Basilosaurus spp.

[Vodmeister]

Basilosaurus spp.


Life restoration of Basilosaurus swimming. © @ Sergio Pérez.

Temporal range: Paleogene; Eocene; Bartonian to early Priabonian (~41.2 to >33.9 Ma)[1][2]

Scientific classification:

Life
Domain: Eukaryota
(unranked): Unikonta
(unranked): Opisthokonta
(unranked): Holozoa
(unranked): Filozoa
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked): Bilateria
Clade: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Clade: Olfactores
Clade: Craniata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Clade: Eugnathostomata
Clade: Teleostomi
Superclass: Tetrapoda
Clade: Reptiliomorpha
Clade: Amniota
Clade: Synapsida
Clade: Eupelycosauria
Clade: Sphenacodontia
Clade: Sphenacodontoidea
Order: Therapsida
Suborder: Cynodontia
Clade: Epicynodontia
Infraorder: Eucynodontia
Parvorder: Probainognathia
Superfamily: Chiniquodontoidea
Clade: Prozostrodontia
Clade: Mammaliaformes
Class: Mammalia
Clade: Holotheria
Superlegion: Trechnotheria
Legion: Cladotheria
Sublegion: Zatheria
Infralegion: Tribosphenida
Subclass: Theria
Clade: Eutheria
Infraclass: Placentalia
Subcohort: Exafroplacentalia
Magnorder: Boreoeutheria
Superorder: Laurasiatheria
Clade: Ungulata
Clade: Cetartiodactyla
Family: †Basilosauridae
Subfamily: †Basilosaurinae
Genus: †Basilosaurus
Species: †B. cetoides
†B. isis

Basilosaurus is an extinct genus of cetacean that lived in the United States, Egypt, Germany, Jordan, the western Sahara[3][4], and possibly Antarctica[5] from the Bartonian to the early Priabonian[1], existing between 41.2 to 33.9 million years ago.

Taxonomy:
Despite the rather unfitting name “Basilosaurus” (“king lizard”), this genus name has priority over Zeuglodon and several other synonyms.[1] Currently, the two known valid species are B. cetoides (the type species) and B. isis. There used to be a third species classified in this genus (Basilosaurus drazindai), but this has since been reassigned to the genus Eocetus.[6][7]

Description:
B. cetoides was slightly larger than B. isis[1], at 17-20 meters versus 15-18 meters in total length, respectively.[8] Due to its elongated body it might not have exceeded, or even achieved, 10 tonnes in total body mass.[9] The skull was relatively small for its total body length, with the skull of B. isis at 113 cm long.[10]

The dental formula of B. isis is 3.1.4.2/3.1.4.3.[11] Unlike modern toothed whales, Basilosaurus teeth were clearly heterodont. The upper and lower molars, as well as upper & lower premolars 2-4 were double-rooted and high-crowned; these teeth sported a central cusp and anteroposteriorly oriented accessory denticles. The molars were smaller, more closely spaced, and lower-crowned. Incisors and canines were monocuspid.[11]


Skeleton of Basilosaurus compared to Dorudon. From [8].


Skull of B. isis. Note the clearly heterodont dentition in comparison to modern odontocetes. Image source.

Basilosaurus had extremely reduced hindlimbs. These were of no use for locomotion on land or underwater, but the retention of joints and insertions for muscles, among others, might suggest some use for assisting reproduction.[12] It may be, however, that the hindlimbs had no clear function. Once hindlimbs became unnecessary in cetaceans, there may have been a long period of time where they existed in a highly reduced form before disappearing completely.[13]

Biology:
The serpentine body of Basilosaurus may suggest anguilliform locomotion. The very dense ribs, oxygen isotope chemistry of the teeth, and the fact that Basilosaurus remains have only been found in marine deposits, are all evidence of a fully marine animal.[13]

The lower jaw contained a very large mandibular foramen with thin walls, suggesting the presence of a fat pad that detected sound waves underwater. Basilosaurus had bony external ear canals unlike modern cetaceans, but all other hearing adaptations are indicative of a fully marine animal. Therefore, the remaining adaptations for hearing airborne sound were likely vestigial.[13]

Basilosaurus was an apex predator in its ecosystem, just like other cetaceans such as Livyatan melvillei and Orcinus orca.[8] Stomach contents of B. cetoides included the remains of fishes and sharks up to 50 cm in length.[14] By contrast, evidence shows that B. isis preyed also preyed upon marine mammals, especially Dorudon calves. Skulls of juvenile Dorudon have been found that match the teeth of B. isis. The prey was sometimes captured with one bite and readjusted for a more powerful killing bite using the premolars.[11] A study on the bite force of B. isis estimated its bite force at the third premolar to be at least ~16,400 N, with a second incisor bite force of at least 10,536 N, showing that Basilosaurus had jaws strong enough to break bones (i.e. the skulls of juvenile Dorudon).[10] It’s been suggested that the long, narrow rostrum of Basilosaurus meant it was unlikely to have rammed its prey like modern orcas do[11], although odontocetes with longirostrine jaws (e.g. bottlenose dolphins) also ram other animals with their rostrum.[15]

