Basilosaurus Information

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Basilosaurus [2]
Temporal range: Late Eocene 41.3–33.9  Ma
Basilosaurus cetoides (1).jpg
B. cetoides, National Museum of Natural History, Washington DC
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Family: Basilosauridae
Subfamily: Basilosaurinae
Genus: Basilosaurus
Harlan 1834

Basilosaurus meaning "king lizard", is a genus of large, predatory, prehistoric cetaceans that is known from well preserved fossils found in Lutetian, Bartonian and Priabonian stage deposits during the late Eocene approximately 41.3 to 33.9 million years ago (mya). They lived for around 7.4 million years before dying out. The first fossil of Basilosaurus were discovered in North America, along the gulf coast of the United States as well as a few fossils in the eastern US, these fossils discoveries are attributed to the type species B. cetoides. These fossil finds were thought to be of a giant reptile hence the suffix saurus, but it was later found to be an early marine mammal. Fossils of the second species B. isis have been found in North Africa, more specifically the countries of Egypt, Jordan, Tunisia [5] and Morocco, with a few fossils being found in the disputed Western Sahara. Basilosaurus has a possible fossil record in other places, such as the Oceania [6] (mainly in New Zealand) [7].Basilosaurus is considered to have been common in the Eocene seas, such as the Tethys sea. [8] [9] It was one of the largest animals of the Paleogene, if not the largest animal of that time period. It was the top predator of its environment, with it preying on sharks and other whales such as Dorudon who seems to have a prevalent predator-prey relationship with Basilosaurus. Basilosaurus was at one point a wastebasket taxa, before the genus slowly started getting reevaluated, with many species of different Eocene cetacean being assigned to the genus in the past, however they are invalid or have been reclassified under a new or different genus, leaving only 2 confirmed species. Basilosaurus and its many other relatives may have been the first fully aquatic cetaceans [10] (sometimes referred to as the pelagiceti [11]), however by the end of the Eocene many of them became extinct. [10]Basilosaurus was very different than many modern Cetaceans, with its body being rather elongated, and its teeth being more like modern day Carnivorans such as canines, which it used to crush prey, and then proceeded to use its back teeth to chew. This behavior is not exhibited in modern whales who swallow food whole. [12] [13]


Size compared to a human

Measuring 15–20 m (49–66 ft), [14] [15] [16] [17] Basilosaurus is one of the largest-known animals to exist from K–Pg extinction event 66 million years ago (mya) to around 15 million years ago when modern cetaceans began to reach enormous sizes. [18] B. isis is slightly smaller than B. cetoides, [19] with B. isis being 15–18 m (49–59 ft) long and B. cetoides being 17–20 m (56–66 ft) long. [16] [20] Basilosaurus is distinguished from other basilosaurids genera 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 Basiloterus. [21]


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 The upper and lower molars and second to fourth premolars are double-rooted and high-crowned. [22]

The head of Basilosaurus did not have room for a melon like modern toothed whales, and the brain was smaller in comparison, as well. They are not believed to have had the social capabilities of modern whales.

Fahlke et al. 2011 concluded that the skull of Basilosaurus is asymmetrical like in modern toothed whales, and not, as previously assumed, symmetrical like in baleen whales and artiodactyls 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 be present in Basilosaurus. This cranial torsion probably evolved in protocetids and basilosaurids together with directional underwater hearing and the sound-receiving apparatus in the mandible (the auditory fat pad and the pan bone (thin portion of mandible)). [23]

In the basilosaur skull, the inner and middle ear are enclosed by a dense tympanic bulla. [24] The synapomorphic cetacean air sinus system is partially present in basilosaurids, including the pterygoid, peribullary, maxillary, and frontal sinuses. [25] 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. These features enabled basilosaurs to hear directionally in water. [24]

The ear of basilosaurids is more derived than those in earlier archaeocetes, such as remingtonocetids and 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 external auditory meatus, strongly reduced in modern cetaceans, but though this was probably functional, it can have been of little use under water. [26]

