The versatile function of the tribosphenic teeth has long been considered to be a key evolutionary innovation that enabled marsupials and placentals to diversify in the Mesozoic times, to be more successful than the mammals without the tribosphenic teeth. Caption for Figure 2. The Mammalian Family Tree and Dual evolution of tribosphenic mammals. Because the tribosphenic teeth have such an unique and intricate structure, paleontologists thought for several decades that it must have had a single origin in the Mesozoic time. The tribosphenic molar is an evolutionary feature adapted for versatile feedings.
All images are grayscale.
Caption for Figure 3. Geography of the Mesozoic Time. Australia, Antarctica, Africa, South America, India and Madagascar used to be clustered together as a unified southern land-mass, known as the Gondwana. And they were far separated from the northern continents where the Mesozoic marsupials and placentals used to live. The relationships of southern tribosphenic mammals, as proposed by Dr. Luo, Professors Cifelli and Kielan-Jaworowska fit nicely with the geography of the world in the Mesozoic times.