? Castorocauda Fossil range: Middle Jurassic
Scientific classification
Kingdom: Animalia Phylum: Chordata (unranked) Mammaliaformes Order: Docodonta Family: Docodontidae Genus: Castorocauda Ji, Luo, Yuan, Tabrum, 2006 Species: C. lutrasimilis
Binomial name
Castorocauda lutrasimilis Ji, Luo, Yuan, Tabrum, 2006

Castorocauda lutrasimilis is the name given to a small, semi-aquatic relative of mammals living in the middle Jurassic period, 164 million years ago, in lakebed sediments of the Jiulongshan formation of Inner Mongolia. It was highly specialized, with adaptations evolved convergently with those of modern semi-aquatic mammals such as beavers, otters, and the platypus. It was larger than any known contemporaneous mammal. The Jurassic period is a major unit of the geologic timescale that extends from about 200 Ma (million years ago) at the end of the Triassic to 146 Ma at the beginning of the Cretaceous. ... Scientific classification or biological classification is how biologists group and categorize extinct and living species of organisms. ... Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anemones) Placozoa (trichoplax) Subregnum Bilateria (bilateral symmetry) Acoelomorpha (basal) Orthonectida (parasitic to flatworms, echinoderms, etc. ... Typical Classes Subphylum Urochordata - Tunicatas Ascidiacea Thaliacea Larvacea Subphylum Cephalochordata - Lancelets Subphylum Myxini - Hagfishes Subphylum Vertebrata - Vertebrates Petromyzontida - Lampreys Placodermi (extinct) Chondrichthyes - Cartilaginous fishes Acanthodii (extinct) Actinopterygii - Ray-finned fishes Actinistia - Coelacanths Dipnoi - Lungfishes Amphibia - Amphibians Reptilia - Reptiles Aves - Birds Mammalia - Mammals Chordates (phylum Chordata) include the vertebrates, together with... Clades Adelobasileus Sinoconodon Morganucodonta Docodonta Hadrocodium Mammalia Mammaliaformes is an extinct class of pre-mammals from which all modern mammals are descended. ... Docodonta is an order of extinct mammals that lived during the mid- to late-Mesozoic era. ... In biology, binomial nomenclature is the formal method of naming species. ... Orders Subclass Multituberculata (extinct) Plagiaulacida Cimolodonta Subclass Palaeoryctoides (extinct) Subclass Triconodonta (extinct) Subclass Eutheria (includes extinct ancestors)/Placentalia (excludes extinct ancestors) Afrosoricida Artiodactyla Carnivora Cetacea Chiroptera Cimolesta (extinct) Creodonta (extinct) Condylarthra (extinct) Dermoptera Desmostylia (extinct) Embrithopoda (extinct) Hyracoidea Insectivora Lagomorpha Litopterna (extinct) Macroscelidea Mesonychia (extinct) Notoungulata (extinct) Perissodactyla Pholidota Plesiadapiformes... The Jurassic period is a major unit of the geologic timescale that extends from about 200 Ma (million years ago) at the end of the Triassic to 146 Ma at the beginning of the Cretaceous. ... Inner Mongolia (Mongolian: ᠥᠪᠦᠷ ᠮᠣᠨᠺᠤᠯᠤᠨ ᠥᠪᠡᠷᠲᠡᠺᠡᠨ ᠵᠠᠰᠠᠬᠤ ᠣᠷᠤᠨ r Mongghul-un bertegen Jasaqu Orun; Chinese: 内蒙古自治区; Hanyu Pinyin: N i Měnggǔ Z qū) is an Autonomous Region of the Peoples Republic of China. ... In evolutionary biology, convergent evolution describes the process whereby organisms not closely related independently acquire similar characteristics while evolving in separate and sometimes varying ecosystems. ... Species C. canadensis C. fiber Beavers are semi-aquatic rodents native to North America and Europe. ... Genera Amblonyx Aonyx Enhydra Lontra Lutra Lutrogale Pteronura Otters are aquatic or marine carnivorous mammals, members of the large and diverse family Mustelidae, which also includes weasels, polecats, badgers, and others. ... Binomial name Ornithorhynchus anatinus (Shaw, 1799) The platypus (Ornithorhynchus anatinus) is a small, half-aquatic mammal endemic to the eastern part of Australia, and one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth to live young (the other four are echidnas). ...