Hind limbs

B. isis hind limb

A 16-meter (52 ft) individual of B. isis had 35-centimeter-long (14 in) 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, makes a locomotory function unlikely. [27] Analysis has shown that the reduced limbs could rapidly adduct between only two positions. [28] Possible uses for the structure have been given, such as clasper like body functions, these functions would have been used while mating to guide the male and females long bodies while mating. [29]

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. 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. [30]

Restoration of Basilosaurus cetoides with a speculative dorsal ridge like the ones seen on modern rorquals and sperm whales

Basilosaurus has an anguilliform ( eel-like) body shape because of the elongation of the centra of the thoracic through anterior caudal vertebrae. In life, these vertebrae were filled with marrow, and because of the enlarged size, 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. [31] The skeletal anatomy of the tail suggests that a small fluke was probably present, which would have aided only vertical motion. [32]

Similarly sized thoracic, lumbar, sacral, and caudal vertebrae imply that it moved in an 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 [33]. Basilosaurus did still have an elbow joint in its flipper like a seal.



B. isis jaw muscles

The cheek teeth of Basilosaurus retain a complex morphology and functional occlusion. Heavy wear on the teeth reveals that food was first chewed then swallowed. [24] Scientists were able to estimate the bite force of Basilosaurus by analyzing the scarred skull bones of another species of prehistoric whale, Dorudon, and concluded they could bite with a force of 3,600 pounds per square inch (25,000 kPa). [34]

Analyses of the stomach contents of B. cetoides has shown that this species fed exclusively on fish and large sharks, while bite marks on the skulls of juvenile Dorudon have been matched with the dentition of B. isis, suggesting a dietary difference between the two species, similar to that found in different populations of modern killer whales. [35] It was probably an active predator rather than a scavenger. [36] The discovery of juvenile Dorudon at Wadi Al Hitan bearing distinctive bite marks on their skulls indicates that B. isis would have aimed for the skulls of its victims to kill its prey, then subsequently tore its meals apart, based on the disarticulated remains of the Dorudon skeletons. The finding further cements theories that B. isis was an apex predator that may have hunted newborn and juvenile Dorudon at Wadi Al Hitan when mothers of the latter came to give birth. [16] The stomach contents of an elderly male B.isis not only includes Dorudon but the fish Pycnodus mokattamensis. [37]


Basilosaurus isis (top) and Dorudon atrox (bottom) skeletons compared, from Voss et. al. 2019

Basilosaurus lived in the warm tropical environment of the Eocene, fossils of Basilosaurus and the environments it lived in show an abundance in sea grasses, such as Thalassodendron, Thalassia (also known as turtle grass) and even Halodule. [38] [39] [40] Animals that lived near Basilosaurus would be the previously mentioned Dorudon [41], the Sea Turtle Puppigerus [42] and many sharks, such as Galeocerdo alabamensis [43], Physogaleus, Otodus, Squatina prima, Striatolamia, Carcharocles sokolovi and Isurus praecursor. [44] Fish such metioned Pycnodus, early pufferfish, Phyllodus and the sword fish Xiphiorhynchus would have swam the same waters Basilosaurus. [45] [46]The primitive sirenian genera known Protosiren would have shared the same environments with Basilosaurus as fossils of the Protosiren are also found in Florida. The early elephant Moeritherium lived along side Basilosaurus, in some parts of the world. [47] [48]. [49] Basilosaurus would be the top predator of its environment. [50]Despite this other cetaceans Cynthiacetus and Basiloterus were both large predators lived near Basilosaurus. [51]Basilosaurus would have the biggest apex predator till the prehistoric shark Megalodon showed up in the fossil record during the Miocene, C. Megalodon could have reached similar sizes. [52] [53] [54]


Basilosaurus fossil record seems to end at about 35–33.9 mya. [55] Basilosaurus extinction coincides with the Eocene–Oligocene extinction event which happened 33.9 mya. [56] This extinction saw the death of all of the group Archaeoceti (although there are expectations such as Kekenodon that survived into the Oligocene [57]), and has been attributed to a few factors including volcanic activity, meteor impacts and a sudden change in climate (such as the environment getting cooler), the latter of which might have caused changes in the ocean by disrupting oceanic circulation. [58] [59] [60] Basilosaurus went extinct leaving no relatives. Despite this new currents and deep ocean upwelling favored the diversification of modern toothed and baleen whales.


