Earliest-known Mammals: Some of the earliest-known mammals include Eozostrodon, Deltatheridium, Jeholodens, Megazostrodon, Triconodon, and Zalambdalestes. Eozostrodon was one of the first true mammals; it lived during the late Triassic period and early Jurassic period, about 210 million years ago.
The period between the extinction of the dinosaurs and the present day is called the Age of Mammals or Cenozoic. Mammals appeared on the earth long before the extinction of the dinosaurs; in fact, dinosaurs and mammals originated within 10 million years of each other, in the late Triassic about 200 million years ago.
