Complex sentence: Buxolestes is an extinct genus of semi-aquatic, placental mammals belonging to the family Pantolestidae that took part in the first placental evolutionary radiation during the Middle Eocene (50-40 mya).
Split into simpler sentences: Buxolestes is an extinct genus of semi-aquatic, placental mammals belonging to the family Pantolestidae. Species in this genus were part of the first placental evolutionary radiation during the Middle Eocene (50-40 mya).