Eusmilus
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Eusmilus ('true sabre') is a prehistoric genus of nimravid that lived in Europe and North America during the Late Eocene to Early Oligocene epochs (34.7–29.5 mya).[1][2]
Taxonomy
There are three valid species of Eusmilus, E. bidentatus and E. villebramarensis. Ekgmoiteptecela MacDonald, 1963 was synonymized with Eusmilus by some authors, but is actually synonymous with Hoplophoneus.[1] The third species, E. adelos, was described in 2021, and stands as the largest species in the genus.[2]
One study performed in 2016 moved all North American species to Hoplophoneus.[1]
The discovery of E. adelos, meanwhile, suggests that nimravids went along derived evolutionary pathways; conical-toothed, dirk-toothed, and scimitar-toothed, and that their evolutionary paths split in two, leading to saber-toothed and conical-tooth forms that convergently evolved with those of true felids tens of millions of years later. Its discovery also suggests that several species of Hoplophoneus were actually species of Eusmilus genus instead.[2]
Description
E. bidentatus was estimated to have weighed Script error: No such module "convert"., making it no larger than a lynx, and is estimated at a shoulder height of Script error: No such module "convert"..[3][4][5] E. sicarius was considerably larger than E. bidentatus, being about the size of a large leopard.[6] The largest species, E. adelos, was similar in size to a small lion, estimated to have weighed Script error: No such module "convert".. This makes it the largest hoplophoneinae nimravid and one of the largest nimravids known, just behind Dinailurictis, Quercylurus, and Barbourofelis.[2]
Eusmilus had developed long saber teeth and looked like a saber-toothed cat, but was actually a so-called '"false saber-tooth"' and only bore this resemblance convergently. E. sicarius had very large upper canines and a massive flange at the front of the lower jaw, compared to Hoplophoneus.[7]
Eusmilus had lost many other teeth, possessing only 26 instead of the 44 usually seen in carnivore mammals. Its mouth could open to an angle of 90 degrees, allowing the creature to properly use its saber teeth. Bony flanges projected from Eusmilus ' lower jaw to protect the sabers (this is also seen in the unrelated marsupial Thylacosmilus and felid Megantereon).
Paleobiology
Growth and development
Eusmilus cubs and adolescents have been discovered, and examinations of their skeletons indicates that their saber-teeth emerged late in life, indicating the animals were dependent on their mothers for a relatively long period. The milk teeth of Eusmilus, upon their eruption, were large enough to allow it to hunt effectively. The added advantage of these milk sabers was that because of the late growth of the permanent sabers, if the milk saber-teeth were damaged, the nimravid had a chance to grow a new set of saber-teeth, allowing it to continue hunting.[8]
Predatory behavior
Barrett speculated the E. adelos could have hunted rhinoceratids, tapirids, and anthracotheriids, due to its large size.[2] Supplementary material from Lautenschlager et al. 2020 suggests E. bidentatus had a jaw gape of 107.32 degrees. Due to its actual jaw gape being over 90 degrees, the authors suggest it may have had a specialization towards larger bodied prey.[9] There is fossil evidence of conflict between Eusmilus and Nimravus, another genus of nimravid.[10]
Analysis on the elbow morphology suggests Eusmilus shows relative cursoriality compared to other nimravids. E. adelos was a pounce-pursuit predator, which may have been an adaptation for open habitats. E. cerebralis was recovered as an ambush predator, but found in localities that borders woodland and shrub environments, suggesting it lived in more open environments than other sympatric nimravids.[11]
References
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- ↑ Castellanos, Miguel (2024). Hunting Types in North American Eocene and Oligocene Carnivores and Implications for Nimravid Extinction (Graduate Research Thesis & Disserations)
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