Complex sentence: The first dorsal fin is about a third larger than the second and originates over the pelvic fin origins, while the second dorsal fin is located midway between the first dorsal and the caudal fin.
Split into simpler sentences: The first dorsal fin is about a third larger than the second and originates over the pelvic fin origins. The second dorsal fin is located midway between the first dorsal and the caudal fin.