Pakicetidae is an extinct family of Archaeoceti that lived during the Early Eocene in Pakistan. Unlike modern cetaceans, they had well-developed limbs and were capable of walking.
Basilosaurus is a genus of large, predatory, prehistoric archaeocete whale from the late Eocene, approximately 41.3 to 33.9 million years ago (mya). First described in 1834, it was the first archaeocete and prehistoric whale known to science. Fossils attributed to the type species B. cetoides were discovered in the United States. They were originally thought to be of a giant reptile, hence the suffix "-saurus", Ancient Greek for "lizard". The animal was later found to be an early marine mammal, prompting attempts at renaming the creature, which failed as the rules of zoological nomenclature dictate using the original name given. Fossils were later found of the second species, B. isis, in 1904 in Egypt, Western Sahara, Morocco, Jordan, Tunisia, and Pakistan. Fossils have also been unearthed in the southeastern United States and Peru.
Dorudon ("spear-tooth") is a genus of extinct basilosaurid ancient whales that lived alongside Basilosaurus 40.4 to 33.9 million years ago in the Eocene. It was a small whale, with D. atrox measuring 5 metres (16 ft) long and weighing 1–2.2 metric tons. Dorudon lived in warm seas around the world and fed on small fish and mollusks. Fossils have been found along the former shorelines of the Tethys Sea in present-day Egypt and Pakistan, as well as in the United States, New Zealand and Western Sahara.
Archaeoceti, or Zeuglodontes in older literature, is a paraphyletic group of primitive cetaceans that lived from the Early Eocene to the late Oligocene. Representing the earliest cetacean radiation, they include the initial amphibious stages in cetacean evolution, thus are the ancestors of both modern cetacean suborders, Mysticeti and Odontoceti. This initial diversification occurred in the shallow waters that separated India and Asia 53 to 45 mya, resulting in some 30 species adapted to a fully oceanic life. Echolocation and filter-feeding evolved during a second radiation 36 to 35 mya.
Zygorhiza ("Yoke-Root") is an extinct genus of basilosaurid early whale known from the Late Eocene of Louisiana, Alabama, and Mississippi, United States, and the Bartonian to the late Eocene of New Zealand . Specimens reported from Europe are considered Dorudontinae incertae sedis.
Cynthiacetus is an extinct genus of basilosaurid early whale that lived during the Late Eocene Specimens have been found in the southeastern United States and Peru.
Remingtonocetidae is a diverse family of early aquatic mammals of the order Cetacea. The family is named after paleocetologist Remington Kellogg.
Gaviacetus is an extinct archaeocete whale that lived approximately 45 million years ago. Gaviacetus was named for its characteristic narrow rostrum and the fast pursuit predation suggested by its unfused sacral vertebrae.
Basiloterus is an extinct genus of late-Eocene archaeocete whale from the Drazinda Formation in southwestern Punjab, Pakistan and possibly also the Barton Group of England. Known from two isolated lumbar vertebrae, the elongated nature of these elements has been taken as possible evidence that Basiloterus was a close relative of the better-known Basilosaurus. This was also the reasoning behind its name, which roughly translates to "another king". However, publications since then not only lead to some major changes of the internal relationships within Basilosauridae but have also called into question how diagnostic elongated vertebrae are for members of this group, as other early whales have developed similar anatomy independently. Though the identity of Basiloterus as a basilosaurid is generally maintained, its exact position within more recent interpretations of the family is unclear.
Chrysocetus is a genus of extinct archaeocete ceteceans belonging to the Basilosauridae that is known from the Late Eocene of the eastern United States and western Africa. Across its range two species are known, the American Chrysocetus healyorum and the African Chrysocetus fouadassii, named in 2001 and 2015 respectively. Chrysocetus was a comparably small basilosaurid, larger than Saghacetus and Tutcetus but smaller than most other members of this group. In addition to being noted for its well preserved hip bones, Chrysocetus is unique amongst basilosaurids for possibly having only had a single set of teeth. Though the fusion of the skeleton indicate that the holotype was a juvenile or subadult, the teeth represent the adult condition, having lead to the hypothesis that unlike other basilosaurids and like modern whales, Chrysocetus did not replace its teeth but rather kept a single set throughout its life.
The Qasr el Sagha Formation is a geological formation located in Egypt. The formation is part of the Wadi El Hitan World Heritage Site. The Qasr el Sagha Formation overlies the Birket Qarun Formation and is overlain by the Gebel Qatrani Formation. The sandstones and shales of the formation were deposited in a deltaic to shallow marine environment. It dates to the Late Eocene.
Pontogeneus is a genus of extinct cetacean known from fossils recovered from the Late Eocene sediments of the southeastern United States.
Basilosaurinae is a subfamily of cetaceans archaeocetes containing two genera: Basilosaurus and Basiloterus. They were characterized by elongated distal thoracic vertebrae, lumbar, and proximal sacrococcygeal. All known members of the subfamily are larger than their relatives of the Dorudontinae subfamily except Cynthiacetus.
Saghacetus is an extinct genus of basilosaurid early whale, fossils of which have been found in the Upper Eocene Qasr el Sagha Formation, Egypt.
Supayacetus is an extinct genus of basilosaurid cetacean from the Middle Eocene Paracas Formation of Peru. It has been noted for its relatively small size and basal morphology, with the sternum bearing close resemblance to those of protocetids. Due to this, it has been traditionally placed as one of the basalmost basilosaurids, except for a 2023 study that places it within the family Pachycetinae close to Neoceti. Supayacetus is monotypic, meaning the genus includes only a single species: S. muizoni.
Babiacetus is an extinct genus of early cetacean that lived during the late Lutetian middle Eocene of India . It was named after its type locality, the Harudi Formation in the Babia Hills, Kutch District, Gujarat, India.
Masracetus is an extinct genus of basilosaurid ancient whale known from the Late Eocene of Egypt.
Eocetus is an extinct protocetid early whale known from the early-late Eocene Giushi Formation in Gebel Mokattam, outside Cairo, Egypt. Fossil remains have also been discovered in the Aridal Formation of the Sahara Desert in southwestern Morocco.
Pachycetinae is an extinct subfamily of basilosaurid cetaceans that lived during the middle Eocene. The best-dated remains stem from Bartonian strata, but some finds suggest that they could have first appeared during the Lutetian and may have survived until the Priabonian. Fossils of pachycetines are chiefly known from the southern United States, Ukraine, Morocco and Germany, among others. They differ from other basilosaurids in having pachyostotic and osteosclerotic vertebrae and ribs, making them denser and heavier by comparison. Based on this it has been suggested that these whales lived in shallow waters and that these thickened bones act as a buoyancy control as seen in sirenians. Analysis of the teeth suggests that pachycetines had a varying diet, with the robust teeth of the larger Pachycetus indicating that it possibly fed on sharks, whereas the more gracile teeth of Antaecetus suggest a diet of smaller prey items. The clade currently only includes two genera, Antaecetus and Pachycetus, but a 2023 study suggests that the Peruvian Supayacetus may at least be a close relative.
