Toothy, Rodent-like Reptile Is Our Ancient Forebear

(Credit: Jorge Blanco) They're toothy, furry and tiny, but their existence kicked off an evolutionary success story 240 million years in the making. Cynodonts are some of the earliest ancestors of mammals, often referred to as ‘mammal-like reptiles.’ They first arose around 260 million years ago, just before the greatest extinction of all time which claimed 95 percent of all life on Earth. In particular, probainoganthian cynodonts are crucial in guiding our understanding of evolutionary history prior to the emergence of Mammaliaformes — the group that includes all mammals, and their ancestors. All modern mammals, even ourselves, evolved from these early, rodent-like critters. Even the jaws and skulls of cynodonts were very ‘mammal-like’, with a robust form and canines very similar to many modern species. Research by Agustín Martinelli and colleagues from Brazil has now revealed two new species of probainognathian cynodont from the Late Triassic, around 230 million years ago, of the Rio Grande do Sul state in southern Brazil. This forms part of an ongoing project into the evolutionary relationships between cynodonts and the earliest mammals in South America.