| Mammalodon Temporal range: Late Oligocene, | |
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| Skull | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Infraorder: | Cetacea |
| Family: | † Mammalodontidae |
| Genus: | † Mammalodon Pritchard, 1939 |
| Species | |
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Mammalodon is an extinct genus of archaic baleen whale belonging to the family Mammalodontidae.
| Mammalodon within Mysticeti | |||||||||||||||||||||||||||||||||
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| Phylogenetic tree showing Mammalodon at the base of Mysticeti [1] |
The fossils of Mammalodon were found to be around 25.7–23.9 million years old, dating to the Late Oligocene. The holotype for M. colliveri, NMV P199986 though formerly MUGD 1874, is an incomplete skull of an adult individual collected in 1932 by George Baxter Pritchard, Alan Frostick, and Frederick Stanley Colliver—to which owes the species name—in Jan Juc, Victoria in Australia; specimen NMV P17535, consisting of a lower left molar, probably also belongs to NMV P199986. NMV P173220 consists of a left periotic bone. NMV P199587 is a partial skeleton, consisting of part of the head, spine, and arm; specimen NMV P198871, an ulna, very likely also belongs to NMV P199587. [1] The second species, M. hakataramea, was discovered in the Kokoamu Greensand of New Zealand. [2] [3] [4] Mammalodon fossils have been found in Australia and New Zealand
Mammalodon was, at first, considered to be a member of Archaeoceti, an ancient group of whales, which was evidenced by its apparent ancient features, such as the variety of differently shaped teeth in its jaw (heterodonty) that modern whales lack. Mammalodon was first considered to be a baleen whale in a 1982 study despite having no baleen; instead, they cited other similarities such as loosely sutured bones in the snout, a broad and flat roof of the mouth, and an unjointed mandibular symphysis between the two halves of the jawbone. It belongs to the family Mammalodontidae, along with Janjucetus . These whales and Llanocetus may form a clade of toothed baleen whales of the Southern Hemisphere, a sister clade to Aetiocetidae and more modern baleen-bearing baleen whales. [1]
The name Mammalodon is said to be derived from English mammal and Ancient Greek odontos tooth, meaning "mammal tooth", as its molar teeth are similar to those found in terrestrial carnivores. [1] The Ancient Greek for "tooth" is, however, odous (ὀδούς). [5]
Mammalodon, with a length of 3 metres (9.8 ft), was smaller and more primitive than modern baleen whales. [6] Unlike other baleen whales, Mammalodon had a blunt and rounded snout. The left maxilla—upper jaw—of specimen NMV P199986 preserved four premolars and three molars, and the space between the teeth (diastema) increased towards back into the mouth. The molars decreased in size back into the mouth, like in archaeocetes, and the bottom jaw had two more molars than the upper jaw. The specimen's lower jaw indicates it had 24 lower teeth in all, all tightly spaced together. The upper teeth all looked the same (monodonty), whereas the bottom teeth varied in shape (polydonty) which is an ancient characteristic of whales. There were three lower incisor teeth, and one upper incisor with possibly two or three vestigial incisors. The teeth were likely never replaced, and the whale had the same set of teeth throughout its life. The single upper incisor was markedly smaller than the other teeth, and smaller than the upper incisors of Janjucetus. The cheek teeth—molars and premolars—were all double-rooted, and the lower molars were serrated and triangular. [1] [7]
In the holotype of M. colliveri, only the second vertebra of the neck—the axis—is preserved. Unlike in modern baleen whales, but similar to archaeocetes and the ancient toothed baleen whale Aetiocetus , the breastbone is composed of several pieces. The top-most breastbone, the manubrium, is T-shaped and wider than is long like archaeocetes, but plate-like and compressed like modern baleen whales. Unlike in modern whales though similar to archaeocetes, the thyrohyoid bone of the hyoid apparatus used to hold up the tongue is large and tubular as opposed to plate-like. It probably had a fused mandibular symphysis linking the two halves of the jaw together, unlike in later and modern baleen whales. [1]
As with the closely related genus Janjucetus , Mammalodon lacked baleen, instead possessing well-developed teeth. As such, it was not able to filter-feed in the same manner as extant baleen whales, making its diet and ecological niche a mystery. [7] As the teeth are widely spaced, they may have developed a method of filter-feeding unlike that of other whales. It may have been a bottom filter feeder, its blunt snout helping to suck up organisms from the sea floor. [1]
Baleen whales, also known as whalebone whales, are a parvorder of carnivorous marine mammals of the infraorder Cetacea which use keratinaceous baleen plates in their mouths to sieve planktonic creatures from the water. Mysticeti comprises the families Balaenidae, Balaenopteridae (rorquals), Eschrichtiidae and Cetotheriidae. There are currently 16 species of baleen whales. While cetaceans were historically thought to have descended from mesonychians, molecular evidence instead supports them as a clade of even-toed ungulates (Artiodactyla). Baleen whales split from toothed whales (Odontoceti) around 34 million years ago.
