Why do fish have vertical tail fins and whales have horizontal

Whale, Fishapedia

All Fish Have Vertical Tails While All Whales Have Horizontal Tails. Why?

Homology or convergent trait?

Mark P. Witton's Blog: A tale of plesiosaur tails: vertical fins or horizontal flukes?

실제 고래의 뒷다리와 꼬리뼈는 어떻게 생겼을까? - 포텐 터짐 최신순 - 에펨코리아

How to tell the difference between a shark and dolphin by their fins

Cetacea - Wikipedia

BBC Science Focus Magazine - Yan Wong

Fin - Wikipedia

Why do some fish have vertical tails, and others have horizontal tails? - Quora