Final answer:
The Beach Boys' 'Pet Sounds' and The Beatles' 'Sergeant Pepper's Lonely Hearts Club Band' contributed to the emergence of progressive rock, a sub-genre later dominated by bands like Pink Floyd and Yes.
Step-by-step explanation:
The albums 'Pet Sounds' by The Beach Boys and 'Sergeant Pepper's Lonely Hearts Club Band' by The Beatles were instrumental in the development of the progressive rock sub-genre of rock music.
This genre emerged in the late 1960s and early 1970s, characterized by a blending of rock with other musical influences like classical, jazz, and world music, complex compositions, and often conceptual album themes. Bands like Pink Floyd and Yes are quintessential examples of progressive rock, often pushing the boundaries of traditional rock music with extended instrumental passages, conceptual albums, and elaborate live shows.