Wiki: Hyaenodonta - upcScavenger

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Hyaenodonta ("hyena teeth") is an extinct order of hypercarnivorous Placentalia mammals of clade Pan-Carnivora from mirorder Ferae. Hyaenodonts were important mammalian predators that are believed to have arose either in the Late Cretaceous or Early Paleocene within Europe, and persisted well into the Late Miocene.

Characteristics

Hyaenodonts are characterized by long, often disproportionately large skulls, slender jaws, and slim bodies. They generally ranged in size from at the shoulder. While Simbakubwa may have been up to (surpassing the modern polar bear in size), this estimate is suspect due to being based on skull-body size ratios derived from Felidae, which have much smaller skulls for their body size. Other large hyaenodonts include two close and later-surviving relatives of Simbakubwa, Hyainailouros, and Megistotherium (the latter likely being the largest in the group), and the much earlier-living Hyaenodon gigas (the largest species from genus Hyaenodon), which may have been as large as high at the shoulder, and weighed about . Most hyaenodonts, however, were in the range, equivalent to a mid-sized dog. The anatomy of their skulls show that they had a particularly acute sense of smell, while their teeth were adapted for shearing, rather than crushing.

Hyaenodonts were ancestrally plantigrade, but the later, larger forms were generally digitigrade or semidigitigrade. Because of their size range, it is probable that different species hunted in different ways, which allowed them to fill many different predatory Ecological niche, with small or medium-sized forms filling roles similar to Mustelidae or smaller felids of today while the larger forms functioned as Apex predator focusing on larger prey, wielding their mighty jaws as their principal weapon as they lacked grasping forelimbs. The in hyaenodonts are generally the second upper and third lower molars. However, some hyaenodonts possessed as many as three sequential pairs of carnassials or carnassial-like molar teeth in their jaws. Hyaenodonts, like all “creodonts”, lacked post-carnassial crushing molar teeth, such as those found in many carnivoran families, especially the Canidae and Ursidae, and thus lacked dental versatility for processing any foods other than meat.Wang, Xiaoming; and Tedford, Richard H. (2008). "Dogs: Their Fossil Relatives and Evolutionary History." New York: Columbia University Press

Hyaenodonts differed from Carnivora in that they replaced their deciduous dentition slower in development than carnivorans. Studies on Hyaenodon show that juveniles took 3 to 4 years in the last stage of tooth eruption, implying a very long adolescent phase. In North American forms, the first upper premolar erupts before the first upper molar, while European forms show an earlier eruption of the first upper molar.

At least one hyaenodont lineage, subfamily Apterodontinae, was specialized for aquatic, otter-like habits.

Range

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.Solé, Floréal & Smith, Thierry (2013). "Dispersals of placental carnivorous mammals (Carnivoramorpha, Oxyaenodonta & Hyaenodontida) near the Paleocene-Eocene boundary: a climatic and almost worldwide story" Geologica Belgica 16/4: 254–261 Afterwards, they dispersed into Asia from either Europe or India, and finally, North America from either Europe or Asia.Wang, Xiaoming; Qiu, Zhanxiang and Wang, Banyue (2005). "Hyaenodonts and carnivorans from the early Oligocene to early Miocene Xianshuihe Formation, Lanzhou Basin, Gansu Province, China" Palaeontologia Electronica Vol. 8, Issue 1; 6A: 14p.

They were important hypercarnivores in Eurasia, Africa, and North America during the Oligocene, but declined towards the end of the epoch, with nearly the entire order becoming extinct by the close of the Oligocene. Several representatives of this order, including hyainailourids Megistotherium, Simbakubwa, Hyainailouros, Sectisodon, Exiguodon, Sivapterodon, Metapterodon, and Isohyaenodon, the prionogalid Prionogale, the teratodontid Dissopsalis and the youngest species of genus Hyaenodon, H. weilini, survived into or evolved during the Miocene, of which, only Dissopsalis persisted into the Late Miocene.

Extinction

The extinction of hyaenodonts has been debated by experts. Many experts have argued that their extinction was due to competition with the Carnivora.

(2025). 9780521515290, Cambridge University Press. ISBN 9780521515290

Several experts have hypothesized that competitive displacement from the invading carnivorans forced African hyaenodonts to vary in size and become more hypercarnivorous. Borths (2019) argued that carnivorans had larger and more complex brains, which enables them to steal carcasses from solitary hyaenodonts due to their gregarious lifestyle. Lang et al. (2021) 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.

However, this hypothesis has been contested by many experts. One analysis on hyaenodonts and carnivorans within the Cypress Hills Formation, found that only the smaller hyaenodonts and carnivorans had significant niche overlap, while larger hyaenodonts and carnivorans (Such as H. horridus and Hoplophoneus) had very distinct niches, suggesting competition-driven extinctions were not likely in this formation and instead climate change was the contributor to their extinction during the Late Eocene. The global climatic cooling of the earliest Oligocene resulted in drier, more open landscapes and resulted in the extinction of large browsing herbivores, including brontotheres. With their relatively shorter legs, they were likely at a disadvantage in the increasingly open environments. However, the authors cautioned this does not exclude the possibility of competitive-driven extinctions among early and middle Eocene hyaenodonts, or of competitive interactions with carnivorans that drove hyaenodonts toward more extreme niches, indirectly leading to their extinction. In addition, studies have found that brain size in carnivorans has no correlation to sociality.

Morales et al. (2008) argued the extinction of African hyaenodonts was due to the aridification of Africa, as they were more adapted for forested environments than to savannas, steppes, or deserts.

Classification and phylogeny

Relations

Hyaenodonts were considerably more widespread and successful than the Oxyaenidae, the other clade of mammals originally classified along with the hyaenodonts as part of Creodonta.Lambert, David and the Diagram Group (1985): The Field Guide to Prehistoric Life. Facts on File Publications, New York. 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 Pangolins 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.Prevosti, F. J., & Forasiepi, A. M. (2018). "Introduction. Evolution of South American Mammalian Predators During the Cenozoic: Paleobiogeographic and Paleoenvironmental Contingencies"

Taxonomy