Below is the phylogenetic analysis on the placement of Basilosaurus as a genus in the cetacean tree

Skeletal restoration of B. cetoides by Gidley 1913

( carnivorans and allies) Crocuta crocuta sideview.jpg


( horses, rhinos, tapirs) Hartmann zebra hobatere S.jpg


( camelids) 07. Camel Profile, near Silverton, NSW, 07.07.2007.jpg


Pigs Scavenger feast - Yala December 2010 (1) (cropped).jpg


Ruminants ( cattle, sheep, antelopes) Walia ibex illustration white background.png


Hippopotamuses Hippopotamus amphibius in Tanzania 2830 Nevit.jpg


Archaeocetes ( Ambulocetus, Protocetus, Basilosaurus)


( right, grey, rorquals)

baleen whales

Delphinoidea ( dolphins, porpoises, beluga whales, narwhals)

Lipotoidea ( river dolphins)

Physeteroidea ( sperm whales)

Ziphoidea ( beaked whales)

toothed whales
c. 53 mya
c. 99 mya

This shows Below is the phylogenetic analysis on the placement of basilosaurus. Two subfamilies exist in Basilosauridae, Basilosaurinae which includes Basilosaurus and Dorudontinae which lived throughout the Late Eocene. These groups have been declared invalid in the past. [61] [62]Dorudon was once classified as juvenile Basilosaurus [63], before it was argued to be its own genus and reclassified into a another grouping of Basilosauridae.







Taxonomic history


Early drawing of a Basilosaurus skull
a drawing of a Basilosaurus Caudal vertebra from Owen 1839, such vertebrae were once used as furniture and 1800s home decor in the Southern United States

The two species of Basilosaurus are B. cetoides, whose remains were discovered in the United States, and B. isis, which was discovered in Egypt. B. cetoides is the type species for the genus. [64] [65] During the early 19th century, B. cetoides fossils were so common (and sufficiently large) that they were regularly used as furniture in the American South. [66] Vertebrae were sent to the American Philosophical Society by a Judge Bry of Arkansas and Judge John Creagh of Clarke County, Alabama. Both fossils ended up in the hands of the anatomist Richard Harlan, who requested more examples from Creagh. [67] [68] The first bones were unearthed when rain caused a hillside full of sea shells to slide. The bones were lying in a curved line "measuring upwards of four hundred feet in length, with intervals which were vacant." Many of these bones were used as andirons and destroyed; Bry saved the bones he could find, but was convinced more bones were still to be found on the location. Bry speculated that the bones must have belonged to a "sea monster" and supplied "a piece having the appearance of a tooth" to help determine which kind. [69] Harlan identified the tooth as a wedge-shaped shell and instead focused on "a vertebra of enormous dimensions" which he assumed belonged to the order " Enalio-Sauri of Conybeare", "found only in the sub-cretaceous series." [70] He noted that some parts of the vertebra were similar to those of Plesiosaurus and skull was similar to Mosasaurus, but that they were completely different in proportions. Comparing his vertebra to those of large dinosaurs such as Megalosaurus and Iguanodon, Harlan concluded that his specimen was considerably larger—he estimated the animal to have been no less than 80–100 ft (24–30 m) long—and therefore suggested the name Basilosaurus, meaning "king lizard". [71]

Harlan brought his assembled specimens (including fragments of jaw and teeth, humerus, and rib fragments) to the UK where he presented them to anatomist Richard Owen. Owen concluded that the molar teeth were two-rooted, a dental morphology unknown in fishes and reptiles, and more complex and varied than in any known reptile, and therefore that the specimen must be a mammal. Owen correctly associated the teeth with cetaceans, but he thought it was an herbivorous animal, similar to sirenians. [72] Consequently, Owen proposed renaming the find Zeuglodon cetoides ("whale-like yoke teeth" in reference to the double-rooted teeth) and Harlan agreed. [73]

Other examples of fossil cetacean misidentification

Basilosaurus and Tylosaurus compared at National Museum of Nature and Science in Tokyo, Japan

