A recent study by scientists from the American Museum of Natural History and the Instituto Argentino de Nivología, Glaciología, y Ciencias Ambientales investigated the hunting techniques of an extinct carnivorous marsupial relative, Thylacosmilus atrox. Despite having wide-set eyes, like a cow or a horse, Thylacosmilus was an efficient predator with its ‘ever-growing’ canines that extended across the top of its skull. This ‘marsupial sabertooth’ lived in South America until its extinction about three million years ago and belonged to Sparassodonta, a group of highly carnivorous mammals related to living marsupials. The study found that Thylacosmilus could achieve about 70% visual field overlap, allowing it to judge the position of prey before pouncing.

Unlike most carnivorous animals with forward-facing orbits, the orbits of Thylacosmilus were primarily laterally positioned, meaning that the visual fields did not overlap sufficiently for the brain to integrate them in 3D. However, the study found that Thylacosmilus could compensate for this by orienting its orbits almost vertically to increase visual field overlap as much as possible. The researchers concluded that compensation was the key to understanding how the skull of Thylacosmilus was put together, with the growth pattern of the canines during early cranial development having displaced the orbits away from the front of the face.

The study found that Thylacosmilus was successful in predation despite having such unique cranial modifications. Lateral displacement of the orbits was not the only modification that Thylacosmilus developed to accommodate its canines while retaining other functions. It also developed a bony structure to close off the eye sockets from the side, another example of convergence among unrelated species. Scientists still question why Thylacosmilus developed the unique adaptation of large canines that required re-engineering of the whole skull. The canines of Thylacosmilus did not wear down, like the incisors of rodents, and just continued growing at the root, eventually extending almost to the rear of the skull.

Overall, this study offers insights into the unusual hunting techniques of Thylacosmilus and sheds light on how the unique adaptations of extinct species allowed them to thrive in their respective ecosystems. The research highlights the importance of considering how extinct species could compensate for anatomical limitations in their hunting strategies.

The new research was published in the journal Communications Biology.

References

• AMNH. (2023, March 21). Ancient “Marsupial Sabertooth” Likely Saw in 3D. American Museum of Natural History; American Museum of Natural History. https://www.amnh.org/explore/news-blogs/research-posts/ancient-marsupial-sabertooth-likely-saw-in-3d
• Gaillard, C., MacPhee, R. D. E., & Forasiepi, A. M. (2023). Seeing through the eyes of the sabertooth Thylacosmilus atrox (Metatheria, Sparassodonta). Communications Biology, 6(1), 257. https://doi.org/10.1038/s42003-023-04624-5