Simplify the following text for a Grade 13 native English-speaking person.
Original: He also found early horses , flying reptiles , the Cretaceous and Jurassic dinosaurs ; Apatosaurus and Allosaurus , and described the toothed birds of the Cretaceous ; Ichthyornis and Hesperornis .
Simplified: He also found early horses , the Cretaceous and Jurassic dinosaurs Apatosaurus and Allosaurus , and described the toothed birds of the Cretaceous ; Ichthyornis and Hesperornis .