Complex sentence: In fact, "killer" may be more apt in the case of the pygmy killer whale than its larger cousin; when a number of pygmy killers were brought into captivity in Hawaii and South Africa they were extremely aggressive--even killing other poolmates.
Split into simpler sentences: In fact, "killer" may be more apt in the case of the pygmy killer whale than its larger cousin. When a number of pygmy killers were brought into captivity in Hawaii and South Africa they were extremely aggressive--even killing other poolmates.