Wikipedia
Prozostrodon was an advanced cynodont that was closely related to the ancestors of mammals. The remains were found in Brazil and are dated to the middle Triassic. It was originally described as a species of Thrinaxodon and was probably fairly similar to that genus in overall build. The sole find has a skull length of 6.7 cm, indicating the whole animal may have been the size of a cat, though there is some doubt as to whether the find represents an adult individual. The teeth were typical of advanced cynodonts, and the animal was probably a small carnivore hunting lizards and other small prey.
Later analysis indicated Prozostrodon was more closely related to the mammals than to the Thrinaxodon species, and it was given its own genus. Cladistic analysis indicates its closest relatives gave rise to the first mammaliaforms and therefore to the crown group mammals. Prozostrodon was found in the Geopark of Paleorrota, Santa Maria Formation, Brazil and is deposited in the paleontology museum of the UFRGS.