Whales and dolphins evolved large brains in the same way as primates and having a broad diet may have been the trigger
Source:
https://www.newscientist.com/article/2216683-whales-evolved-large-brains-in-the-same-way-that-we-did/?utm_campaign=RSS%7CNSNS&utm_source=NSNS&utm_medium=RSS&utm_content=home