A “ marsupial sabertooth ” roamed the jungles of South America until its quenching 3 million class ago . Thylacosmilus atroxwas a member of the Sparassondonta , a group of mammalian carnivore that are related to today ’s marsupials . Thought to have weighed 100 kilograms ( 220 pound ) , this creature had all the hallmarks of a successful ambuscade predatory animal except for a deviation in one key feature . Thylacosmilus ’ eyes were positioned on the side of its head much like a target species , such as a moo-cow or antelope , rather than facing forward like a distinctive top marauder .
Eye position is a key adaption for selection in all species . Cows and otherherbivorousprey animals typically have eye sockets or orbits placed on the side of their head give them a wide field of vision and permit them to look out for anysabertoothmarsupials that might be sneaking up on them . By contrast , most predators have frontwards - facing eye with socket both facing the same direction on the grimace to enable stereoscopic , or 3-D , vision . This adaptation helps the predator judge the distance from the target before pouncing .
Thylacosmilusbucks this movement by being thought to be a big predator , while at the same time having a prey - like eye position – and now scientists think they have figured out why . Thylacosmilusis consider to have had a diet that was at least 70 percentage meat suggest it was a successful ambush predator . But the unusual place of the middle socket on the side of the skull means that there was not enough overlap for its vision to mix into 3D.
A reconstruction of the skull of Thylacosmilus atrox shows the enormous canine teeth and eye socket position. Image Credit: © Jorge Blanco
The answer to why the eyes are in such an unusual position for a predatory species also lies in the skull . In short , Thylacosmilushadenormous teeththat never stopped growing . Unlike a rodent such as abeaver , which has ever - produce tooth that are wear out down by gnaw at behaviour , the roots ofThylacosmilus ’ canines continue grow over the top of the skull . These eyetooth were so bombastic that they took up most of the room in the skull , mean the eye position were force sidewards .
“ You ca n’t understand cranial organization inThylacosmiluswithout first confront those enormous eyetooth , ” said pencil lead author Charlène Gaillard , a Ph.D. student in the Instituto Argentino de Nivología , Glaciología , y Ciencias Ambientales ( INAGLIA ) , in astatement . “ They were n’t just large ; they were ever - spring up … This had consequences , one of which was that no room was available for the orbits in the common carnivore billet on the front of the brass . ”
By using CT scan and 3D reconstruction , the team comparedThylacosmilus’eye position with other carnivores and mammals . A typicalcathas an orbital convergence of around 65 degrees butThylacosmiluswas thought to have an orbital convergence value of only 35 degrees .
Despite this , researcher believe the eyes sat forward within the optic sockets , come out out somewhat and therefore increasing that orbital convergence value by more than bivalent . They also hint that the eyeball diameter was bang-up inThylacosmiluscompared to other metatherians , further compensating .
" Thylacosmiluswas 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 optic field overlap as much as potential , ” say Colorado - writer Analia M. Forasiepi , also in INAGLIA and a researcher in CONICET , the Argentinian science and enquiry bureau . “ Even though its orbit were not favorably positioned for 3D sight , it could achieve about 70 pct of visual field overlap – obviously , enough to make it a successful participating predator . ”
Despite the strange morphology of the ancient sabertooth , the species managed to hold up successfully as an ambuscade predator until around 3 million years ago .
“ We may consider it as an anomaly because it does n’t meet within our preconceived category of what a proper mammal carnivore should look like , but development makes its own pattern , ” concluded Forasiepi .
The written report is published inCommunications Biology .