It has been suggested that the different Basilosaurus species had different diets, similar to how modern orca populations show considerable variation and specialization in diet.[11] It is indeed true that B. cetoides fed on fishes and sharks, and that B. isis fed on other cetaceans. B. isis, however, did not feed exclusively on marine mammals, as the stomach contents of an adult male B. isis specimen include the remains of both juvenile Dorudon and the fish Pycnodus mokattamensis.[8]

Extinction:
Basilosaurus has no living descendants, and did not give rise to any later whales.[16] It is possible that the progressive cooling of the Earth’s climate[16] changed ocean circulation, leading to the extinction of Basilosaurus.[17]

References:

[1] Thewissen, J. G. (Ed.). (2013). The emergence of whales: evolutionary patterns in the origin of Cetacea (Vol. 1). Springer Science & Business Media. pp. 32-33.
[2] stratigraphy.org/ICSchart/ChronostratChart2021-05.pdf
[3] paleobiodb.org/classic/basicTaxonInfo?taxon_no=63132
[4] paleobiodb.org/classic/basicTaxonInfo?taxon_no=53287
[5] REGUERO, M. A. (2019). [url=https://www.researchgate.net/publication/335383837_Antarctic_Paleontological_Heritage_Late_Cretaceous-Paleogene_vertebrates_from_Seymour_Marambio_Island_Antarctic_PeninsulaAntarctic Paleontological Heritage: Late Cretaceous–Paleogene vertebrates from Seymour (Marambio) Island, Antarctic Peninsula[/url]. Advances in Polar Science, 328-355.
[6] Gingerich, P. D., & Zouhri, S. (2015). New fauna of archaeocete whales (Mammalia, Cetacea) from the Bartonian middle Eocene of southern Morocco. Journal of African Earth Sciences, 111, 273-286.
[7] Jan van Vliet, H., Lambert, O., Bosselaers, M., S Schulp, A., & WM Jagt, J. (2019). A Palaeogene cetacean from Maastricht, southern Limburg (The Netherlands). Cainozoic research, 19(1), 95-113.
[8] Voss, M., Antar, M. S. M., Zalmout, I. S., & Gingerich, P. D. (2019). Stomach contents of the archaeocete Basilosaurus isis: Apex predator in oceans of the late Eocene. PloS one, 14(1), e0209021.
[9] McHenry, C. R. (2009). Devourer of gods. The palaeoecology of the Cretaceous pliosaur Kronosaurus queenslandicus.
[10] 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.
[11] Fahlke, J. M. (2012). Bite marks revisited—evidence for middle-to-late Eocene Basilosaurus isis predation on Dorudon atrox (both Cetacea, Basilosauridae). Palaeontologia Electronica, 15(3), 32A.
[12] Gingerich, P. D., Smith, B. H., & Simons, E. L. (1990). Hind limbs of Eocene Basilosaurus: evidence of feet in whales. Science, 249(4965), 154-157.
[13] www.nyit.edu/medicine/basilosaurus_spp
[14] Swift, C., & Barnes, L. (1996). Stomach Contents of Basilosaurus Cetoides: Implications for the Evolution of Cetacean Feeding Behavior, and Evidence for Vertebrate Fauna of Epicontinental Eocene Seas. The Paleontological Society Special Publications, 8, 380-380. doi:10.1017/S2475262200003828
[15] Cotter, M. P., Maldini, D., & Jefferson, T. A. (2012). “Porpicide” in California: Killing of harbor porpoises (Phocoena phocoena) by coastal bottlenose dolphins (Tursiops truncatus). Marine Mammal Science, 28(1), E1-E15.
[16] Ivany, L. C., Patterson, W. P., & Lohmann, K. C. (2000). Cooler winters as a possible cause of mass extinctions at the Eocene/Oligocene boundary. Nature, 407(6806), 887-890.
[17] web.archive.org/web/20140313151405/http://www.encyclopediaofalabama.org/face/Article.jsp?id=h-1386

[Vodmeister]

[creature386]

It's great that you try to revive the profiles with own material, but what about that one post about directional hearing which I have edited (to make it more our own material)?

