mesonychids limbs and tail description

Mesonychid dentition consisted of molars modified to generate vertical shear, thin blade-like lower molars, and carnassial notches, but no true carnassials. Adapted fromWritten in Stone: Evolution, the Fossil Record, and Our Place in Nature, by Brian Switek. Beyond Ambulocetus, it is easy to trace the ancestry directly to modern cetaceans[8]: Sinonyx (land-dwelling) -> Pakicetus (swims occasionally) -> Ambulocetus natans (swims predominantly) -> Rodhocetus (paddling reduced hind legs) -> Basilosaurus (vestigial hind limbs) -> Dorudon. However, the limb bones are quite dense, a trait that aquatic animals use to keep from floating to the surface. Cour. Their most characteristic feature was that they had primitive hooves. Unlike all modern and possibly all other fossil cetaceans, it had four fully functional, long legs. A similar position occurs in the hippopotamus and suggests that this early whale swam submerged, except for its eyes. Journal of Vertebrate Paleontolgy 29:1289-1299. Dissacus was a jackal-sized predator that has been found all over the Northern Hemisphere, but species of a closely related or identical genus, Ankalagon, from the early to middle Paleocene of New Mexico, were far larger, growing to the size of a bear. In this case, the resemblances to early whales would be due to convergent evolution among ungulate-like herbivores that developed adaptations related to hunting or eating meat. Sinonyx jiashanensis However, unlike the cases of sea otters and pinnipeds (seals, sea lions, and walruses, whose limbs are functional both on land and at sea), it is not easy to envision what the first whales looked like. Even in so extreme a case as this, if the supply of insects were constant, and if better adapted competitors did not already exist in the country, I can see no difficulty in a race of bears being rendered, by natural selection, more and more aquatic in their structure and habits, with larger and larger mouths, till a creature was produced as monstrous as a whale. vertebrae, and significant portions of fore and hind limbs. These hoofed Mesonychia ("Middle Claws") are an extinct order of medium to large-sized carnivorous mammals that were closely related to artiodactyls (even-toed ungulates), and to cetaceans (dolphins and whales). club mentor toastmasters; is simpson stopper poisonous to dogs; karin uzumaki mother name; Industrial Training August 29, 2018. While on land, its elbow and knee were habitually flexed, and its feet were solidly planted on the ground, unlike modern hoofed mammals, which stand on their toes. Van Valen hypothesized that some mesonychids may have been marsh dwellers, mollusk eaters that caught an occasional fish, the broadened phalanges [finger and toe bones] aiding them on damp surfaces. A population of mesonychids in a marshy habitat might have been enticed into the water by seafood. Raoellids likeIndohyuswere the closest relatives to whales, with hippos being the next closest relatives to both groups combined. Posted on jnius 1, 2021 by jnius 1, 2021 by Nature 361:444-445. As nouns the difference between limb and tail is that limb is a major appendage of human or animal, used for locomotion (such as an arm, leg or wing) or limb can be (astronomy) the apparent visual edge of a celestial body while tail is . %PDF-1.2 % (Why do the limbs form, and then why do they atrophy?) January 17, 2017. by wherewillsciencetakeyou. Dissacus was a jackal-sized predator that has been found all over the Northern Hemisphere,[3] but species of a closely related or identical genus, Ankalagon, from the early to middle Paleocene of New Mexico, were far larger, growing to the size of a bear. Permalink . A few experts unite Mesonychia with the whales to form the clade "Cete." Mesonychids possess unusual triangular molar teeth that are similar to those of Cetacea (whales and dolphins), especially those of the archaeocetes, as well as having similar skull anatomies and other morphologic traits. mitsubishi outlander phev cargo space. Gingerich (2003) suggested instead that Ambulocetus used alternate leg paddling to move through the water (i.e. [3], The mesonychids were an unusual group of condylarths with a specialized dentition featuring tri-cuspid upper molars and high-crowned lower molars with shearing surfaces. This conflict between the paleontological and molecular hypotheses seemed intractable. Triisodontidae. While analyzing the relationships of ancient meat-eating mammals in 1966, however, the evolutionary biologist Leigh Van Valen was struck by the similarities between an extinct group of land-dwelling carnivores called mesonychids and the earliest known whales. Blog Home Uncategorized mesonychids limbs and tail. nutrition partner kaiser salary. This global catastrophe cleared the way for a major radiation of mammals. They first appeared in the Early Paleocene and went into a sharp decline at the end of the Eocene and Date: May 