Just about everyone has heard about sabertooth cats or as they are more popularly known but incorrectly named, "sabertooth tigers," but not everyone is aware that there are many different types of fossil cats with enlarged canines (the saber). In many of these cats the size of the saber varied so species with shorter, dagger like canines are called dirk-toothed, cats with medium-sized canines are scimitar-toothed, along with the larger sabertooths. Despite the fact that there are many different types of cats with enlarged canines, the overall record of these animals as fossils is limited compared to many other animals. The fossil record of sabertooths from the Monument, as in most fossil faunas, is extremely scanty and only provides a limited amount of information.
In 1933, C.L. Gazin of the Smithsonian described a partial jaw with one tooth as a new species of sabertooth which he called Machairodus (?) hesperus, now referred to as Megantereon hesperus. Besides this jaw, the only other sabertooth bone from Hagerman available to Gazin was a second metatarsal (one of the bones of the arch of the foot). Not much of a record to go on, but this is often the case for the fossil record of large carnivores; there are only a small number of specimens for a particular species with which to work.
From an ecological standpoint there are two good reasons why large carnivores such as sabertooth cats are rare as fossils. In any given area there will always be more herbivores or plant eaters than carnivores or meat eaters. Whether we are talking about mice to feed hawks or bison to feed wolves, there has to be a larger population of prey than predators or else the predators would soon run out of food and starve. Usually only five percent or less of the local populations of animals is comprised of predators. Since there are so many more herbivores, they have a better chance to be preserved as fossils than carnivores. The second factor is the body size of the predator. The larger the predator, the more food and space each individual requires for its survival, so the lower the density of the population. A low population density means less chance for preservation in the fossil record unless you have an unusual situation like tar pits. Put these two factors together, low density combined with smaller populations (compared to herbivores) an it's no surprise large carnivores such as a sabertooth cat are not at all common as fossils. So the discovery of any parts at all of a large predator is a special event to a vertebrate paleontologist. Gazin's two pieces of sabertooth cat had beaten the odds.
Since Gazin's original work, the number of bones of sabertooths at Hagerman has not increased by much. Following years of field work at the Monument in the 1960's by the University of Michigan under the direction of C.W. Hibbard, only one other specimen, a fragment of a lower tooth, was found. In his study of the carnivores from Hagerman published in 1970, P.R. Bjork also described a fourth metacarpal from the Smithsonian collections for a total of four specimens. Based on this sample, Bjork concluded that there were actually two types of sabertooths at Hagerman, the one described by Gazin and a second genus called Ischyrosmilus. Obviously, any additional specimens would greatly help our understanding of the Hagerman sabertooths.
Some specimens were found by park service field crews conducting field work on the Monument. A sabertooth cat humerus was found by one of our volunteers, Hugh Harper. Additional exploration in the area where the humerus was found has turned up part of the canine (saber) of the cat and a complete wrist bone called the scapholunar. As I've already noted, every little bit is important and helps fill in another piece of the puzzle. For example, the partial canine preserves serrations, similar to those on a steak-knife, along its front and back edges. These serrations which make it easier to slice through the skin of thick- skinned prey are not present in all sabertooth cats, and its presence or absence is used to tell different sabertooths apart. For example, the genus Megantereon, lacks these serrations on its upper canines, but they are present on the canines of Ischyrosmilus. Based on our new specimens, it would seem that our new discoveries are the latter sabertooth. What is needed is a closer examination and comparison of our new bones with material from other collections in order to confirm their identity, or better yet, perhaps more bones will be found in the same area.
In order to better understand the sabertooth cats from Hagerman, both work in the field and other collections is needed.
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