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Animal Database
Animal Database
Basilosaurus cetoides
Basilosaurus cetoides skeleton
Scientific Classification
Kingdom Animalia
Phylum Chordata
Class Mammalia
Order Cetacea
Family †Basilosauridae

Basilosauridae is a paraphyletic family of extinct cetaceans that lived during the late middle to the early late Eocene, known from all continents. They were probably the first fully aquatic cetaceans.


Basilosaurids ranged in size from 4 to 16 m (13 to 52 ft). Like all arachaeocetes, they lacked the telescoping skull of modern whales. Their dentition is easily distinguishable from that of other archaeocetes: they lack upper third molars and the upper molars lack protocones, trigon basins, and lingual third roots. The cheek teeth have well-developed accessory denticles. The hindlimbs are strongly reduced and does not articulate with the vertebral column which lack true sacral vertebrae.

Basilosaurid forelimbs have broad and fan-shaped scapulae attached to a humerus, radius, and ulna which are flattened into a plane to which the elbow joint was restricted, effectively making pronation and supination impossible. Because of a shortage of forelimb fossils from other arachaocetes, it is not known if this arrangement is unique to basilosaurids. Some of the characteristics of basilosaurids are also present in Georgiacetus.

Genus Basiloterus[]

Basiloterus husseini was a late Eocene primitive whale. As with all other members of Basilosauridae, it was a hypercarnivorous predator.

Fossil finds[]

Basiloterus husseini is the closest known relative of Basilosaurus, but was not as large or elongated. Basiloterus husseini is found in late Eocene strata of Pakistan.

Genus Ancalecetus[]

Ancalecetus (from Greek ankale, "bent arm", and ketos, "whale") is an extinct genus of early whale known from the Late Eocene (Priabonian, 37.2 to 33.9 million years ago) Birket Qarun Formation (29.3°N 30.0°E, paleocoordinates 24.6°N 26.2°E) in Wadi Al-Hitan, Egypt. The species is named after anthropologist and primate researcher Elwyn L. Simons who discovered the type specimen in 1985.


Tooth wear show that Ancalecetus, like other basilosaurids, fed on larger prey, probably fish, that required mastication before swallowing and that the type specimen survived into adulthood. The unfused mandibular symphysis reaches as far posteriorly as P2. The large mandibular foramina, which contain the auditory fat pad in modern whales, is very well-preserved in Ancalecetus.


The well-preserved forelimbs are the most distinctive parts of A. simonsi. A broad scapula and a ball-and-socket shoulder joint is characteristic of cetaceans, but Ancalecetus lacks both.

The interior surface of the narrow scapula is not broadly curved as in most cetaceans, but tightly curved. The roughened vertebral border suggests the presence of a cartilaginous extension that extends the surface of the scapula like in modern cetaceans. Compared to other cetaceans, the infraspinous fossa is smaller, the caudal border is less curved and not oriented posteriorly. The glenoid cavity is very shallow and directed posteriorly, rather than ventrally like in other cetaceans. Likewise, the oddly folded acromion is pointing ventrally and posteriorly, and not anteriorly as in other cetaceans.

Unlike in other basilosaurids, the humerus of Ancalecetus is flattened and has a relatively small head. The distal end has flat, textured surfaces for the articulation of the radius and ulna; these bones are fused on the left limb and tightly fitting and the right side, and neither permitted motion at the elbow joint.

Genus Chysocetus[]

Chrysocetus healyorum is an extinct basilosaurid whale described on the basis of a single subadult specimen from the late middle or early late Eocene of Orangeburg County, South Carolina (33.3°N 80.4°W, paleocoordinates 33.3°N 72.5°W).

The type specimen includes: a partial skull; hyoid apparatus; lower jaws; teeth; all cervical, some thoracic and some lumbar vertebrae; ribs and sternum; left forelimb elements; and pelves. The specimen includes portions of much of the body, but while some of the bones are fairly complete, others are damaged, particularly the skull. The pelves resemble those of Basilosaurus, documenting a similar stage of hind limb reduction in dorudontines and suggesting that Chrysocetus was not able to support its body on land. The acetabulum for articulation of the femur is well formed and indicates that the hip joint was functional. Chrysocetus is distinguishable from other described dorudontines based on body size, characteristics of the teeth, and forelimb elements. Absence of deciduous teeth in a subadult individual of Chrysocetus may be indicative of an early stage of the evolution of monophyodonty.

