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.
The evolution of cetaceans is thought to have begun in the Indian subcontinent from even-toed ungulates (Artiodactyla) 50 million years ago (mya) and to have proceeded over a period of at least 15 million years. Cetaceans are fully aquatic mammals belonging to the order Artiodactyla and branched off from other artiodactyls around 50 mya. Cetaceans are thought to have evolved during the Eocene, the second epoch of the present-extending Cenozoic Era. Molecular and morphological analyses suggest Cetacea share a relatively recent closest common ancestor with hippopotami and that they are sister groups. Being mammals, they surface to breathe air; they have five finger bones (even-toed) in their fins; they nurse their young; and, despite their fully aquatic life style, they retain many skeletal features from their terrestrial ancestors. Research conducted in the late 1970s in Pakistan revealed several stages in the transition of cetaceans from land to sea.
Ambulocetus is a genus of early amphibious cetacean from the Kuldana Formation in Pakistan, roughly 48 or 47 million years ago during the Early Eocene (Lutetian). It contains one species, Ambulocetus natans, known solely from a near-complete skeleton. Ambulocetus is among the best-studied of Eocene cetaceans, and serves as an instrumental find in the study of cetacean evolution and their transition from land to sea, as it was the first cetacean discovered to preserve a suite of adaptations consistent with an amphibious lifestyle. Ambulocetus is classified in the group Archaeoceti—the ancient forerunners of modern cetaceans whose members span the transition from land to sea—and in the family Ambulocetidae, which includes Himalayacetus and Gandakasia.
Ambulocetidae is a family of early cetaceans from Pakistan. The genus Ambulocetus, after which the family is named, is by far the most complete and well-known ambulocetid genus due to the excavation of an 80% complete specimen of Ambulocetus natans. The other two genera in the family, Gandakasia and Himalayacetus, are known only from teeth and mandibular fragments. Retaining large hindlimbs, it was once thought that they could walk on land—indeed, their name means "walking whales"—, but recent research suggests they may have been fully aquatic like modern cetaceans. Though the research has some limits that cast doubt on this conclusion.
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.
Pilgrimella is an extinct early Eocene genus of anthracobunid, a group of stem perissodactyls. It was a ground dwelling grazer with massive bilophodont molars Dental remains of this animal have been found in Chorlakki, Punjab province, Pakistan, and in the Subathu Formation in North-West India.
Pakotitanops is a genus of poorly known brontothere represented only by a few tooth fragments. Its fossil dates from the middle Eocene Kuldana Formation, in the Ganda Kas area of Pakistan. Because this species is known only from a few tooth fragments it is difficult to compare it to other species to determine if it is indeed a distinct species and to what other species it is mostly closely related.
Pakicetus is an extinct genus of amphibious cetacean of the family Pakicetidae, which was endemic to Indian Subcontinent during the Ypresian period, about 50 million years ago. It was a wolf-like mammal, about 1–2 m long, and lived in and around water where it ate fish and other animals. The name Pakicetus comes from the fact that the first fossils of this extinct amphibious whale were discovered in Pakistan. The vast majority of paleontologists regard it as the most basal whale, representing a transitional stage between land mammals and whales. It belongs to the even-toed ungulates with the closest living non-cetacean relative being the hippopotamus.
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.
Protocetus atavus is an extinct species of primitive cetacean from Egypt. It lived during the middle Eocene period 45 million years ago. The first discovered protocetid, Protocetus atavus was described by Fraas 1904 based on a cranium and a number of associated vertebrae and ribs found in middle Lutetian Tethyan marine limestone from Gebel Mokattam near Cairo, Egypt.
Himalayacetus is an extinct genus of carnivorous aquatic mammal of the family Ambulocetidae. The holotype was found in Himachal Pradesh, India, in what was the remnants of the ancient Tethys Ocean during the Early Eocene. This makes Himalayacetus the oldest archaeocete known, extending the fossil record of whales some 3.5 million years.
Nalacetus is an extinct pakicetid early whale, fossils of which have been found in Lutetian red beds in Punjab, Pakistan. Nalacetus lived in a fresh water environment, was amphibious, and carnivorous. It was considered monophyletic by Cooper, Thewissen & Hussain 2009. It was said to be wolf-sized and one of the earliest forms of the order Cetacea.
Ichthyolestes is an extinct genus of archaic cetacean that was endemic to Indo-Pakistan during the Lutetian stage. To date, this monotypic genus is only represented by Ichthyolestes pinfoldi.
Kutchicetus is an extinct genus of early whale of the family Remingtonocetidae that lived during Early-Middle Eocene in what is now the coastal border of Pakistan and India. It is closely related to Andrewsiphius with which it was synonymized by Gingerich et al. 2001. Thewissen & Bajpai 2009 proposed a new clade, Andrewsiphiinae, for the two species. Later authors, however, still accept both as separate genera.
The Raoellidae, previously grouped within Helohyidae, are an extinct family of semiaquatic digitigrade artiodactyls in the clade Whippomorpha. Fossils of raoellids are found in Eocene strata of South Asia and Southeast Asia.
Remingtonocetus is an extinct genus of early cetacean freshwater aquatic mammals of the family Remingtonocetidae endemic to the coastline of the ancient Tethys Ocean during the Eocene. It was named after naturalist Remington Kellogg.
Remingtonocetidae is a diverse family of early aquatic mammals of the order Cetacea. The family is named after paleocetologist Remington Kellogg.
Attockicetus is an extinct genus of remingtonocetid early whale known from the Middle Eocene (Lutetian) Kuldana Formation in the Kala Chitta Hills, in the Attock District of Punjab, Pakistan.
Johannes Gerardus Marie (Hans) Thewissen is a Dutch-American paleontologist known for his significant contributions to the field of whale evolution. Thewissen's fieldwork has led to the discovery of key fossils that have shed light on the transition of whales from land to water, including the discovery of Ambulocetus, Pakicetus, Indohyus, and Kutchicetus. In addition to his work on fossil discoveries, Thewissen also studies modern bowhead and beluga whales in Alaska, focusing on their biology and the implications of this knowledge for management and conservation efforts. His research has been instrumental in deepening our understanding of cetacean evolution and the adaptations that allowed these mammals to transition from terrestrial to fully aquatic lifestyles.
The Kuldana Formation is a fossil-bearing geological formation of Lutetian age which crops out in northern Pakistan. The abundant fossil remains were deposited by rivers and estuaries crossing an arid to semi-arid environment, between several marine transgressions. Its fossil fauna is best known for the early cetaceans Indohyus, Pakicetus and Ambulocetus, that helped to shed a new light on the evolution of whales, but it also features a large number of early ungulates, rodents and primates.
