Oligocene Nimravid Eusmilus
Eusmilus sicarius
Brule Formation (Scenic Mbr.)
Middle Oligocene (Orellan)
Custer County, South Dakota
Presented here is a remarkable example of a very rare Nimravid. This specimen is a composite of two individuals (the skull from one and the lower jaws from another) that were discovered in the same area of the White River Badlands of South Dakota. This example is very complete considering the rarity of the genus. The skull is 7" long.

The skull is over 90% complete. The missing areas are about 50% of each zygoma and other small areas of restoration. There is some distortion in the skull and one saber. The preservation of the teeth is excellent and among some of the best of any Eusmilus that we have seen in other collections. This animal was in its prime with fused sutures and little wear on the teeth. The bone is covered with a light ferruginous coating. The sabers are complete and original to the skull. They are 70 mm long on the inside curve and 80 mm long on the outside curve. These measurements are of enamel only. The sabers are very thin, half as thick as a Hoplophoneus. Because they are so thin they fracture easily as can be seen in the photos but have been expertly prepared and have a very impressive appearance.

The lowers are from a separate specimen. However, they match closely (from a slightly larger individual) and were found in the same area. Pm3 and Pm4 are preserved in both jaws. The lower left canine and i3 are preserved as well. The right lower canine and all other incisors are missing. The right coronoid
is missing. The lower jaws are 150 mm long at the longest point. The flanges are 90 mm long from the opening of the canine alveoli to the terminus of the flange. Both flanges are complete.

Pre-preparation photographs are available.

Out of all of the nimravids,‭ ‬mammalian predators better known as the‭ ‘‬false sabre-toothed cats‭’‬,‭ ‬Eusmilus seems to have been one of the most dangerous.‭ ‬Not only did Eusmilus grow to be one of the largest known nimravids at up to two and a half meters long,‭ ‬but a skull of its smaller relative Nimravus has been found with skull damage that is an almost precise match for the teeth of Eusmilus.‭ ‬This however may have been a case of one predator warning another away rather than an attempt of killing to feed since the wounds on the individual Nimravus in question actually healed.‬‬‬‬‬‬‬
As anyone who is already familiar with nimravids knows,‭ ‬Eusmilus looked like one of the later sabre toothed cats,‭ ‬but was in fact no way related them beyond being a member of the Carnivora.‭ ‬Nimravids like Eusmilus evolved down a separate genetic line,‭ ‬but found themselves living in a world where there was a predatory niche open for cat-like predators.‭ ‬Growing large and possessing enlarged upper canine teeth that were almost as long as the skull,‭ ‬Eusmilus would have been a hunter of other medium to large sized animals.‬‬‬‬‬‬
The enlarged canines that are nicknamed‭ ‘‬sabre-teeth‭’ ‬were the primary killing tools employed by Eusmilus and analysis of the skeleton supports this.‭ ‬The muscle attachment points on the skull show that Eusmilus actually had weak jaw closing muscles,‭ ‬but this was to allow for a wide jaw opening angle.‭ ‬Reconstructions of Eusmilus show that its jaw could open to an impressive ninety degrees wide,‭ ‬thirty degrees more than a modern African lion‭ (‬Panthera leo‭)‬.‭ ‬However this still pales in comparison to the later Smilodon which had the ability to open its jaws one hundred and twenty degrees wide.‭ ‬These wide jaw opening angles allow for the sabre-teeth to be brought into use without the lower jaw getting in the way.‭‬‬‬‬‬‬‬‬‬‬‬