Genus Mascracetus[]

Masracetus (from Arabic Masr, "Egypt", and Greek ketos, "whale") is an extinct genus of basilosaurid ancient whale known from the Late Eocene (Priabonian, 37.2 to 33.9 million years ago) of Egypt.

Masracetus was briefly described in an addendum by Gingerich 2007 and is known from just an assemblage of vertebrae and a poorly reconstructed skull from 1908. The lumbar vertebrae are large but relatively short (anteroposteriorly) compared to those of other archaeocetes; the diameter is almost the same as for Basilosaurus isis but the length is less than half of the latter. Masracetus is larger than Cynthiacetus.

The species name honours Richard Markgraf, palaeontologist Ernst Stromer's fossil collector, who collected the type specimen in 1905.

Masracetus' type locality is the Birket Qarun Formation in Dimê (29.5°N 30.7°E, paleocoordinates 24.9°N 26.6°E) north of lake Birket Qarun, but specimens have also been found in the Qattara Depression and Fayum.

Genus Saghacetus[]

Saghacetus is an extinct genus of basilosaurid early whale, fossils of which have been found in the Upper Eocene (middle Priabonian, 37.2 to 33.9 million years ago) Qasr el Sagha Formation, Egypt (29.7°N 30.8°E, paleocoordinates 25.0°N 26.7°E).

The name Saghacetus was established by Gingerich 1992 to group the ancient species Dorudon osiris, D. zitteli, D. sensitivius and D. elliotsmithii on a single species, Saghacetus osiris. This species is distinguished from other members of the subfamily Dorudontinae by its smaller size and the slightly elongated proximal lumbar and caudal vertebrae.

Saghacetus is smaller than its contemporary Stromerius, both of which are smaller than the older Dorudon.

Genus Stromerius[]

Stromerius is an extinct genus of basilosaurid early whale known from the Late Eocene (Priabonian, 37.2 to 33.9 million years ago) of Fayum, Egypt (29.6°N 30.6°E, paleocoordinates 24.9°N 26.5°E).

Stromerius is known from several well-preserved vertebrae. Distinguishing features for the genus include: long and forward-pointing metapophyses (bony processes) on the lumbar vertebrae; a relatively short lumbar spine with only twelve vertebrae of which four are interpreted as homologous to sacral vertebrae; one of the two thoracic vertebrae found has a dorsally-pointing neural spine interpreted as anticlinal (i.e. the spines of the other vertebrae are inclined towards this specific vertebra) which is a primitive retention in Stromerius not present in other basilosaurids. Stromerius is larger than the contemporary Saghacetus but smaller than the older Dorudon.

Genus Zygorhiza[]

Zygorhiza kochii ("Koch's Yoke-Root") is an extinct species of cetacean.


Zygorhiza was a smaller, less elongated, 6 m (20 ft) long relative of the famous Basilosaurus. Its bodily proportions were similar to those of modern whales, although, unlike modern species, it had a distinct neck, and flippers which could be moved at the elbow. Its hind limbs were rudimentary. Zygorhiza's 1 m (3 ft 3 in) skull had fearsome jaws with deadly teeth. Unlike modern cetaceans, it had a neck with seven vertebrae.

State symbol[]

Zygorhiza kochii is the state fossil of Mississippi. The mounted specimen in the Mississippi Museum of Natural Science in Jackson is commonly referred to as "Ziggy".


Family Basilosauridae

 Genus Supayacetus
 Genus Ocucajea  
 Genus Basilotritus
Subfamily Basilosaurinae
 Genus Basilosaurus 
  B. cetoides
  B. drazindai
  B. isis
  B. wanklyni
  B. vredensis
  B. caucasicus
  B. paulsoni
  B. puschi
  B. harwoodi
 Genus Basiloterus
  B. husseini
Subfamily Dorudontinae 
 Genus Ancalecetus
  Ancalecetus simonsi
 Genus Chrysocetus
  Chrysocetus healyorum
 Genus Cynthiacetus
  Cynthiacetus maxwelli
  Cynthiacetus peruvianus
 Genus Dorudon
  Dorudon atrox
  Dorudon serratus
 Genus Masracetus
  Masracetus markgrafi
 Genus Pontogeneus
  Pontogeneus brachyspondylus
 Genus Saghacetus
  Saghacetus osiris
 Genus Stromerius
  Stromerius nidensis
 Genus Zygorhiza
  Zygorhiza kochii
Subamily Kekenodontinae
 Genus Kekenodon 
 Genus Phococetus