14, 2022. Some members of the group are known only from skulls and jaws, or have fragmentary postcranial remains. Description. This condition is called pachyosteosclerosis, and whales are the only mammals known to have such a heavily thickened involucrum. Under this scenario, Ambulocetus rarely, if ever, came out on land. The order is sometimes referred to by its older name "Acreodi". [13], This article is about the prehistoric ungulate. It was a wolf-like animal, not the slick, seal-like animal that had originally been envisioned. The ungulate group is one of the largest and most successful branches of mammals. Age: Technically speaking, the term "mesonychid" refers specifically only to the members of the family Mesonychidae, such as the species of the genus Mesonyx. New York: Fowler & Wells. The anatomist William Henry Flower pointed out that seals and sea lions use their limbs to propel themselves through the water while whales lost their hind limbs and swam by oscillations of their tail. This, in combination with its inferred diet (see below) and inferred ability to walk on the bottom, suggests that it attacked its prey from below. These animals would have migrated to North America via the Bering land bridge. In Asia, the record of their history suggests they grew gradually larger and more predatory over time, then shifted to scavenging and bone-crushing lifestyles before the group became extinct. Mesonychia ("Middle Claws ") are an extinct order of medium to large-sized carnivorous mammals that were closely related to artiodactyls (even-toed ungulates ), and to cetaceans ( dolphins and whales ). Like other dorundontines, Zygorhiza had a body similar to modern cetaceans with flipper-like forelimbs, rudimentary hind limbs, a vertebral column adapted for oscillatory swimming, and a tail fluke. Another extinct whale calledSqualodon, a fossil dolphin with a wicked smile full of triangular teeth, similarly hinted that whales had evolved from meat-eating ancestors. Brys donation was soon matched, and even exceeded, by that of Judge John Creagh from Alabama. That said, how frequently Ambulocetus traveled on land is unclear. View original page. What springs to mind when you think of a whale? These forms, likeRodhocetus, were nearly entirely aquatic, and some later protocetids, likeProtocetusandGeorgiacetus, were almost certainly living their entire lives in the sea. 62 Reviews (415) 237-3870 Website. Locomotion: The skull ofPakicetusexhibited just this condition. The order is sometimes referred to by its older name "Acreodi". Since other carnivores such as the creodonts and condylarths were either rare or absent in these animal communities, mesonychians most likely dominated the large predator niche in the Paleocene of Asia. Typified by hooves and sometimes by horns or antlers, today these creatures fill most of the existing niches for large herbivores all over the world. The fact that it was found in freshwater deposits and did not have specializations of the inner ear for underwater hearing showed that it was still very early in the aquatic transition, and Gingerich and Russell thought ofPakicetusas an amphibious intermediate stage in the transition of whales from land to sea, though they added the caveat that Postcranial remains [bones other than the skull] will provide the best test of this hypothesis. The scientists had every reason to be cautious, but the fact that a transitional whale had been found was so stupendous that full-body reconstructions ofPakicetusappeared in books, magazines and on television. Thewissen, J.G.M and Hussain, S.T. 10. I suggest instead that body appendages such as arthropod and vertebrate limbs and chordate tails are evolutionarily divergent duplicates (paramorphs) of the main body axis, that is, its duplicates, albeit devoid of endodermal component. How was the gap between a walking mammal and a swimming whale bridged? caesars . Like otters, the legs and feet would push backward together, the spine would arch, and the tail would have moved upward. "Triisodontidae" may be paraphyletic. Historical Epoch: Early Eocene (50 million years ago) Size and Weight: About three feet long and 50 pounds. The mesonychids bore a strong, albeit superficial, resemblance to wolves.Early mesonychids had five digits on their feet, which probably rested flat on the ground during walking (plantigrade locomotion), but later mesonychids had four digits that ended in tiny hoofs on all of their toes and were increasingly well adapted to running.. Like running members of the even ilwu-pma benefit plans renner petroleum gas card mesonychids limbs and tail description. Cookie Policy california rich brian / wind river canyon accident / wind river canyon accident Why do you suppose this happens? They are not closely related to any living mammals. Mesonychids were the first mammalian carnivores after the extinction of the dinosaurs.. By the turn of the 20th century the oldest fossil whales were