36-399: Middle: Castorocauda lutrasimilis ( Docodonta ), Shenshou lui ( Haramiyida ); Bottom: Tachyglossus aculeatus ( Monotremata ), Ursus arctos ( Theria ). Mammaliaformes ("mammalian forms") is a clade of synapsid tetrapods that includes the crown group mammals and their closest extinct relatives; the group radiated from earlier probainognathian cynodonts during
72-538: A tactile sense, was an ancestral trait of mammals. Mammals preserved with fur from the Chinese Yixian Formation show little hair on the tail, whereas the fur outline preserved on the Castorocauda tail was 50% wider than the pelvis . The first quarter is covered by guard hairs , the middle half by scales and little hair cover and the last quarter by scales with some guard hair. Beavers have
108-521: A 2010 review of docodonts, Docodonta was split into Docodontidae , Simpsonodontidae and Tegotheriidae , with Castorocauda considered incertae sedis with indeterminate affinities . Simpsonodontidae is now considered to be paraphyletic and thus invalid, and Castorocauda appears to have been most closely related to Dsungarodon , which came from the Junggar Basin of China and probably ate plants and soft invertebrates. Castorocauda
144-469: A critical point which allowed for a massive expansion into different habitats. Castorocauda is the earliest known aquatic mammaliaform, pushing back the first appearance of mammaliaform aquatic adaptations by over 100 million years. The teeth interlocked while biting, suggesting that they were strictly used for gripping; the recurved molars were likely used to hold slippery prey; and the teeth shapes are convergent with seals and Eocene whales, suggesting
180-421: A similar ecological standing. Based on these, its adaptations to swimming and digging and its large size, Castorocauda was probably comparable to the modern day platypus , river otters and similar semi-aquatic mammals in ecology and fed primarily on fish ( piscivory ). The Daohugou Beds also include several salamanders , numerous pterosaur species (of which many likely were piscivorous), several insects,
216-470: A straight row, and interlocked during biting. This feature is similar to the ancestral condition in Mammaliaformes (such as in triconodonts ) but is a derived character (it was specially evolved instead of inherited) in Castorocauda . The lower jaw contained 4 incisors , 1 canine , 5 premolars and 6 molars. The forelimbs of Castorocauda are very similar to those of the modern platypus:
252-688: A very similar tail. Evidence of fur and assumed heightened tactile senses indicate it had a well-developed neocortex , a portion of the brain unique to mammals which, among other things, controls sensory perception . Adelobasileus Sinoconodon Morganucodon Megazostrodon Haramiyavia Thomasia Megaconus Eleutherodon Sineleutherus Sibirotherium Tegotherium Hutegotherium Itatodon Krusatodon Agilodocodon Simpsonodon Tashkumyrodon Castorocauda Dsungarodon Borealestes Docofossor Docodon Haldanodon Hadrocodium Crown mammals Castorocauda
288-425: Is a gland found within the eye's orbit that occurs in tetrapods (reptiles, amphibians, birds and mammals) that possess a nictitating membrane . The gland can be compound tubular or compound tubuloalveolar , and the fluid it secretes ( mucous , serous or lipid ) varies between different groups of animals. In some animals, it acts as an accessory to the lacrimal gland , secreting fluid that eases movement of
324-488: Is a member of the order Docodonta , an extinct group of mammaliaforms . Mammaliaformes includes mammal-like creatures and the crown mammals (all descendants, living or extinct, of the last common ancestor of all living mammals). Docodonts are not crown mammals. When Castorocauda was first described in 2006, it was thought to be most closely related to the European Krusatodon and Simpsonodon . In
360-469: Is a term of phylogenetic nomenclature . In contrast, the assignment of organisms to class Mammalia has traditionally been founded on traits and, on this basis, Mammalia is slightly more inclusive than Mammaliaformes. In particular, trait-based taxonomy generally includes Adelobasileus and Sinoconodon in Mammalia, though they fall outside the Mammaliaformes definition. These genera are included in
396-575: Is later considered as misidentification of Neogene shrew . Tritylodontidae Castorocauda Castorocauda is an extinct, semi-aquatic, superficially otter -like genus of docodont mammaliaforms with one species, C. lutrasimilis . It is part of the Yanliao Biota , found in the Daohugou Beds of Inner Mongolia , China dating to the Middle to Late Jurassic . It
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#1732780901102432-525: Is part of a Middle Jurassic mammaliaform diversification event, wherein mammaliaforms radiated into a wide array of niches and evolved several modern traits, such as more modern mammalian teeth and middle ear bones. It was previously thought that mammals were small and ground-dwelling until the Cretaceous–Paleogene boundary (K–Pg boundary) when dinosaurs went extinct. The discovery of Castorocauda , and evidence for an explosive diversification in
468-600: Is the largest known Jurassic mammaliaform. It is the earliest known mammaliaform with aquatic adaptations or a fur pelt . It was also adapted for digging, and its teeth are similar to those of seals and Eocene whales, collectively suggesting it behaved similarly to the modern-day platypus and river otters and ate primarily fish. It lived in a wet, seasonal, cool temperate environment – which possibly had an average temperature not exceeding 15 °C (59 °F) – alongside salamanders, pterosaurs, birdlike dinosaurs, and other mammaliaforms. The holotype specimen , JZMP 04117,
