The largest prehistoric animals include both vertebrate and invertebrate species. Many of them are described below, along with their typical range of size (for the general dates of extinction, see the link to each). Many species mentioned might not actually be the largest representative of their clade due to the incompleteness of the fossil record and many of the sizes given are merely estimates since no complete specimen have been found. Their body mass, especially, is largely conjecture because soft tissue was rarely fossilized. Generally the size of extinct species was subject to energetic and biomechanical constraints.

Non-mammalian synapsids (Synapsida)

Caseasaurs (Caseasauria)

The herbivorous Alierasaurus was the largest caseid and the largest amniote to have lived at the time, with an estimated length around 6–7 m. Cotylorhynchus hancocki is also large, with an estimated length and weight of at least 6 m and more than 500 kg.

Edaphosaurids (Edaphosauridae)

The largest edaphosaurids were Lupeosaurus at 3 m long and Edaphosaurus, which could reach even more than 3 m in length.

Sphenacodontids (Sphenacodontidae)

The biggest carnivorous synapsid of Early Permian was Dimetrodon, which could reach 4.6 m and 250 kg. The largest members of the genus Dimetrodon were also the world's first fully terrestrial apex predators.

Tappenosauridae

The Middle Permian Tappenosaurus was estimated at 5.5 m in length, nearly as large as the largest dinocephalians.

Therapsids (Therapsida)

Anomodonts (Anomodontia)

The plant-eating dicynodont Lisowicia bojani is the largest-known of all non-mammalian synapsids, at about 4.5 m long, 2.6 m tall, and 9000 kg in body mass. However, in 2019 its weight was later more reliably estimated by modelling its mass from the estimated total volume of its body. These estimates varied depending on the girth of its rib cage and the amount of soft tissue modelled around the skeleton, with an overall average weight of 5.9 metric tons (6.5 short tons), and a lowermost estimate with minimal body fat and other tissues at 4.9 metric tons (5.4 short tons) and a maximum of 7 metric tons (7.7 short tons) at its bulkiest.

Biarmosuchians (Biarmosuchia)

The Late Permian Eotitanosuchus (a possible synonym to Biarmosuchus ) may have been over 2.5 m in length, possibly up to 6 m and more than 600 kg in weight for adult specimens.

Dinocephalians (Dinocephalia)

The largest carnivorous non-mammalian synapsids was the dinocephalian Anteosaurus, which was 5 - 6 m long, and weighed 500 - 600 kg. Fully grown Titanophoneus from the same family Anteosauridae likely had a skull of 1 m long.

Gorgonopsians (Gorgonopsia)

Inostrancevia latifrons is the largest known gorgonopsian, with a skull length of more than 60 cm, a total length approaching 3.5 m and a mass of 300 kg. Rubidgea atrox is the largest African gorgonopsian, with skull of nearly 45 cm long. Other large gorgonopsians include Dinogorgon with skull of ~40 cm long, Leontosaurus with skull of almost 40 cm long, and Sycosaurus with skull of ~38 cm long.

Therocephalians (Therocephalia)

The largest of therocephalians is Scymnosaurus, which reached a size of the modern hyena.

Non-mammalian cynodonts (Cynodontia)

Mammals (Mammalia)

Non-therian mammals

Gobiconodonts (Gobiconodonta)

The largest gobiconodont and the largest well-known Mesozoic mammal was Repenomamus. The known adult of Repenomamus giganticus reached a total length of around 1 m and an estimated mass of 12 - 14 kg. With such parameters it surpassed in size several small theropod dinosaurs of the Early Cretaceous. Gobiconodon was also a large mammal, it weighed 5.4 kg, had a skull of 10 cm in length, and had 35 cm in presacral body length.

Multituberculates (Multituberculata)

The largest multituberculate, Taeniolabis taoensis is the largest non-therian mammal known, at a weight possibly exceeding 100 kg.

Monotremes (Monotremata)

Metatherians (Metatheria)

Marsupials (Marsupialia)

Non-placental eutherians

Cimolestans (Cimolesta)

The largest known cimolestan is Coryphodon, 1 m high at the shoulder, 2.5 m long and up to 700 kg of mass. Barylambda was also a huge mammal, at 650 kg. Wortmania and Psittacotherium from the group Taeniodonta were among the largest mammals of the Early Paleocene. Lived as soon as half a million years after K–Pg boundary, Wortmania reached 20 kg in body mass. Psittacotherium, which appeared two million years later, reached 50 kg.

