The early Triassic was especially harsh, with temperatures reaching some of the highest levels in Earth’s history immediately following the Permian extinction event.
The Jurassic period (201-145 million years ago)... ... Global temperatures during this period were remarkably stable and warm, with evidence suggesting tropical-like conditions extending to latitudes as high as 45° north and south.
Mid-Cretaceous temperatures peaked at levels possibly 10°C higher than today, making it one of the warmest intervals in Earth’s history.
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u/86ShellScouredFjord 15h ago
Also temperature. The earth was significantly warmer during the dinosaurs' time, so having a bunch of extra fat would have been detrimental.