Basilosauridae

Basilosauridae is a paraphyletic family of extinct cetaceans. They lived during the middle to the early late Eocene and are known from all continents, including Antarctica.[1][2] They were probably the first fully aquatic cetaceans.[3][4]

Basilosauridae
Temporal range: Late Eocene, 45–33.9 Ma [1]
Skull of the genus Saghacetus.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Family: †Basilosauridae
Cope 1868[1]
Genera

See text

Characteristics
Drawing of Dorudon skeleton.
Cynthiacetus, mounted skeleton.
Zygorhiza, mounted skeleton.

Basilosaurids ranged in size from 4 to 16 m (13 to 52 ft) and were fairly similar to modern cetaceans in overall body form and function.[5] 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.[6] 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 arachaocetes, it is not known if this arrangement is unique to basilosaurids, as some of the characteristics are also seen in Georgiacetus.[3]

As archaeocetes, Basilosaurids lacked the telescoping skull of present whales. Their jaws were powerful,[7] 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.[3] While they were unable to support body weight on land, they might assissted as claspers during copulation.[8] Analysis of tail vertebrate from Basilosaurus and Dorudon indicate they possessed small flukes.[9]

Taxonomy

Basilosaurinae was proposed as a subfamily containing two genera: Basilosaurus and Basiloterus.[10] 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.[11] It was declared an invalid subgroup of Basilosauridae by Uhen 2013.[10]

Systematics

See also

Notes
  1. Basilosauridae in the Paleobiology Database
  2. Fostowicz-Frelik 2003
  3. Uhen 2002
  4. 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
  5. Uhen M. (2004). "Form, Function, and Anatomy of Dorudon Atrox (Mammalia, Cetacea): An Archaeocete from the Middle to Late Eocene of Egypt". Papers on Paleontology 34: p. 1-222
  6. Oceans of Kansas: a Natural History of the Western Interior Sea. Indiana University Press. ISBN 9780253345479.
  7. 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
  8. 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
  9. 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
  10. Basilosauridae in the Paleobiology Database. Retrieved July 2013.
  11. Uhen 2008

References
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