Leptictids (Leptictida)

The largest leptictid ever discovered is Leptictidium tobieni from the Middle Eocene of Germany. It had a skull 101 mm long, head with trunk 375 mm long, and tail 500 mm long. Close European relatives from the same family Pseudorhyncocyonidae had skulls of 67 - 101 mm in length.

Tenrecs and allies (Afroscida)

The larger of the two species of bibymalagasy (Plesiorycteropus madagascariensis), extinct tenrec relatives from Madagascar, is estimated to have weighed from 10 to 18 kilograms (21 to 40 lb).

Even-toed ungulates (Artiodactyla)

Cetaceans (Cetacea)

Odd-toed ungulates (Perissodactyla)

Phenacodontids (Phenacodontidae)

The largest known phenacodontid is Phenacodus. It was 1.5 m long and weighed up to 56 kg.

Dinoceratans (Dinocerata)

The largest known dinoceratan was Eobasileus with skull length of 102 cm, 2.1 m tall at the back and 1.5 m tall at the shoulder. Another huge animal of this group was Uintatherium, with skull length of 76 cm, 1.5 m tall at the shoulder, 4 m in length and 2.25 t, the size of a rhinoceros. Despite their large size, Eobasileus as well as Uintatherium had a very small brain.

Carnivores (Carnivora)

Caniformia

Feliformia

Hyaenodonts (Hyaenodonta)

The largest hyaenodont was Simbakubwa at 1,500 kg. Another giant hyaenodont, Megistotherium reached 500 kg and had a skull of 66.4 cm in length.

Oxyaenids (Oxyaenidae)

The largest known oxyaenid was Sarkastodon weighing in at 800 kg.

Mesonychians (Mesonychia)

Some mesonychians reached a size of a bear. Such large were Mongolonyx from Asia and Ankalagon from North America. Another large mesonychian is Harpagolestes with a skull length of a half a meter in some species.

Bats (Chiroptera)

Found in Quaternary deposits of South and Central Americas, Desmodus draculae had a wingspan of 0.5 m and a body mass of up to 60 g. Such proportions make it the largest vampire bat that ever evolved.

Hedgehogs, gymnures, shrews, and moles (Eulipotyphla)

The largest known animal of the group Eulipotyphla was Deinogalerix, measuring up to 60 cm in total length, with a skull up to 21 cm long.

Rodents (Rodentia)

Rabbits, hares, and pikas (Lagomorpha)

The biggest known prehistoric lagomorph is Minorcan giant lagomorph Nuralagus rex at 12 kg.

Pangolins (Pholidota)

The largest pangolin was the extinct Manis palaeojavanica Its total length is measured up to 2.5 m.

Primates (Primates)

Elephants, mammoths, and mastodons (Proboscidea)

Sea cows (Sirenia)

According to reports, Steller's sea cows have grown to 8 to 9 m long as adults, much larger than any extant sirenians. The weight of Steller's sea cows is estimated to be 8 - 10 MT. With its direct ancestor the Cuesta sea cow being around 9 m (30 ft) long and possibly 10 tonnes (11 short tonnes) in weight.

Arsinoitheres (Arsinoitheriidae)

The largest known arsinoitheriid was Arsinoitherium. A. zitteli would have been 1.75 m tall at the shoulders, and 3 m long. A. giganteum reached even larger size than A. zitteli.

Hyraxes (Hyracoidea)

Some of the prehistoric hyraxes were extremely large compared to modern small relatives. The largest hyracoid ever evolved is Titanohyrax ultimus. With the mass estimation in rage of 600 kg to over 1300 kg it was close in size to Sumatran rhinoceros. Another enormous hyrax is Megalohyrax which had skull of 391 mm in length and reached the size of tapir. More recent Gigantohyrax was three times as large as the extant relative Procavia capensis, although it is noticeably smaller than earlier Megalohyrax and Titanohyrax.

Desmostylians (Desmostylia)

The largest known desmostylian was a species of Desmostylus, with skull length of 81.8 cm and comparable in size to the Steller's sea cow. Paleoparadoxia is also known as one of the largest desmostylians, with body length of 3.03 m.

Armadillos, glyptodonts and pampatheres (Cingulata)

The largest cingulate known is Doedicurus, at 4 m long, 1.5 m high and reaching a mass of approximately 1910 to 2370 kg. The largest species of Glyptodon, Glyptodon clavipes, reached 3 - 3.3 m in length and 2 tonne in weight.