Whatever, I don't want to spam, so my post in the profile on carnivora:

Snively, E., Fahlke, J. BITE FORCE OF THE EOCENE WHALE BASILOSAURUS ISIS CONSISTENT WITH POWERFUL ANTERIOR SEIZURE AND POSTERIOR CRUSHING OF LARGE PREY

Estimating bite forces of fossil whales is potentially informative about their trophic interactions and evolution. Basilosaurus isis was a large archaeocete from the late Eocene Birket Qarun Formation (Egypt). Juveniles of its fellow basilosaurid Dorudon atrox bear bite marks attributable to B. isis, suggesting high bite forces that crushed bone. To test the capability of B. isis to inflict these traces, isometric adductor forces were estimated with the dry skull method, and finite element (FE) analysis yielded reaction forces at cranial tooth positions and jaw joints. Several specific tensions were applied to estimate muscle forces. Varying thickness of plate elements tested the sensitivity of reaction forces in FE models with accurate external geometry, but different element characteristics. Results indicate that B. isis exerted 16,400-20,000 N at its upper P3, and relatively greater anterior bite forces than possible for crocodilians. Joint reaction force was greater on the balancing side than the active side in unilateral bites. Reaction force magnitudes were insensitive to model formulation, and stresses varied predictably with element thickness. Tooth forces in the Basilosaurus isis model are consistent with bite marks on Dorudon fossils, and seizing prey with the anterior teeth (as proposed for other archaeocetes and probable in river dolphins). Bite forces are slightly greater than expected for skull width from regressions for carnivorous mammals, but lower than estimated for some large reptiles. Uniform reaction forces from all models suggest that plate elements are useful for estimating bite force when only surface data are available. However, plate models are only heuristic for stress and strain in complex biological structures.

[creature386]

Below a paper on the diet of B. isis. I am going to post the information on B. cetoides it has here:

Bite marks revisited – evidence for middle-to-late Eocene Basilosaurus isis predation on Dorudon atrox (both Cetacea, Basilosauridae) by Julia M. Fahlke. Museum für Naturkunde - Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstraße 43, D-10115 Berlin, Germany [e-mail]

Stomach contents have been identified for two basilosaurids: Basilosaurus cetoides fed on teleost fish and sharks of up to 50 cm in length (Swift and Barnes, 1996), and Dorudon atrox preyed on at least two different fish (Uhen, 2004).


B. isis' diet (with some information on cetoides):

Stomach contents of B. cetoides from the late Eocene of North America have been identified as remains of fishes and sharks (Swift and Barnes, 1996), and the authors assumed that fish was the typical food of archaeocetes. This assumption gains support from stomach contents of D. atrox, consisting of various kinds of fish (Uhen, 2004). However, this study shows that at least Basilosaurus isis did not, or at least not exclusively, consume fish but very likely also marine mammals. Although the exact body size of the living juvenile D. atrox cannot be estimated precisely due to allometric growth, the size of the cranial pieces analyzed here (widths of the frontal shields of over 20 cm) and adult body lengths of D. atrox of about 5 m (Uhen, 2004) imply that these Dorudon calves were significantly longer than the 50 cm body length estimated for sharks and fishes consumed by B. cetoides (Swift and Barnes, 1996). These large-scale regional dietary differences between members of the genus Basilosaurus are reminiscent of dietary specialization in genetically and morphologically distinct populations of the modern killer whale. In the northeastern Pacific, resident killer whales are known to have special- ized on (salmonid) fish, transient killer whales feed on mammals, and offshore killer whales have been shown to consume sharks (Ford et al., 2011). Com- parable dietary specializations are also known from killer whale populations in the North Atlantic (Foote et al., 2009; Foote, 2011) and the Antarctic (Pit- man, 2011).Ford et al. (2011) attributed abrasive tooth wear in offshore killer whales to denticles embed- ded in shark skin. Similarly abrasive wear on the teeth of B. isis, in addition to the breakage and spalling of enamel and dentin that has been attributed to bone crushing (Fahlke et al., 2010), might possibly be a result of the consumption of sharks that were sympatric with B. isis in the mid- dle to late Eocene (e.g., Case and Cappetta, 1990; Underwood et al., 2011). An analysis of the tooth wear of B. cetoides and comparison with that of B. isis would shed further light on this issue, but is beyond the scope of this paper.

In other words, the scene you saw in Walking with Beasts was true for at least one Basilosaurus species.
I thought it would be interesting to compare the food of the different Basilosaurus species/populations. I don't know if the orca analogy is so good because we compare regional populations with different species. This is not so important anyway. I don't know if the tooth wear point interests you. To my knowledge, there is no study on that. But it could mean that the idea of different diets is false, if B. isis really was also a shark eater. I anyway am not really convinced by that because obtaining regional trend is very hard, even in extant animals (where you have a sample of hundreds), let alone extinct!

