Complex sentence: In 1946, Reg Sprigg noticed "jellyfishes" in rocks from Australia's Ediacara Hills, which are now recognized as coming from the Ediacaran period, but were thought at the time to have been formed in the Cambrian.
Split into simpler sentences: In 1946, Reg Sprigg noticed "jellyfishes" in rocks from Australia's Ediacara Hills. However, while these are now recognized as coming from the Ediacaran period, they were thought at the time to have been formed in the Cambrian.