and '' Remingtonocetus'', suggesting an earlier onset of

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

enlargement than previously assumed in whale evolution. Notably, the

olfactory bulbs The olfactory bulb (Latin: ''bulbus olfactorius'') is a grey matter, neural structure of the vertebrate forebrain involved in olfaction, the sense of odor, smell. It sends olfactory information to be further processed in the amygdala, the orbitof ...

and tracts were well-developed, comprising up to 3.8% of the endocast volume, a value comparable to that of some terrestrial

mammals A mammal () is a vertebrate animal of the class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle e ...

. The anatomy of the

nasal cavity The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nas ...

, including the dorsal nasal meatus and vomeronasal groove, further supports the interpretation that ''Protocetus'' retained functional airborne

olfaction The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, ...

. These findings challenge the long-held view that olfactory capabilities regressed early in cetacean evolution and suggest that the reduction of olfactory structures may have occurred later, potentially only after the emergence of fully aquatic forms like basilosaurids.

References

Notes

Sources

* * * Protocetidae Monotypic prehistoric cetacean genera Fossil taxa described in 1904 Paleogene mammals of Asia Eocene mammals of Africa {{paleo-whale-stub

Description

Skull

See also

References

Notes

Sources