Baleen is a filter-feeding system inside the mouths of baleen whales. To use baleen, the whale first opens its mouth underwater to take in water. The whale then pushes the water out, and animals such as krill are filtered by the baleen and remain as a food source for the whale. Baleen is similar to bristles and consists of keratin, the same substance found in human fingernails, skin and hair. Baleen is a skin derivative. Some whales, such as the bowhead whale, have longer baleen than others. Other whales, such as the gray whale, only use one side of their baleen. These baleen bristles are arranged in plates across the upper jaw of whales.
Incisors are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight. Opossums have 18, whereas armadillos have none.
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 marine 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 5 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.
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.
Janjucetus is an extinct genus of cetacean, and a basal baleen whale (Mysticeti), from the Late Oligocene around 25 million years ago (mya) off south-east Australia, containing one species J. hunderi. Unlike modern mysticetes, it possessed large teeth for gripping and shredding prey, and lacked baleen, and so was likely to have been a predator that captured large single prey animals rather than filter feeding. However, its teeth may have interlocked, much like those of the modern-day filter-feeding crabeater seal, which would have allowed some filter-feeding behaviour. Its hunting behaviour was probably similar to the modern-day leopard seal, probably eating large fish. Like baleen whales, Janjucetus could not echolocate; however, it did have unusually large eyes, and so probably had an acute sense of vision. The only specimen was found on the Jan Juc beach, where the remains of the extinct whales Mammalodon, Prosqualodon and Waipatia have also been discovered.
Mammalodontidae is a family of extinct whales known from the Oligocene of Australia and New Zealand.
Aetiocetus is a genus of extinct basal mysticete, or baleen whale that lived 33.9 to 23.03 million years ago, in the Oligocene in the North Pacific ocean, around Japan, Mexico, and Oregon, U.S. It was first described by Douglas Emlong in 1966 and currently contains known four species, A. cotylalveus, A. polydentatus, A. tomitai, and A. weltoni. These whales are remarkable for their retention of teeth and presence of nutrient foramina, indicating that they possessed baleen. Thus, Aetiocetus represents the transition from teeth to baleen in Oligocene mysticetes. Baleen is a highly derived character, or synapomorphy, of mysticetes, and is a keratinous structure that grows from the palate, or roof of the mouth, of the whale. The presence of baleen is inferred from the fossil record in the skull of Aetiocetus. Aetiocetus is known from both sides of the Pacific Ocean: it was first documented in Oregon, United States, but it is also known from Japan and Mexico. The genus is currently constrained to the Northern hemisphere and has little value in biostratigraphic studies of the Oligocene due to its limited occurrences across the Pacific.
