The Ordovician Period is divided into seven stages two each in the early and middle epochs and three in the late epoch.
Middle: epoch-averaged rank/group size.
During the Middle Jurassic Epoch (174.1 million to 163.5 million years ago), the earliest snakes evolved.
The second was centred on eastern Tennessee in the Middle Ordovician Epoch.
The Kamasian, or Second, Pluvial of the middle Pleistocene Epoch corresponds to the Mindel in Europe.
The first mammals probably derived from small carnivorous chiniquodontids or trithelodonts sometime in the Middle Triassic Epoch (245.9 million to 228.7 million years ago).
Burgess Shale, fossil formation containing remarkably detailed traces of soft-bodied biota of the Middle Cambrian Epoch (520 to 512 million years ago).
The oldest known fossil is that of a cockatoo from Queensland dating to the Early to Middle Miocene Epoch (23.8 to 11.2 million years ago).
Ida (Darwinius masillae), nickname for the remarkably complete but nearly two-dimensional skeleton of an adapiform primate dating to the middle Eocene Epoch (approximately 47 million years ago).
Platystrophia, genus of extinct brachiopods (lamp shells) occurring as fossils in marine rocks of the Middle Ordovician epoch to about the middle of the Silurian period (i.e., from about 472 million to 423 million years ago).
