Which were more reliable, teeth or genes? All our content comes from Wikipedia and under the Creative Commons Attribution-ShareAlike License. In Benton, M. J. In 2001, archaeocetes possessing this bone were finally described, and the results were unmistakable. The bulla is the bone of the skull that formed the floor of a cavity that housed the middle ear ossicles (the malleus, incus, and stapes). Mesonychidae was named by Cope (1880). The thickened part of the auditory bulla was suspended from the skull, allowing it to vibrate in response to sound waves propagating through the skull. Studies coming out of the field of molecular biology conflicted with the conclusion of the paleontologists that whales had evolved from mesonychids, however. "Triisodontidae" may be paraphyletic. This shift allowed the fully aquatic whales to expand their ranges to the shores of other continents and diversify, and the sleeker basilosaurids likeDorudon,BasilosaurusandZygorhizapopulated the warm seas of the late Eocene. In 2007, Thewissen and other collaborators announced thatIndohyus, a small deer-like mammal belonging to a group of extinct artiodactyls called raoellids, was the closest known relative to whales. 1993. Cooper, L.N., Thewissen, J.G.M., and Hussain, S.T. Size: The term "mesonychid" is often used to refer to any of the various members of the order Mesonychia, though most experts prefer to use it to refer to the members of the family Mesonychidae, with many experts using the term "mesonychian" to refer to the order as a whole. Discuss with your teammates what traits you would expect to find (in the head , limbs , tail , . It uses its long limbs to swim in a 'doggy paddle' style. Throughout the Paleocene and Eocene, several genera, including Dissacus, Pachyaena and Mesonyx would radiate out from their ancestral home in Asia and into Europe and North America, where they would give rise to new mesonychid genera. 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. 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. The link between other ungulates and whales is thought to be mesonychids, extinct four-legged mammals that sometimes feasted on fish at river edges. 1988, the feature they thought united Andrewsarchus and Cetacea (they include a cladogram with a list of synapomorphies for each node (or at least for many)) was arrangement of incisors in a fore-and-aft line: early whales (and I'm not sure how many really early Cetaceans were known when they wrote) have all three incisors in a line, Andrewsarchus has M3 behind rather than beside M2, which they saw as an intermediate step towards the Cetacean condition. Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls. Not long after the true identity ofBasilosauruswas resolved, Charles Darwins theory of evolution by means of natural selection raised questions about how whales evolved. Part I! This conflict makes his soul a battlefield, where the forces that wish this reconciliation fight those that do not and reject the alternative solutions they offer. Although many skeletal elements of Pakicetus have been found, all were isolated, and our knowledge of Pakicetus comes from educated guesses that associate these bones together to form partial skeletons. Given these uncertainties, we have decided to focus on the genus Pakicetus, instead of any particular species. One possible conclusion is that Andrewsarchus has been incorrectly classified. as compared with mesonychids. And there is yet more to come: the hapalodectids are next. This idea was contested by O'Leary (1998), however, and it's mostly agreed that, while Dissacus is a basal mesonychid, Hapalodectes is a member of another mesonychian clade that we'll be looking at later on. The order is sometimes referred to by its older name Acreodi. Hr6prGO]di3nO[wK]DQ %H'U : yqsOa&'gR@&,CEN~I.{8Kei^I&. Long-snouted marsupial martens and false thylacines, Marsupial 'bears' and marsupial sabre-tooths, Because it would be wrong not to mention a sperm whale named like a tyrannosaur, http://viergacht.deviantart.com/art/Harpagolestes-133779748, http://www.archive.org/details/introductiontoos1885flow, The Lab Leak Theory Was Dismissed As Trump Xenophobia - Now Deniers Say It Was Not Accepted Because of Trump Xenophobia, DAN5/P1: Homo Erectus Early Cranial Capacity Was More Like Australopiths Such As 'Lucy', DART Made A Big Difference In Ability To Accurately Calculate Asteroid Deflections, The Subsidies Paradox: Affordable Food Versus The Environment, Degrowth communism as asolution for climate change. The University of Michigan But the conflict was not without hope of resolution. 