The age of dinosaurs, in one sentence
The Mesozoic Era is the 186-million-year stretch of Earth’s history (from about 252 million to 66 million years ago) during which dinosaurs dominated land ecosystems. It is split into three periods: the Triassic, the Jurassic, and the Cretaceous — and each period has its own iconic species, its own climate, and its own dinosaur toys that kids should recognize.
This guide walks through each period at a level a curious 7-year-old can understand, with the key species, the key events, and a few notes on which modern dinosaur figures match each era.
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The Triassic Period (252-201 million years ago)
What the world looked like
Earth had one giant continent, Pangaea. Climate was hot and dry — much of Pangaea was desert. No grass (grass would not evolve for another 100+ million years). No flowers.
The biggest event at the start of the Triassic was the Permian-Triassic extinction, the worst mass extinction in Earth’s history. It killed around 90-95% of all marine species and 70% of land vertebrates. The survivors had an empty world to inherit.
What the dinosaurs looked like
Early dinosaurs in the Triassic were small, bipedal, and not particularly impressive. The first true dinosaurs appeared around 230 million years ago and were maybe 3-6 feet long. They shared the world with larger rauisuchians, crocodile relatives, and the first mammals.
Key Triassic species
- Eoraptor — one of the earliest known dinosaurs, about 3 feet long
- Herrerasaurus — another early predator, 10-15 feet long
- Plateosaurus — an early long-necked dinosaur, ancestor of sauropods
- Coelophysus — a small, agile theropod that hunted in packs
Triassic figures you can buy
Triassic figures are the rarest category. Safari Ltd and CollectA both make Herrerasaurus and Plateosaurus, but you will not find Triassic dinosaurs at big-box stores. This is the “really into it” part of a collection.
The Jurassic Period (201-145 million years ago)
What the world looked like
Pangaea began to break apart. The climate became wetter and more tropical. Forests of cycads, ferns, and conifers spread. Still no flowers.
What the dinosaurs looked like
The Jurassic is when dinosaurs got big. Really big. Sauropods — the long-necked, long-tailed giants — evolved into the largest land animals in history. Theropods diversified. Stegosaurs showed up. This is the period most kids picture when they think “dinosaur.”
Key Jurassic species
- Brachiosaurus — 85 feet long, 40 tons. The giant of the Jurassic.
- Diplodocus — 90+ feet long, longer than Brachiosaurus but lighter
- Apatosaurus — another huge sauropod, famously misidentified as “Brontosaurus” for decades
- Stegosaurus — plate-backed, spike-tailed, walnut-sized brain
- Allosaurus — the Jurassic’s apex predator, 30+ feet long
- Archaeopteryx — the first bird (or very-close-to-first), with feathers and teeth
Jurassic figures you can buy
Jurassic dinosaurs dominate the figure market. Every major brand makes Brachiosaurus, Stegosaurus, Allosaurus, and Diplodocus. Schleich’s Brachiosaurus and Safari Ltd’s Allosaurus are the standard starters. See our figures guide for our current top picks.
The Cretaceous Period (145-66 million years ago)
What the world looked like
Continents kept drifting toward their modern positions. The climate was warm — sometimes tropical as far north as the Arctic Circle. Flowering plants evolved and spread (starting around 130 million years ago), changing ecosystems forever. Bees co-evolved with the flowers.
What the dinosaurs looked like
The Cretaceous is the period most kids’ favorite dinosaurs come from. Every famous movie dinosaur — T-Rex, Triceratops, Velociraptor, Spinosaurus — is Cretaceous.
Key Cretaceous species
- Tyrannosaurus rex — 40 feet long, 9 tons, the most famous predator in Earth’s history
- Triceratops — 30 feet long, 3-horned, frilled, North America’s most iconic herbivore
- Velociraptor — only 3 feet tall, feathered, much smaller than Jurassic Park suggested
- Spinosaurus — 50+ feet long, semi-aquatic, probably the largest carnivorous dinosaur ever
- Ankylosaurus — the living tank, covered in bony armor with a club tail
- Parasaurolophus — the one with the tube on its head, used for communication
- Pteranodon — a pterosaur (flying reptile), not technically a dinosaur but Cretaceous
Cretaceous figures you can buy
Cretaceous dinosaurs dominate every dinosaur figure line. T-Rex, Triceratops, and Velociraptor are the 3 bestsellers in almost every brand. The Schleich Large T-Rex, Safari Ltd Wild Safari Triceratops, and Safari Ltd feathered Velociraptor are all good Cretaceous starters.
How the Mesozoic ended
66 million years ago, a 6-mile-wide asteroid hit what is now the Yucatán Peninsula in Mexico. The impact triggered global wildfires, a “nuclear winter” of dust and debris blocking sunlight, and collapsed food chains. Over the following years or decades, non-avian dinosaurs went extinct. This is called the K-Pg extinction event (or the K-T extinction in older texts).
The survivors of the K-Pg extinction included mammals (small and burrowing, so they survived the chaos), crocodiles, turtles, and — importantly — birds, the direct descendants of small theropod dinosaurs. Modern birds are the last living dinosaurs.
FAQ
Q: How long did the dinosaurs exist?
A: Around 165 million years, from 230 million to 66 million years ago.
Q: What killed the dinosaurs?
A: An asteroid impact 66 million years ago, possibly combined with volcanic activity. Birds survived and are still with us today.
Q: Which period did T-Rex live in?
A: T-Rex lived during the late Cretaceous, from about 68 to 66 million years ago — right at the end of the Mesozoic.
Q: Which period did Brachiosaurus live in?
A: Late Jurassic, about 154-150 million years ago.
Q: Is the Jurassic period or the Cretaceous period the “age of dinosaurs”?
A: Both. The age of dinosaurs is the full Mesozoic — all three periods. The Jurassic gets the brand recognition because of Jurassic Park, but dinosaurs were most diverse during the Cretaceous.
Q: Were humans alive at the same time as dinosaurs?
A: No. Non-avian dinosaurs went extinct 66 million years ago. Humans evolved about 300,000 years ago. The gap between the last non-bird dinosaur and the first human is larger than the gap between Stegosaurus and Tyrannosaurus.
Related reading
- Types of dinosaurs: classification explained
- Feathered dinosaurs and which toys get it right
- T-Rex vs Spinosaurus: who wins?
- Dinosaur figures collection
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