At the beginning of the Pliocene, South America had been isolated from the rest of the world for millions of years and a very specific fauna had developed there. The carnivores that occupy this immense island count among their ranks the terrible Thylacosmilus, with frightening saber teeth. But these huge canines have a drawback, they take up a lot of space on the skull of the carnivore, to the point that scientists wonder how it could see well in front of it!
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The predator commonly referred to as the “saber-toothed marsupial” is part of a group of carnivores called Sparassodonta, which are in fact metatherians closely related to modern day marsupials. During the isolation of the South American continent, they were the main carnivorous mammals. Thylacosmilustheir most famous representative who lived between 9 and 3 million years before our era, certainly has impressive canines, but they raise a major question.
The Bovine-Eyed Predator
A fundamental difference between carnivorous animals and herbivores is the placement of the eyes. While prey must constantly watch in all directions and most often have their eyes positioned laterally on the skull, predators instead benefit from stereoscopic vision to be able to estimate distances. Their eyes are therefore oriented forwards and ensure a strong convergence of their fields of vision, so that the brain can create a 3D image. However, the placement of the orbits of Thylacosmilus comes up against the implantation of his huge canines. These are not only disproportionate, they also grow continuously, like the incisors of rodents, so that they fit all the way to the top of the marsupial’s skull and leave too little room for the eye sockets to be forward facing.
Profound adaptations of the orbital region are often observed in saber-toothed predators, such as the famous saber-toothed felines (among which Smilodonbut also Hoplophoneus, Machairodus or Megantereon), more Thylacosmilus is an extreme case. The predator of a hundred kilos therefore finds himself with lateralized eyes, while scientists assume that he was a hypercarnivore, that is to say that his diet consisted of at least 70% meat. How to reconcile these two characteristics which seem opposite? This is what researchers from the American Museum of Natural History and of theArgentine Institute of Nivology, Glaciology, and Environmental Sciences from Mendoza, Argentina, whose study recently appeared in Communications Biology.
Their work has shown that the overlapping of the fields of vision of the metatherian’s eyes is indeed very low for a carnivore, around 35°, whereas that of a cat is 65°. But Thylacosmilus was probably not unable to see in 3D either, because other parameters come into account in estimating the stereoscopy of vision. The frontalization and the verticality (see diagram above), the orientation of the orbits in relation to two horizontal axes of the skull, are also to be considered, and in our predator they are very high. This allows it to increase its overlap of ” field of vision at approximately 70° “, explains Analía Forasiepi, co-author of the study, ” which was obviously enough to make him an accomplished predator ».