Anteaters and sloths (Pilosa)

The largest known pilosan is Eremotherium, a ground sloth with an estimated weight of up to 6.55 tonne and a length of up to 6 m, which is as big as a bull African bush elephant. The closely related ground sloth Megatherium attained similarly large dimensions.

Astrapotherians (Astrapotheria)

Some of the largest known astrapotherians weighed about 3–4 tonne, including the genus Granastrapotherium and some species of Parastrapotherium (P. martiale). The skeleton remains suggests that the species Hilarcotherium miyou was even larger, with a weight of 6.456 tonne.

Litopterns (Litopterna)

The largest known litoptern was Macrauchenia, which had three hoofs per foot. It was a relatively large animal, with a body length of around 3 m.

Notoungulates (Notoungulata)

The largest notoungulate known of complete remains is Toxodon. It was about 2.7 m in body length, and about 1.5 m high at the shoulder and resembled a heavy rhinoceros. Although incomplete, the preserved fossils suggests that Mixotoxodon were the most massive member of the group, with a weight about 3.8 tonne.

Pyrotherians (Pyrotheria)

The largest mammal of the South American order Pyrotheria was Pyrotherium at 2.9 – in length and 1.8 – in weight.

Reptiles (Reptilia)

Lizards and snakes (Squamata)

Turtles, tortoises and close relatives (Pantestudines)

Cryptodira

Side-necked turtles (Pleurodira)

The largest freshwater turtle of all time was the Miocene podocnemid Stupendemys, with an estimated parasagittal carapace length of 2.86 m and weight of up to 1145 kg. Carbonemys cofrinii from the same family had a shell that measured about 1.72 m, complete shell was estimated at 1.8 m.

Macrobaenids (Macrobaenidae)

The largest macrobaenids were the Early Cretaceous Yakemys, Late Cretaceous Anatolemys, and Paleocene Judithemys. All reached 70 cm in carapace length.

Meiolaniformes

The largest meiolaniid was Meiolania. Meiolania platyceps had a carapace 100 cm long and probably reached over 3 m in total body length. An unnamed Late Pleistocene species from Queensland was even larger, up to 200 cm in carapace length. Ninjemys oweni reached 100 cm in carapace length and 200 kg in weight.

Sauropterygians (Sauropterygia)

Placodonts and close relatives (Placodontiformes)

Placodus was among the largest placodonts, with a length of up to 3 m.

Nothosaurs and close relatives (Nothosauroidea)

The largest nothosaur as well as the largest Triassic sauropterygian was Nothosaurus giganteus at 7 m in length.

Plesiosaurs (Plesiosauria)

Proterosuchids (Proterosuchidae)

Proterosuchus fergusi is the largest known proterosuchid with a skull length of 47.7 cm and a possible body length of 3.5 - 4 m.

Erythrosuchids (Erythrosuchidae)

The largest erythrosuchid was Erythrosuchus africanus with a maximum length of 4.75 - 5 m.

Phytosaurs (Phytosauria)

Some of the largest known phytosaurs include Redondasaurus with a length of 6.4 m and Smilosuchus with a length of more than 7 m.

Non-crocodylomorph pseudosuchians (Pseudosuchia)

Crocodiles and close relatives (Crocodylomorpha)

[Large crocodylomorphs (†Deinosuchus, †Purussaurus,

†Gryposuchus, †Euthecodon, †Sarcosuchus, and modern Crocodylus porosus) compared to a human | upload.wikimedia.org/wikipedia/commons/c/c2/Large///crocodyliformes.svg]

Aegyptosuchids (Aegyptosuchidae)

The Late Cretaceous Aegisuchus was originally estimated to reach 15 m in length by the lower estimate and as much as 22 m by the upper estimate although a length of over 15 m is likely a significant overestimate. However, this estimation is likely to be a result of miscalculation, and its length would be only around 3.9 m.

Crocodylians (Crocodylia)

Paralligatorids (Paralligatoridae)

The largest paralligatorid was likely Kansajsuchus, estimated at up to 8 m long.

Tethysuchians (Tethysuchia)

Stomatosuchids (Stomatosuchidae)

Stomatosuchus, a stomatosuchid, was estimated at 10 m in length.