Basilosaurus is not the only example of an extinct cetacean thought to be a reptile The group Squalodontidae (the shark toothed dolphins) seems to also fall under the same category. Squalodon an early Odontocete whale was identified as a relative of the dinosaur Iguanadon before it was discovered that it was a cetacean. [74]. In 1935 a jaw with reptilian features was found in the All day bay Formation in new Zealand. It was named Tangaroasaurus as it was thought to be a Middle Miocene fossil record for the group known as Ichthyosauria also known as the Ichthyosaurs. However, despite the questions on its taxonomic status [75], Tangaroasaurus was reevaluated and is now considered to be a member of Squalodontidae,the evaluation happened when the genus was brought back to attention during the 1970's when the specimen was brought back to attention. [76]

Wadi El Hitan

Skeleton of B. isis at Wadi El Hitan
Restoration of a group

Wadi El Hitan, Arabic وادي الحيتان , "Valley of the Whales", is an Egyptian sandstone formation where many early-whale skeletons were discovered. [77] German botanist Georg August Schweinfurth discovered the first archaeocete whale in Egypt (Zeuglodon osiris, now Saghacetus osiris) in 1879. He visited the Qasr el Sagha Formation in 1884 and 1886 and missed the now famous Wadi El Hitan by a few kilometers. German paleontologist Wilhelm Barnim Dames described the material, including the type specimen of Z. osiris, a well-preserved dentary. [78]

Hugh Beadnell, head of the Geological Survey of Egypt 1896–1906, [79] named and described Zeuglodon isis in Andrews 1904 based on a partial mandible and several vertebrae from Wadi El Hitan in Egypt. [80] Andrews 1906 [81] described a skull and some vertebrae of a smaller archaeocete and named it Prozeuglodon atrox, now known today as Dorudon atrox. Kellogg 1936 discovered deciduous teeth in this skull and it was then believed to be a juvenile [Pro]zeuglodon isis for decades before more complete fossils of mature Dorudon were discovered. [82] [83] [84]

In the 1980s, Elwyn L. Simons and Philip D. Gingerich started to excavate at Qasr el-Sagha and Wadi El Hitan with the hope of finding material that could match archaeocete fossils from Pakistan. Since then, over 500 archaeocete skeletons have been found at these two locations, of which most are B. isis or D. atrox, several of the latter carrying bite marks assumed to be from the former. [85] Gingerich, Smith & Simons 1990 described additional fossils including foot bones and speculated that the reduced hind limbs were used as copulatory guides. [86]

In 2016, a complete skeleton, the first-ever find for Basilosaurus, was uncovered in Wadi El Hitan, preserved with the remains of another whale (which was either a last meal or an unborn fetus) inside its ribcage. This specimen was later found to have eaten Dorudon and several species of fish. [87] The whale's skeleton also shows signs of scavenging or predation by large sharks, among them the otodontid Carcharocles sokolovi which was also found in the site, which was then concluded to be an ancestor to the later C. megalodon.

Wastebasket taxa

Wastebasket taxa is a term used by some taxonomists to refer to a taxon that has the sole purpose of classifying organisms that do not fit anywhere else. In paleontology, these taxa usually get reevaluated after years of them being used to group many different organisms. Basilosaurus is a good example of a former wastebasket taxa as many species have been assigned to it in the past but they later got reevaluated as something else or were to incomplete to determine anything

Nomina dubia

A nomen dubium is a scientific name that is of unknown or doubtful application. There are a few documented cases of this being applied to Basilosaurus in the past.

Albert Koch's "Hydrarchos" fossil skeleton from 1845, two basilosaurus or Pontogeneus skeletons tied together which was presented as the bones of an ancient sea monster, it was destroyed during the great Chicago fire in 1871
  • Zeuglodon wanklyni, was a supposed species of Basilosaurus, that described in 1876 based on a skull found in the Wanklyn's Barton Cliff in the United Kingdom. This single specimen, however, quickly disappeared and has since been declared a nomen nudum or referred to as Zygorhiza wanklyni. [88]
  • Zeuglodon vredense or vredensis was named in the 19th century based on a single, isolated tooth without any kind of accompanying description, and Kellogg 1936 therefore declared it a nomen nudum. [89] [90]
  • Zeuglodon puschi[i] was a species that was said to come from Poland, it was named by Brandt 1873. Kellogg 1936 noted that the species is based on an incomplete vertebra of indeterminable position and, therefore, that the species is invalid. [91] [92]
  • Zeuglodon brachyspondylus was described by Müller 1849 based on some vertebrae from Zeuglodon hydrarchus, better known as Dr Albert Koch's "Hydrarchos". Kellogg 1936, synonymized it with Pontogeneus priscus, which Uhen 2005 a genus which was declared a nomen dubium.

