Nib asked
How did dinosaurs get so big?
Only the long-necked sauropods grew past fifty tonnes, and they did it through how they were built and bred: many small eggs, fast growth, air-filled bones, and a long neck on a tiny head.
6 steps, drawn by Nib. Read it here, or watch him draw it. Updated .
1not all giants
First, a correction: most dinosaurs were not giants. Many were turkey-sized. The record holders were long-necked sauropods, over fifty tonnes, against six for an elephant.
2not the usual guesses
People guess weak gravity, extra oxygen, or endless food. Researchers checked all three and rejected them. Sauropods were big because of how their bodies and lives were built.
a common mix-upDinosaurs did not get huge because of lower gravity, more oxygen or an overabundance of food; a 2011 review rejected all three.
3many eggs, fast growth
Reason one: they laid eggs. A female could lay many small eggs, and the hatchlings, smaller than soccer balls, grew up to five kilograms a day. An elephant raises one calf at a time.
4air-filled bones
Reason two: air-filled bones. Like birds, sauropods had air sacs that reached into their skeleton, making a huge body far lighter than its size suggests.
5long neck, tiny head
Reason three: a long neck on a tiny head. A sauropod swallowed leaves without chewing, so its head stayed light, and its neck swept a huge area without moving its feet.
6the whole idea
So, the whole idea: not gravity, oxygen or food, but a body plan. Many eggs, light air-filled bones, and a long neck on a tiny head let sauropods pass fifty tonnes.
Dinosaurs didn't get huge by luck of air or gravity: sauropods were built to be giants, from egg to neck.