The arrangement and pattern of teeth shown in a herbivorous mammalian ancestor, Tiarajudens eccentricus, having large protruding canines has puzzled researchers since the discovery of the mammalian four years ago.
After intense study, the researchers have now concluded that T. eccentricus, which lived on earth 270 million years ago, used these sabre-like teeth for inter-specific male-male combat -- much like what we see between male deer today.
"Fossils always surprise us. Now they show us that 270 million years ago, two forms of inter-specific combat, represented in deer today, were already present in the forerunners of mammals," said lead researcher Juan Carlos Cisneros.
The results were published in the journal Royal Society Open Science
Sabre-teeth are known to belong to the large Permian predators gorgonopsians (also known as sabre-tooth reptiles), and in the famous sabre-tooth cats from the Ice Age.
The discovery of T. eccentricus, a Brazilian species, also allowed for a reanalysis of the South African species Anomocephalus africanus, discovered 10 years earlier.
The two species have several similar features that clearly indicated they are closely related but the African species lack the sabre-tooth canines of its Brazilian cousin.
In the Middle Permian epoch around 270 million years ago, the first communities with diverse, abundant tetrapod herbivores were evolving.
In deer today, enlarged canines are used in male-male displays during fighting. The long canine in the herbivore T. eccentricus is interpreted as an indication of its use in a similar way, and is the oldest evidence where male herbivores have used their canines during fights with rivals.
"It is incredible to think that features found in deer such as the water deer, musk deer and muntjacs today were already represented 270 million years ago," Cisneros said.