The Thylacosmilus had wide-set eyes more typical of a herbivore (Picture: Jorge Blanco)
A terrifying sabre-toothed marsupial had such huge fangs its eyes were at the side of its head, like a horse or cow, according to new research.
The roots went right back to its braincase, producing unique vision for catching prey by pushing its eyes out wide.
A study published in the journal Communications Biology found that Thylacosmilus atrox could shed fresh light on the evolution of meat-eaters.
About the size of a jaguar, the pouched beast would have been a deadly hunter, capable of seeing nearly 360 degrees without moving.
‘You can’t understand cranial organisation in Thylacosmilus without first confronting those enormous canines,’ said lead author Charlene Gaillard, a PhD student at the Argentine Institute of Nivology, Glaciology and Environmental Sciences (INAGLIA).
Sabre-toothed beast, sheds light on the evolution of carnivores (Picture: Fiona Jackson For Mailonline)
‘They weren’t just large, they were ever-growing, to such an extent the roots continued over the tops of their skulls. This had consequences, one of which was that no room was available for the orbits in the usual carnivore position on the front of the face,’
Grazing animals need to check all around so they can flee rapidly in case of attack but this is the first time the phenomenon has been identified in a carnivore.
Skulls of carnivores normally have forward-facing eye sockets, or orbits, to enable 3D or ‘stereoscopic’ vision but the Thylacosmilus had wide-set eyes more typical of a herbivore.
It was more closely related to kangaroos and koalas than Smilodons, the famous sabre-toothed cat that died out at the end of the last Ice Age.
‘Compensation appears to be the key to understanding how the skull of Thylacosmilus was put together,’ said Professor Ross MacPhee, of the American Museum of Natural History, a co-author on the study.
Thylacosmilus’ teeth were larger than those of any other known sabretooth (Picture: Fiona Jackson For Mailonline)
‘In effect, the growth pattern of the canines during early cranial development would have displaced the orbits away from the front of the face, producing the result we see in adult skulls,’
MacPhee attributes the odd orientation of the orbits in Thylacosmilus to a morphological compromise between the primary function of the cranium, which is to hold and protect the brain and sense organs.
The cranium likely performed a collateral function unique to this species, which was to provide enough room for the development of the enormous canines.
The international team used CT scans and 3D virtual reconstructions to assess orbital organisation in a number of fossil and modern mammals.
Forward-facing eye sockets is important for judging the position of prey before pouncing.
About the size of a jaguar, the pouched beast would have been a deadly hunter, capable of seeing nearly 360 degrees without moving (Picture: Fiona Jackson For Mailonline)
Thylacosmilus was a member of a group known as sparassodonts, highly carnivorous mammals related to living marsupials.
Most carnivorous mammals resembled placental carnivores like cats and dogs having forward-facing eyes.
But the Thylacosmilus, an animal with a mainly meat-based diet, had eyes positioned like those of a herbivore, facing mostly laterally. In this situation, visual fields do not overlap sufficiently for the brain to integrate them in 3D.
‘Thylacosmilus was able to compensate for having its eyes on the side of its head by sticking its orbits out somewhat and orienting them almost vertically, to increase visual field overlap as much as possible,’ said co-author Dr Analia Forasiepi, also from INAGLIA.
‘Even though its orbits were not favorably positioned for 3D vision, it could achieve about 70 percent of visual field overlap-evidently, enough to make it a successful active predator,’
Most carnivorous mammals resembled placental carnivores like cats and dogs having forward-facing eyes (Picture: Fiona Jackson For Mailonline)
Lateral displacement of the orbits was not the only modification Thylacosmilus developed to accommodate its canines while retaining other functions.
Placing the eyes on the side of the skull brings them close to the temporal chewing muscles, which might result in deformation during eating.
To control for this, some mammals, including primates, have developed a bony structure that closes off the eye sockets from the side. Thylacosmilus did the same thing.
‘It might have made predation easier in some unknown way. But, if so, why didn’t any other sparassodont – or for that matter, any other mammalian carnivore – develop the same adaptation convergently?’ said Gaillard.
‘The canines of Thylacosmilus did not wear down, like the incisors of rodents. Instead, they just seem to have continued growing at the root, eventually extending almost to the rear of the skull,’
Thylacosmilus was a member of a group known as sparassodonts, highly carnivorous mammals related to living marsupials (Picture: Fiona Jackson For Mailonline)
For its size, Thylacosmilus’ teeth were larger than those of any other known sabretooth, going back to within millimetres of its very small brain case.
‘To look for clear-cut adaptive explanations in evolutionary biology is fun but largely futile,’ said Dr Forasiepi.
‘One thing is clear. Thylacosmilus was not a freak of nature, but in its time and place it managed, apparently quite admirably, to survive as an ambush predator,’
‘We may view it as an anomaly because it doesn’t fit within our preconceived categories of what a proper mammalian carnivore should look like, but evolution makes its own rules.’
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Thylacosmilus had wide-set eyes more typical of a herbivore.