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. 1995]. Mesonychid dentition consisted of molars modified to generate vertical shear, thin blade-like lower molars, and carnassial notches, but no true carnassials. The bulla was in turn connected to the chain of middle ear bones (i.e. The cervical vertebrae were relatively long, compared to those of modern whales; Ambulocetus must have had a flexible neck. Archaic ungulates ("Condylarthra"). [13][14] One possible conclusion is that Andrewsarchus has been incorrectly classified. There is a grain of truth in the cat versus dog question. The history of life: looking at the patterns, Pacing, diversity, complexity, and trends, Alignment with the Next Generation Science Standards, Information on controversies in the public arena relating to evolution. While later mesonychids evolved a suite of limb adaptations for running similar to those in both wolves and deer, their legs remained comparatively thick. 1999. See you there. [4] In contrast to arctocyonids, the mesonychids had only four digits furnished with hooves supported by narrow fissured end phalanges. One unresolved question is how exactly did Pakicetus catch its prey? ScienceBlogs is where scientists communicate directly with the public. Most paleontologists now doubt that whales are descended from mesonychids, and instead suggest that whales are either descended from, or share a common ancestor with, the anthracotheres, the semi-aquatic ancestors of hippos. They first appeared in the Early Paleocene, undergoing numerous speciation events during the Paleocene, and Eocene. Mesonychids first appeared in the early Paleocene, went into a sharp decline at the end of the Eocene, and died out entirely when the last genus, Mongolestes, became extinct in the early Oligocene. 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. 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. Together these fossil whales hung in a kind of scientific limbo, waiting for some future discovery to connect them with their land-dwelling ancestors. These "wolves on hooves" were probably one of the more important predator groups in the late Paleocene and Eocene ecosystems of Europe (which was an archipelago at the time), Asia (which was an island continent), and North America. Contrary to Huxleys carnivore hypothesis, Flower thought that ungulates, or hoofed mammals, shared some intriguing skeletal similarities with whales. A recent study found mesonychians to be basal euungulates most closely related to the "arctocyonids" Mimotricentes, Deuterogonodon and Chriacus. A later genus, Pachyaena, entered North America by the earliest Eocene, where it evolved into species that were at least as large. Little more than the back of the animals skull had been recovered, but it possessed a feature that unmistakably connected it to cetaceans. 2006. In some localities, multiple species or genera coexisted in different ecological niches. Cookie Settings. A new species of mesonychian mammal from the lower Eocene of Mongolia and its phylogenetic relationships. Among other taxa, Pachyaena and Sinonyx appear to be successively more basal relative to the Harpagolestes + Mesonyx clade. Mesonychids probably originated in China, where the most primitive mesonychid, Yangtanglestes, is known from the early Paleocene. These "wolves on hooves" are an extinct order of carnivorous mammals, closely related to artiodactyls.. Mesonychids first appeared in the early Palaeocene with the genus Dissacus.They went in decline at the end of the Eocene, and became extinct in the early Oligocene. Triisodontidae. 2007. But, because they are mammals, we know that they must . The group of animals that had the most features common to the earliest primitive whales found was called the Mesonychids . Age: Now that we've all survived Judgment Day, we can stop looking for ways to stop the Terminators, and go back to the search for dark matter. From Fowler, O.S. Some members of the group are known only from skulls and jaws, or have fragmentary postcranial remains. It appeared that Van Valen had been right, andPakicetuswas just the sort of marsh-dwelling creature he had envisioned. Skulls and teeth have similar features to early whales, and the family was long thought to be the ancestors of cetaceans. I've been in Romania and Hungary where I had a great time - saw lots of neat animals (fossil and living) and hung out with some