"And God created great whales, and every living creature that moveth, which the waters brought forth abundantly, after their kind, and every winged fowl after his kind: and God saw that it was good." --Genesis 1:21
Science Daily: How Whales Have Changed Over 35 Million Years.
Large whales, small whales and medium-sized whales all appeared early in the history of whales, with the large whales eating mostly plankton, small whales eating fish and medium-sized whales eating squid.
"Those differences were probably in place by 25 million years ago at the latest, and for many millions of years, they have not changed very much," said the study's lead author, Graham Slater, a National Science Foundation-funded UCLA postdoctoral scholar in Alfaro's laboratory. "It's as if whales split things up at the beginning and went their separate ways. The distribution of whale body size and diet still corresponds to these early splits."