Basilosaurid

Basilosauridae is a family of extinct cetaceans. They lived during the middle to the early late Eocene and are known from all continents, including Antarctica. They were probably the first fully aquatic cetaceans.Buono M, Fordyce R.E., Marx F.G., Fernández M.S. & Reguero M. (2019). "Eocene Antarctica: a window into the earliest history of modern whales". ''Advances in Polar Science'' 30(3): p. 293-302. doi
10.13679/j.advps.2019.0005
/ref> The group is noted to be a paraphyletic assemblage of stem group whales from which the monophyletic Neoceti are derived.

Characteristics

Basilosaurids ranged in size from and were fairly similar to modern cetaceans in overall body form and function. Some genera tend to show signs of convergent evolution with mosasaurs by having long serpentine body shape, which suggests that this body plan seems to have been rather successful. Basilosaurid forelimbs have broad and fan-shaped scapulae attached to a humerus, radius, and ulna which are flattened into a plane to which the elbow joint was restricted, effectively making pronation and supination impossible. Because of a shortage of forelimb fossils from other archaeocetes, it is not known if this arrangement is unique to basilosaurids, as some of the characteristics are also seen in ''Georgiacetus''.

As archaeocetes, Basilosaurids lacked the telescoping skull of present whales. Their jaws were powerful,Snively E, Fahlke J.M. & Welsh R.C. (2015). "Bone-Breaking Bite Force of ''Basilosaurus isis'' (Mammalia, Cetacea) from the Late Eocene of Egypt Estimated by Finite Element Analysis". ''PLOS ONE'' 10(2): e0118380 with a dentition easily distinguishable from that of other archaeocetes: they lack upper third molars and the upper molars lack protocones, trigon basins, and lingual third roots. The cheek teeth have well-developed accessory denticles.

Unlike modern whales, basilosaurids possessed small hindlimbs with well defined femur, lower leg and feet. They were, however, very small and did not articulate with the vertebral column, which also lack true sacral vertebrae. While they were unable to support body weight on land, they might have assisted as claspers during copulation.Gingerich P.D., Smith B.H., Simons E.L. (1990). "Hind limbs of eocene ''basilosaurus'': evidence of feet in whales". ''Science'' 249(4965): p. 154–157. doi:10.1126/science.249.4965.154 Analysis of tail vertebrate from ''Basilosaurus'' and ''Dorudon'' indicate they possessed small flukes.Philip D. Gingerich, Mohammed Sameh M. Antar und Iyad S. Zalmot: "''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 doi:10.1371/journal.pone.0225391

Taxonomy

Basilosaurinae was proposed as a subfamily containing two genera: ''Basilosaurus'' and '' Basiloterus''.. Retrieved July 2013. They were characterized by elongated distal thoracic vertebrae, lumbar, and proximal sacrococcygeal. All known members of the subfamily are larger than their relatives of the Dorudontinae subfamily except ''Cynthiacetus''.

Systematics

*Family Basilosauridae
** Subfamily Basilosaurinae
*** Genus ''Basilosaurus''
*** Genus '' Basiloterus''
*** Genus '' Basilotritus''
*** Genus ''Eocetus''
*** Genus '' Platyosphys''
** Subfamily Dorudontinae
*** Genus '' Ancalecetus''
*** Genus '' Chrysocetus''
*** Genus ''Cynthiacetus''
*** Genus ''Dorudon''
*** Genus '' Masracetus''
*** Genus '' Ocucajea''
*** Genus ''Saghacetus''
*** Genus ''Stromerius''
*** Genus '' Supayacetus''
*** Genus ''Zygorhiza''

See also

* Evolution of cetaceans
* Leviathan

Notes

References

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{{Taxonbar, from=Q2670162

Prehistoric mammal families
Paraphyletic groups