Alamosaurus
- When: Late Cretaceous
(70–66 mya) - Where: North America
- What: Sauropod
- Weight: 30–70 metric tons
- Length: 21–30 meters
- Diet: Herbivorous
- Discovered: 1922
Albertosaurus
- When: Late Cretaceous
(70–68 mya) - Where: North America
- What: Theropod
- Weight: 2 metric tons
- Length: 9 meters
- Diet: Carnivorous
- Discovered: 1905
Allosaurus
- When: Late Jurassic
(155–145 mya) - Where: North America
- What: Theropod
- Weight: 2–4 tons
- Length: 8–12 meters
- Diet: Carnivorous
- Discovered: 1877
Amargasaurus
- When: Early Cretaceous
(129–122 mya) - Where: South America
- What: Sauropod
- Weight: 2–3 tons
- Length: 9–10 meters
- Diet: Herbivorous
- Discovered: 1991
Ankylosaurus
- When: Late Cretaceous
(68–66 mya) - Where: North America
- What: Ankylosaur
- Weight: 6–8 tons
- Length: 6–8 meters
- Diet: Herbivorous
- Discovered: 1908
Antarctopelta
- When: Late Cretaceous
(76–70 mya) - Where: Antarctica
- What: Ankylosaur
- Weight: 1–2 metric tons
- Length: 4 meters
- Diet: Herbivorous
- Discovered: 2006
Apatosaurus
- When: Late Jurassic
(155–150 mya) - Where: North America
- What: Sauropod
- Weight: 20–30 tons
- Length: 21–22 meters
- Diet: Herbivorous
- Discovered: 1877
Archaeopteryx
- When: Late Jurassic
(150 mya) - Where: Europe
- What: Avialan theropod
- Weight: 0.5–1 kg
- Length: 0.5 meters
- Diet: Carnivorous
- Discovered: 1861