the surface of the mandible, which in the most extreme cases can result in the loss of several teeth due to bony pathological growths. The exact cause of this condition (i.e., infection, virus, parasite) and why it seems to only occur in small sparassodonts is unknown, though this condition has also been documented in microbiotherians. Extinction After the middle Miocene, sparassodonts began to slowly decline in diversity. Basal borhyaenoids are last known from the early late Miocene (Pseudolycopsis cabrerai and Lycopsis viverensis), and after this time were at least partially replaced by large-bodied basal sparassodonts such as Stylocynus. It has been suggested that this shift in dominance was due to the more omnivorous habits of basal sparassodonts, which may have been better able to exploit the more seasonal climates of South America during the late Neogene. Borhyaenids are last known from the latest Miocene, though only fragmentary remains of this group are known from this period. Later remains assigned to this group have since been reidentified as thylacosmilids or procyonids. By the Pliocene, only two families of sparassodonts remained in South America, the Hathliacynidae and the Thylacosmilidae. Pliocene hathliacynid remains are rare, and it is possible that these animals may have competed with the large carnivorous didelphids such as Lutreolina that appeared around this time. Hathliacynids are last definitively known from the early Pliocene, though their remains are rare. The thylacosmilids, on the other hand, were more successful and abundant, being some of the only large mammalian carnivores in South America during the Pliocene, before dying out during a faunal turnover in the middle of the epoch (the youngest specimens of thylacosmilids are ~3.3 Ma). It is still not certain why Sparassodonta declined in diversity and became extinct during the late Cenozoic, but it appears as though competition from eutherian carnivorans was not a factor, as the placental analogues of sparassodonts (dogs, weasels, and saber-toothed cats) did not enter South America until the middle Pleistocene, several million years after their sparassodont counterparts became extinct. Sparassodonts did coexist with Cyonasua-group procyonids during the late Miocene and Pliocene, but Cyonasua-group procyonids appear to have been primarily omnivorous and filled ecological niches that sparassodonts never occupied, which may be one reason that these animals were able to colonize South America despite the diverse predator guild in the late Miocene. The overall decline in sparassodont diversity from the late Miocene to the end of