In this task, we ask you to elaborate the sentence without changing its general meaning. You can do so by explaining further the input sentence, using more precise wording, adding qualifiers and auxiliary information etc.

The Middle Triassic is the second of three epochs of the Triassic period .
In the geologic timescale , the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided .