Gazelle : The Palestinian Biological Bulletin (ISSN 0178 – 6288) . Number 134, February 2016, pp. 1-44. | Page 7

7

Anatomy
Measuring 12–20 m (40–65 ft), Basilosaurus cetoides is the largest known ocean
animal of the Late Eocene. B. isis is slightly smaller than B. cetoides (Wikipedia).

Cranium
The dental formula for Basilosaurus isis is 3.1.4.2 (Upper) and 3.1.4.3 (Lower). The
upper and lower molars and second to fourth premolars are double rooted and
high-crowned (Wikipedia).
The head of Basilosaurus did not have room for a melon like modern day toothed
whales, and the brain was smaller in comparison as well. It is believed that they
therefore did not have the social capabilities of modern whales (Wikipedia).
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
whale 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).
In the Basilosaur skull, the inner and middle ear are enclosed by a dense
tympanic bulla. The synapomorphic cetacean air sinus system is partially present
in basilosaurids, including the pterygoid, peribullary, maxillary, and frontal
sinuses. 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 (Wikipedia).
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, even-though this was probably functional, it can have been of
little use under water (Wikipedia).

Spine
No complete Basilosaurus skeleton is known, but 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 non-overlapping
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 7 cervical, 18 thoracic, 20 lumbar and
sacral, and 25 caudal vertebrae. It can be assumed that the vertebral formula of B.
cetoides is the same (Wikipedia).
Gazelle : The Palestinian Biological Bulletin – Number 134 – February 2016