Sauropods

Despite being the largest land animals ever, sauropod dinosaurs laid surprisingly small eggs relative to their body size. The largest known dinosaur eggs (Macroelongatoolithus) were about 45–60 cm long, yet the adults that laid them might weigh 40–70 tonnes. This is because eggshell thickness is limited by the need for oxygen exchange — a larger egg would suffocate the embryo. Hatchlings were therefore tiny compared to adults, growing at astonishing rates throughout their lives.

Argentinosaurus, a titanosaur sauropod from Cretaceous Argentina, is estimated to have weighed between 70 and 100 tonnes — potentially the heaviest land animal in Earth's history. It measured up to 35–40 metres long. To support its enormous bulk, its vertebrae were larger than a full-grown human. Sauropods as a group were the largest land animals ever, far exceeding any mammal.