It might be a little-known fact that the first two albums of the Monkeys were actually played by The Wrecking Crew, an extremely talented group of session musicians who provided backing for many artists and want-to-be-musicians.
They subsequently became the most requested session musicians in Los Angeles, playing behind many popular recording artists including Jan and Dean, Sonny & Cher, the Mamas and the Papas, the 5th Dimension, Frank Sinatra, and Nancy Sinatra. The musicians were sometimes used as "ghost players" on recordings credited to rock groups, such as the Byrds' debut rendition of Bob Dylan's "Mr. Tambourine Man" (1965), the first two albums by the Monkees, and the Beach Boys' 1966 album Pet Sounds.
For more on the Wrecking Crew:
https://en.wikipedia.org/wiki/The_Wrecking_Crew_(music)