Editing Basilosaurus (section)

== Description ==
[[File:Basilosaurus SIZE 01.png|thumb|left|Size compared to a human]]

''Basilosaurus'' is one of the largest animals known to exist between the [[Cretaceous–Paleogene extinction event|K–Pg extinction event]] 66 million years ago (mya) and around 15 million years ago when modern [[cetacea]]ns began to reach enormous sizes.<ref>{{cite web |url=https://naturalhistory.si.edu/onehundredyears/featured_objects/Basilosaurus.html |title=Explore Our Collections Basilosaurus |website=Smithsonian natural history museum |archive-url= https://web.archive.org/web/20160331223414/https://naturalhistory.si.edu/onehundredyears/featured_objects/Basilosaurus.html |archive-date=31 March 2016 }}</ref><ref>{{cite journal|year=2012|title=Evolution of Whales from Land to Sea|journal=Proceedings of the American Philosophical Society|volume=156|issue=3|pages=309–323|url=http://prod.lsa.umich.edu/content/dam/paleontology-assets/paleontology-documents/1560305Gingerich.pdf|last1=Gingerich|first1=P. D.|access-date=31 July 2019|archive-date=18 January 2021|archive-url=https://web.archive.org/web/20210118150642/http://prod.lsa.umich.edu/content/dam/paleontology-assets/paleontology-documents/1560305Gingerich.pdf|url-status=live}}</ref> ''B. cetoides'' measured {{convert|17|-|20|m|ft}} long and ''B. isis'' measured {{convert|15|-|18|m|ft}} long.<ref name=Basilo2019/> A 1998 study estimated that ''B. cetoides'' weighed more than {{convert|5.8|MT|ST}} and ''B. isis'' weighed nearly {{convert|6.5|MT|ST}},<ref>{{cite book|last1=Gingerich|first1=P.D.|editor1=Thewissen, J. G. M.|chapter=15. Paleobiological perspectives on Mesonychia, Archaeoceti, and the origin of whales|title=The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea|chapter-url=http://www-personal.umich.edu/~gingeric/PDFfiles/PDG341_OriginWhales.pdf|publisher=Springer|location=New York|year=1998|pages=423–449|doi=10.1007/978-1-4899-0159-0|isbn=978-1-4899-0159-0|s2cid=30660655|access-date=8 September 2013|archive-date=18 May 2022|archive-url=https://web.archive.org/web/20220518203140/http://www-personal.umich.edu/~gingeric/PDFfiles/PDG341_OriginWhales.pdf|url-status=live}}</ref> while the 2025 study estimated that a {{convert|18.35|m|ft}} long ''B. cetoides'' weighed {{convert|15|MT|ST}}.<ref>{{cite journal|author1=Paul, G.S.|author2=Larramendi, A.|year=2025|title=Further trimming down the marine heavyweights: ''Perucetus colossus'' did not come close to, much less exceed, the tonnage of blue whales, and the latter are not ultra-sized either|journal=Palaeontologia Electronica|volume=28|issue=1|at=28.1.a6|doi=10.26879/1435|url=https://palaeo-electronica.org/content/2025/5431-trimming-down-perucetus|doi-access=free}}</ref> ''Basilosaurus'' is distinguished from other genera of basilosaurids by its larger body size and its more elongated posterior thoracic, lumbar, and anterior caudal [[vertebrae]]. ''Basilosaurus'' does not have the vertically oriented metapophyses seen in its closest relative the basilosaurid known as ''[[Basiloterus]]''. ''Basilosaurus'' is considered to be the largest of archeocete whales.<ref name="New Archaeoceti 2027">{{Cite journal| last1 = Gingerich | first1 = P. D.| last2 = Arif | first2 = M| last3 = Bhatti | first3 = M Akram| last4 = Anwar | first4 = M| last5 = Sanders | first5 = William J| title = ''Basilosaurus drazindai'' and ''Basiloterus hussaini'', New Archaeoceti (Mammalia, Cetacea) from the Middle Eocene Drazinda Formation, with a Revised Interpretation of Ages of Whale-Bearing Strata in the Kirthar Group of the Sulaiman Range, Punjab (Pakistan)| year = 1997 | journal = Contributions from the Museum of Paleontology, University of Michigan | volume = 30 | issue = 2 | pages = 55–81| oclc = 742731913 | hdl = 2027.42/48652}}</ref><ref>{{cite web |title=Basilosaurus description |url=https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=36681&is_real_user=1 |website=PBDB |access-date=23 July 2019 |archive-date=6 August 2021 |archive-url=https://web.archive.org/web/20210806225248/https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=36681&is_real_user=1 |url-status=live }}</ref>

