Hylaeosaurus
- When: Early Cretaceous
(136–130 mya) - Where: Europe
- What: Ankylosaur
- Weight: 1–2 tons
- Length: 5–6 meters
- Diet: Herbivorous
- Discovered: 1833
Hylonomus
- When: Carboniferous
(312 mya) - Where: North America
- What: Reptile
- Weight: 20 grams
- Length: 20 cm
- Diet: Insectivorous
- Discovered: 1859
Ichthyosaurus
- When: Early Jurassic
(199–190 mya) - Where: Europe
- What: Ichthyosaur
- Weight: 180 kg
- Length: 2–3 meters
- Diet: Piscivorous
- Discovered: 1825
Iguanodon
- When: Early Cretaceous
(139–124 mya) - Where: Europe
- What: Ornithopod
- Weight: 3–5 tons
- Length: 9–11 meters
- Diet: Herbivorous
- Discovered: 1825
Irritator
- When: Early Cretaceous
(112 mya) - Where: South America
- What: Theropod
- Weight: 1 metric ton
- Length: 8 meters
- Diet: Piscivorous
- Discovered: 1996
Kentrosaurus
- When: Late Jurassic
(155–150 mya) - Where: Africa
- What: Stegosaur
- Weight: 1–2 tons
- Length: 4–5 meters
- Diet: Herbivorous
- Discovered: 1915
Kronosaurus
- When: Early Cretaceous
(125–100 mya) - Where: Australia, South America
- What: Pliosaur
- Weight: 10–11 metric tons
- Length: 10 meters
- Diet: Carnivorous
- Discovered: 1924
Lambeosaurus
- When: Late Cretaceous
(76–75 mya) - Where: North America
- What: Hadrosaur
- Weight: 5 metric tons
- Length: 9–15 meters
- Diet: Herbivorous
- Discovered: 1923