| Aardonyx early long-neck | Aardonyx celestae | Early Jurassic (Hettangian · Sinemurian) · roughly 201.4 to 192.9 million years ago | 2010 | 2 m · 7 ft | 8 m · 26 ft | Not established | Aardonyx was formally named in 2010 by A. M. Yates and colleagues. |
| Abdarainurus long-neck giant | Abdarainurus barsboldi | Late Cretaceous (Campanian) · roughly 83.6 to 72.2 million years ago | 2020 | 2.6 m · 9 ft | 15 m · 49 ft | 10 tonnes | Abdarainurus was formally named in 2020 by A. O. Averianov and A. V. Lopatin. The name honors a person tied to the fossil or its study. |
| Abditosaurus long-neck giant | Abditosaurus kuehnei | Late Cretaceous (Maastrichtian) · roughly 72.2 to 66 million years ago | 2022 | 3.5 m · 11 ft | 17.5 m · 57 ft | 14 tonnes | In 2022, B. Vila and colleagues published the name Abditosaurus. The name means “forgotten lizard.” |
| Abelisaurus sharp-clawed runner | Abelisaurus comahuensis | Late Cretaceous (Campanian) · roughly 83.6 to 72.2 million years ago | 1985 | 2.3 m · 8 ft | 9 m · 30 ft | 1.6–3 tonnes | Abelisaurus was formally named in 1985 by J. F. Bonaparte and F. E. Novas. The name honors a person tied to the fossil or its study. |
| Abrictosaurus bird-hipped dinosaur | Abrictosaurus consors | Early Jurassic (Hettangian · Sinemurian) · roughly 201.4 to 192.9 million years ago | 1975 | 0.2 m · 1 ft | 1.2 m · 4 ft | 45 kg · 99 lb | In 1975, J. A. Hopson published the name Abrictosaurus. The name means “wakeful lizard.” |
| Abrosaurus long-neck giant | Abrosaurus dongpoi | Middle Jurassic · Late Jurassic (Bajocian–Oxfordian) · roughly 170.9 to 154.8 million years ago | 1989 | Not established | 9.1 m · 30 ft | 6 tonnes | In 1989, H. Ouyang published the name Abrosaurus. |
| Abydosaurus long-neck giant | Abydosaurus mcintoshi | Early Cretaceous (Albian) · roughly 113.2 to 100.5 million years ago | 2010 | 5 m · 16 ft | 18.3 m · 60 ft | 26 tonnes | The genus Abydosaurus dates to 2010, the year D. Chure and colleagues described it. The name means “abydos lizard.” |
| Acantholipan armored dinosaur | Acantholipan gonzalezi | Late Cretaceous (Santonian) · roughly 85.7 to 83.6 million years ago | 2018 | 1.2 m · 4 ft | 5.7 m · 19 ft | Not established | In 2018, H. E. Rivera-Sylva and colleagues published the name Acantholipan. |
| Acanthopholis armored dinosaur · Doubtful name | Acanthopholis horrida | Late Cretaceous (Cenomanian) · roughly 100.5 to 93.9 million years ago | 1867 | Not established | 3–5.5 m · 10–18 ft | 380 kg · 838 lb | The genus Acanthopholis dates to 1867, the year T. H. Huxley described it. The name means “spiny scales.” |
| Achelousaurus horned dinosaur | Achelousaurus horneri | Late Cretaceous (Campanian) · roughly 83.6 to 72.2 million years ago | 1995 | 2 m · 7 ft | 6 m · 20 ft | 3 tonnes | In 1995, S. D. Sampson published the name Achelousaurus. The name means “achelous lizard.” |
| Acheroraptor sharp-clawed runner | Acheroraptor temertyorum | Late Cretaceous (Maastrichtian) · roughly 72.2 to 66 million years ago | 2013 | Not established | 3.3–3.4 m · 11–11 ft | 60–100 kg · 132–220 lb | In 2013, D. C. Evans and colleagues published the name Acheroraptor. The name means “underworld thief.” |
| Achillesaurus sharp-clawed runner · Disputed | Achillesaurus manazzonei | Late Cretaceous (Santonian) · roughly 85.7 to 83.6 million years ago | 2007 | Not established | Not established | Not established | The genus Achillesaurus dates to 2007, the year A. G. Martinelli and E. I. Vera described it. The name honors a person tied to the fossil or its study. |
