Discovered four years ago, and following an updated and more in-depth study of the herbivorous mammalian ancestor, Tiarajudens eccentricus, researchers from Brazil and South Africa can now present a meticulous description of the skull, skeleton and dental replacement of this Brazilian species.
They also learned that 270 million years ago, the interspecific combat and fighting we see between male deer today were already present in these forerunners of mammals.
This description by Brazilian researcher, Dr Juan Carlos Cisneros, and his co-authors from the Evolutionary Studies Institute at the University of the Witwatersrand, Professor Fernando Abdala and Dr Tea Jashasvili, is published in an article, titled: Tiarajudens eccentricus and Anomocephalus africanus, two bizarre anomodonts (Synapsida, Therapsida) with dental occlusion from the Permian of Gondwana in the journal, Royal Society Open Science, on 15 July 2015.
Saber-teeth are known to belong to the large Permian predators' gorgonopsians (also known as saber-tooth reptiles), and in the famous saber-tooth cats from the Ice Age.
When Tiarajudens eccentricus was discovered it had some surprises install: Despite large protruding saber-tooth canines and occluding postcanine teeth, it was an herbivore. The discovery of this 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 of the saber-tooth canines of its Brazilian cousin. In the Middle Permian, where these Gondwana cousins were living, 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," says Cisneros.
The researchers found the Tiarajudens' marginal teeth are also located in a bone from the palate called epipterygoid. "This is an extraordinary condition as no other animal in the lineage leading to mammals show marginal dentition in a bone from the palate," says Abdala.
In another group of mammal fossil relatives, dinocephalians - that lived at the same time as anomodonts, some of the bones in their foreheads were massively thickened. This can be interpreted as being used in head-butting combat, a modern behaviour displayed by several deer species today.
"Fossils are always surprising us. Now they show us unexpectedly that 270 million years ago two forms of interspecific combat represented in deer today, were already present in the forerunners of mammals," says Cisneros.
ABOUT THE AUTHORS
Juan Carlos Cisneros was born in El Salvador, Central America. He did his undergraduate studies at the Universidade Federal do Mato Grosso do Sul and Universidade Federal do Rio Grande do Sul in Brazil, and completed his PhD in Palaeontology at the University of the Witwatersrand, South Africa. He currently lectures in Palaeontology at the Universidade Federal do Piauí, Teresina, Brazil. His main interest is in Permian and Triassic tetrapods. He has worked in the Karoo and in the Paraná Basin in southern Brazil, and is currently exploring the Parnaíba Basin in northern Brazil.
Fernando Abdala is Reader of the Evolutionary Studies Institute at the University of the Witwatersrand, South Africa. He did his entire career at the National University of Tucuman, north-western Argentina where he researched on the evolution and ontogeny of South American cynodonts. He did his postdoctoral studies at the Pontificia Universidade Catolica de Rio Grande do Sul in Brazil and at the Bernard Price Institute for Palaeontological Research (Wits). He has published extensively on the taxonomy, ontogeny and evolution of cynodonts and, when he moved to South Africa, he also conducted researched on therocephalians and basal therapsids. He is member of an Argentinean team studying cranial ontogeny in living marsupials.
Tea Jashashvili is senior researcher in the Evolutionary Studies Institute, University of the Witwatersrand, South Africa. Jashashvili received her MD Diploma of Medical Doctor of General Practice, Tbilisi State Medical University, Georgia. She completed her graduate degrees at the National Museum of Natural History, Paris, and International PhD Diploma at the University of Ferrara. She undertook postdoctoral research in the Anthropologisches Institut und Museum, Universität Zürich, Switzerland, and conducted her postdoctoral research at the Evolutionary Studies Institute, University of the Witwatersrand.