Original: The first armored agnathans—the Ostracoderms, precursors to the bony fish and hence to the tetrapods (including humans)—are known from the middle Ordovician, and by the Late Silurian the agnathans had reached the high point of their evolution.
Simplified: The first armored agnathans the Ostracoderms, precursors to the bony fish and hence to the tetrapods (including human beings), are known from the middle Ordovician, and by the Late Silurian the agnathans had reached the high point of their evolution.