=== 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>

=== Hind limbs ===
[[File:Basilosaurus isis hindlimb.JPG|thumb|right|upright|''B. isis'' hind limb]]
A {{Convert|16|m|ft|adj=mid|sp=us}} individual of ''B. isis'' had {{Convert|35|cm|in|adj=mid|-long|sp=us}} hind limbs with fused tarsals and only three digits. The limited size of the limb and the absence of an articulation with the sacral vertebrae make a locomotory function unlikely.<ref>{{Cite journal | last1 = Bejder | first1 = Lars | last2 = Hall | first2 = Brian K. | author2-link = Brian K. Hall | title = Limbs in whales and limblessness in other vertebrates: mechanisms of evolutionary and developmental transformation and loss | year = 2002 | journal = Evolution and Development | volume = 4 | issue = 6 | pages = 445–458 | url = http://whitelab.biology.dal.ca/lb/Bejder%20and%20Hall.pdf | doi = 10.1046/j.1525-142x.2002.02033.x | pmid = 12492145 | s2cid = 8448387 | access-date = 1 October 2005 | archive-date = 10 April 2021 | archive-url = https://web.archive.org/web/20210410222928/http://whitelab.biology.dal.ca/lb/Bejder%20and%20Hall.pdf | url-status = live }}</ref> Analysis has shown that the reduced limbs could rapidly adduct between only two positions.<ref name="pmid-17836967">{{cite journal |title=Hind limbs of eocene basilosaurus: evidence of feet in whales. |journal=Science |volume=249 |issue=4965 |pages=154–157 |pmid=17836967 |bibcode=1990Sci...249..154G |last1=Gingerich |first1=Philip D. |last2=Smith |first2=B. Holly|author2-link=B. Holly Smith |last3=Simons |first3=Elwyn L. |s2cid=35307146 |year=1990 |doi=10.1126/science.249.4965.154 }}</ref> Possible uses for the structure have been given, such as [[clasper]]-like body functions (compare to the function of [[pelvic spur]]s, the last vestiges of limbs in certain modern snakes). These limbs would have been used to guide the animals' long bodies during mating.<ref>{{cite web |title=Basilosaurid FOSSIL MAMMAL |url=https://www.britannica.com/animal/basilosaurid |website=Encyclopedia Britannica}}</ref>

=== Spine and movement ===
A complete ''Basilosaurus'' skeleton was found in 2015, and several attempts have been made to reconstruct the vertebral column from partial skeletons. {{Harvnb|Kellogg|1936}} estimated a total of 58 vertebrae, based on two partial and nonoverlapping skeletons of ''B. cetoides'' from Alabama. More complete fossils uncovered in Egypt in the 1990s allowed a more accurate estimation: the vertebral column of ''B. isis'' has been reconstructed from three overlapping skeletons to a total of 70 vertebrae with a vertebral formula interpreted as seven cervical, 18 thoracic, 20 lumbar and sacral, and 25 caudal vertebrae. The vertebral formula of ''B. cetoides'' can be assumed to be the same.<ref name=zalmout2000/>
[[File:Basilosaurus cetoides.png|thumb|left|[[Paleoart|Restoration]] of ''Basilosaurus cetoides'']]
''Basilosaurus'' has an anguilliform ([[eel]]-like) body shape because of the elongation of the [[Body of vertebra|centra]] of the thoracic through anterior caudal vertebrae. In life, these vertebrae were filled with marrow, and because of the enlarged size, this made them buoyant. ''Basilosaurus'' probably swam predominantly in two dimensions at the sea surface, in contrast to the smaller ''[[Dorudon]]'', which was likely a diving, three-dimensional swimmer.<ref>{{Cite book| last = Gingerich| first = P. D.| chapter = Paleobiological Perspectives on Mesonychia, Archaeoceti, and the Origin of Whales| pages = 424–439| title = The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea| series = Advances in Vertebrate Paleobiology| volume = 1| editor-last = Thewissen| editor-first = J. G. M.| year = 1998| publisher = Springer| chapter-url = http://www-personal.umich.edu/~gingeric/PDFfiles/PDG341_OriginWhales.pdf| isbn = 9780306458538| access-date = 8 September 2013| archive-date = 18 May 2022| archive-url = https://web.archive.org/web/20220518203140/http://www-personal.umich.edu/~gingeric/PDFfiles/PDG341_OriginWhales.pdf| url-status = live}}</ref> The skeletal anatomy of the tail suggests that a small fluke was probably present, which would have aided only vertical motion.<ref>{{cite web |title=Basilosaurus spp. |url=https://www.nyit.edu/medicine/basilosaurus_spp |website=College of Osteopathic Medicine |publisher=Robert Boessenecker and Jonathan Geisler |access-date=22 June 2019 |archive-date=31 December 2018 |archive-url=https://web.archive.org/web/20181231105613/https://www.nyit.edu/medicine/basilosaurus_spp |url-status=live }}</ref>

Similarly sized thoracic, lumbar, sacral, and caudal vertebrae imply that it moved in an [[Fish locomotion#Swimming|anguilliform]] fashion, but predominantly in the vertical plane. Paleontologist [[Philip D. Gingerich]] theorized that ''Basilosaurus'' may also have moved in a very odd, horizontal anguilliform fashion to some degree, something completely unknown in modern cetaceans. The vertebrae appear to have been hollow, and likely also fluid-filled. This would imply that ''Basilosaurus'' typically functioned in only two dimensions at the ocean surface, compared with the three-dimensional habits of most other cetaceans. Judging from the relatively weak axial musculature and the thick bones in the limbs, ''Basilosaurus'' is not believed to have been capable of sustained swimming or deep diving, or [[terrestrial locomotion]].<ref>{{cite book |title=Great Transformations in Vertebrate Evolution |date=July 2015 |publisher=KENNETH P. DIAL, NEIL SHUBIN, AND ELIZABETH L. BRAINERD |isbn=9780226268255 |url=https://books.google.com/books?id=zb5TCgAAQBAJ&q=basilosaurus+moved+like+an+eel&pg=PA248}}</ref>