504-471: The Late Triassic . It is defined as the clade originating from the most recent common ancestor of Morganucodonta and the crown group mammals; the latter is the clade originating with the most recent common ancestor of extant Monotremata , Marsupialia and Placentalia . Besides Morganucodonta and the crown group mammals, Mammaliaformes also includes Docodonta and Hadrocodium . Mammaliaformes
540-487: The clam shrimp Euestheria and some birdlike dinosaurs. No fish are known from specifically the Daohugou Beds, but the related Linglongta locality contains undetermined ptycholepiformes . Other mammals include the flying-squirrel -like Volaticotherium , the burrowing Pseudotribos , the oldest known eutherian Juramaia . the rat -like Megaconus and the gliding Arboroharamiya . The plant life of
576-462: The humerus widens towards the elbow ; the forearm bones have hypertrophied (large) epicondyles (where the joint attaches); the radial and ulnar joints are widely separated; the ulna has a massive olecranon (where it attaches to the elbow); the wrist bones are block-like; and the finger bones are robust. Docodontans were likely burrowing creatures and had a sprawling gait , and Castorocauda may have also used its arms for rowing, similar to
612-562: The 3.2 cm (1.35 in) Hadrocodium must have had fur, therefore, but the 10 cm (3.94 in) Morganucodon might not have needed it. The docodont Castorocauda , further removed from crown group mammals than Hadrocodium , had two layers of fur, guard hairs and underfur, as do mammals today. It is possible that early mammaliaforms had vibrissae ; Tritheledontidae , a group of cynodonts , probably had whiskers. A common ancestor of all therian mammals did so. Indeed, some humans even still develop vestigial vibrissal muscles in
648-449: The Mammaliaformes, but these traits are difficult to study in the fossil record. Evidence of lactation is present in morganucodontans , via tooth replacement patterns. Combined with the more basal tritylodontids that also display evidence of lactation, this seems to imply that milk is an ancestral characteristic in this group. However, the fairly derived Sinoconodon appears to have uniquely discarded milk altogether. Prior to hatching,
684-531: The Middle Jurassic – such as the appearance of eutriconodontans , multituberculates , australosphenidans , metatherians and eutherians , among others – disproves this notion. This may have been caused by the breakup of Pangaea , which started in the Early to Middle Jurassic and diversified habitats and niches, or modern traits that had been slowly accumulating since mammaliaforms evolved until reaching
720-517: The Tiaojishan Formation was dominated by cycadeoids (mainly Nilssonia and Ctenis ), leptosporangiate ferns and ginkgophytes and has pollen remains predominantly from pteridophytes and gymnosperms , which indicate a cool temperate and wet climate with distinct wet and dry seasons, possibly with an annual temperature of below 15 °C (59 °F). [REDACTED] Harderian gland The Harderian gland
756-414: The broader clade Mammaliamorpha , defined phylogenetically as the clade originating with the last common ancestor of Tritylodontidae and the crown group mammals. This wider group includes some families that trait-based taxonomy does not include in Mammalia, in particular Tritylodontidae and Brasilodontidae . Animals in the clade Mammaliaformes are often called mammaliaforms , without the e . Sometimes,
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#1732780901102792-407: The centrum) on the headward side and another on the tailward side, making the centrum appear somewhat like the letter H from the top-view looking down. This tail anatomy is similar to beavers and otters, which use their tails for paddling and propulsion. Fur was preserved on the holotype, and it is the earliest known pelt ; this showed that fur, with its many uses including heat retention and as
828-498: The hindlimbs remained "primitive"; this tendency is in some effect still seen in modern therian mammals, which often have more sprawling hindlimbs. In some forms, the hind feet likely bore a spur similar to those found in the platypus and echidnas . Such a spur would have been connected to a venom gland for protection or mating competition. Hadrocodium lacks the multiple bones in its lower jaw seen in reptiles . These are still retained, however, in earlier mammaliaforms. With
864-430: The milk glands would provide moisture to the leathery eggs, a situation still found in monotremes. The early mammaliaforms did have a harderian gland . In modern mammals, this is used for cleaning the fur , indicating that they, contrary to their cynodont ancestors, had a furry covering. An insulative covering is necessary to keep a homeothermic animal warm if it is very small, less than 5 cm (1.97 in) long;
900-456: The nictitating membrane. Research has proposed that the gland has several other functions, including that of a photoprotective organ, a location of immune response , a source of thermoregulatory lipids, a source of pheromones , and a site of osmoregulation . In mammals , the gland secretes an oily substance used to preen the fur. The presence or absence of this gland is one of the cues used by palaeontologists to determine when fur evolved in
936-427: The pace of digestion is a necessity. The drawback to the fixed dentition is that worn teeth cannot be replaced, as was possible for the reptiliomorph ancestors of mammaliaforms. To compensate, mammals developed prismatic enamel , characterized by crystallite discontinuities that helped spread out the force of the bite. Lactation , along with other characteristically mammalian features, is also thought to characterize
