🦖 FIRST DINOSAURS: EORAPTOR & HERRERASAURUS
PAGE 1 OF 5 — SMALL BEGINNINGS
~230 MA
THE DAWN THIEF
In the dusty valleys of what is now Argentina, the first members of Dinosauria were dog-sized, bipedal, and easy to overlook. Eoraptor, the 'dawn thief', scampered on two legs about 231 million years ago. Herrerasaurus was a sharper predator on the same ancient landscape. They carried the blueprint giants would later exaggerate: legs under the body, special hip sockets, and fast movement. The age of monsters started small.
🌅 DAWN THIEF
🌅 Eoraptor ≈ 231 million years ago
🇦🇷 Ischigualasto = 'Valley of the Moon'
🦖 Decades before first T. rex
🇦🇷 Ischigualasto = 'Valley of the Moon'
🦖 Decades before first T. rex
"Small, fast, and built to last."
DAWN!
SIZE
📏 Dog-sized, not giant
🏃 Bipedal runners
🦴 Light, hollow-ish bones
🏃 Bipedal runners
🦴 Light, hollow-ish bones
PLACE
🇦🇷 Famous fossil site in Argentina
🪨 River stones hold bones
🔬 Still studied today
🪨 River stones hold bones
🔬 Still studied today
PAGE 2 OF 5 — WHAT MAKES A DINOSAUR?
CHECKLIST
THE DINOSAUR HIP SOCKET
True dinosaurs share a checklist palaeontologists love: an open hip socket with a hole where the thigh locks in, legs held straight under the body (not sprawling like a crocodile), and special ankle and neck features. Eoraptor and Herrerasaurus show that package, archosaurs in ancestry, dinosaurs by anatomy. Many Triassic reptiles look similar until you check the hip, that hole is the giveaway.
🦴 THE DINOSAUR CHECKLIST
🦴 Open hip socket = dinosaur hallmark
🐊 Crocs sprawl; dinos stand tall
🔬 Details matter in fossil ID
🐊 Crocs sprawl; dinos stand tall
🔬 Details matter in fossil ID
REAL!
HIP
🦴 Hole in hip where leg attaches
🏃 Efficient upright walking
⚡ Less energy per step
🏃 Efficient upright walking
⚡ Less energy per step
ANKLE
🦶 Hinge-like ankle bones
🚫 Not crocodile-style sprawl
🏃 Built for running
🚫 Not crocodile-style sprawl
🏃 Built for running
TEETH
🦷 Eoraptor: mixed diet teeth
🍖 Herrerasaurus: more predatory
🔀 Flexible early lifestyles
🍖 Herrerasaurus: more predatory
🔀 Flexible early lifestyles
PAGE 3 OF 5 — TRIASSIC UNDERDOGS
RIVALS
🐊 Low-slung armoured hunters
🦷 Bigger than early dinosaurs
🏜️ Ruled dry supercontinent
🦷 Bigger than early dinosaurs
🏜️ Ruled dry supercontinent
LUCK
🌋 Extinction cleared competitors
🦕 Dinosaurs spread worldwide
🌿 New plant groups fuel giants
🦕 Dinosaurs spread worldwide
🌿 New plant groups fuel giants
TRIASSIC
OUTSHADOWED AT FIRST
For millions of years dinosaurs were underdogs. Giant crocodile-line predators like Postosuchus ruled the Triassic, armoured, fierce, and dominant. Early dinosaurs stayed small and quick at the margins. After the Triassic–Jurassic extinction (~201 Ma), many rivals vanished and dinosaurs finally exploded into every size and shape.
🐊 TRIASSIC KINGS
🐊 Pseudosuchians dominated early Triassic
🌋 Triassic–Jurassic extinction ~201 Ma
📈 Then dinosaurs diversify fast
🌋 Triassic–Jurassic extinction ~201 Ma
📈 Then dinosaurs diversify fast
WAIT!
PAGE 4 OF 5 — FROM THESE, EVERYTHING
LEGACY
ANCESTORS OF ALL DINOS
From these humble starters came the entire dinosaur dynasty: sauropods with necks like cranes, stegosaurs with plates, triceratops with horns, and T. rex with bone-crushing jaws, plus birds. Every branch shares the same Triassic body plan; evolution then experimented for 165 million years with size, armour, feathers, and speed.
🌳 ONE FAMILY TREE
🦕 Sauropods: biggest land animals ever
🪶 Theropods → birds still alive
🛡️ Ornithischians: horns and plates
🪶 Theropods → birds still alive
🛡️ Ornithischians: horns and plates
ALL!
SAUROPODS
🦕 Long necks, pillar legs
🌿 Ate tonnes of plants daily
🦴 Hollow bones kept weight down
🌿 Ate tonnes of plants daily
🦴 Hollow bones kept weight down
THEROPODS
🦖 Two-legged predators
🪶 Feathers → flight later
🐦 Only living dinosaur branch
🪶 Feathers → flight later
🐦 Only living dinosaur branch
ORNTISCHIANS
🛡️ Stegosaurus, Triceratops
🦴 Different hip than theropods
🌿 Many were plant-eaters
🦴 Different hip than theropods
🌿 Many were plant-eaters
PAGE 5 OF 5 — VISIT THE DAWN
FOSSILS
STILL IN THE ROCKS
You can still walk where Eoraptor scurried. Ischigualasto Provincial Park in Argentina preserves Triassic river channels and ash beds with exquisite fossils. Museums worldwide display casts of Herrerasaurus, reminders that the mightiest dynasties begin as small, fast survivors in a harsh world.
🦕 KEY LEGACY
🇦🇷 Ischigualasto = UNESCO fossil park
🦴 New digs still find early dinos
📖 Topic 08: archosaurs came first
🦴 New digs still find early dinos
📖 Topic 08: archosaurs came first
DIG!
RECAP
🦕 Eoraptor ~231 Ma
🦖 Herrerasaurus predator
🇦🇷 Argentina fossil heritage
🦖 Herrerasaurus predator
🇦🇷 Argentina fossil heritage
REMEMBER
🦕 KEY FACTS
🦎 Archosaurs came first
📖 Topic 08: before dinosaurs
📖 Topic 08: before dinosaurs
🧠 QUIZ TIME!
FIRST DINOSAURS: EORAPTOR & HERRERASAURUS · 5 QUESTIONS
QUESTION 01
Where were Eoraptor and Herrerasaurus found?
QUESTION 02
Early dinosaurs were mostly what size?
QUESTION 03
A key dinosaur hip trait is…
QUESTION 04
Birds descend from which dinosaur group?
QUESTION 05
Dinosaurs became dominant mainly after…
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