still represented byBasilosaurusand similar forms likeDorudonandProtocetus, all of which were fully aquaticthere were no fossils to bridge the gap from land to sea. Fur covered with a head that is becoming whale shaped with sharp teeth. The mesonychids were the first group to become larger carnivores. massachusetts update covid Uncategorized. contains some random words for machine learning natural language processing Pakicetus is an extinct genus of amphibious cetacean of the family Pakicetidae, which was endemic to Pakistan during the Eocene. Organized bony struts in the leg bones of Ambulocetus and a solid connection between its pelvis and the base of its spine suggest that it could have supported its body weight on land. What features can be seen in the skull of Ambulocetus indicate that it could hear underwater sound. For this reason, scientists had long believed that mesonychids were the direct ancestor of Cetacea, but the discovery of well-preserved hind limbs of archaic cetaceans, as well as more recent phylogenetic analyses[8][9][10] now indicate cetaceans are more closely related to hippopotamids and other artiodactyls than they are to mesonychids, and this result is consistent with many molecular studies. For this reason, scientists had long believed that mesonychids were the direct ancestor of Cetacea, but the discovery of well-preserved hind limbs of archaic cetaceans, as . Wij zijn de specialist in Cad Cam services. Mesonychians have been extinct since the early Oligocene, but there are occasional, unconfirmed sightings of cat or dog-like predators with hooves. malleus, incus, stapes), which transmitted the sound to the organ of hearing. He asked for more bones, and Creagh soon sent parts of the skull, jaws, limbs, ribs, and backbone of the enigmatic creature. American black bear, with a long stout tail, and a wide head as large as that of a grizzly bear. citrus county sheriff jobs near hamburg; mesonychids limbs and tail. Darwin had done no such thing, but the jeering caused him to modify the passage in subsequent editions of the book. But, because they are mammals, we know that they must have evolved from land-dwelling ancestors. We do not collect or store your personal information, and we do not track your preferences or activity on this site. But, long ago, not all ungulates were herbivores. Mesonychids are carnivorous mammals, and some are closely related to dolphins. from artiodactyls)[7], it has been argued that the transition from mesonychians to cetaceans is easy to follow from the fossil evidence. Its tail is longer and more muscular, too. Mesonychians possess unusual triangular molar teeth that are similar to those of Cetacea (whales and dolphins), especially those of the archaeocetids, as well as having similar skull anatomies and other morphologic traits. Since other carnivores such as the creodonts and Carnivora were either rare or absent in these animal communities, mesonychids most likely dominated the large predator niche in the Paleocene of Asia. However, it had rather short, strong hind limbs, with huge feet (each toe with a tiny mesonychid-type hoof!). In some localities, multiple species or genera coexisted in different ecological niches. Home; About Us. (1995); and to Cete by Archibald (1998);[7] and to Mesonychia by Carroll (1988), Zhou et al. These earliest cetaceans were not like the whales we know today, and only recently have paleontologists been able to recognize them. . Mesonychid dentition consisted of molars modified to generate vertical shear, thin blade-like lower molars, and carnassial notches, but no true carnassials. Early mesonychids probably walked on the flats of their feet (plantigrade), while later ones walked on their toes (digitigrade). As described in the comments above, all known skeletons of Pakicetus are composites created by gathering isolated bones. It had limbs like a land animal and webbed toes in replacement for fins, suggesting that it recently changed from land to water through evolution. These ancestral creatures were stranger than anyone ever expected. Which were more reliable, teeth or genes? Rodhocetus (from Rodho, the geological anticline at the type locality, and cetus, Latin for whale) is an extinct genus of protocetid early whale known from the Lutetian of Pakistan. Mesonychians in North America were by far the largest predatory mammals during the early Paleocene to middle Eocene. Size: We use cookies to see how our website is performing. One branch of the ungulate family, called the mesonychids, were predators. Reconstructions of pakicetids that followed the discovery of composite skeletons often depicted them with fur; however, given their close relationships with hippos, they more likely had sparse body hair. If the early ancestors of whales had large, broad tails, that could explain why they evolved such a unique mode of swimming. Many North American species of skinks, for example, have bright blue tails when they are young. Intermediate cetacean forms such as Ambulocetus and Pakicetus especially closely resemble Mesonychians with their fully functioning legs and similar tooth morphology. They are not closely related to any living mammals. Underwater sound would have entered the skull of Pakicetus and caused its bulla to vibrate. Mesonychians probably originated in Asia, where the most primitive mesonychid, Yangtanglestes, is known from the early Paleocene. 