972-413: The platypus. There are traces of soft tissue between the toes, suggesting webbed hind feet. It likely also had claws , and the holotype shows a spur on the hind ankle, which, in male platypuses, is venomous. Castorocauda likely had 14 thoracic , 7 lumbar , 3 sacral and 25 tail vertebrae. Like some mammals, it had plated ribs, and the ribs extended into the lumbar vertebrae. Plating occurred on
1008-587: The possible exception of Megazostrodon and Erythrotherium (as well as placental mammals), all mammaliforms possess epipubic bones, a possibly synapomorphy with tritylodontids , which also have them. These pelvic bones strengthen the torso and support abdominal and hindlimb musculature. They, however, prevent the expansion of the abdomen, and so force species that possess them to either give birth to larval young (as in modern marsupials ), or produce minuscule eggs that hatch into larval young (as in modern monotremes ). Most mammaliforms, therefore, probably had
1044-662: The proximal margins (the part of the rib closest to the vertebra), and, in Castorocauda , they may have served to increase the insertion area (the part of a muscle which moves while contracting ) of the iliocostalis muscle on the back, which would interlock nearby ribs and better support the torso of the animal. Plated ribs are present in arboreal (tree-dwelling) and fossorial (burrowing) xenarthrans ( sloths , anteaters , armadillos and relatives). The tail vertebrae are flattened dorsoventrally (shortened vertically and widened more horizontally); and each centrum has two pairs of transverse processes (which jut out diagonally from
1080-908: The same constraints, and some species could have borne pouches. The cladogram below follows the analysis of Luo and colleagues in 2015 . Tritylodontidae Pachygenelus Adelobasileus Sinoconodon Megazostrodon Morganucodon Haldanodon Castorocauda Thomasia Haramiyavia Megaconus Shenshou Eleutherodon Sineleutherus Arboroharamiya Xianshou Shuotheriidae Monotremata Fruitafossor Eutriconodonta Tinodon Multituberculata expanded below Expanded from above Spalacotheriida Henkelotherium Dryolestes Amphitherium Peramus Vincelestes Nanolestes Kielantherium Aegialodon Marsupialia Placentalia Cladogram based on Rougier et al. (1996) with Tikitherium included following Luo and Martin (2007). However, Tikitherium
1116-589: The spelling mammaliforms is used. The origin of crown-group mammals extends back to the Jurassic , with extensive findings in the Late Jurassic outcrops of Portugal and China . The earliest confirmed specimens of fur are found in them, demonstrating that the ancestors of mammals had already developed fur. Early mammaliaforms were generally shrew -like in appearance and size, and most of their distinguishing characteristics were internal. In particular,
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1152-427: The structure of the mammaliaform (and mammal) jaw and the arrangement of teeth are nearly unique. Instead of having many teeth that are frequently replaced, mammals have one set of baby teeth and later one set of adult teeth that fit together precisely. This is thought to aid in the grinding of food to make it quicker to digest. Endothermic animals require more calories than those that are ectothermic , so speeding up
1188-431: The upper lip. Thus, it is possible that the development of the whisker sensory system played an important role in mammalian development, more generally. Like monotremes today, the legs of early mammaliaforms were somewhat sprawling, giving a rather "reptilian" type of gait. However, there was a general tendency to have more erect forelimbs, forms like eutriconodonts even having a fundamentally modern forelimb anatomy while
1224-991: Was discovered in the Daohugou Beds of the Jiulongshan Formation in the Inner Mongolia region of China, which dates to about 159–164 million years ago (mya) in the Middle to Late Jurassic . It comprises a partial skeleton including an incomplete skull but well-preserved lower jaws, most of the ribs, the limbs (save for the right hind leg), the pelvis and the tail. The remains are so well preserved that there are elements of its soft anatomy and hair. The genus name Castorocauda derives from Latin Castor " beaver " and cauda "tail", in reference to its presumed beaver-like tail. The species name lutrasimilis derives from Latin lutra " otter " and similis "similar", because some aspects of its teeth and vertebrae are similar to modern otters. Castorocauda
1260-404: Was part of an explosive Middle Jurassic radiation of Mammaliaformes moving into diverse habitats and niches . Its discovery in 2006, along with the discovery of other unusual mammaliaforms, disproves the previous hypothesis of Mammaliaformes remaining evolutionarily stagnant until the extinction of the non-avian dinosaurs . Weighing an estimated 500–800 g (1.1–1.8 lb), Castorocauda
1296-617: Was the largest of known docodonts. The preserved length from head to tail is 425 mm (16.7 in), but in life it was much larger. Based on the dimensions of the platypus, the lower weight limit was estimated to be 518 g (1.1 lb) in life, and the upper 700 to 800 g (1.5 to 1.8 lb), making it the largest known Jurassic mammaliaform, surpassing the previous record of 500 g (1.1 lb) for Sinoconodon . It had specialized teeth that curve backwards to help it hold onto slippery fish, as seen in modern seals and also ancestral whales. The first two molars have cusps in
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