Diet '', a large specialised sabre-toothed sparassodont Sparassodonts were carnivorous, and with the exception of some basal members of all members of this group were
hypercarnivorous (having diets composed of more than 70% meat). Only
Hondadelphys and
Stylocynus appear to have exhibited adaptations for
omnivory, and even then
Stylocynus may have had a more
mesocarnivorous diet similar to
canids than an omnivorous one. Sparassodont
coprolites from the
Santa Cruz Formation preserve the bones of
chinchillid and
octodontoid rodents inside them. Bite marks from medium-sized sparassodonts have been found on the small
notoungulate Paedotherium. Stable isotope data from the early late Miocene
Lycopsis viverensis and
Thylacosmilus atrox suggests that these species fed on
C3 grazers in open habitats, likely notoungulates. Bite marks likely pertaining to hathliacynid sparassodonts have been found on the remains of penguins and flightless marine ducks in ancient seabird nesting colonies, suggesting that sparassodonts raided seabird colonies for eggs, carrion, and other prey like many predatory mammals do today. Borhyaenid and proborhyaenid sparassodonts have been interpreted as being capable of crushing bones similar to modern
hyenas,
wolverines, or the
Tasmanian devil (
Sarcophilus harrisii) based on their deep jaws, bulbous premolars with deep roots and pronounced wear at their tips, extensive fused or interlocking
mandibular symphyses, large
masseteric fossae, microfractures in their tooth enamel, and high estimated bite forces.
Australohyaena antiquua shows particularly pronounced adaptations for bone-cracking, with a very deep jaw and strongly arched
nasals similar to what is seen in modern
hyaenids. Most sparassodonts were
plantigrade,
Borhyaena has been suggested to have been
digitigrade but this has been questioned. this has been supported by fossil tracks. One unusual aspect of sparassodont paleoecology is that at most fossil localities their remains are nearly ten times rarer than would be expected based on comparisons with carnivorous mammals at fossil sites in other parts of the world. The exact reasons for this are not clear, though this appears to be a broader pattern applicable to other groups of Cenozoic South American terrestrial carnivores (i.e.,
terror birds). However, this has not been tested further. Sparassodonts have relatively large and complex brains for metatherians, comparable to those of some Australian marsupials like
Australian possums, though the body masses used to produce these estimates of relative brain size are low compared later studies suggesting these values could be overestimated. A 2025 endocast analysis reveals that some morphological characters found in extant marsupials were present in stem marsupials such as sparassodonts. It also reveals that hathliacynids had similar
EQ to the extant
didelphids, on the other hand, large borhyaenoids had small brain cases for their size. Wounds have been documented on the face of specimens of
Borhyaena tuberata and
Sipalocyon gracilis, potentially suggesting aggressive habits similar to the modern
Tasmanian devil (
Sarcophilus harrisii).
Senses Sparassodonts appear to have had very little
binocular vision, with
borhyaenids having the greatest degree of depth perception (but still lower than modern carnivorans) and the eyes of
Thylacosmilus facing almost completely to the sides. However, later studies have found that
Thylacosmilus likely held its head in a downward-facing position, which would have allowed for more binocular vision than previously thought.
Pathology Several specimens of hathliacynids (
Sipalocyon and
Cladosictis) show a pathological disorder characterized by the presence of growths on the surface of the mandible, which in the most extreme cases can result in the loss of several teeth due to bony pathological growths.
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. Some have proposed that this shift in dominance was because of the more omnivorous habits of basal sparassodonts, which may have been more adapted to the more seasonal South American climates of 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). 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 the Pliocene may be linked to the climatic cooling that characterised the Late Neogene and the onset of the
Quaternary glaciation. Additionally, the increased aridity of South America caused by the uplift of the Andes was likely responsible as well. ==References==