page_title: Thylacosmilus
section_title: Diet and feeding
hierarchical_section_title: Thylacosmilus / Palaeobiology / Diet and feeding
caption_attribution_description: Centres of arcs described by the upper canine teeth. (A) Smilodon fatalis and (B) Thylacosmilus atrox. The distance of the centre from the jaw joint in Thylacosmilus atrox suggests that considerable translation as well as rotation was involved in the insertion of the canine teeth. Landmark positions shown on Thylacosmilus atrox. (C) lateral and (D) frontal views of right hand side landmarks. Curves shown in colour relate to Landmark point Von Mises mean stresses. Right hand side landmarks only shown.
context_page_description: Thylacosmilus is an extinct genus of saber-toothed metatherian mammals that inhabited South America from the Late Miocene to Pliocene epochs. Though Thylacosmilus looks similar to the "saber-toothed cats", it was not a felid, like the well-known North American Smilodon, but a sparassodont, a group closely related to marsupials, and only superficially resembled other saber-toothed mammals due to convergent evolution. A 2005 study found that the bite forces of Thylacosmilus and Smilodon were low, which indicates the killing-techniques of saber-toothed animals differed from those of extant species. Remains of Thylacosmilus have been found primarily in Catamarca, Entre Ríos, and La Pampa Provinces in northern Argentina.
context_section_description: Recent comparative biomechanical analysis have estimated the bite force of T. atrox, starting from maximum gape, at 38 newtons (8.5 lbf), much weaker than that of a leopard, suggesting its jaw muscles had an insignificant role in the dispatch of prey. Its skull was similar to that of Smilodon in that it was much better adapted to withstand loads applied by the neck musculature, which, along with evidence for powerful and flexible forelimb musculature and other skeleton adaptations for stability, support the hypothesis that its killing method consisted on immobilization of its prey followed by precisely directed, deep bites into the soft tissue driven by powerful neck muscles. It has been suggested that its specialized predatory lifestyle could be linked to more extensive parental care than in modern marsupial predators.
   
  In 1988 Juan C. Quiroga published a study on the cerebral cortex of two proterotherids and Thylacosmilus. The study examines endocranial casts of two Thylacosmilus specimens: MLP 35-X-41-1 (from the Montehermosan age in Catamarca Province), which represents a natural cast of the left half of the cranial cavity lacking the anterior part of the olfactory bulbs and the brain hemispheres; and MMP 1443 (from the Chapadmalalan age in Buenos Aires Province), which is a complete, artificial cast that shows some ventral displacement but with the anterior right part of the brain hemisphere and olfactory bulb. Quiroga's analysis showed that the somatic nervous system of Thylacosmilus represented 27% of the entire cortex, with the visual area representing 18% and the auditory area 7%. The paleocortex was more than 8%. The sulci of the cortex are relatively complex and similar in pattern and number to the modern diprotodont marsupials. Compared with Macropus and Trichosurus, Thylacosmilus had less development of the maxillar area with respect to the mandibular area, and the rhinal fissure is taller than in Macropus and Thylacinus. This disproportion between the maxillar and mandibular areas, which are roughly similar in marsupials, seems to be a consequence of the extreme development of the neck and mandibular musculature, used in the functioning of the osteodentary anatomy of this animal. However, the area dedicated to the oral-mandible region comprises 42% of the somatic area. The comparison between the endocranial casts of Thylacosmilus and a proterotherid specimen (possibly a species coevolving with Thylacosmilus and a potential prey item) indicates that Thylacosmilus had only half of the encephalization and a quarter of the cortical area, however it has more somatized areas, similar visual areas and less auditory area, which suggests different sensomotoric qualities between both animals.
  A 2005 study published by Wroe et al. analysing bite-forces with the use of regressions on body mass and applying the model of "dry skull" in which the jaw is modeled as a lever based in relations between the skull dimensions and the jaw muscles, was employed in some extinct and extant placental and metatherian predatory mammals. Thylacosmilus atrox reached the lowest value in that analysis, just barely surpassed by Smilodon fatalis. The authors concluded that both taxa, with low bite forces and peculiar cranial and postcranial anatomies, had a killing technique to dispatch large bodied preys without a true analogue between modern taxa.
  An analysis by Goswami et al. in 2010 tested if the metatherian mode of reproduction has produced any constraint in their cranial morphological evolution. Using landmarks in the skulls of several eutherian and metatherian meat-eating lineages, they compared the ecomorphological convergences in these groups. Metatherian lineages, including specialised forms as Thylacoleo and Thylacosmilus, showed values in morphospace more similar to caniniforms than felids, due that even the shortening of the skull and reduction of postcanine teeth are not so drastic as in felids, despite them often being compared to feliform eutherians. The study shows that in any case, metatherians could be so diverse in crani
caption: CT scans of the skulls of Smilodon and Thylacosmilus, showing the extent of the canines (red) within the jaw, with Thylacosmilus skull in side and front view below
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