Simplify the following text for a Grade 11 native English-speaking person.
Original: Though less famous than the Cambrian explosion , the Ordovician featured an adaptive radiation , the Ordovician radiation , that was no less remarkable ; marine faunal genera increased fourfold , resulting in 12 % of all known Phanerozoic marine fauna .
Simplified: Though less famous than the Cambrian explosion , the Ordovician featured an adaptive radiation , which was no less remarkable . Marine genera increased fourfold , resulting in 12 % of all known Phanerozoic marine fauna .