Hyaenodonta

Classification Hyaenodonts were considerably more widespread and successful than the oxyaenids, the other clade of mammals originally classified along with the hyaenodonts as part of Creodonta. In 2015 phylogenetic analysis of Paleogene mammals, by Halliday et al., monophyly of Creodonta was supported and was placed in the clade Ferae, closer to Pholidota than to Carnivora. However, order Creodonta is now considered to be a polyphyletic wastebasket taxon containing two unrelated clades assumed to be closely related (or ancestral) to Carnivora. Hyaenodonta and Oxyaenodonta are now considered their own distinct orders. Evolution Hyaenodonts are believed to have evolved in Europe either during the Late Cretaceous or Early Paleocene. Hyaenodonts soon dispersed into Africa and India, implying close biogeographical connections between these areas. Afterwards, hyaenodonts dispersed into Asia from either Europe or India, and finally, North America from either Europe or Asia. In Africa, hyaenodonts saw an increase in subfamilial richness after the end of the Early Eocene Climatic Optimum. During the middle to late Eocene, hyaenodonts, along with carnivorans, would replace oxyaenids, mesonychians, and miacoids in North America and in Europe. During the Paleogene, hyaenodonts were the dominant group of carnivores in Africa and Europe. The order saw a massive decline globally at the end of the Eocene to early Oligocene due to the decline of favorable prey and the expansion of open environments. Interestingly, in Afro-Arabia, the hyainailouroids experienced a rebound in diversity from the late Oligocene to the early Miocene. Several Miocene representatives of this order, include hyainailourids Megistotherium, Simbakubwa, Hyainailouros, Sectisodon, Exiguodon, Sivapterodon, Metapterodon, and Isohyaenodon, the prionogalid Prionogale, the teratodontid Dissopsalis and Hyaenodon. Taxonomy == Characteristics ==

Size They generally ranged in size from at the shoulder. Other large hyaenodonts include the hyainailourine Hyainailouros and the much earlier-living Hyaenodon gigas and Hyaenodon mongoliensis (The largest species of the genus, Hyaenodon), both species had a skull length of and are estimated to be similar in size to Hyainailouros. Most hyaenodonts, however, were in the range, equivalent to a mid-sized dog. Skull and dentition '' , Hyaenodon, and Oxyaena Compared to carnivorans, who have one pair of carnassial teeth, hyaenodonts possessed as many as three sequential pairs of carnassials or carnassial-like molar teeth in their jaws. Their skulls are known to have high sagittal crests which supported attachment for powerful temporalis muscles. Hyaenodonts, like all "creodonts", lacked post-carnassial crushing molar teeth, such as those found in many carnivoran families, especially the Canidae and Ursidae. but the later, larger forms were generally digitigrade or semidigitigrade. Diet While hyaenodonts were hypercarnivorous predators, Lesmesodon was found to have been an insectivorous based on chewing cycle analysis. Despite this, hyaenodonts weren't as versatile in their diet as carnivorans. == Extinction ==

(around 1920) In North America, hyaenodonts experienced a terminal decline from the Eocene to Oligocene, with Hyaenodon being the only genus present in North America during the Oligocene before going extinct. Lang and colleagues found that the evolutionary success of carnivorans compared to hyaenodonts may have been largely influenced by the retention of a basal morphotype throughout their evolutionary history. The authors also suggested that carnivorans likely contributed in some way to the extinction of hyaenodonts, with the difference in functional morphology and adaptive potential of their carnassials possibly being a factor. (far left), Cynelos eurydon, Afrosmilus africanus and Hyainailouros napakensis (far right) Within Africa, experts had hypothesized that hyaenodonts suffered from competitive displacement, as the invading carnivorans forced hyainailourids to tend towards carnivory. In support of this hypothesis, as even some of the smallest Miocene hyainailourids, Isohyaenodon and Mlanyama, showed adaptations towards hypercarnivory compared to older, mesocarnivorous hyaenodonts such as Boualitomus and Pakakali. Borths and Stevens, in their 2019 paper, argued that pack hunting carnivorans had larger and more complex brains, suggesting this enabled them to steal carcasses from large, solitary hyainailourines. Among large hyainailourids, the discovery of Simbakubwa suggests the evolution of large hyainailourines was thought to have been changes in the herbivore fauna instead of competition with carnivorans. with the relative size of the anterior brain having a larger correlation to sociality than overall brain size. Experts also argued due to the absence of canids (who dispersed into Africa by the latest Miocene), pack hunting would be difficult to assess among carnivorans in early Miocene Africa. Furthermore, vegetation in the early Miocene was generally more closed, preventing pack hunting and shorter, high speed chases from being effective. Morales and colleagues argued the decline of hyainailourids was due to the increase in aridity, as they were more adapted for forested environments as opposed to savannas, steppes, or deserts. Despite recovering North American hyaenodonts as a relatively cursorial clade, Castellanos also hypothesized due their short distal limbs, hyaenodonts had less cursorial adaptations than contemporary amphicyonids and couldn't exploit open environments as well which likely led to their extinction in addition to the extinction of large browsing prey. Grande Coupure saw an extinction rate of 60% of western European mammalian lineages. The event correlates with abrupt shift towards a icehouse world, which stems from the expansion of the Antarctic ice sheets and saw sea level decline by . No evidence of competitive replacement by carnivorans have been found in Europe as hyaenodonts were more diverse than carnivorans up until the Grand Coupure. Instead, the extinction of European hyaenodonts in the Oligocene is believed to have been caused by climatic changes rather than competition with carnivorans. == See also ==