3 0 obj << /Linearized 1 /O 5 /H [ 677 158 ] /L 5375 /E 5050 /N 1 /T 5198 >> endobj xref 3 14 0000000016 00000 n 0000000624 00000 n 0000000835 00000 n 0000000988 00000 n 0000001184 00000 n 0000001289 00000 n 0000001393 00000 n 0000001499 00000 n 0000001552 00000 n 0000002666 00000 n 0000003413 00000 n 0000004908 00000 n 0000000677 00000 n 0000000815 00000 n trailer << /Size 17 /Info 2 0 R /Root 4 0 R /Prev 5189 /ID[<4e5292bec552ff6cdecba3d79dd8a517><4e5292bec552ff6cdecba3d79dd8a517>] >> startxref 0 %%EOF 4 0 obj << /Type /Catalog /Pages 1 0 R >> endobj 15 0 obj << /S 36 /Filter /FlateDecode /Length 16 0 R >> stream These later mesonychids had hooves, one on each toe, with four toes on each foot. Mammals diversified in the shadow of the great archosaurs, and they remained fairly small and secretive until the non-avian dinosaurs were wiped out by a mass extinction 65 million years ago. The molars were laterally compressed and often blunt and were probably used for shearing meat or crushing bones. 1994). Mesonychidae is an extinct family of small to large-sized omnivorous-carnivorous mammals. The surviving mammals and birds evolved into many of the ecological niches previously occupied by dinosaurs and pterosaurs. Mesonychids (Figure 42) also resembled large wolves, but these, unlike the arctocyonids were carnivores (Benton 2005). [2] Some researchers now consider the family a sister group either to whales or to artiodactyls, close relatives rather than direct ancestors. Given these uncertainties, we have decided to focus on the genus Pakicetus, instead of any particular species. Thus the thickened bulla of Pakicetus is interpreted as a specialization for hearing underwater sound. The semi-aquatic otters and beavers, he claimed, were better alternative models for the earliest terrestrial ancestors of whales. [3] This process is called adaptive radiation. Like the Paleocene family Arctocyonidae, mesonychids were once viewed as primitive carnivorans, and the diet of most genera probably included meat or fish. As strange as modern whales are, their fossil predecessors were even stranger. One particular ankle bone, the astragalus, had the potential to settle the debate. With the permission of the publisher, Bellevue Literary Press. A later genus, Pachyaena, entered North America by the earliest Eocene, where it evolved into species that were at least as large. Critics took it to mean he was proposing that bears were direct ancestors of whales. Many species are suspected of being fish-eaters, though some of these reconstructions may be influenced by earlier theories that the group was ancestral to cetaceans. Toggle navigation. The head had a long snout with no blowhole. When the genes and amino acid sequences of living whales were compared with those of other mammals, the results often showed that whales were most closely related to artiodactylseven-toed ungulates like antelope, pigs, and deer. Limbs and tail: Description; Did it swim? Pachyaena Pakicetus Ambulocetus Rodhocetus Basilosaurus Zygorhiza Year reported Country where found Geological age (mya) Habitat (land, fresh water, shallow sea, open ocean) Skull, teeth, ear structure types most like whale or land mammal? Range: One branch of the ungulate family, called the mesonychids, were predators. whales came to be after millions of years of evolution. The family tree, including Ungulates. As E.D. [1], Mesonychids possess unusual triangular molar teeth that are similar to those of Cetacea (whales and dolphins), especially those of the archaeocetes, as well as having similar skull anatomies and other morphologic traits. One important difference from otters is that in Ambulocetus the feet, not the tail, would have provided the main force for swimming. Darwin was widely ridiculed for this passage. USA Distributor of MCM Equipment mesonychids limbs and tail Accept Cookies, Osteopathic Manipulative Medicine Research. Mesonychids probably originated in China, where the most primitive mesonychid, Yangtanglestes, is known from the early Paleocene. Cetaceans, like many other mammals, have ear bones enclosed in a dome of bone on the underside of their skulls called the auditory bulla. 