xkcd #3204: Dinosaurs And Non-Dinosaurs
Title text:
Staplers are actually in Pseudosuchia, making them more closely related to crocodiles than to dinosaurs.
Transcript:
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Source: https://xkcd.com/3204/
Basically all life on Earth that's not some bacteria or fungi originally developed in the oceans, and only later adapted to life on land. If you go back far enough, the common ancestor of anything that walks, crawls, or flies ultimately originally swam.
At the same time, all mammals are evolved from a common ancestor on land, which means that whales, seals, dolphins, etc. are the evolutionary result of land-based mammals "re-entering" the ocean.