Notosuchians (Notosuchia)

Thalattosuchians (Thalattosuchia)

Basal crocodylomorphs

Redondavenator was the largest Triassic crocodylomorph ever recorded, with a skull of at least 60 cm in length. Another huge basal crocodylomorph was Carnufex at 3 m long even through that is immature.

Pterosaurs (Pterosauria)

Choristoderes (Choristodera)

The largest known choristoderan, Kosmodraco dakotensis (previously known as Simoedosaurus dakotensis ) is estimated to have had a total length of around 5 m.

Tanystropheids (Tanystropheidae)

Tanystropheus, the largest of all tanystropheids, reached up to 5 m in length.

Thalattosaurs (Thalattosauria)

The largest species of thalattosaur, Miodentosaurus brevis grew to more than 4 m in length. The second largest member of this group is Concavispina with a length of 3.64 m.

Ichthyosaurs (Ichthyosauria)

In April 2018, paleontologists announced the discovery of a previously unknown ichthyosaur that may have reached lengths of 26 m making it one of the largest animals known, rivaling some blue whales in size. These remains were later named Ichthyotitan and it has been estimated to reach up to 25 m, which makes it the largest ichthyosaur and the largest marine reptile ever. Another large ichthyosaur was the Late Triassic Shastasaurus sikanniensis at 21 m in length and 81.5 t in weight. Another, larger ichthyosaur was found in 1850 in Aust. Its remains seemed to surpass the measurements of the other ichthyosaur, but the researchers commented that the remains were too fragmentary for a size estimate to be made. Another huge ichthyosaur was Shonisaurus popularis at 15 m in length and 29.7 t in weight. The largest Middle Triassic ichthyosaur as well as the largest animal of that time was Cymbospondylus youngorum at 17.65 m in length and 44.7 t in weight.

Tangasaurids (Tangasauridae)

The largest tangasaurid was Hovasaurus with an estimated snout-vent length of 30 - 35 cm and a tail of 60 cm.

Pareiasaurs (Pareiasauria)

Largest pareiasaurs reached up to 3 m in length. Such sizes had Middle Permian Bradysaurus, Embrithosaurus, and Nochelesaurus from South Africa, and the Late Permian Scutosaurus from Russia. The most robust Scutosaurus had 1.16 t in body mass.

Captorhinids (Captorhinidae)

The heavy built Moradisaurus grandis, with a length of 2 m, is the largest known captorhinid. The second largest captorhinid was Labidosaurikos with the largest adult skull specimen 28 cm long.

Non-avian dinosaurs (Dinosauria)

Sauropodomorphs (Sauropodomorpha)

The largest of non-sauropod sauropodomorphs ("prosauropod") was Euskelosaurus. It reached 12.2 m in length and 2 MT in weight. Another huge sauropodomorph Yunnanosaurus youngi reached 13 m long.

Sauropods (Sauropoda)

Other huge sauropods include Argentinosaurus, Alamosaurus, and Puertasaurus with estimated lengths of 30 - 33 m and weights of 50 - 80 tonne. Patagotitan was estimated at 37 m in length and 57 tonne in average weight, and was similar in size to Argentinosaurus and Puertasaurus. Giant sauropods like Supersaurus, Sauroposeidon, and Diplodocus probably rivaled them in length but not in weight. Dreadnoughtus was estimated at 49 t in weight and 26 m in length, but the most complete individual was immature when it died. Turiasaurus is considered the largest dinosaur from Europe, with an estimated length of 30 m and a weight of 50 t. However, lower estimates at 21 m and 30 t would make it smaller than the Portuguese Lusotitan, which reached 24 m in length and 34 t in weight. Many large sauropods are still unnamed and may rival the current record holders:

Non-avian theropods (Theropoda)

Armoured dinosaurs (Thyreophora)

The largest-known thyreophoran was Ankylosaurus at 9 m in length and 6 tonne in weight. Stegosaurus was also 9 m long but around 5 tonne tonnes in weight.

Marginocephalians (Marginocephalia)

Pachycephalosaurs (Pachycephalosauria)

The largest pachycephalosaur was the eponymous Pachycephalosaurus. Previously claimed to be at 7 m in length, it was later estimated about 4.5 m long and a weight of about 450 kg.

Ceratopsians (Ceratopsia)

The largest ceratopsian known is Triceratops horridus, along with the closely related Eotriceratops xerinsularis both with estimated lengths of 9 m. Pentaceratops and several other ceratopsians rival them in size. Titanoceratops had one of the longest skull of any land animal, at 2.65 m long.

