Beige articulated 3D-printed T-Rex and smaller stegosaurus figures on a light oak desk beside an open dinosaur book, two small beige dinosaur-egg trinket boxes and a pencil for scale, in soft daylight

Types of Dinosaurs: Main Groups, T. rex and Stegosaurus

6 min read Updated October 4, 2026 By Kahaus · printed in Poland

In short

Dinosaurs fall into two big branches, lizard-hipped and bird-hipped, and into a handful of main groups: theropods, sauropods, armoured dinosaurs, ornithopods and horned dinosaurs.
T. rex was a two-legged theropod from the very end of the Cretaceous; Stegosaurus was a four-legged plant-eater with back plates from the Late Jurassic. Around 80 million years lie between them.
Pterosaurs and sea reptiles such as plesiosaurs were not dinosaurs. Birds are: they descend from small theropods.

Types of dinosaurs are easier to sort than the long names suggest. Scientists have named around a thousand species so far, yet almost all of them fit into a handful of groups that you can recognise by the legs, the neck and whatever grows on the back or the head.

We print dinosaur figures, so we wanted to get the family tree right ourselves. Below: the main groups in one table, the two branches behind them, a short look at T. rex, a longer one at Stegosaurus, and the animals that are often called dinosaurs but are not.

The main types of dinosaurs at a glance

Group	How to recognise it	Well-known examples	Food
Theropods	Walked on two legs, three main toes, sharp teeth in most	Tyrannosaurus, Allosaurus, Velociraptor, Spinosaurus	Mostly meat or fish
Sauropods	Very long neck and tail, small head, four pillar-like legs	Diplodocus, Brachiosaurus, Argentinosaurus	Plants
Stegosaurs	Plates or spikes along the back, spiked tail, small head	Stegosaurus, Kentrosaurus	Plants
Ankylosaurs	Low, wide body covered in bony armour; some had a tail club	Ankylosaurus, Euoplocephalus	Plants
Ornithopods	Beak, no armour, walked on two or four legs; some had head crests	Iguanodon, Parasaurolophus, Edmontosaurus	Plants
Ceratopsians (horned dinosaurs)	Beak, bony neck frill, often horns	Triceratops, Styracosaurus, Protoceratops	Plants

Two branches: lizard-hipped and bird-hipped

Since the 19th century, dinosaurs have been divided by the shape of their hip bones. In lizard-hipped dinosaurs (saurischians) the pubic bone points forward, as in lizards. This branch holds the theropods and the sauropods with their early relatives. In bird-hipped dinosaurs (ornithischians) the same bone points backwards. All of them were plant-eaters: stegosaurs, ankylosaurs, ornithopods, horned dinosaurs and the dome-headed pachycephalosaurs.

The names are a little misleading. Birds descend from small theropods, so they come from the lizard-hipped branch, not the bird-hipped one.

Dinosaurs appeared in the Triassic, roughly 230 to 240 million years ago, flourished through the Jurassic and the Cretaceous, and died out about 66 million years ago, all except the birds.

T. rex facts in brief: the best-known theropod

Tyrannosaurus rex shows what makes a theropod: it walked on two strong hind legs, held its body level and balanced a huge head with a long tail. It lived in western North America at the very end of the Cretaceous, roughly 68 to 66 million years ago, and at around 12 metres long it was one of the largest land predators ever.

Its arms were short, with two fingers on each hand, while many other theropods had three. Not every theropod was a giant: Velociraptor was about the size of a turkey and had feathers. We go through the skull, teeth and arms bone by bone in our T. rex skeleton guide.

Beige articulated 3D-printed T-Rex figure, 15.5 cm, lying on an oak desk next to a notebook and a pencil — Our flexi T-Rex, 15.5 cm: a stylised theropod for the desk. See the product →

Beige articulated 3D-printed stegosaurus figure, 11.4 cm, on an oak desk next to a notebook and a pencil — The flexi stegosaurus, 11.4 cm, with the plates along its back. See the product →

Stegosaurus facts: plates, tail spikes and a small head

Stegosaurus is a dinosaur most people recognise by its outline alone. It lived in the Late Jurassic, roughly 155 to 145 million years ago; most finds come from western North America, and one from Portugal.

Size. Adults were roughly 6 to 9 metres long and walked on four legs.
Plates. Two rows of large bony plates ran along the neck, back and tail. They sat in the skin and were not attached to the spine. What they were for is still debated: display, recognising one another and perhaps regulating body temperature.
Tail spikes. The tail ended in four long spikes, used for defence. Palaeontologists call this weapon a thagomizer, a word borrowed from a Far Side cartoon by Gary Larson.
Head and food. The head was small and narrow and carried low to the ground, with a toothless beak at the front and small cheek teeth behind. Stegosaurus ate low-growing plants.

What is not a dinosaur

A practical test is the legs: dinosaurs held them straight under the body, like a horse or a bird, while lizards and crocodiles sprawl theirs out to the sides.

Pterosaurs, such as Pteranodon, were flying reptiles and close relatives of dinosaurs, but a separate group.
Plesiosaurs, ichthyosaurs and mosasaurs were marine reptiles.

Today's lizards are not small dinosaurs either, however ancient a bearded dragon may look. The only living dinosaurs are birds.

Dinosaurs for the desk: our figures

Our articulated T-Rex, 15.5 cm, and the flexi stegosaurus, 11.4 cm, are printed from PLA in one piece, with the joints already in place: no assembly, no glue. Both come in ten colours. To be honest, they are stylised desk figures and fidgets for dinosaur fans, not scale models: you will recognise the group at a glance, but do not count vertebrae on them.

All dinosaurs hatched from eggs, even the giant sauropods, whose eggs were about the size of a football at most. Our two dinosaur egg trinket boxes with raised spots and with a cracked shell are 6.7 cm tall and open into two halves, with room inside for a ring, a pair of earrings or a coin. They are decorations, not copies of real fossil eggs and not food containers.

Beige dinosaur egg trinket box with raised spots, 6.7 cm, on an oak console next to a stack of books — Egg trinket box with raised spots, 6.7 cm. See the product →

Beige dinosaur egg trinket box with a cracked-shell pattern, 6.7 cm, on a light wooden cabinet next to books and a vase — The cracked-shell version, same size. See the product →

For bones rather than skin, there is the flexi T-Rex skeleton, 15.5 cm, and the Triceratops kit card, 25 cm, a horned dinosaur you snap together by hand without glue. All of them are in our Dinosaurs collection; more articulated animals, from sharks to lizards, are in Flexi Animals.

Safety: the articulated T-Rex and the stegosaurus are marked 14+ because of small parts; we see them as collectibles and desk fidgets for teens and adults. All our articulated figures and the Triceratops kit have small parts and are not suitable for children under 3.

See all our dinosaurs

Questions about dinosaur types

How many types of dinosaurs were there?

Around a thousand species have been named so far, and new ones are described every year. The exact figure depends on who is counting, because some names turn out to describe the same animal.

Did T. rex and Stegosaurus live at the same time?

No. Stegosaurus lived in the Late Jurassic and T. rex at the very end of the Cretaceous, around 80 million years later. That gap is longer than the 66 million years between T. rex and us.

Did Stegosaurus have a second brain?

No. There is a widened space in the spine above the hips, which gave rise to the old idea of a “second brain”. The real brain was in the head, and it was small for an animal of that size.