| Achillobator sharp-clawed runner | Achillobator giganticus | Late Cretaceous (Cenomanian–Santonian) · roughly 100.5 to 83.6 million years ago | 1999 | 1.3 m · 4 ft | 4.5–5 m · 15–16 ft | 250–350 kg · 551–772 lb | Achillobator was formally named in 1999 by A. Perle and colleagues. The name means “achilles hero.” |
| Acristavus beaked plant-eater | Acristavus gagslarsoni | Late Cretaceous (Campanian) · roughly 83.6 to 72.2 million years ago | 2011 | 1.9 m · 6 ft | 8 m · 26 ft | 3 tonnes | In 2011, T. A. Gates and colleagues published the name Acristavus. The name means “non-crested grandfather.” |
| Acrocanthosaurus sharp-clawed runner | Acrocanthosaurus atokensis | Early Cretaceous (Aptian · Albian) · roughly 121.4 to 100.5 million years ago | 1950 | 4 m · 13 ft | 11–12.2 m · 36–40 ft | 7.5–8.4 tonnes | Acrocanthosaurus was formally named in 1950 by J. W. Stovall and W. Langston. |
| Acrotholus dome-headed dinosaur | Acrotholus audeti | Late Cretaceous (Santonian) · roughly 85.7 to 83.6 million years ago | 2013 | Not established | Not established | Not established | The genus Acrotholus dates to 2013, the year D. C. Evans and colleagues described it. |
| Adamantisaurus long-neck giant | Adamantisaurus mezzalirai | Late Cretaceous (Campanian · Maastrichtian) · roughly 83.6 to 66 million years ago | 2006 | Not established | 13–18 m · 43–59 ft | 5–14.4 tonnes | In 2006, R. M. Santucci and R. J. Bertini published the name Adamantisaurus. The name honors a person tied to the fossil or its study. |
| Adasaurus sharp-clawed runner | Adasaurus mongoliensis | Late Cretaceous (Maastrichtian) · roughly 72.2 to 66 million years ago | 1983 | 0.6 m · 2 ft | 2.4–3.5 m · 8–11 ft | 36–87 kg · 79–192 lb | In 1983, R. Barsbold published the name Adasaurus. The name means “evil lizard.” |
| Adelolophus beaked plant-eater | Adelolophus hutchisoni | Late Cretaceous (Campanian) · roughly 83.6 to 72.2 million years ago | 2014 | Not established | 8.2 m · 27 ft | Not established | The genus Adelolophus dates to 2014, the year T. A. Gates and colleagues described it. The name means “unknown crest.” |
| Adeopapposaurus early long-neck | Adeopapposaurus mognai | Early Jurassic (Hettangian–Toarcian) · roughly 201.4 to 174.7 million years ago | 2009 | 0.8 m · 3 ft | 2.9 m · 10 ft | 60 kg · 132 lb | Adeopapposaurus was formally named in 2009 by R. N. Martínez. The name means “far eating lizard.” |
| Adratiklit plated dinosaur | Adratiklit boulahfa | Middle Jurassic (Bathonian · Callovian) · roughly 168.2 to 161.5 million years ago | 2020 | 1.7 m · 6 ft | 7 m · 23 ft | 4 tonnes | Adratiklit was formally named in 2020 by S. C. R. Maidment and colleagues. The name means “mountain lizard.” |
| Adynomosaurus beaked plant-eater | Adynomosaurus arcanus | Late Cretaceous (Maastrichtian) · roughly 72.2 to 66 million years ago | 2019 | Not established | Not established | Not established | The genus Adynomosaurus dates to 2019, the year A. Prieto-Márquez and colleagues described it. |
| Aegyptosaurus long-neck giant | Aegyptosaurus baharijensis | Late Cretaceous (Cenomanian) · roughly 100.5 to 93.9 million years ago | 1932 | 3 m · 10 ft | 15 m · 49 ft | 7 tonnes | Aegyptosaurus was formally named in 1932 by E. Stromer. |
| Aeolosaurus long-neck giant | Aeolosaurus rionegrinus | Late Cretaceous (Campanian · Maastrichtian) · roughly 83.6 to 66 million years ago | 1987 | 3 m · 10 ft | 14–18.1 m · 46–59 ft | 6–14.7 tonnes | Aeolosaurus was formally named in 1987 by J. E. Powell. The name honors a person tied to the fossil or its study. |