Ornithopods (Ornithopoda)

Birds (Aves)

The largest bird in the fossil record may be the extinct elephant bird species Aepyornis maximus of Madagascar, whose closest living relative is the kiwi. Giant elephant birds exceeded 2.3 m in height, and average a mass of 850 kg The largest fowl was the mihirung Dromornis stirtoni of Australia. It exceeded 2.7 m in height, and average a mass of 500 kg Another contender is Brontornis burmeisteri, an extinct flightless bird from South America which reached a weight of 319 kg and a height of approximately 2.8 m. The tallest recorded bird was Pachystruthio dmanisensis, a relative of the ostrich. This particular species of bird stood at 3.5 m tall and average a mass of 450 kg The largest known flightless neoave was the terror bird Paraphysornis brasiliensis of South America, the Brazilian terror bird exceeded 240 kg in mass,

Table of heaviest extinct bird species

Enantiornitheans (Enantiornithes)

One of the largest enantiornitheans was Enantiornis, with a length in life of around 78.5 cm, hip height of 34 cm, weight of 6.75 kg, and wingspan comparable to some of the modern gulls, around 1.2 m. Gurilynia was the largest Mesozoic bird from Mongolia, with a length of 53 cm, hip height of 23.2 cm, and weight of 2.1 kg.

Avisauridae

The Late Cretaceous Avisaurus was almost as large as Enantiornis. It had a wingspan around 1.2 m, a length of 72 cm, hip height of 31.5 cm, and weight of 5.1 kg. Even larger could be the Soroavisaurus. One tibiotarsus (PVL-4033) indicates an animal with a length of 80 cm, hip height of 35 cm, and weight of 7.25 kg. However, according to Walker and Dyke (2009) which considered PVL-4033 as Martinavis sp., its tibiotarsus length is 85.6 mm, much shorter than that of Lectavis (156 mm tibiotarsus) which the same book estimated a length of 41 cm, hip height of 30 cm, and weight of 1.15 kg''. Mirarce'' was comparable in size to a turkey, much larger than most of other enantiornitheans.

Pengornithidae

One of the biggest Early Cretaceous enantiornithine bird was Pengornis at 50 cm in length and skull length of 54.7 mm.

Gargantuaviidae

Gargantuavis is the largest known bird of the Mesozoic, a size ranging between the cassowary and the ostrich, and a mass of 140 kg like modern ostriches. In 2019 specimens MDE A-08 and IVPP-V12325 were measured at 1.8 m in length, 1.3 m in hip height, and 120 kg in weight.

Dromornithiformes

The largest dromornithid was Dromornis stirtoni over 3 m tall and 528 - 584 kg in mass for males.

Gastornid (Gastornithiformes)

Large individuals of Gastornis reached up to 2 m in height. Weight of Gastornis ranges from 100 kg to 156 kg and sometimes to 180 kg for European specimens and from 160 kg to 229 kg for North American.

Waterfowl (Anseriformes)

Possibly flightless, the Miocene Garganornis ballmanni was larger than any extant members of Anseriformes, with 15.3 - 22.3 kg in body mass. Another huge anseriform was the flightless New Zealand goose (Cnemiornis). It reached 15 - 18 kg, approaching in size to small species of moa.

Swans (Cygnini)

The largest known swan was the Pleistocene giant swan (Cygnus falconeri), which reached a bill-to-tail length of about 190 - 210 cm, a weight of around 16 kg, and a wingspan of 3 m. The New Zealand swan (Cygnus sumnerensis) weighed up to 10 kg, compared to the related extant black swan at only 6 kg. The large marine swan Annakacygna yoshiiensis from the Miocene of Japan far exceeded the extant mute swan in both size and weight.

Anatinae

Finsch's duck (Chenonetta finschi) reached 1 - 2 kg in weight, surpassing related modern Australian wood duck (800 g).

Pelicans, ibises and allies (Pelecaniformes)

Storks and allies (Ciconiiformes)

The largest known of Ciconiiformes was Leptoptilos robustus, standing 1.8 m tall and weighing an estimated 16 kg. Ciconia maltha is a relatively large species of Ciconia, with a height of over 5 ft and a wingspan up to 10 ft across.

Cranes (Gruiformes)

A large true crane (Gruinae) from the late Miocene (Tortonian) of Germany was equal in size to the biggest extant cranes and resembled the long-beaked Siberian crane (Leucogeranus leucogeranus).