neat people. To me, a layman, the skull compares much better to entelodonts than to *Mesonyx* and kin. While the limb proportions and hoof-like phalanges indicate cursoriality, the limbs were relatively stout and show that it cannot have been a long-distance pursuit runner. He envisioned a hypothetical cetacean ancestor easing itself into the shallows: We may conclude by picturing to ourselves some primitive generalized, marsh-haunting animals with scanty covering of hair like the modern hippopotamus, but with broad, swimming tails and short limbs, omnivorous in their mode of feeding, probably combining water plants with mussels, worms, and freshwater crustaceans, gradually becoming more and more adapted to fill the void place ready for them on the aquatic side of the borderland on which they dwelt, and so by degree being modified into dolphin-like creatures inhabiting lakes and rivers, and ultimately finding their way into the ocean. (1995), Geisler and McKenna (2007) and Spaulding et al. > to be up to snuff, compared to modern carnivorans, their We all know why this is, of course: it's because the Earth's oceans float atop the rocks and dirt that make up what we know as, "You still don't get it, do you? With this new context, however, the stubby, seal-like form forPakicetusdepicted in so many places began to make less and less sense. Huxley thought thatBasilosaurusat least represented the type of animal that linked whales to their terrestrial ancestors. There don't seem to be very many reconstructions of these critters available online.http://viergacht.deviantart.com/art/Harpagolestes-133779748, Very nice, Viergacht! Hornbills, hoopoes and woodhoopoes are all similar in appearance and have been classified together in a group termed Bucerotes. As you well know, normal matter here on Earth is, Mesonyx and the other mesonychid mesonychians (mesonychians part IV), Because we all love Paleogene 'ungulates', Five things you didn't know about armadillos. For previous articles on Paleogene mammals see And for other stuff on neat and obscure fossil mammals see Archibald, J. D. 1998. What springs to mind when you think of a whale? Unlike all modern and possibly all other fossil cetaceans, it had four fully functional, long legs. homestead high school staff. If blue whales built statues to each other theyd be smaller then these.Simon Hoggart (b. The only tail vertebra found is long, making it likely that the tail was also long. Journal of Paleontology 81:176-200. It had a long muzzle, teeth that were very similar to later archaeocetes, a reduced . Activity 1 - Whales in Transition | PDF | Organisms | Nature - Scribd Various genera and species coexisted in some locations, as hunters and omnivores or scavengers. Darwin had done no such thing, but the jeering caused him to modify the passage in subsequent editions of the book. Mesonychid taxonomy has long been disputed and they have captured . Most paleontologists now doubt that whales are descended from mesonychids, and instead suggest mesonychians are descended from basal ungulates, and that cetaceans are descended from advanced ungulates (Artiodactyla), either deriving from, or sharing a common ancestor with, anthracotheres (the semiaquatic ancestors of hippos). Goodbye Tet Zoo ver 2. However, recent work indicates that Pachyaena is paraphyletic (Geisler & McKenna 2007), with P. ossifraga being closer to Synoplotherium, Harpagolestes and Mesonyx than to P. gigantea. But, because they are mammals, we know that they must have evolved from land-dwelling ancestors. 1846. Mesonychids have often been reconstructed as resembling wolves albeit superficially, but they would have appeared very different in life. - . These later mesonychids had hooves, one on each toe, with four toes on each foot. Critics took it to mean he was proposing that bears were direct ancestors of whales. Ankalagon was larger than Dissacus (though the only known species, A. saurognathus, was originally described as a species of Dissacus) and is sometimes said to have been North America's first large mammalian predator. The largest hunters probably competed with biggest hyenodonts, but some may survived occupying more specialized niches. Mesonychid - Wikipedia It was only about 10 million years after this extinctionand more than 250 million years since the earliest tetrapods crawled out onto landthat the first whales evolved. They were endemic to North America and Eurasia during the Early Paleocene to the Early Oligocene, and were the earliest group of large carnivorous mammals in Asia. The fossil record was so sparse that no definite determination could be made, but in a thought experiment included inOn the Origin of Species, Darwin speculated about how natural selection might create a whale-like creature over time: In North America the black bear was seen by [the explorer Samuel] Hearne swimming for hours with widely open mouth, thus catching, like a whale, insects in the water. [7] Some genera may need revision to clarify the actual number of species or remove ambiguity about genera (such as Dissacus and Ankalagon).[5]. 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. mesonychids limbs and tail With a short lower spine stiffened by revolute joints, they would have run with stiff backs like modern ungulates rather than bounding or loping with flexible spines like modern Carnivorans. I think the prezygapophyses and postzygapophyses are incorrectly identified in the essay. pastor tom mount olive baptist church text messages / london drugs broadway and vine / mesonychids limbs and tail. Forgot to say great post! The American Phrenological Journal and Miscellany, Vol. This condition is called pachyosteosclerosis, and whales are the only mammals known to have such a heavily thickened involucrum. Underwater sound would have entered the skull of Pakicetus and caused its bulla to vibrate. homestead high school staff. They were major predators in the Northern Hemisphere from shortly after the demise of the dinosaurs until about 30 million years ago, and the shape of their teeth resembled those of whales likeProtocetus. When the unnerved scientists gathered the fragments, they noticed that the bone now revealed the inner ear. They would have resembled no group of living animals. Why did the largest fossil reptile that ever lived have mammal-like teeth? Contributions from the Museum of Paleontology, the University of Michigan 28, 289-319. New morphological evidence for the phylogeny of Artiodactyla, Cetacea, and Mesonychidae. Pioneers who cleared land in Alabama and Arkansas frequently found enormous round bones. Accept Cookies, Osteopathic Manipulative Medicine Research. Mesonychidae Some mesonychids are reconstructed as predatory (comparable to canids), others as scavengers or carnivore-scavengers with bone-crushing adaptations to their teeth (comparable to the large hyenas), and some as omnivorous (comparable to pigs, humans, or black bears). Thewissen, J.G.M., Williams, E.M., Roe, L.J., and Hussain, S.T.. 2001. With a short lower spine stiffened by revolute joints, they would have run with stiff backs like modern ungulates rather than bounding or loping with flexible spines like modern Carnivorans. The only tail vertebra found is long, making it likely that the tail was also long. Though not a series of direct ancestors and descendants, each genus represents a particular stage of whale evolution. 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. Mesonychia | Fossil Wiki | Fandom Mesonychids are a mostly Eocene group that originated in the Paleocene; Mesonyx, from the Middle Eocene of North America, was the first member of the group to be named (Cope published the name in . This page was last updated at 2022-07-17 03:07 UTC. & McKenna, M. C. 2007. At last, whales could be firmly rooted in the mammal evolutionary tree. The molars were laterally compressed and often blunt, and were probably used for shearing meat or crushing bones. The two most basal taxa are Dissacus and Ankalagon (Archibald 1998, O'Leary 1999, 2001, Geisler & McKenna 2007). He had found vertebrae and other fragments while blasting on his property and also sent off a few samples to the Philadelphia society. These hoofed predators came in diverse forms, from tiny to horse-sized. & Geisler, J. H. 1999. Richard Harlan reviewed the fossils, which were unlike any he had seen before. Huxley in 1871, Darwin asked whether the ancient whale might represent a transitional form. These features suggest to some authors that Harpagolestes was a carrion feeder (Szalay & Gould 1966, Archibald 1998). 