Here the PDF: palaeo-electronica.org/content/pdfs/341.pdf

[Grey]

www.dailymail.co.uk/sciencetech/article-3110718/Fossils-reveal-whale-inside-whale-eaten-shark-Grave-40-million-year-old-marine-creatures-Egypt.html

[Infinity Blade]

© @ Bran-Artworks

---

Anyway, I've been trying to track down the source that found Basilosaurus' vertebrae to be hollow and filled with fluid with no real luck. If anyone knows of it, it would be much appreciated.

The reason why I desire the source is because I recall it being pointed out (albeit on an untrustworthy source, although it makes sense) that with fluid-filled, hollow vertebrae, pressure imbalance between said fluid and deep water outside could damage the vertebrae. Therefore, Basilosaurus wouldn't really have been suited to life in the open ocean; rather, it was apparently a shallow water inhabitant. In other words, Walking with Beasts got it mixed up when it portrayed Basilosaurus as an open ocean inhabitant uncomfortable with shallow waters; it was apparently the other way around.

[jhg]

Jul 17, 2015 7:32:55 GMT 5 Infinity Blade said:

© @ Bran-Artworks

---

Anyway, I've been trying to track down the source that found Basilosaurus' vertebrae to be hollow and filled with fluid with no real luck. If anyone knows of it, it would be much appreciated.

The reason why I desire the source is because I recall it being pointed out (albeit on an untrustworthy source, although it makes sense) that with fluid-filled, hollow vertebrae, pressure imbalance between said fluid and deep water outside could damage the vertebrae. Therefore, Basilosaurus wouldn't really have been suited to life in the open ocean; rather, it was apparently a shallow water inhabitant. In other words, Walking with Beasts got it mixed up when it portrayed Basilosaurus as an open ocean inhabitant uncomfortable with shallow waters; it was apparently the other way around.

Maybe this'll do: www.prehistoric-wildlife.com/species/b/basilosaurus.html

[Infinity Blade]

Well, I know Prehistoric Wildlife may claim this, but it didn't give a citation for that claim, so I still can't take really take it at face value.

[creature386]

I've found this when researching estimates on Basilosaurus' mass:
link.springer.com/article/10.1007/s10914-015-9304-y
It provides an allometric equation not applicable to Basilosaurus and has a table with the body masses of a select amount of specimens. The largest is 20 t. Although it is listed as Dorudon atrox, the text notes that it was likely a Basilosaurus.

[elosha11]

creature386, nice find. 20 tons at 17 to 20 meters? That's incredibly gracile. I would have thought an adult would have been at least 30 tons at that length. But what was the estimated length of the specimen? Perhaps it wasn't max size.

[Grey]

Markus Buhler worked a lot on Basilosaurus and deduced a similar weight by sculpting a rigorous model.

The question is the max length, some sources suggest at least 21 m.

[elosha11]

Basilosaurus really is basically a whale/snake. Incredibly long and thin/light animal. I'm sure that was a function of its adaption to its environment, but it seems quite unique - and at odds with - the remainder of cetacean development.

[Infinity Blade]

Biogeographic, stratigraphic, and environmental distribution of Basilosaurus (Mammalia, Cetacea) in North America with a review of the late Eocene shoreline in the southeastern coastal plain

A new specimen of Basilosaurus cetoides was discovered on the banks of the Flint River in Albany, Georgia, USA, in 2010. This fossil, which was the most complete specimen of the species from Georgia to date, consisted of five nearly complete and two partial post-thoracic vertebrae, tentatively identified as S4 through Ca6. During excavation, however, the site was looted and most of the specimen was lost to science. Nonetheless, we use this discovery as an opportunity to update the current state of knowledge on the stratigraphic, biogeographic, and environmental distribution of Basilosaurus in North America, as well as the position of the late Eocene shoreline in the southeastern United States. The results show that Basilosaurus was most abundant across the southeastern coastal plain during the early to middle Priabonian, coincident with the late Eocene maximum marine transgression. The decline in Basilosaurus localities is associated with the retreating shoreline of the terminal Eocene. The majority of Basilosaurus localities fall well south of the position of the late Eocene shoreline hypothesized in this study, suggesting the genus favored middle to outer neritic zones of the epicontinental sea. The comparatively low number of Priabonian specimens in the Atlantic Coastal Plain versus the Gulf Coastal Plain, then, suggests the presence of shallow zones in the Atlantic Coastal Plain that may have limited the distribution of Basilosaurus across the region. The hypothesized shoreline of this study ultimately differs from earlier reconstructions by extending the Mississippi embayment at the Bartonian/Priabonian boundary farther north than previously noted.

www.cambridge.org/core/journals/journal-of-paleontology/article/abs/biogeographic-stratigraphic-and-environmental-distribution-of-basilosaurus-mammalia-cetacea-in-north-america-with-a-review-of-the-late-eocene-shoreline-in-the-southeastern-coastal-plain/5DAA31E6C6D4EB745D22FC6F837AC0A8