Stratigraphic time - taxa
genus Abelisaurus Bonaparte & Novas, 1985 - Abel's lizard (Upper Cretaceous)
genus Abies Mill. - fir (Hauterivian - recent)
species Abies elegans Sedova (Upper Cretaceous)
subfamily Abietoideae Lindl. Emend Pilger & Melchior (Hauterivian - recent)
infraorder Achelata Scholtz & Richter, 1995 (Lower Triassic - recent)
suborder Acipenseroidei (Upper Cretaceous - recent)
superorder Actinistia (Middle Devonian - recent)
species Actinophyma spectabile Cotteau & Gauthier, 1895 (Upper Cretaceous)
class Actinopterygii Klein, 1885 - ray-finned fishes (Upper Silurian - recent)
suborder Adephaga Schellenberg, 1806 (Hettangian - recent)
subfamily Aesalinae MacLeay, 1819 (Cenomanian - recent)
tribus Aesalini MacLeay, 1819 (Upper Cretaceous - recent)
family Agamidae Gray, 1827 - agamas (Upper Cretaceous - recent)
subfamily Agrypninae Candèze, 1857 (Cenomanian - recent)
genus Aigialosuchus Persson, 1960 (Cretaceous)
genus Alavesia Waters & Arillo, 1999 (Cenomanian - recent)
species Aletopelta coombsi Kirkland & Ford, 2001 (Upper Cretaceous)
subfamily Aleuropteryginae (Callovian - recent)
order Alexornithiformes Brodkorb, 1976 (Upper Cretaceous)
family Alligatoridae Gray, 1844 (Upper Cretaceous - recent)
genus Allostrophus Hsiao, Ślipiński, Yu, Deng & Pang, 2018 (Upper Cretaceous)
species Allostrophus cretaceus Hsiao, Ślipiński, Yu, Deng & Pang, 2018 (Upper Cretaceous)
order Ambystomatoidea (Upper Cretaceous - recent)
family Amiidae Bonaparte, 1831 - bowfins (Upper Jurassic - recent)
order Amiiformes Hay, 1929 - bowfins (Lower Triassic - recent)
subfamily Amnestinae Hart, 1919 (Aptian - recent)
kingdom Amoebozoa Lühe, 1913 emend. Cavalier-Smith, 1998 (Neoproterozoic - recent)
family Amorphoscelidae Stål, 1877 (Aptian - recent)
subfamily Amorphoscelinae Stål, 1877 (Aptian - recent)
tribus Amorphoscelini Stål, 1877 (Aptian - recent)
family Amphiumidae Garden in Smith, 1821 - amphiumas (Upper Cretaceous - recent)
order Amphiumoidea (Upper Cretaceous - recent)
subfamily Anaidinae Nikolajev, 1996 (Lower Cretaceous - recent)
genus Anatotitan Chapman & Brett-Surman, 1990 (Upper Cretaceous)
species Anatotitan copei (Lull & Wright, 1942) (Upper Cretaceous)
species Anatotitan longiceps Marsh, 1890 (Upper Cretaceous)
species Ancyloceras renauxianus d'Orbigny, 1842 (Cretaceous)
family Anguidae Gray, 1825 - glass lizards (Upper Cretaceous - recent)
family Aniliidae Stejneger, 1907 - cylinder snakes (Cretaceous - recent)
species Animantarx ramaljonesi Carpenter et al., 1999 (Upper Cretaceous)
suborder Anisoneura Lioy, 1864 (Upper Triassic - recent)
infraorder Anisopodomorpha Tuomikoski, 1961 (Upper Triassic - recent)
family Ankylosauridae Brown, 1908 (Upper Cretaceous)
species Ankylosaurus magniventris Brown, 1908 (Upper Cretaceous)
genus Antarctopelta Salgado & Gasparini, 2006 (Upper Cretaceous)
species Antarctopelta oliveroi Salgado & Gasparini, 2006 (Upper Cretaceous)
family Anthribidae Billberg, 1820 - fungus weevils (Middle Jurassic - recent)
suborder Apocrita Gerstäcker, 1867 (Berriasian - recent)
infraclass Apoda Oppel, 1810 (Lower Jurassic - recent)
family Aradidae Brullé, 1836 (Cenomanian - recent)
superfamily Aradoidea Brullé, 1836 (Cenomanian - recent)
species Araucaria fricii Velen. ex E.Bayer 1893 (Coniacian)
family Araucariaceae Henkel & Hochst. (Oxfordian - recent)
family Arbaciidae Gray, 1855 (Lower Cretaceous - recent)
genus Archaeodraena Jäch & Yamamoto, 2017 (Cretaceous)
species Archaeodraena cretacea Jäch & Yamamoto, 2017 (Cretaceous)
genus Archaeomalthodes Hsiao, Ślipiński & Pang, 2016 (Upper Cretaceous)
species Archaeomalthodes rosetta Hsiao, Ślipiński & Pang, 2016 (Upper Cretaceous)
superorder Archosauria (Lopingian - recent)
cohors Archosauromorpha Huene, 1946 (Lopingian - recent)
suborder Archostemata Kolbe, 1908 (Upper Triassic - recent)
genus Armanopimpla Kopylov, 2010 (Cretaceous)
phylum Arthropoda Gravenhorst, 1843 - arthropods (Cambrian - recent)
species Arthurdactylus conandoylensis Frey & Martill, 1994 (Upper Cretaceous)
family Asilidae Kirby & Spence, 1817 - robber flies (Cenomanian - recent)
superfamily Asiloidea (Cenomanian - recent)
infraorder Asilomorpha Rohdendorf, 1961 (Callovian - recent)
family Astacidae Latreille, 1802 - crayfishes (Upper Jurassic - recent)
infraorder Astacidea Latreille, 1802 (Lower Jurassic - recent)
superfamily Astacoidea Latreille, 1802 - Crayfishes (Upper Jurassic - recent)
class Asteroidea De Blainville, 1830 (Lower Ordovician - recent)
family Atelestidae Hennig, 1970 (Cenomanian - recent)
subfamily Atelestinae Hennig, 1970 (Cenomanian - recent)
genus Atlantochelys Agassiz, 1849 (Upper Cretaceous)
subfamily Attageninae Laporte de Castelnau, 1840 (Cenomanian - recent)
tribus Attagenini Laporte de Castelnau, 1840 (Cenomanian - recent)
genus Attagenus Latreille, 1802 (Cenomanian - recent)
genus Aucasaurus Coria Chiappe & Dingus, 2002 - auca lizard (Upper Cretaceous)
suborder Auchenorrhyncha Duméril, 1806 - cicadas and leafhoppers (Artinskian - recent)
class Aves Linnaeus, 1758 - birds (Upper Jurassic - recent)
genus Avimimus Kurzanov, 1981 (Upper Cretaceous)
family Azhdarchidae Nessov, 1984 (Upper Cretaceous)
family Bainguidae Borsuk-Bialynicka, 1984 (Upper Cretaceous)