1998. View full document Become a Member Its type genus is Mesonyx. Summary written by Jonathan Geisler and Melody Ho. A typical example of these animals (e.g. Mesonychids in North America were by far the largest predatory mammals during the early Paleocene to middle Eocene. These earliest cetaceans were not like the whales we know today, and only recently have paleontologists been able to recognize them. They had large heads with relatively long necks. As in most land mammals, the nose was situated at the tip of the snout. How? The phylogenetic position of cetaceans: further combined data analyses, comparisons with the stratigraphic record and a discussion of character optimization. There is evidence to suggest that some genera were sexually dimorphic. These forms, likeRodhocetus, were nearly entirely aquatic, and some later protocetids, likeProtocetusandGeorgiacetus, were almost certainly living their entire lives in the sea. This puts mesonychids as a distant relative of cetaceans rather than an ancestor, and their somewhat similar morphology was possibly a result of convergent evolution. 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. Functional and behavioral implications of vertebral structure in Pachyaena ossifraga (Mammalia, Mesonychia). 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. The basic design of all these animals is more similar than you might think. It's on the blood-feeding behaviour of, So sorry for the very short notice. A startling discovery made in the arid sands of Pakistan announced by University of Michigan paleontologists Philip Gingerich and Donald Russell in 1981 finally delivered the transitional form scientists had been hoping for. Cats vs dogs: in terms of evolution, are we barking up the wrong tree? Bulletin of the American Museum of Natural History 132, 127-174. The long-snouted and otter-like remingtonocetids appeared next, including small forms like the 46-million-year-oldKutchicetus. While, as noted earlier and elsewhere, Pachyaena and other mesonychids are often imagined as wolf-like, the good data we have on the osteology of this animal show that it was quite different from a canid in many respects. Becoming_Whales.doc - Unit: Evolution Advanced Biology, The last four articles that have appeared here were all scheduled to publish in my absence. Based on the orientations of the wear facets, Pakicetus sheared its prey into smaller pieces before swallowing. Its tail was long and slender, with no evidence of use for swimming. As E.D. One genus, Dissacus, had successfully spread to Europe and North America by the early Paleocene. Harpagolestes and Mesonyx appear to be sister-taxa, and the most derived of mesonychids (O'Leary & Geisler 1999, Geisler 2001, Thewissen et al. 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. & Gingerich, P. D. 1992. These "wolves on hooves" were probably one of the more important predator groups in the late Paleocene and Eocene ecosystems of Europe (which was an archipelago at the time), Asia (which was an island continent), and North America. But what kind of animal was it? 8. No one quite knew what to make of them. & Rose, K. D. 1995. > predators might have some credit after all. 133-161. There was no straight-line march of terrestrial mammals leading up to fully aquatic whales, but an evolutionary riot of amphibious cetaceans that walked and swam along rivers, estuaries and the coasts of prehistoric Asia. Thewissen and colleagues described the long-sought skeleton (as opposed to just the skull) ofPakicetusattocki. As I recall Prothero et al. Mesonychids first appeared in the early Paleocene, went into a sharp decline at the end of the Eocene, and died out entirely when the last genus, Mongolestes, became extinct in the early Oligocene. By the time the first mammals evolved 200 million years ago, however, dinosaurs were the dominant vertebrates. The cervical vertebrae were relatively long, compared to those of modern whales; Ambulocetus must have had a flexible neck. Mesonychid dentition consisted of molars modified to generate vertical shear, thin blade-like lower molars, and carnassial notches, but no true carnassials. Recently scientists determined which group of prehistoric artiodactyls gave rise to whales. In Janis, C. M., Scott, K. M. & Jacobs, L. L. (eds) Evolution of Tertiary Mammals of North America. . Theropods, several crurotarsan clades and, to a certain degree, even entelodonts did just fine with ziphodont teeth; Australia's top mammalian predator wasn't a dasyurid, but *Thylacoleo*. Darwin was widely ridiculed for this passage. The molars were laterally compressed and often blunt, and were probably used for shearing meat or crushing bones. The early representatives of these groups appeared about 33 million years ago and ultimately gave rise to forms as diverse as the Yangtze River dolphin and the gigantic blue whale. He tentatively assigned it the name Basilosaurus. (1995); and to Cete by Archibald (1998);[7] and to Mesonychia by Carroll (1988), Zhou et al. Update now. While preparing the underside of the skull ofIndohyus, a student in Thewissens lab broke off the section covering the inner ear. They were also most diverse in Asia, where they occur in all major Paleocene faunas. Sensory Abilities: The manus of Pachyaena gigantea (Mammalia: Mesonychia). Raoellids likeIndohyuswere the closest relatives to whales, with hippos being the next closest relatives to both groups combined. Many of the skeletons of the earliest archaeocetes were extremely fragmentary, and they were often missing the bones of the ankle and foot. The molars were laterally compressed and often blunt and were probably used for shearing meat or crushing bones. In C. M. Janis, K. M. Scott, and L. L. Jacobs (eds. 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. The molars have steeply inclined wear facets that formed when the upper and lower teeth contacted during chewing. Technically speaking, the term "mesonychid" refers specifically only to the members of the family Mesonychidae, such as the species of the genus Mesonyx. As strange as modern whales are, their fossil predecessors were even stranger. Cambridge University Press, pp. 1998. Cetaceans, like many other mammals, have ear bones enclosed in a dome of bone on the underside of their skulls called the auditory bulla. Since other predators, such as creodonts and Carnivora, were either rare or absent in these animal communities, mesonychids most likely dominated the large predator niche in the Paleocene of eastern Asia. 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. Riley Black is a freelance science writer specializing in evolution, paleontology and natural history who blogs regularly for Scientific American. Systematic Biology 48, 455-490. About 375 million years ago, the first tetrapodsvertebrates with arms and legspushed themselves out of the swamps and began to live on land. However, the close grouping of whales with hippopotami in cladistic analyses only surfaces following the deletion of Andrewsarchus, which has often been included within the mesonychids. whales came to be after millions of years of evolution. Recent fossil discoveries have overturned this idea; the consensus is that whales are highly derived artiodactyls. Mesonychids first appeared in the early Paleocene, went into a sharp decline at the end of the Eocene, and died out entirely when the last genus, Mongolestes, became extinct in the early Oligocene. 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. ScienceBlogs is a registered trademark of Science 2.0, a science media nonprofit operating under Section 501(c)(3) of the Internal Revenue Code. Diet: With the permission of the publisher, Bellevue Literary Press. [2], Hapalodectidae Adult fish, chickens, dogs, and lizards don't look much like humans. Its tail is longer and more muscular, too. Harpagolestes, known from several North American and Asian species, is a notably robust-skulled mesonychid with proportionally large canines, a deep lower jaw, and relatively broad post-canine teeth that are often heavily worn [skull of H. uintensis shown here, from Szalay & Gould (1966)]. Harlan traveled to London in 1839 to present Basilosaurus to some of the leading paleontologists and anatomists of the day. Mesonychid dentition consisted of molars modified to generate vertical shear, thin blade-like lower molars, and carnassial notches, but no true carnassials. Mesonychids fared very poorly at the close of the Eocene epoch, with only one genus, Mongolestes,[6] surviving into the Early Oligocene epoch. Pachyaena is reasonably well-known (Zhou et al. Hb``a``Z b. 2_%v>sr&u ! Pachyaena , or Sinonyx ) looked . 2023 Smithsonian Magazine Ambulocetus's skull was quite cetacean (Novacek 1994). There is evidence to suggest that some genera were sexually dimorphic. Szalay, F. S. & Gould, S. J. All rights reserved. Mesonychids exemplified a wide variety of appearances, ranging from those similar to wolves, hyenas, bears, and dogs (Jehle 2010). [12] However, the close grouping of whales with hippopotami in cladistic analyses only surfaces following the deletion of Andrewsarchus, which has often been included within the mesonychids. Mesonychia ("middle claws ") is an extinct taxon of small- to large-sized carnivorous ungulates related to artiodactyls. There were bone-cracking scavengers, small jackal or fox-like generalists, large wolf-like hunters, and so on. Mesonyx and the other mesonychid mesonychians - ScienceBlogs