If there's one member of a band who writes all of the music, it would be fair to assume that forming the band was their idea, and that they were a founding member. However, the lead songwriters in these six bands weren't even members when the bands originally formed.

1. The Mothers of Invention

Despite the fact that the Mothers of Invention are typically thought of as Frank Zappa's backing band, they actually formed in 1964 independently of Zappa. Originally an R&B cover band known as "The Soul Giants," Zappa joined as a replacement for the band's original guitarist, but quickly took over as bandleader when he convinced the other members to play his own music rather than cover songs, in an attempt to secure a record deal. The plan obviously worked, and by 1966, the Mothers' debut album Freak Out! was released.

2. Heart

Though Heart was often presented as a duo consisting of sisters Ann and Nancy Wilson, it was actually a six-piece band that formed before either of the Wilson sisters had joined. In the mid-'60s, bassist Steve Fossen and guitarist Roger Fisher formed a band called the Army, which went through various name changes, one of which was "Heart." Ann Wilson joined as a singer in the early '70s, at which point the name of the band was "Hocus Pocus," but when her sister Nancy joined as a guitarist in 1974, the band switched its name back to "Heart," and the Wilson sisters took over songwriting.

3. The Replacements

The Replacements originally formed in 1978 as a trio under the name "Dogbreath," which consisted of guitarist Bob Stinson, his younger brother Tommy on bass, and Chris Mars on drums, playing sloppy instrumental covers of classic rock songs. However, when a musician named Paul Westerberg overheard Dogbreath rehearsing in the Stinson's basement one day, he offered to become their singer and rhythm guitarist. Westerberg eventually become Dogbreath's chief songwriter, and by 1980, they had changed their name to the Replacements.

4. Oasis

Much like Heart, Oasis was fronted by a pair of siblings, though the band actually formed without either of them. Originally known as "The Rain," the band changed its name to "Oasis" when Liam Gallagher joined as a vocalist. When Liam's brother Noel saw Oasis live, however, he thought they would be much better if he was writing their music, and joined Oasis as its lead guitarist and chief songwriter.

5. The Cranberries

Originally formed in 1989 as "The Cranberry Saw Us," the Cranberries' original lead vocalist was a guy named Niall Quinn. After he left in 1990, however, the band hired Dolores O'Riordan to replace him, whose soaring vocals and dream-pop songwriting became the group's signature sound.

6. Sunny Day Real Estate

One of the defining bands of '90s emo, Sunny Day Real Estate brought the fledgling genre away from its hardcore roots towards something darker and more melodic, in large part due to the highly emotional vocal style of lead singer Jeremy Enigk. However, Enigk wasn't an original member of the band, and joined only after the band had already released a seven-inch single as a three-piece, with guitarist Dan Hoerner on vocals. After Enigk joined, however, he began collaborating with Hoerner in writing the band's music.

What are some other bands that originally formed without their lead songwriter? Let us know down in the comments section!