Homotherini

Homotherini Temporal range: Early Miocene–Late Pleistocene PreЄ Є O S D C P T J K Pg N
Skeleton of Homotherium serum from Friesenhahn cave, Texas Memorial Museum, University of Texas at Austin, Austin, Texas
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Family:	Felidae
Subfamily:	†Machairodontinae
Tribe:	†Homotherini Fabrini, 1890
Genera
†Amphimachairodus †Homotherium (type) †Lokotunjailurus †Nimravides †Xenosmilus

Homotherini is an extinct tribe of carnivoran mammals of the family Felidae (true cats). The tribe is commonly known as scimitar-toothed cats. These saber-toothed cats were endemic to North America, Europe, Asia, Africa, and South America^[1] from the Miocene to Pleistocene living from c. 23 Ma until c. 12,000 years ago.^[2]

Description

Compared to the usually massively built dirk-toothed phenotype, apparent in Smilodon, Megantereon and Barbourofelis (just to list a few), their upper canines were smaller than those of equally sized cats that had the dirk-tooth phenotype, but they had serrated edges.^[3][4] The scimitar-toothed phenotype has also evolved independently in other mammal families.^[5]

Evolution

The scimitar tooth form was used to assist in the hunting of herbivorous megafauna. With its hyper sharp and serrated form it was perfect for ripping flesh off of downed prey. Sadly if this tooth would come into contact with bone it could get caught, serrations worn off, or even completely broken thus leaving the organism without a food source, leading to starvation and death.^[6][7]

There is a debate about how both the scimitar-tooth and the dirk-tooth evolved in felines and other mammals. the two sides of the debate revolve around whether it was derived from a sexual dimorphic trait or if it was completely natural selection that drove the creation of these phenotypes. The argument for sexual dimorphic origins stems from the fact that in mammals sexual dimorphic traits manifest as tools for males to compete for females. It is believed that the scimitar-tooth and the dirk-tooth were originally only in males for use in competition but then with the rise of mega-herbivores it became favorable for females to take up the trait as well.^[8] The natural selection side of the debate argues that the scimitar and dirk-tooth both evolved because of the unfilled niche of predation of mega-herbivores so the trait evolved to take advantage of said niche.^[9]

References

1. Rincon, A., Prevosti, F., & Parra, G. (2011). New saber-toothed cat records (Felidae: Machairodontinae) for the Pleistocene of Venezuela, and the Great American Biotic Interchange Journal of Vertebrate Paleontology, 31 (2), 468-478 doi:10.1080/02724634.2011.550366
2. Paleobiology Database: Homotherini Basic info.
3. Martin, L.D., (1989). Fossil history of the terrestrial Carnivora. In: Gittleman J.L., ed. Carnivore behaviour, ecology, and evolution, Vol. 1. Ithaca, IL: Cornell University Press, 536-568.
4. Van Valkenburgh, B. 2007. Deja vu: the evolution of feeding morphologies in the Carnivora. Integrative and Comparative Biology 47:147-163.
5. Meloro, C., and G. J. Slater. 2012. Covariation in the skull modules of cats: the challenge of growing saber-like canines. Journal of Vertebrate Paleontology 32:677-685.
6. Van Valkenburgh, B. 2007. Deja vu: the evolution of feeding morphologies in the Carnivora. Integrative and Comparative Biology 47:147-163.
7. Slater, G. J., and B. Van Valkenburgh. 2008. Long in the tooth: evolution of sabertooth cat cranial shape. Paleobiology 34:403-419.
8. Randau, M., C. Carbone, and S. T. Turvey. 2013. Canine evolution in sabretoothed carnivores: natural selection or sexual selection? Plos One 8.
9. Van Valkenburgh, B., and T. Sacco. 2002. Sexual dimorphism, social behavior, and intrasexual competition in large Pleistocene carnivorans. Journal of Vertebrate Paleontology 22:164-169.