Shorebirds (Charadriiformes)

Miomancalla howardi was the largest known charadriiform of all time, weighing approximately 0.6 kg (1.3 lb) more than the second-largest member, the great auk (Pinguinus impennis).

Hesperornithines (Hesperornithes)

The largest known of the hesperornithines was Canadaga arctica at 2.2 m long.

New World vultures (Cathartiformes)

One of the heaviest flying birds of all time was Argentavis, a Miocene teratornithid. The immense bird had a wingspan estimated up to 5.09 - 6.5 m and a weight up to 70 to 72 kg. Argentavis humerus was only slightly shorter than an entire human arm. Another huge teratorn was Aiolornis, with a wingspan of around 5 m. The Pleistocene Teratornis merriami reached 13.7 kg and 2.94 – in wingspan, with lower size estimates still exceeding the largest specimens of California condor (Gymnogyps californianus).

Seriemas and allies (Cariamiformes)

The largest known-ever Cariamiforme and largest phorusrhacid or "terror bird" (highly predatory, flightless birds of America) was Brontornis, which was about 175 cm tall at the shoulder, could raise its head 2.8 m above the ground and could have weighed as much as 400 kg. The immense phorusrhacid Kelenken stood 3 m tall with a skull 716 mm long (460 mm of which was beak), had the largest head of any known bird. South American Phorusrhacos stood 2.4-2.7 m (7.9-8.8 ft) tall, and weighed nearly 130 kg, as much as a male ostrich. The largest North American phorusrhacid was Titanis, which reached a height of approximately 2.5 m (8.2 ft), slightly taller than an African forest elephant.

Accipitriforms (Accipitriformes)

The largest known bird of prey ever was the enormous Haast's eagle (Hieraaetus moorei), with a wingspan of 2.6 to 3 m, relatively short for their size. Total length was probably up to 1.4 m in female and they weighed about 10 to 15 kg. Another giant extinct hawk was Titanohierax about 7.3 kg that lived in the Antilles and The Bahamas, where it was among the top predators. An unnamed late Quaternary eagle from Hispaniola could be 15–30% larger than the modern golden eagle (Aquila chrysaetos). Some extinct species of Buteogallus surpassed their extant relatives in size. Buteogallus borrasi was about 33% larger than the modern great black hawk (B. urubitinga). B. daggetti, also known as "walking eagle", was around 40% larger than the savanna hawk (B. meridionalis). Eyles's harrier (Circus eylesi) from the Pleistocene-Holocene of New Zealand was more than twice heavier than the extant C. approximans.

Moa (Dinornithiformes)

The tallest known bird was the South Island giant moa (Dinornis robustus), part of the moa family of New Zealand that went extinct about 500 years ago. It stood up to 3.7 m tall, and weighed approximately half as much as a large elephant bird due to its comparatively slender frame.

Tinamous (Tinamiformes)

MPLK-03, a tinamou specimen that existed during the Late Pleistocene in Argentina, possibly belongs to the modern genus Eudromia and surpacces extant E. elegans and E. formosa in size by 2.2–8% and 6–14%, respectively.

Elephant birds (Aepyornithiformes)

The largest bird in the fossil record may be the extinct elephant birds (Vorombe, Aepyornis) of Madagascar, which were related to the ostrich. They exceeded 3 m in height and 500 kg in weight.

Ostriches (Struthioniformes)

With 450 kg in body mass, Pachystruthio dmanisensis from the lower Pleistocene of Crimea was the largest bird ever recorded in Europe. Despite its giant size, it was a good runner. A possible specimen of Pachystruthio from the lower Pleistocene of Hebei Province (China) was about 300 kg in weight, twice heavier than the common ostrich (Struthio camelus). Remains of the massive Asian ostrich (Struthio asiaticus) from the Pliocene indicate a size 20% bigger than adult male of the extant Struthio camelus.

Pigeons and doves (Columbiformes)

The largest pigeon relative known was the dodo (Raphus cucullatus), possibly exceeding 1 m in height and weighing as much as 28 kg, although recent estimates have indicated that an average wild dodo weighed much less at approximately 10.2 kg.

Pheasants, turkeys, gamebirds and allies (Galliformes)

The largest known of the Galliformes was likely the giant malleefowl, which could reach 7 kg in weight.

