Their ancestors appeared around the same time as the first small mammals, and they were probably able to survive because they were evolving— and growing—at the same time as their mammalian predators.
Os seus antepassados apareceram  quase ao mesmo tempo que os primeiros mamíferos pequenos, e, provavelmente conseguiram sobreviver porque estavam a evoluir — e a crescer — ao mesmo tempo que os seus predadores mamíferos.