Why Were Prehistoric Animals So Big?

The other day I stopped by the American Museum of Natural History to visit their newest dinosaur display: the Titanosaur!

Discovered just last year in Argentina, this new species hasn’t officially received a name yet, but it is one of the largest dinosaurs yet discovered – the museum reconstruction is 122 feet long – and a lot of the skeleton has been uncovered between several specimens, unlike most poorly-known large sauropods.

The new titanosaur mount at the AMNH,
Photo by me, standing directly under the tip of the tail.

The media-hype over this skeleton, and the recent scientific reports about massive ancient giraffes and giant marine crocodiles, has a lot of people revisiting an old question: why were prehistoric animals so much bigger than their modern-day relatives?

Have You Seen "Prehistoric Beast?"

I only recently learned of a short film from 1984 called Prehistoric Beast.

Wait, don’t Google it yet!  Let me give you some backstory.

Dinosaurs have been a consistent feature of movies for almost as long as there have been movies. And they've played some pretty major roles in cinema history: the first well-known animated film character was a dinosaur; some of the most iconic early stop-motion animation was done with dinosaurs; and one of the most successful and recognizable movie characters of all time is a dinosaur, just to give some examples.