Simplify the following text for a Grade 8 native English-speaking person.
Original: Elephant birds are an extinct family of flightless birds found only on the island of Madagascar and comprising the genera Aepyornis and Mullerornis .
Simplified: Elephant birds are an extinct family of flightless birds found only on the island of Madagascar . The group had two genera , Aepyornis and Mullerornis , and seven species .