Brygmophyseter, known as the biting sperm whale, is an extinct genus of toothed whale in the sperm whale family with one species, B. shigensis. When it was first described in 1994, the species was placed in the genus Scaldicetus based on tooth morphology, but this was later revised in 1995. In 2006, it was classified into the genus Naganocetus, which is considered to be a junior synonym. The only known specimen, a nearly complete skeleton, was dated to be around 16–15 million years old. Brygmophyseter is thought to have been 6.5–7 meters (21–23 ft) long, and it probably had 11 or 12 teeth in the upper and lower jaws. Brygmophyseter is part of a group of macroraptorial sperm whales which tended to be apex predators using their large teeth to catch struggling prey such as whales. It had a spermaceti organ which was probably used for biosonar like in the modern sperm whale. The whale has made an appearance on The History Channel's TV series Jurassic Fight Club.
Livyatan is an extinct genus of macroraptorial sperm whale containing one known species: L. melvillei. The genus name was inspired by the biblical sea monster Leviathan, and the species name by Herman Melville, the author of the famous novel Moby-Dick about a white bull sperm whale. It is mainly known from the Pisco Formation of Peru during the Tortonian stage of the Miocene epoch, about 9.9–8.9 million years ago (mya); however, finds of isolated teeth from other locations such as Chile, Argentina, United States (California), South Africa and Australia imply that either it or a close relative survived into the Pliocene, around 5 mya, and may have had a global presence. It was a member of a group of macroraptorial sperm whales and was probably an apex predator, preying on whales, seals and so forth. Characteristically of raptorial sperm whales, Livyatan had functional, enamel-coated teeth on the upper and lower jaws, as well as several features suitable for hunting large prey.
Eomysticetus is an extinct genus of baleen whale from the late Oligocene (Chattian) Chandler Bridge Formation of South Carolina.
Llanocetus is a genus of extinct toothed baleen whales from the Late Eocene of Antarctica. The type species, Llanocetus denticrenatus, reached gigantic proportions, with the juvenile specimen reaching an estimated 8 m (26 ft) in length; a second, unnamed species, known only from three isolated premolar teeth, reached an estimated total body length of up to 12 m (39 ft). Like other contemporary baleen whales of the Eocene, Llanocetus completely lacked baleen in its jaws. It was probably a suction feeder like the modern beaked and pygmy right whales.
Eomysticetidae is a family of extinct mysticetes belonging to Chaeomysticeti. It is one of two families in the basal chaeomysticete clade Eomysticetoidea.
Aetiocetidae is an extinct family of toothed baleen whales known from the Oligocene. The whales are from the North Pacific Ocean and ranged in size from 3 to 8 metres long. Many of the described specimens were discovered from the Upper Oligocene of the Japanese Morawan Formation, the largest known one from the Morawan's Upper tuffaceous siltstone. Other formally described extinct toothed mysticetis from this time are smaller, from 3 to 4 metres in length. Mysticeti with true baleen are seen in fossils from the Upper Oligocene. The monophyly of the family is still uncertain, as are the evolutionary relationship between the early toothed baleen whales and the early and extant edentulous baleen whales. However, the cladistic analyses of Coronodon and Mystacodon seem to indicate that Aetiocetidae and Llanocetidae are more closely related to crown Mysticeti than to Mammalodontidae, Coronodon, and Mystacodon.
Lentiarenium was an early sea cow from the Late Oligocene (Chattian) Linz-Melk Formation of Austria. Known since the mid 19th century, Lentiarenium was long considered to be a species of Halitherium until a 2016 analysis showed it to be distinct.
Mystacodon is a genus of toothed baleen whale from the Late Eocene Yumaque Member of Paracas Formation of the Pisco Basin in southwestern Peru. It is the oldest known baleen whale, and was probably a suction feeder of small prey on the seafloor.
Coronodon is a genus of toothed (transitional) baleen whales from the Early Oligocene Ashley and Chandler Bridge formations of South Carolina. The genus contains three species: the type species C. havensteini, and additional species C. newtonorum and C. planifrons.
Yamatocetus canaliculatus is an extinct species of eomysticetid baleen whale from the Late Oligocene of Japan.
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.
