Editing Basilosaurus (section)

=== Cranium ===
[[File:Basilosaurus isis and cetoides skulls compared.png|thumb|right|upright|Comparison of the skulls of ''Basilosaurus isis'' (fossil at [[Naturmuseum Senckenberg]], top) and ''B. cetoides'' (fossil from the [[North American Museum of Ancient Life]], bottom)]]
The [[dental formula]] for ''B. isis'' is {{DentalFormula|upper=3.1.4.2|lower=3.1.4.3}}. The upper and lower molars and second to fourth premolars are double-rooted and high-crowned.<ref name=fahlke2012>{{Cite journal| last = Fahlke | first = Julia M.| title = Bite marks revisited – evidence for middle-to-late Eocene ''Basilosaurus isis'' predation on ''Dorudon atrox'' (both Cetacea, Basilosauridae)| year = 2012 | journal = Palaeontologia Electronica | volume = 15 | issue = 3| url = http://palaeo-electronica.org/content/pdfs/341.pdf}}</ref>

The head of ''Basilosaurus'' did not have room for a [[Melon (cetacean)|melon]] like modern toothed whales, and the brain was smaller in comparison, as well. They are not believed to have had the [[Animal echolocation|echolocation]] capabilities nor the social dynamics of extant cetaceans. {{citation needed|date=November 2024}}

A 2011 study concluded that the skull of ''Basilosaurus'' is asymmetrical like in modern toothed whales, and not, as previously assumed, symmetrical like in baleen whales and [[Even-toed ungulate|artiodactyls]] (which are closely related to cetaceans). In modern toothed whales, this asymmetry is associated with high-frequency sound production and echolocation, neither of which is thought to have been present in ''Basilosaurus''. This probably evolved to detect sound underwater, with a fatty sound-receiving pad in the mandible.<ref>{{Cite journal| last1 = Fahlke | first1 = Julia M.| last2 = Gingerich | first2 = Philip D.| last3 = Welsh | first3 = Robert C.| last4 = Wood | first4 = Aaron R.| title = Cranial asymmetry in Eocene archaeocete whales and the evolution of directional hearing in water| year = 2011 | journal = PNAS | volume = 108 | issue = 35 | pages = 14545–14548| doi = 10.1073/pnas.1108927108 | pmid=21873217 | pmc=3167538| bibcode = 2011PNAS..10814545F| doi-access = free}}</ref>

In the skull, the inner and middle ear are enclosed by a dense [[tympanic bulla]].<ref name="GinUhe-1998">{{Cite journal| last1 = Gingerich | first1 = P. D.| last2 = Uhen | first2 = Mark D.| title = Likelihood estimation of the time of origin of Cetacea and the time of divergence of Cetacea and Artiodactyla| year = 1998 | journal = Palaeontologia Electronica | volume = 1 | issue = 2 | page = 4| url = http://palaeo-electronica.org/1998_2/ging_uhen/text.pdf }}</ref> The [[Synapomorphy|synapomorphic]] cetacean air [[Sinus (anatomy)|sinus]] system is partially present in basilosaurids, including the pterygoid, peribullary, maxillary, and frontal sinuses.<ref>{{Cite journal| last1 = Racicot | first1 = Rachel A.| last2 = Berta | first2 = Annalisa| title = Comparative Morphology of Porpoise (Cetacea: Phocoenidae) Pterygoid Sinuses: Phylogenetic and Functional Implications| year = 2013 | journal = Journal of Morphology | volume = 274 | issue = 1 | doi=10.1002/jmor.20075 | pmid = 22965565| page=50<!-- only citing page 50 -->| s2cid = 2617769}}</ref> The [[periotic bone]], which surrounds the inner ear, is partially isolated. The [[mandibular canal]] is large and laterally flanked by a thin bony wall, the pan bone or acoustic [[Fenestra (anatomy)|fenestra]]. These features enabled basilosaurs to hear directionally in water.<ref name="GinUhe-1998" />

The ear of basilosaurids is more derived than those in earlier [[archaeocete]]s, such as [[Remingtonocetidae|remingtonocetids]] and [[Protocetidae|protocetids]], in the acoustic isolation provided by the air-filled sinuses inserted between the ear and the skull. The basilosaurid ear did, however, have a large [[Ear canal|external auditory meatus]], strongly reduced in modern cetaceans, but, though this was probably functional, it can have been of little use under water.<ref>{{Cite journal |last1=Nummela |first1=Sirpa |last2=Thewissen |first2=J. G. M. |last3=Bajpai |first3=Sunil |last4=Hussain |first4=Taseer|last5=Kumar |first5=Kishor |s2cid=4372872 |title=Eocene evolution of whale hearing |year=2004 |journal=Nature |volume=430 |issue=7001 |pages=776–778 |doi=10.1038/nature02720 |pmid=15306808 |bibcode=2004Natur.430..776N }}</ref>