xkcd #3204: Dinosaurs And Non-Dinosaurs
Title text:
Staplers are actually in Pseudosuchia, making them more closely related to crocodiles than to dinosaurs.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3204/
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.