Xenosmilus

Xenosmilus is an extinct genus of homotherin machairodontine (saber-toothed cat) that was discovered in Florida in 2001. It has one species, Xenosmilus hodsonae.

Discovery and naming
The new genus and species Xenosmilus hodsonae was described in 2001 based on a nearly complete skeleton (BIOPSI 101) from the Florida site Haile 21A, with a second partial skeleton (UF 60,000) as the paratype. Both skeletons came from Early Pleistocene-aged rocks in Florida.

The genus name Xenosmilus was derived from the Greek ξένος/ meaning "strange", and σμίλη/ meaning "knife". The species name hodsonae honors Debra Hodson, the wife of a researcher.

Description
Two fairly intact specimens were found by amateur fossil hunters in 1983 (1981 by some sources) in the Haile limestone mines in Alachua County, Florida. In 1994, the fossils were examined, and it was decided that the cats were of an entirely new genus. The fossils were of Irvingtonian age (1.8 to 0.3 Ma). Xenosmilus has also been found in quarries dating to the end Blancan such as Inglis 1a and Haile 7g, dating it up to 2 million years ago. The skull of Xenosmilus was 33 cm in length. Because the skeletons were found beside each other, some suspect Xenosmilus was a social mammal. Found alongside the two skeletons were dozens of peccary bones. It seems likely, with their muscular builds, that X. hodsonae preyed upon peccaries. Physically, the cat reached around 1 m tall at the shoulder, and is estimated about the same size or larger than Smilodon fatalis, though the body mass estimates of the holotype is around 118 kg. A 2019 book suggested a body mass range of 300 - 350 kg.

Classification
Xenosmilus is in the tribe Homotherini in the subfamily Machairodontinae of the cat family. A paper published in 2022 proposed that Xenosmilus is a more derived member of the tribe Machairodontini (another name for Homotherini), and that Homotherium venezuelensis should be reassigned to Xenosmilus.

Paleobiology
Before the discovery of Xenosmilus, all known saber-toothed cats fell into two general categories. Dirk toothed cats had long upper canines and stout legs. Scimitar toothed cats had only mildly elongated canines, and long legs. Xenosmilus broke these groupings by possessing both stout muscular legs and body, and short broad upper canines. Unlike most other saber-toothed cats, all of Xenosmilus's teeth were serrated, not just its fangs and incisors. Xenosmilus differs from Homotherium and most other cats in the lack of a gap separating the last incisor tooth and the canine, as well as the loss of the p3 tooth. Notably only the later species of Smilodon have also lost the p3 tooth. The way its top teeth were lined up also allowed Xenosmilus to concentrate its bite force on two teeth at a time.

Xenosmilus has also been theorized by some to have hunted via a "bite and retreat" strategy using its teeth to inflict deep wounds because of the way its canines and incisors could operate as a unit during a bite, leading to Xenosmilus bearing the occasional moniker of "cookie-cutter cat". Studies published in 2022 suggest that Xenosmilus and other machairodonts such as Smilodon were also capable of efficiently removing meat from a kill without damaging their teeth, as evidenced by bite marks on the bones of Platygonus. This same study also suggests that machairodonts could consume at least smaller bones when feeding, similar to lions.