1846. Pakicetus has a similar body design, but a head more closely resembling archaic cetaceans. But where skeletons are known, they indicate that mesonychids had large heads with strong jaw muscles, relatively long necks, and robust bodies with robust limbs that could run effectively but not rotate the hand or reach out to the side. Be after millions of years of Evolution limb bones are quite dense, a trait that aquatic animals to... Tail would have provided the main force for swimming historical Epoch: early Eocene ( 50 million years ago Size. Sometimes referred to by its older name `` Acreodi '' and Our Place in Nature by. Covered with a long snout with no blowhole ancestors of whales had large, broad,... To become larger carnivores Evolution, the limb bones are quite dense, trait... Hind limbs, with huge feet ( plantigrade ), while later walked. Likeindohyuswere the closest relatives to both groups combined adapted fromWritten in Stone: Evolution, spine. Toe with a tiny mesonychid-type hoof! ) largest and most successful of... Modified to generate vertical shear, thin blade-like lower molars, and Place... Long ago, not all ungulates were herbivores know that they must have evolved from land-dwelling ancestors only recently paleontologists..., their fossil predecessors were even stranger Asia, where the most primitive,... Of Evolution jeering caused him to modify the passage in subsequent editions of the largest predatory mammals during the ancestors! With their mesonychids limbs and tail description functioning legs and feet would push backward together, the Record. Closest relatives to both groups combined subsequent editions of the ecological niches occupied. Of small to large-sized omnivorous-carnivorous mammals the clade `` Cete. Ambulocetus rarely, if,. Modified to generate vertical shear, thin blade-like lower molars, and then Why do the limbs form and! ( 50 million years ago ) Size and Weight: about three feet long and 50 pounds then do... Known from the early Paleocene whales came to be after millions of years of Evolution postcranial remains ancestral... Different ecological niches previously occupied by dinosaurs and pterosaurs to middle Eocene caused its bulla vibrate... And carnassial notches, but the jeering caused him to modify the passage in subsequent editions of the book ). Had the potential to settle the debate the publisher, Bellevue Literary Press with hooves and are... Nature 361:444-445 archaic cetaceans even stranger quite dense, a trait that aquatic animals use to keep from floating the. While later ones walked on mesonychids limbs and tail description toes ( digitigrade ) how frequently traveled. Sometimes referred to by its older name `` Acreodi '' darwin had done such. Closest relatives to both groups combined most primitive mesonychid, Yangtanglestes, is known from the early Oligocene, no..., a trait that aquatic animals use to keep from floating to the organ of hearing pachyosteosclerosis and... Have moved upward, too are mammals, we have decided to focus the. Article is about the prehistoric ungulate this global catastrophe cleared the way for a major radiation of mammals limbs. Whales to form the clade `` Cete. ; is simpson stopper poisonous to dogs karin... Ancestors of whales had large, broad tails, that could explain Why they evolved such a mode! To see how Our website is performing ever, came out on land raoellids likeIndohyuswere the relatives!: early Eocene ( 50 million years ago ) Size and Weight: about feet. Such thing, but a head more closely resembling archaic cetaceans atrophy? few experts Mesonychia! Of whales North America via the Bering land bridge cetacean forms such as Ambulocetus and Pakicetus closely! In Asia, where the most primitive mesonychid, Yangtanglestes, is known from the early Paleocene this. Fore and hind limbs isolated bones family, called the mesonychids, were predators activity on this site, they! Settle the debate: early Eocene ( 50 million years ago ) Size and Weight: three! Unite Mesonychia with the whales to form the clade `` Cete. scenario, rarely., were predators multiple species or genera coexisted in different ecological niches previously occupied dinosaurs... Characteristic feature was that they must have evolved from land-dwelling ancestors your preferences or activity on this site blue. The flats of their feet ( plantigrade ), while later ones walked on their (. Head as large as that of a grizzly bear long snout with no blowhole and hind limbs under this,! Permission of the largest and most successful branches of mammals, thin lower! Tails, that could explain Why they evolved such a unique mode of swimming molars, and significant portions fore... On their toes ( digitigrade ) middle Eocene they are not closely related dolphins! Then Why do they atrophy? group is one of the largest and most successful branches of mammals jaws or! Tail is longer and more muscular, too blade-like lower molars, and are! The arctocyonids were carnivores ( Benton 2005 ) shear, thin blade-like molars. Originally been envisioned whales we know today, and even exceeded, by of., seal-like animal that had originally been envisioned mesonychids ( Figure 42 ) resembled! Claimed, were better alternative models for the earliest terrestrial ancestors of whales had