Songbirds (Passeriformes)

The largest known songbird is the extinct giant grosbeak (Chloridops regiskongi) at 11 in long.

Cormorants and allies (Suliformes)

Grebes (Podicipediformes)

The largest known grebe, the Atitlán grebe (Podylimbus gigas), reached a length of about 46 –.

Bony-toothed birds (Odontopterygiformes)

The largest known of the Odontopterygiformes— a group which has been variously allied with Procellariiformes, Pelecaniformes and Anseriformes and the largest flying birds of all time other than Argentavis were the huge Pelagornis, Cyphornis, Dasornis, Gigantornis and Osteodontornis. They had a wingspan of 5.5 – and stood about 1.2 m tall. Exact size estimates and judging which one was largest are not yet possible for these birds, as their bones were extremely thin-walled, light and fragile, and thus most are only known from very incomplete remains.

Woodpeckers and allies (Piciformes)

The largest known woodpecker is the possibly extinct imperial woodpecker (Campephilus imperialis) with a total length of about 56 –.

Parrots (Psittaciformes)

The largest known parrot is the extinct Heracles inexpectatus with a length of about 1 meter (3.3 feet).

Penguins (Sphenisciformes)

One of the heaviest penguins ever known is Kumimanu fordycei, with a body mass estimate of 148 to 159.7 kg, derived from humerus measurements. Another example is Palaeeudyptes klekowskii of Antarctica, with a bill-to-tail length estimated at 2.02 m and an estimated body weight of 84.2 kg, slightly smaller than previous estimates. The Eocene Anthropornis nordenskjoeldi is comparable in size, and was once estimated to reach lengths of 2.05 m and a weight of 108 kg. However, recent estimation from humerus measurements put A. nordenskjoeldi more in the range of 67 kg in weight. Other large penguins include the New Zealand giant penguin (Pachydyptes pondeorsus) weighing around 65.4 to 94.6 kg, and Icadyptes salasi at 52.8 to 73.0 kg.

Owls (Strigiformes)

The largest known owl of all time was the Cuban Ornimegalonyx at 43.3 in tall probably exceeding 9 kg.

Amphibians (Amphibia)

The largest known amphibian of all time was the 30 ft long temnospondyl Prionosuchus.

Lissamphibians (Lissamphibia)

Frogs and toads (Anura)

The largest known frog ever was an as yet unnamed Eocene species that was about 58 - 59 cm. The Late Cretaceous Beelzebufo grew to at least 23.2 cm (snout-vent length), which is around the size of a modern African bullfrog.

Salamanders, newts and allies (Urodela)

Diadectomorphs (Diadectomorpha)

The largest known diacectid, herbivorous Diadectes, was a heavily built animal, up to 3 m long, with thick vertebrae and ribs.

Anthracosauria

The largest known anthracosaur was Anthracosaurus, with skull about 40 cm in length.

Embolomeri

The longest member of this group was Eogyrinus attheyi, species sometimes placed under genus Pholiderpeton. Its skull had length about 41 cm.

Temnospondyls (Temnospondyli)

The largest known temnospondyl amphibian is Prionosuchus, which grew to lengths of 9 m. Another huge temnospondyl was Mastodonsaurus giganteus at 6 m long. Unnamed species of temnospondyl from Lesotho is partial, but possible body length estimation is 7 m.

Fishes (Pisces)

Fishes are a paraphyletic group of non-tetrapod vertebrates.

Jawless fish (Agnatha)

Conodonts (Conodonta)

Iowagnathus grandis is estimated to have length over 50 cm.

Heterostracans (Heterostraci)

Some members of Psammosteidae such as Obruchevia and Tartuosteus are estimated to reached up to 2 m.

Thelodonts (Thelodonti)

Although known from partial materials, Thelodus parvidens (=T. macintoshi) is estimated to reached up to 1 m.

Cephalaspidomorphs (Cephalaspidomorphi)

A species of Parameteoraspis reached up to 1 m.

Spiny sharks (Acanthodii)

The largest of the now-extinct Acanthodii was Xylacanthus grandis, an ischnacanthiform based on a ~35 cm long jaw bone. Based on the proportions of its relative Ischnacanthus, X. grandis had an estimated total length of 2.5 m.