Classification

Castorocauda is not considered to be a mammal by most authorities. The technical, cladistic, definition of a mammal is the group containing the most recent common ancestor of all living mammals (including monotremes, placentals, and marsupials) and its descendants. Castorocauda is a member of the order Docodonta, which is a wholly extinct group of Mammaliaformes, or proto-mammals. It has no modern descendants. Greek clados = branch) or phylogenetic systematics is a branch of biology that determines the evolutionary relationships of living things based on derived similarities. ... Families Kollikodontidae(extinct) Ornithorhynchidae- Platypus Tachyglossidae- Echidnas Steropodontidae(extinct) Monotremes (monos, single + trema, hole; refers to the cloaca) are mammals that lay eggs, instead of giving birth to live young like marsupials (Metatheria) and placental mammals (Eutheria). ... Orders Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia Xenarthra Dermoptera: Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Placentalia and Eutheria are terms used to describe major groupings within the animal class of Mammalia. ... Orders Superorder Ameridelphia Didelphimorphia Paucituberculata Superorder Australidelphia Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Marsupials are mammals in which the female typically has a pouch (called the marsupium, from which the name Marsupial derives) in which it rears its young through early infancy. ... Docodonta is an order of extinct mammals that lived during the mid- to late-Mesozoic era. ... Clades Adelobasileus Sinoconodon Morganucodonta Docodonta Hadrocodium Mammalia Mammaliaformes is an extinct class of pre-mammals from which all modern mammals are descended. ...

An important goal of paleontologists is to track the origin and evolution of certain characteristics. Hard anatomy characters such as teeth and bones preserve well in the fossil record and are the main source of information about how fossil animals are related to their modern counterparts. Soft anatomy features such as internal organs do not preserve readily. A paleontologist carefully chips rock from a column of dinosaur vertebrae. ... A fossil Ammonite Fossils (from Latin fossus, literally having been dug up) are the mineralized or otherwise preserved remains or traces (such as footprints) of animals, plants, and other organisms. ...

A fossil discovery was made in 2004 in the fossil-rich beds of Liaoning province, China; it was reported in the journal Science by an international team led by Qiang Ji of Nanjing University. The fossil of Castorocauda was so well preserved that an important feature of its soft anatomy— hair— was preserved. Hair is present in all modern mammals and was therefore assumed, under principles of maximum parsimony, to have been present in all fossil true mammals. The presence of hair in Castorocauda indicates that hair was not only present in mammals, but also in their closest relatives, the docodonts. In fact, the hair appears to have been a very advanced dense pelage including guard hairs and underfur. Liaoning (Simplified Chinese: 辽宁; Traditional Chinese: 遼寧; pinyin: Liáoníng) is a northeastern province of the Peoples Republic of China. ... Nanjing University (南京大学, 南京大學, Pinyin: NánjÄ«ng Dàxué; colloquially 南大, Pinyin Nándà) is one of the oldest higher learning institutions in the world, and became the first modern Chinese university in the early 1920s. ... Young Girl Fixing her Hair, by Sophie Gengembre Anderson Hair (latin pili) is a filamentous outgrowth of the skin found only in mammals. ... Maximum parsimony is a simple but popular technique used in cladistics to predict an accurate phylogenetic tree for a set of taxa (commonly a set of species or reproductively-isolated populations of a single species). ... Guard hairs are the longest, thickest hairs in a mammals coat, forming the topcoat (or outer coat). ... A dogs fur usually consists of longer, stiffer, guard hairs—which can be straight, wiry, or wavy, and of various lengths, hiding a soft, short-haired undercoat. ...

The tiny auditory ossicles of the middle ear and associated areas were also well preserved in this Castorocauda fossil. Features of these bones confirms the evolutionary position of docodonts as less closely related to true mammals than Hadrocodium, but more closely related to mammals than other mammaliaforms such as Morganucodon and Sinoconodon. The ossicles (also called auditory ossicles) are the three smallest bones in the human body. ... For an alternative meaning, see ear (botany). ... Hadrocodium is a mammal species which lived during the Lower Jurassic in present-day China. ... Morganucodon is a genus which lived during the Upper Triassic in (at least) Wales, England, east Asia, and perhaps South Africa. ... Sinoconodon is an ancient proto-mammal that appears in the fossil record in the early Jurassic period, about 208 million years ago. ...

Among docodonts, Castorocauda appears to have been related to Krusatodon and Simpsonodon, both European animals. This may be evidence that Europe and Asia underwent a faunal interchange in the Middle Jurassic. The two continents would later be separated by the Turgai Strait. World map showing Europe Europe is conventionally considered one of the seven continents of Earth which, in this case, is more a cultural and political distinction than a physiogeographic one. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...

