This is an article from Curious Kids, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky! You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.
Could you please tell me how many dinosaurs in total lived on Earth during all periods? – Viren, age 6, Scotch College, Victoria.
This is a really great question.
The short answer is we know of about 900 valid dinosaur species that existed. “Valid” means scientists know the dinosaur from enough of the skeleton bones to feel pretty sure that it differs from all other known dinosaurs. There are hundreds of others which have been named, but are not considered “valid” as they were not based on well-enough preserved fossils.
To give you the long answer, first I need to explain what a dinosaur is, and when they lived.
What exactly is a dinosaur, anyway?
Dinosaurs were a group of medium to large reptiles that lived between 235 million years ago and 66 million years ago. Not many people know this, but the main thing that makes a dinosaur a dinosaur is their foot structure; they have a special kind of ankle joint. Their feet bones are like that of a bird.
Dinosaurs lived during three periods of geological time – the Triassic period (which was 252-201 million years ago), the Jurassic period (about 201-145 million years ago) and the Cretaceous period (145-66 million years ago). These three periods together make up the Mesozoic Era.
Just how many dinosaurs in total lived on Earth during the Mesozoic era is impossible to answer. One study by a Polish scientist called Jerzy Trammer estimated that the total dinosaur combined weight was greater than all the mammals on Earth today, but their individual numbers were much lower than species of today’s living mammals.
Birds are descended from one group of dinosaurs called the predatory theropods. Theropods have hollow bones and three-toed limbs. Dinosaurs from the Tyrannosaurus are a type of predatory theropods. So, technically speaking, all living birds are “living dinosaurs”.
Views expressed in this article are the opinions of the author(s) and do not necessarily reflect the views of Epoch Times.