Chapter 02

The Triassic Dawn

How the dinosaurs started small, stayed modest, and outlived the competition.

Reconstruction of Plateosaurus, a long-necked plant-eating dinosaur standing on two legs in an arid Triassic landscape — Plateosaurus, an early long-necked plant-eater and one of the best-known dinosaurs of the Late Triassic. — paleoart, CC-BY via Wikimedia Commons

After the worst day in the history of life, the survivors inherited a hot, dry supercontinent. The first dinosaurs were among them, and almost nothing about those small, plain animals hinted at what their descendants would become.

The Triassic period runs from roughly 252 to 201 million years ago, and it opens in the aftermath of catastrophe. The end-Permian extinction, the largest mass dying in the history of life, had just erased most species on land and in the sea. The Mesozoic world that recovered was strange and impoverished, and the animals rebuilding it were starting almost from scratch.

This is where the dinosaurs come from. Not as kings, but as bit players in a world that already belonged to other reptiles.

One continent, hot and dry

In the Triassic, nearly all the world's land was fused into a single supercontinent, Pangaea. With so much interior far from any ocean, large parts of it were hot, arid, and strongly seasonal. There were no flowering plants and no grasses. Vegetation meant ferns, cycads, conifers, and their relatives.

A single landmass meant animals could in principle walk from pole to pole, and the early dinosaur groups did spread widely. It also meant there were few barriers, so similar faunas turn up across what are now scattered continents.

The first dinosaurs were small

The earliest dinosaurs appear in the Late Triassic, and the honest description of them is modest. Many were small, lightly built animals that walked on two legs. They were not the biggest, not the most numerous, and not obviously destined to take over anything.

From very early on the lineage split along a fundamental divide that still organizes the family tree today: the saurischian dinosaurs on one side and the ornithischian dinosaurs on the other. Out of the saurischian branch came two groups that would matter enormously later, the meat-eating theropods and the long-necked sauropodomorphs.

The early theropods were lightly built hunters, fast on two legs, with grasping hands and bladed teeth. They were small predators in a world of larger competitors. Their descendants would eventually include animals like Allosaurus and Tyrannosaurus, but nothing in the Triassic versions promised that.

Plateosaurus grows large

If you want to see the future taking shape, look at the early sauropodomorphs. These were the long-necked plant-eaters, and one of them, Plateosaurus, is among the best-known dinosaurs of the entire Triassic.

Plateosaurus lived in what is now Central and Northern Europe in the Late Triassic, roughly 214 to 204 million years ago. It was a bipedal herbivore with a small skull set on a long, flexible neck, plump plant-crushing teeth, and short but muscular arms ending in grasping hands with large claws on three fingers. Those claws were probably used in feeding and defence, though that reading is an inference, not something a bone states outright.

PlateosaurusLate TriassicAn early long-necked plant-eater that shows the sauropodomorph body plan starting to scale up in the Triassic.read the entry →

What makes Plateosaurus so useful is its sheer abundance. Over 100 skeletons have been found, some of them nearly complete, which is why it is one of the dinosaurs best known to science. The fossils are so common in Swabia, Germany, that the animal earned the nickname Schwabischer Lindwurm, the Swabian lindworm.

It also did something unusual: its fully grown adults did not all converge on one size. Instead the animals showed strong developmental plasticity, so adult length and weight varied considerably. Most individuals lived at least 12 to 20 years, but the maximum life span is not known.

Reconstruction of Plateosaurus walking on two legs, with a long neck and small head, in a dry Late Triassic setting — Plateosaurus is reconstructed as a two-legged browser. The pose and posture are interpretations built from the skeletons; the bones themselves show a small skull, long neck, and short, powerfully built arms. — paleoart, CC-BY via Wikimedia Commons

Was Plateosaurus a sauropod? And what does "flat lizard" even mean?

Plateosaurus is a basal, or early, sauropodomorph, part of the broader lineage that later produced the giant four-legged sauropods. It was not yet one of those giants. As for the name, it probably means "broad lizard", from the Greek word platys. It is often translated as "flat lizard", but that meaning came from a later, secondary reading of the same word, and von Meyer's original 1837 description gave no etymology at all.

For the curious → How settled is the species list for Plateosaurus?

Less settled than its fame suggests. Three species are currently treated as valid: P. trossingensis, P. longiceps, and P. gracilis. Many other names have been assigned over the years, and there are numerous genus-level synonyms. There is no broad consensus on the species taxonomy of plateosaurid dinosaurs. Even the type species changed: it was P. engelhardti until 2019, when a ruling found that name undiagnostic and moved the honour to P. trossingensis.

The luck of the end-Triassic

Around 201 million years ago, at the boundary between the Triassic and the Jurassic, another mass extinction struck. It is tied to a vast pulse of volcanic activity as Pangaea began to pull apart, and it wiped out many of the reptile groups that had been keeping dinosaurs in a supporting role.

Crucially, the dinosaurs came through it. With many rivals gone, the survivors found a world with far more room and far less competition. This is the central, slightly humbling fact of dinosaur history: they did not fight their way to the top in the Triassic. They were modest animals that happened to be standing in the right place when the stage was cleared for them.

Dinosaurs started small and got lucky. The Triassic did not crown them. It just removed almost everything that stood in their way.

That is the shape of the Triassic dawn. A ruined world recovering under one hot continent. A new group of reptiles, small and unremarkable, splitting early into the branches that would one day rule. Long-necked plant-eaters like Plateosaurus already growing large, lightly built hunters already running on two legs, and then an extinction that opened the door. What walked through it would define the next 130 million years.

It is easy to imagine the dinosaurs as inevitable, as if the Triassic were just a waiting room before greatness. The bones tell a quieter story. They began as ordinary survivors of a broken world, no grander than the animals around them, and they endured one more catastrophe that their rivals did not. Everything that came after, every giant and every monster, grew out of that small, lucky start.