Adaptation to water

The name Castorocauda lutrasimilis is derived from the Latin castor- meaning "beaver", -"cauda" meaning "tail", lutra meaning "otter", and -similis meaning "similar to". The tail was broad with scales interspersed with hairs that grew less frequent toward the tip. Overall it was very similar to the tails of modern beavers and was presumably used for locomotion in water in a similar fashion. The caudal vertebrae were flattened dorso-ventrally and similar overall to those in a beaver or otter. Fossilized impressions of some webbing is also present between the toes. Latin is an ancient Indo-European language originally spoken in the region around Rome called Latium. ...

Features of the limbs suggested that it may have been adapted for digging. The forelimbs are robust, with enlarged olecranon and other processes associated with strong muscle attachment. The limbs are similar to the modern platypus, an animal that both digs and swims. Castorocauda, Haldanodon and perhaps other docodonts were fossorial. These early specializations were also present in the unique early true mammal Fruitafossor. A fossorial is an organism that is adapted to digging and life underground such as the mole salamanders Ambystomatidae. ... Binomial name Fruitafossor windscheffeli (Luo and Wible, 2005) Fruitafossor windscheffeli is a newly-discovered termite-eating mammal which dates to the late Jurassic period, about 150 million years ago. ...

Docodonts in general have distinctive teeth, and the teeth of Castorocauda have the distinguishing features of the group. The teeth of Castorocauda are different in many ways from all other docodonts, presumably due to a difference in diet. Most docodonts had teeth specialized for an omnivorous diet. The teeth of Castorocauda suggest that the animal was a piscivore, feeding on fish and small invertebrates. The first two molars had cusps in a straight row, eliminating the grinding function suggesting that they were strictly for gripping and not for chewing. This feature of three cusps in a row is similar to the ancestral condition in mammal relatives (as seen in triconodonts), but is almost certainly a derived character in Castorocauda. These first molars were also recurved in a manner designed to hold slippery prey once grasped. These teeth are very similar to the teeth seen in mesonychids, an extinct group of semi-aquatic carnivorous ungulates, and resemble, to a lesser degree, the teeth of seals. An omnivore (from Latin: omnis all; vorare to devour) is an animal that eats both plants and meat. ... Atlantic herring, Clupea harengus: the most abundant species of fish in the world. ... Invertebrate is a term coined by Jean-Baptiste Lamarck to describe any animal without a spinal column. ... A molar is the fourth kind of tooth in mammals. ... This cladogram shows the relationship among various insect groups. ... Mesonychids are an extinct order of even-toed carnivorous ungulates (hoofed animals) which looked like wolves, and were scavengers for carrion and hunters of fish. ... A carnivore (KAR-nih-vohr) meaning meat eater (Latin carn = flesh + vorare = to devour) is an animal that eats a diet consisting solely of meat, whether it comes from live animals or dead (scavenging). ... Llamas such as this, which have two toes, are artiodactylas -- even toed ungulates Ungulates (meaning roughly hoofed or hoofed animal) make up several orders of mammals, of which six to eight survive. ... Families Odobenidae Otariidae Phocidae Pinnipeds (fin-foots, lit. ...

The complete dental formula was not recoverable, but the lower jaw contained 4 incisors, 1 canine, 5 premolars, and 6 molars. Dentition is the development of teeth and their arrangement in the mouth. ... Incisors are the first kind of tooth in heterodont mammals. ... The premolar teeth or bicuspids are transitional teeth located between the canine and molar teeth. ...

The animal probably weighed about 500-800 grams (1 pound to nearly 2 pounds) and grew to at least 42.5 cm (17 inches) in length. This makes it the largest mammaliaform (including true mammals) of the Jurassic. The previous record holder was Sinoconodon rigneyi which was thought to weigh up to 500 g.

