Simplify the following text for a Grade 10 native English-speaking person.
Original: He named these Pteranodon ( Occidentalia ) occidentalis ( for the now-disused species P. occidentalis ) and Pteranodon ( Sternbergia ) sternbergi . However , the name Sternbergia was preoccupied , and in 1978 Miller re-named the species Pteranodon ( Geosternbergia ) sternbergi , and named a third subgenus\/species combination for P. longiceps , as Pteranodon ( Longicepia ) longiceps .
Simplified: Pteranodon longiceps had a straight crest that went backwards , and Pteranodon sternbergi had a bigger , flatter crest that went upward .