| Maiacetus Temporal range: Middle Eocene, | |
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| Maiacetus skeleton cast at Musee d'Histoire Naturelle, Brussels | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Infraorder: | Cetacea |
| Family: | † Protocetidae |
| Subfamily: | † Protocetinae |
| Genus: | † Maiacetus Gingerich et al., 2009 |
| Species | |
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Maiacetus ("mother whale") is a genus of early cetacean from the Habib Rahi Formation of Pakistan.
The genus contains a single species, Maiacetus inuus, first described in 2009 on the basis of two specimens, including a specimen which has been interpreted as a pregnant female and her fetus. [1] This represents the first description of a fetal skeleton of an archaeocete. The position of the fetus (head-first) suggests that the animal gave birth on land. [2] Modern whales generally give birth tail first, while land mammals give birth head first. That the Maiacetus should give birth on land is not so implausible because this whale is semiaquatic or amphibious. Maiacetus represents the transition of land mammals back to the oceans where these animals were living on the land-sea interface and going back and forth. [3]
However, Hans Thewissen, discoverer of Ambulocetus , has questioned these conclusions, suggesting that the smaller skeleton could be a partially digested meal. Even if the small skeleton is a fetus, Thewissen writes that it may not have been preserved in its normal in-vivo position. [4] Authors pointed out in the original article, however, that the fetal skull has no tooth marks. [1]
The hip bones were strong, suggesting that Maiacetus was able to walk on land; however, the short legs and flat digits would've made walking difficult. Looking at the flattened finger and toe bones, scientists have come to the conclusion that Maiacetus had webbed feet and was most likely amphibious. The teeth of the preserved fossils show similarity to the teeth of Basilosaurus , another genus of prehistoric cetaceans. The incisors are cone-like, linking Maiacetus to modern toothed whales and other extinct cetaceans. The middle ear bones are also similar to those of Basilosaurus and modern whales. [5]
This species is medium-sized with a skeleton 2.6 metres (8.5 ft) in length and an estimated weight of 280 to 390 kilograms (620 to 860 lb). Males are slightly larger than females; of the two adult skeletons found, the one interpreted as male was about 12% larger than the one interpreted as female. [1]
Cetacea is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel themselves through the water with powerful up-and-down movement of their tail which ends in a paddle-like fluke, using their flipper-shaped forelimbs to maneuver.
Rodhocetus is an extinct genus of protocetid early whale known from the Lutetian of Pakistan. The best-known protocetid, Rodhocetus is known from two partial skeletons that taken together give a complete image of an Eocene whale that had short limbs with long hands and feet that were probably webbed and a sacrum that was immobile with four partially fused sacral vertebrae. It is one of several extinct whale genera that possess land mammal characteristics, thus demonstrating the evolutionary transition from land to sea.
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 species included were fox to wolf-sized.
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 southeastern 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. The second species named in 1904, B. isis, lived in the region currently known as the Mediterranean Sea, with fossils found in North Africa and Jordan.
Basilosauridae is a family of extinct cetaceans that lived during the middle to late Eocene. Basilosaurids are known from all continents including Antarctica, and are probably the first fully aquatic cetaceans. The group is noted to be a paraphyletic assemblage of stem group whales from which the monophyletic Neoceti are derived.
Dorudon ("spear-tooth") is a genus of extinct basilosaurid ancient whales that lived alongside Basilosaurus 41.03 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.
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.
Pycnodus is an extinct genus of ray-finned fish from the Eocene period. It is wastebasket taxon, although many fossils from Jurassic or Cretaceous are assigned to this genus, only Eocene species, P. apodus is valid. As its name suggests, it is the type genus of Pycnodontiformes.
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.
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.
Indohyus is an extinct genus of digitigrade even-toed ungulates known from Eocene fossils in Asia. This small chevrotain-like animal found in the Himalayas is one of the earliest-known non-cetacean ancestors of whales.
Zygophyseter varolai is an extinct sperm whale that lived during the Tortonian age of the Late Miocene 11.2 to 7.6 million years ago. It is known from a single specimen from the Pietra Leccese Formation in Italy. It was a member of a stem group of fossil macroraptorial sperm whales also including Brygmophyseter, Acrophyseter, and Livyatan. It probably grew to be around 6.5 to 7 meters in length and shared some characteristics with other raptorials, such as large teeth with tooth enamel that were functional in both the upper and lower jaws which the modern sperm whale lacks. It also had a beak, the ability to echolocate prey, and could have probably swum faster than the modern-day sperm whale which can reach 4 kilometers per hour (2.5 mph). These were probably used in the capture of large prey, such as large fish, seals, and whales. In fact, its common name, the killer sperm whale, refers to its feeding habits that would have had a resemblance to the modern-day killer whale.
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.
Protocetidae, the protocetids, form a paraphyletic, diverse and heterogeneous group of extinct cetaceans known from Asia, Europe, Africa, South America, and North America.
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.
Ankylorhiza is an extinct genus of toothed whale that lived in what is now the United States during the Oligocene epoch, between 29 and 23.5 million years ago. The type and only known species is A. tiedemani, though two fossil skeletons may represent an additional, second species within the genus. Ankylorhiza was about 4.8 meters (16 ft) long, with a long, robust skull bearing conical teeth that were angled forwards at the tip of the snout.
Archaeocete genera by family | |||||||
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| Pakicetidae | |||||||
| Ambulocetidae | |||||||
| Remingtonocetidae | |||||||
| Protocetidae |
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| Basilosauridae |
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