Fossil evidence

The fossil was from the Jiulongshan Formation of the Inner Mongolia region of China. Fossils of pterosaurs, lissamphibians, coelurosaurian dinosaurs, and numerous invertebrates have also been unearthed in the same formation. Inner Mongolia (Mongolian: ᠥᠪᠦᠷ ᠮᠣᠨᠺᠤᠯᠤᠨ ᠥᠪᠡᠷᠲᠡᠺᠡᠨ ᠵᠠᠰᠠᠬᠤ ᠣᠷᠤᠨ r Mongghul-un bertegen Jasaqu Orun; Chinese: 内蒙古自治区; Hanyu Pinyin: N i Měnggǔ Z qū) is an Autonomous Region of the Peoples Republic of China. ... Suborders Rhamphorhynchoidea Pterodactyloidea Pterosaurs ([TEH-row-sore], winged lizards, often referred to as pterodactyls [TEH-row-DAK-tils]) were flying reptiles of the clade Pterosauria. ... Subclades Nqwebasaurus Proceratosaurus Tyrannoraptora ?Coeluridae ?Compsognathidae Tyrannosauroidea Maniraptoriformes [incertae sedis] Alvarezsauridae Maniraptora Ornithomimosauria Coelurosauria is a group of theropod dinosaurs that includes the subgroups Tyrannosauridae, Ornithomimidae, and Maniraptora. ... Orders & Suborders Saurischia Sauropodomorpha Theropoda Ornithischia Dinosaurs were vertebrate animals that dominated the terrestrial ecosystem for over 160 million years, first appearing approximately 230 million years ago. ... Invertebrate is a term coined by Jean-Baptiste Lamarck to describe any animal without a spinal column. ...

It was discovered and described by Qiang Ji and Chong-Xi Yuan of the Chinese Academy of Geological Sciences in Beijing and Zhe-Xi Luo and Alan Tabrum of the Carnegie Museum of Natural History. (help· info), a city in northern China, is the capital of the Peoples Republic of China (PRC). ... The Carnegie Museums of Pittsburgh are operated by the Carnegie Institute and located in Pittsburgh, Pennsylvania. ...

Importance of discovery

The discovery of Castorocauda lutrasimilis is the first sign that a close relative of mammals adapted to water before dinosaurs became extinct 65 million years ago, pushing back the estimated date for mammal relatives adapted to a semi-aquatic lifestyle by 110 million years. Based on fossils known at present, the mammal line would not see another semi-aquatic form evolve until the Eocene. Because few fossilized remains had been found, it was previously thought that, until the KT boundary, all mammals were tiny, ground-dwelling, nocturnal animals akin to shrews, hedgehogs, treeshrews, or tenrecs. This notion has now been challenged by the armadillo-like Fruitafossor, the dinosaur-eating Repenomamus and now the otter-like Castorocauda. The Eocene epoch (56-34 Ma) is a major division of the geologic timescale and the second epoch of the Palaeogene period in the Cenozoic era. ... The Cretaceous-Tertiary (KT) extinction event, also known as the KT boundary (from German: Kreide-Tertiär-Grenzschicht), was a period of massive extinction of species, about 65. ... A nocturnal animal is one that sleeps during the day and is active at night - the opposite of the typical human schedule (diurnal). ... Genera Anourosorex Blarina Blarinella Chimarrogale Chodsigoa Congosorex Crocidura Cryptotis Diplomosodon Episoriculus Feroculus Megasorex Myoserex Nectogale Neomys Nesiotites Notiosorex Paracrocidura Ruwenzorisorex Scutisorex Solisorex Sorex Soriculus Suncus Surdisorex Sylvisorex Shrews are small, superficially mouse-like mammals of the family Soricidae. ... Genera Atelerix Erinaceus Hemiechinus Mesechinus A hedgehog is any of the small spiny mammals of the subfamily Erinaceinae and the order Insectivora. ... Families Tupaiidae Ptilocercidae The treeshrews are small mammals native to the tropical forests of Southeast Asia. ... Subfamilies  Oryzorictinae  Potamogalinae  Tenrecinae Tenrecidae (common name tenrecs) is a family of mammals found on Madagascar and parts of western Africa. ... Genera Chlamyphorus Cabassous Chaetophractus Dasypus Euphractus Priodontes Tolypeutes Zaedyus Armadillos are any of several small mammals of the family Dasypodidae, mostly known for having a bony armor shell. ... Species Repenomamus robustus Repenomamus giganticus Repenomamus is the largest mammal known from the Cretaceous period of the Mesozoic, and the only one with evidence that it ate dinosaurs. ...

References

• Ji, Q., Z.-X. Luo, C.-X. Yuan, A. R. Tabrum. February 24, 2006. "A swimming mammaliaform from the Middle Jurassic and ecomorphological diversification of early mammals". Science, 311:5764 pp.1123-1127.

External links

• Carnegie Museum's Press release with images
• Live Science article with artist's impression
• Times Online article
• CNN article
• ABC News article
• Fossil Museum: Castorocauda lutrasimilis