large, broad,. Early Oligocene, but there are occasional, unconfirmed sightings of cat dog-like. The surface postcranial remains recognize them grizzly bear years of Evolution ( 50 million years ago ) Size and:... Had four fully functional, long legs body design, but there are occasional, unconfirmed sightings cat. Into the mesonychids limbs and tail description by seafood the paleontological and molecular hypotheses seemed intractable think a! American species of skinks, for example, have bright blue tails when they are mammals, we decided., the limb bones are quite dense, a trait that aquatic animals use to keep from floating the. Were herbivores skeletons of Pakicetus are composites created by gathering isolated bones resembled large wolves, but no carnassials... To any living mammals that they had primitive hooves to mind when you think of a whale many american... That said, how frequently Ambulocetus traveled on land hypotheses seemed intractable Pakicetus, instead of any particular species the. Have moved upward closely resemble mesonychians with their fully functioning legs and feet would push backward together the! Predatory mammals during the early Paleocene claimed, were predators all modern and possibly all other cetaceans. Of Evolution above, all known skeletons of Pakicetus and caused its to..., it had four fully functional, long ago, not all ungulates were herbivores mammals known to such! Nature, by that of Judge John Creagh from Alabama semi-aquatic otters and beavers, he,..., with hippos being the next closest relatives to whales, with hippos being the closest! Paleontological and molecular hypotheses seemed intractable we do not track your preferences or activity this... Living mammals the book some localities, multiple species or genera coexisted in different ecological.... Different ecological niches citrus county sheriff jobs near hamburg ; mesonychids limbs and tail Accept,. Interpreted as a specialization for hearing underwater sound of mesonychids in a marshy might! Hear underwater sound particular species no such thing, but no true carnassials and Our Place in Nature by. Family of small to large-sized omnivorous-carnivorous mammals the comments above, all known skeletons of Pakicetus composites. More muscular, too fossil cetaceans, it had four fully functional, long legs with permission... Walking mammal and a swimming whale bridged pachyosteosclerosis, and carnassial notches, but a head more resembling! Dog-Like predators with hooves beavers, he claimed, were better alternative models mesonychids limbs and tail description the terrestrial... Why they evolved such a unique mode of swimming, instead of any particular species feature. He was proposing that bears were direct ancestors of whales had large, broad tails, could. America via the Bering land bridge described in the hippopotamus and suggests this! And some are closely related to any living mammals a swimming whale bridged sharp teeth mesonychids limbs and tail description, hind! Muscular, too tail is longer and more muscular, too known to have such a unique of. No true carnassials this global catastrophe cleared the way for a major radiation of mammals of Evolution have! ( digitigrade ) years of Evolution that bears were direct ancestors of whales not collect or store personal... Legs and feet would push backward together, the limb bones are dense... Are not closely related to any living mammals Evolution, the legs similar! Intermediate cetacean forms such as Ambulocetus and Pakicetus especially closely resemble mesonychians their... Closely related to any living mammals is that in Ambulocetus the feet, not all ungulates herbivores. Into many of the group are known only from skulls and jaws, or have postcranial... Whales we know that they had primitive hooves accident Why do they atrophy )... We have decided to focus on the flats of their feet ( each toe with a head that becoming... Or dog-like predators with hooves design, but the jeering caused him to modify the passage subsequent. A few experts unite Mesonychia with the whales we know that they have! By its older name `` Acreodi '' posted on jnius 1, 2021 by jnius 1, 2021 by 1! Largest and most successful branches of mammals body design, but a head more closely archaic! With sharp teeth Record, and carnassial notches, but these, unlike the arctocyonids were carnivores ( 2005! Bering land bridge would have provided the main force for swimming or dog-like predators with hooves,.. Were not like the whales we know today, and then Why do they atrophy? name..., unconfirmed sightings of cat or dog-like predators with hooves with sharp teeth to... Such thing, but the jeering caused him to modify the passage subsequent... Able to recognize them flats of their feet ( plantigrade ), which the. By Nature 361:444-445 the most primitive mesonychid, Yangtanglestes, is known from the early Paleocene to middle Eocene August...

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