Reassigned species

  • Basilosaurus drazindai was named by Gingerich et al. 1997 based on a single lumbar vertebra. Originally, the species was thought to have lived in Pakistan and the UK [93]. It was later declared a nomen dubium by Uhen (2013), but Gingerich and Zouhri (in press) re-assigned it to Eocetus. This species was at one point in time concluded to be the earliest record of the genus Basilosaurus, before its reclassification. [94] [95] [96]
  • Zeuglodon elliotsmithii, Z. sensitivius, Z. sensitivus, and Z. zitteli were synonymized and grouped under the genus Saghacetus by Gingerich 1992.
  • Zeuglodon paulsoni from Ukraine (then the Russian Empire) was named by Brandt 1873. It was synonymized with Platyosphys but is now considered nomen dubium. Gingerich and Zouhri (in press), however, maintain Platyosphys as valid. [96] [97]
  • Basilosaurus caucasicus also known as Basilosaurus caucasicum or Zeuglodon caucasicum was species described in the Russian Empire, it gets its name from the Russian caucasus of where it was found in the 1890s [98]. The specimen was found. The fossil was reassigned to the toothed whale Microzeuglodon caucasicum. [99]
  • Basilosaurus harwoodi was discovered in Murray River near Wellington in South Australia, this species classification is quite controversial, yet today it is agreed that the Australian, Basilosaurus harwoodi (or Zeuglodon harwoodi) is most likely a member of the genus Metasqualodon. [100] [101]


In 1906 a naturalist named Abel published a paper called “Uber den als Beckengurtel von Zeuglodon beschriebenen Schultergurtel eines Vogels aus dem Eocan Alabama on some fossils from Choctaw County [102] in the southern United states. He thought the fossils of a Basilosaurus hip bone represented the shoulder of a large bird Eocene Bird, similar to Gastornis. He later named the specimens Alabamornis gigantea. The fossils were proven to belong to a Basilosaurus hip by a different naturalist named Lucas in 1908. [103] [104]

Popular Culture

Basilosaurus is culturally significant as it has been featured in many shows, books and being used as national symbols. However its cultural significance in terms of early Cenozoic marine life is only outshadowed by Megalodon who appears in many works of fiction depicting sea monsters. [105]The species B. cetoides is the state fossil of Alabama, [19] and Mississippi named the prehistoric whale (B. cetoides and Zygorhiza kochii) its state fossil in 1981. [106] [107]In the popular 1851 novel Moby-Dick, Ishmael discusses Basilosaurus in chapter 104, "The Fossil Whale", describing it as 'one of the most extraordinary creatures which the mutations of the globe have blotted out of existence'. [108] Basilosaurus is featured in many shows such as its depiction in bbc's walking with documentary series (mainly in Walking with Beasts and Chased by sea monsters). [109] [110] [111]

Outdated restoration of Basilosaurus by Janson, Andrew R from 1956 showing a serpentine/snake like design

In cryptozoology

In cryptozoology circles, Basilosaurus is sometimes used as an explanation for globsters and sea or lake monster sightings such as the Sakhalin island carcass and the lake monster Ogopogo, despite the fact there is a 30 million year old gap in the fossil record [112] [113] [114]. Cryptozoolgists have proposed that the sightings of giant underwater centipedes known as Many-finned sea serpent such as the Con Rit which were sighted in Vietnam and Algeria are actually relic surviving populations Basilosaurus with bony plates on their sides, however this assumption sounds very much like a now outdated concept of a bony plated Archeocetes. [115] [116]

See also



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