Name: Basilosaurus
(King lizard).
Phonetic: Ba-sil-oh-sore-us.
Named By: Richard Harlan - 1847.
Synonyms: Zeuglodon.
Classification: Chordata, Mammalia, Cetacea,
Archaeoceti, Basilosauridae.
Species: B. cetoides (type),
B.
drazindai, B. harwoodi, B. isis, B. caucasicus, B.
paulsoni, B. puschi, B. vredensis, B. wanklyni.
Type: Carnivore.
Size: Average 18 meters long, but size is
dependent on species.
Known locations: USA. Egypt, Wadi Al-Hitan.
Pakistan.
Time period: Bartonian to Priabonian of the Eocene.
Fossil representation: Lots of known specimens.
The
one thing
about Basilosaurus that instantly causes confusion
is its name. When
first studied and named by Richard Harlan, he came to the conclusion
that it was most likely a marine reptile, and so named it
Basilosaurus, or ‘King lizard’. It was not
until the remains
were studied by Richard Owen that they were confirmed as
mammalian. Owen then proposed that Basilosaurus
should be renamed
Zeuglodon (Yoke teeth), but because Basilosaurus
was the
officially registered name, it could not be changed, so Zeuglodon
became a synonym instead of a replacement.
Basilosaurus
represents one
of the earliest whales
although its actually descended from terrestrial
mammals like Ambulocetus.
Evidence for this can be seen in the
flippers. The front flippers still have an elbow joint, something
that today is only seen in seals. The back flippers where the hind
legs would have been in its ancestor are greatly reduced and although
they may have been used to get extra grip on a mate, they would
eventually disappear in later whales. The size of its flippers in
comparison with the massive bulk of its body means that it was almost
certainly an entirely pelagic animal.
The
large jaws of
Basilosaurus housed teeth suitable for catching prey
that would not
have been especially small, perhaps smaller whales or large fish that
while smaller than Basilosaurus, but were still
too large for most
other predators to tackle. Superficially the fossils of Basilosaurus
skulls resemble the skulls of mosasaurs
that swam the oceans tens of
millions of years earlier, disappearing from the fossil record at the
time of the KT extinction 65 million years ago. It is partly for
this reason that Basilosaurus was misidentified as
a reptile because
mosasaur remains were known, yet no one was aware that the early
whales looked so similar. The skull also has a reduced area for the
brain when compared to modern whales. Going on the basis that larger
brained cetaceans are typically more social, Basilosaurus
itself may
have been a solitary predator.
Although
not preserved, the
structure of the tail vertebrae suggests support for a tail fluke as
seen in modern cetaceans. The reduced limbs would probably have
been of
little use in actual locomotion leading to the suggestion that
Basilosaurus used an undulating motion to propel
itself in the water.
This up and down motion may have also provided quick bursts of speed
at prey items.
Study
of the Basilosaurus
skeleton has revealed that it was quite restricted in terms of
movement. Muscle attachments along the spine imply that Basilosaurus
had relatively weak muscles and could neither dive deep nor swim for
extended periods, at least at what may have been pursuit speed for
prey. The vertebrae, unlike modern whales which are solid, were
hollow and likely filled with fluid. This is not an adaptation for a
deep sea creature, as pressure imbalance between the fluid in the
hollow vertebrae and stronger pressure of deep water outside could in
theory cause spinal injury with the vertebrae being crushed if the
pressure became too much. Together, these all point to an animal
that only swam and hunted in waters near the surface.
In
1845, Dr Albert Koch
constructed a composite animal from numerous specimens of Basilosaurus
remains. This composite was named Hydrarchos and
went on a touring
display around the world until its destruction in the Great Chicago
fire in 1871. Aside from never existing, the material was
presented as a sea serpent, not a whale. Also not only was their
more than one Basilosaurus individual used in the
construction,
fossils from other animals were also included. Despite the fact that
other scientists of the time were quick to point out that it did not
represent a real creature, references to it as a real animal are
still sometimes made by those who are not knowledgeable about this
history, although thankfully this is getting rarer.
Further reading
- Hind limbs of eocene Basilosaurus: evidence of
feet in whales".
Science. 249 (4965): 154–157. - Philip D. Gingerich, B. Holly Smith
& Elwyn L. Simons - 1990.
- 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). - Contributions from
the Museum of Paleontology, University of Michigan. 30 (2): 55–81. - P.
D. Gingerich, M. Arif, M. Akram Bhatti, M. Anwar & William J.
Sanders - 1997.
- Priabonian Basilosaurus isis (Cetacea) from the
Wadi Esh-Shallala
Formation: first marine mammal from the Eocene of Jordan. - Journal of
Vertebrate Paleontology. 20 (1): 201–204. I. S. Zalmout, H. A. Mustafa
& P. D. Gingerich - 2000.
- Cranial asymmetry in Eocene archaeocete whales and the evolution of
directional hearing in water. - PNAS. 108 (35): 14545–14548. - Julia M.
Fahlke, Philip D. Gingerich, Roert C. Welsh & Aaron R. Wood -
2011.
- Bite marks revisited – evidence for middle-to-late Eocene
Basilosaurus isis predation on Dorudon atrox (both
Cetacea,
Basilosauridae). - Palaeontologia Electronica. 15 (3). - Julia M.
Fahlke - 2012.
- Basilotritus uheni, a New Cetacean (Cetacea,
Basilosauridae) from the
Late Middle Eocene of Eastern Europe. - Journal of Paleontology. 87
(2): 254–268. - Pavel Gol'din & Evgenij Zvonok - 2013.
- 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. - E. Snively, J. M. Fahlke & R. C.
Welsh - 2015.
- Stomach contents of the archaeocete Basilosaurus isis: Apex predator
in oceans of the late Eocene. - PLOS ONE. 14 (1). e0209021. - Manja
Voss, Mohammed Sameh M. Antar, Iyad S. Zalmout & Philip D.
Gingerich - 2019.