The K-Pg Mass Extinction Wiped Out 75% of All Species, Not Just Dinosaurs

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.

Despite being featured alongside dinosaurs in popular media, pterosaurs were not dinosaurs. They were archosaurs — the same broad group that includes dinosaurs and crocodilians — but evolved flight independently on their own lineage. The first pterosaur appeared around 228 million years ago. The largest, Quetzalcoatlus, had a wingspan of up to 10–11 metres and stood as tall as a giraffe, making it the largest known flying animal in Earth's history.

Micropachycephalosaurus ('tiny thick-headed lizard') from Late Cretaceous China holds the record for the longest dinosaur name at 23 letters. Ironically, it was one of the smallest known dinosaurs, estimated at under 1 metre long. It belonged to the pachycephalosaur family and was first described in 1978 by Chinese palaeontologist Dong Zhiming. Its name is a paradox — meaning small, yet bearing one of the most unwieldy labels in all of palaeontology.

Pachycephalosaurus wielded a dome-shaped skull up to 25 centimetres thick, made of solid bone. Debate continues about whether it used this for head-butting rivals (like bighorn sheep) or flank-butting. Analysis of bone texture reveals healed lesions consistent with high-impact head-to-head contact. Some researchers suggest the domes also served as species and sex recognition signals, as they varied greatly in size and shape between individuals.