Protocetidae

 ( Protocetidae ) 

Protocetidae, the protocetids, form a paraphyletic, diverse and heterogeneous group of extinct known from Asia, Europe, Africa, South America, and North America.

---

Description There were many genera, and some of these are very well known (e.g., Rodhocetus). Known protocetids had large fore- and hindlimbs that could support the body on land, and it is likely that they lived amphibiously: in the sea and on land. It is unclear at present whether protocetids had flukes (the horizontal tail fin of modern cetaceans). However, what is clear is that they are adapted even further to an aquatic life-style. In Rodhocetus, for example, the sacrum – a bone that in land-mammals is a fusion of five vertebrae that connects the pelvis with the rest of the vertebral column – was divided into loose vertebrae. However, the pelvis retain a sacroiliac joint. Furthermore, the nasal openings are now halfway up the snout; a first step towards the telescoped condition in modern whales. Their supposed amphibious nature is supported by the discovery of a pregnant Maiacetus, in which the fossilised fetus was positioned for a head-first delivery, suggesting that Maiacetus gave birth on land. The ungulate ancestry of these early whales is still underlined by characteristics like the presence of hooves at the ends of toes in Rodhocetus.

---

Taxonomy The protocetid subfamilies were proposed by . They placed Makaracetus in its own subfamily ( Makaracetinae) based on its unique adaptations for feeding (including only two incisors in each premaxilla). They then erected two subfamilies for the rest of the protocetids based on their degree of aquatic adaptation:

Protocetinae- Protocetines are Lutetian protocetids with generalized skulls retaining three incisors in the premaxilla and three molars in the maxilla. To the extent postcrania are known (primarily from Rodhocetus, and more recently Peregocetus),Olivier L, Bianucci G, Salas-Gismondi R, Di Celma C, Steurbaut E, Urbina M & de Muizon C (2019). "An amphibious whale from the Middle Eocene of Peru reveals early South Pacific dispersal of quadrupedal cetaceans". Current Biology 29(8): p. 1352–1359.e3. they possess a pelvis similar to those in land-living mammals, a sacrum articulated to the ilia and innominates and large hindlimbs used for foot-powered propulsion. Genera:

Georgiacetinae- Georgiacetines are Bartonian protocetids, considered transitional to the Basilosauridae. Their skulls and dentition are similar to those of protocetines, but the pelvis in Georgiacetus and Aegicetus indicate a reduced sacroiliac joint, with no substantial articulation between backbone and innominates. Until recently, no hindlimb material was known for this subfamily, although the pelvic morphology seemed to hint at a tail-based rather than foot-based mode of aquatic locomotion. The discovery of Aegicetus supports this notion.Gingerich P.D., Antar M.S.M., Zalmout I.S. (2019). " Aegicetus gehennae, a new late Eocene protocetid (Cetacea, Archaeoceti) from Wadi Al Hitan, Egypt, and the transition to tail-powered swimming in whales". PLoS ONE 14(12): e0225391 Genera:

---

Notes

Post Comment