''Eusmilus'' ('true sabre') is a prehistoric

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

nimravid Nimravidae is an extinct family of carnivorans, sometimes known as false saber-toothed cats, whose fossils are found in North America and Eurasia. Not considered to belong to the true cats (family Felidae), the nimravids are generally considered ...

that lived in

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

and

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

during the

Late Eocene The Priabonian is, in the International Commission on Stratigraphy, ICS's geologic timescale, the latest age (geology), age or the upper stage (stratigraphy), stage of the Eocene epoch (geology), Epoch or series (stratigraphy), Series. It spans ...

Early Oligocene The Rupelian is, in the geologic timescale, the older of two age (geology), ages or the lower of two stage (stratigraphy), stages of the Oligocene epoch (geology), Epoch/series (stratigraphy), Series. It spans the time between . It is preceded b ...

epochs (34.7–29.5 mya).

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 ''Hoplophoneus'' (Greek: "murder" (phonos), "weapon" (hoplo)) is an extinct genus of the family Nimravidae, lived in North America and Asia during the Late Eocene to Early Oligocene epochs from 35.7 to 30.5 mya, existing for approximately . Tax ...

''. The third species, ''E. adelos'', was described in 2021, and stands as the largest species in the genus. One study performed in 2016 moved all North American species to ''Hoplophoneus''. The discovery of ''E. adelos'' meanwhile, suggests that nimravids went along derived evolutionary pathways; conical-toothed, dirk-toothed, and scimitar-toothed, with 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.

Description

''E. bidentatus'' was estimated to have weighed , making it no larger than a

lynx A lynx ( ; : lynx or lynxes) is any of the four wikt:extant, extant species (the Canada lynx, Iberian lynx, Eurasian lynx and the bobcat) within the medium-sized wild Felidae, cat genus ''Lynx''. The name originated in Middle Engl ...

, and is estimated a shoulder height of .'' E. sicarius'' was considerably larger than ''E. bidentatus'', being about the size of a large

leopard The leopard (''Panthera pardus'') is one of the five extant cat species in the genus ''Panthera''. It has a pale yellowish to dark golden fur with dark spots grouped in rosettes. Its body is slender and muscular reaching a length of with a ...

. The largest species, ''E. adelos'', was similar in size to a small

lion The lion (''Panthera leo'') is a large Felidae, cat of the genus ''Panthera'', native to Sub-Saharan Africa and India. It has a muscular, broad-chested body (biology), body; a short, rounded head; round ears; and a dark, hairy tuft at the ...

, estimated to have weighed . This makes it the largest holplophonine nimravid and one of the largest nimravids known, just behind ''

Dinailurictis ''Dinailurictis'' was an extinct nimravid carnivoran (or "false sabre-toothed cat") belonging to the subfamily Nimravinae. It was named in 1922, with subsequent material being recovered from Early to Late Oligocene deposits across France and Spa ...

'', ''

Quercylurus ''Quercylurus'' is an extinct nimravid carnivora (or "false sabre-toothed cat") from the Early to Late Oligocene of France and Spain. Its fossils were found in Early Oligocene strata in Quercy. It is known with only one species ''Quercylurus ma ...

'', and ''

Barbourofelis ''Barbourofelis'' is an extinct genus of large, predatory, from a subfamily of feliformia, feliform carnivoran mammals of known as Barbourofelidae, Barbourofelinae, part of the Nimravidae superfamily. ''Barbourofelis'', along with ''Albanosmilus' ...

''. ''Eusmilus'' had developed long saber

teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

and looked like a

saber-toothed cat Machairodontinae (from Ancient Greek μάχαιρα '' machaira,'' a type of Ancient Greek sword and ὀδόντος ''odontos'' meaning tooth) is an extinct subfamily of carnivoran mammals of the cat family Felidae, representing the earliest ...

, 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 In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

, compared to ''Hoplophoneus.'' ''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 Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...

Thylacosmilus ''Thylacosmilus'' is an extinct genus of saber-toothed metatherian mammals that inhabited South America from the Late Miocene to Pliocene epochs. Though ''Thylacosmilus'' looks similar to the "saber-toothed cats", it was not a felid, like the we ...

'' and

felid Felidae ( ) is the Family (biology), family of mammals in the Order (biology), order Carnivora colloquially referred to as cats. A member of this family is also called a felid ( ). The 41 extant taxon, extant Felidae species exhibit the gre ...

Megantereon ''Megantereon'' is an extinct genus of prehistoric machairodontine saber-toothed cat that lived in Eurasia, Africa and possibly North America from the late Pliocene to the Middle Pleistocene. It is a member of the tribe Smilodontini, and close ...

'').

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.

Predatory behavior

Barrett speculated the ''E. adelos'' could've hunted rhinoceratids, tapirids, and anthracotheriids, due to its large size. 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 suggests it may have had a specialization towards larger bodied prey. There is fossil evidence of conflict between ''Eusmilus'' and ''

Nimravus ''Nimravus'' is an extinct genus of "false" saber-toothed cat that lived in North America and Eurasia during the late Eocene and Oligocene epochs 35.3—27.1 mya, existing for approximately . Not closely related to true saber-toothed cats, t ...

'', another genus of nimravid. Analysis on the elbow morphology suggests ''Eusmilus'' show relatively cursorality 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.Castellanos, Miguel (2024)
''Hunting Types in North American Eocene and Oligocene Carnivores and Implications for Nimravid Extinction''
(Graduate Research Thesis & Disserations)

References

External links

Nimravidae Oligocene feliforms Eocene carnivorans Chattian genus extinctions Oligocene mammals of Europe Paleogene France Fossils of France Quercy Phosphorites Formation Fossil taxa described in 1873 Prehistoric carnivoran genera {{paleo-carnivora-stub