Placoderms (Placodermi)

The largest known placoderm was the giant predatory Dunkleosteus. The largest and most well known species was D. terrelli, various estimate put its length around 4.1-10 m in length and 1-4 MT in weight. Another large placoderm, Titanichthys, may have rivaled it in size. Titanichthys is estimated to have a length around 4.1–7.5 m

Cartilaginous fish (Chondrichthyes)

Mackerel sharks (Lamniformes)

Ground sharks (Carcharhiniformes)

The Cenozoic Hemipristis serra was considerably larger than its modern-day relatives and had much larger teeth. Its total length is estimated to be at 6 m long.

Hybodonts (Hybodontiformes)

One of the largest hybodontiforms was the Jurassic Asteracanthus with body length of up to 3 m. Crassodus reifi is known from less materials, however it is estimated that reached over 3 m.

Ctenacanthiformes

The largest member of ctenacanthiformes is Saivodus striatus with estimated length around 6-9 m.

Skates and allies (Rajiformes)

The giant sclerorhynchid Onchopristis reached about 4.25 m in length.

Eugeneodont (Eugeneodontida)

The largest known eugeneodont is an as-yet unnamed species of Helicoprion discovered in Idaho. The specimens suggest an animal that possibly exceeded 12 m in length. Another fairly large eugeneodont is Parahelicoprion. Being more slimmer than Helicoprion, it reached nearly the same size, possibly up to 12 m in length. Both had the largest sizes among the animals of Paleozoic era.

Lobe-finned fish (Sarcopterygii)

Coelacanths (Actinistia)

The largest coelacanth is Cretaceous Mawsonia gigas with estimated total length up to 5.3 m. Jurassic Trachymetopon may have reached size close to that, about 5 m. An undetermined mawsoniid from the Maastrichtian deposits of Morocco probably reached 3.65 - 5.52 m in length.

Lungfish (Dipnoi)

Cretaceous Ceratodus sp. from Western Interior is estimated to had a length around 4 m.

Stem-tetrapods (Tetrapodomorpha)

Ray-finned fish (Actinopterygii)

Acipenseriformes

Pachycormiformes

The largest known ray-finned fish and largest bony fish of all time was the pachycormid, Leedsichthys problematicus, at around 16.5 m long. Earlier estimates have had claims of larger individuals with lengths over 27 m.

Ichthyodectiformes

The largest known of ichthyodectiform fish was Xiphactinus, which measured up to 6.1 m long. Ichthyodectes reached 3 m long, twice lesser than Xiphactinus.

Pycnodontiformes

The largest known pycnodontiform was Gyrodus circularis, with length up to 2 m.

Bichirs (Polypteriformes)

The Late Cretaceous Bawitius was likely the largest bichir of all time. It reached up to 3 m in length.

Opahes, ribbonfishes, oarfishes and allies (Lampriformes)

Megalampris was likely the largest fossil opah. This fish was around 4 m in length when alive, which is twice the length of the largest living opah species, Lampris guttatus.

Salmon and trout (Salmoniformes)

The largest salmon was Oncorhynchus rastrosus, varying in size from 1.9 m and 177 kg to 2.4 m and 200 kg.

Pufferfishes, boxfishes, triggerfishes, ocean sunfishes and allies (Tetraodontiformes)

Lizardfishes (Aulopiformes)

The largest lizardfish was Stratodus which could reach length of 5 m.

Echinoderms (Echinodermata)

Crinozoa

Sea lilies (Crinoidea)

The longest stem of Seirocrinus subangularis reached over 26 m.

Asterozoa

Starfish (Asteroidea)

Helianthaster from Hunsrück Slate had a radius of about 25 cm.

Graptolites (Graptolithina)

The longest known graptoloid graptolite is Stimulograptus halli at 1.45 m. It was found in Silurian deposits of the United Kingdom.

Kinorhynchs (Kinorhyncha)

Cambrian kinorhynchs from Qingjiang biota, also known as "mud dragons", reached 4 cm in length, much larger than extant relatives that grow only a few millimeters in length.

Arthropods (Arthropoda)

Dinocaridida

Gilled lobopodians

Based on the findings of mouthparts, the Cambrian gilled lobopodian Omnidens amplus is estimated to have been 1.5 m. It is also known as the largest Cambrian animal known to exist.

Radiodont (Radiodonta)

The largest known radiodont is Aegirocassis benmoulai, estimated to have been at least 2 m long.

Chelicerata

Sea spiders (Pycnogonida)

The largest fossil sea spider is Palaeoisopus problematicus with legspan about 32 cm.

Horseshoe crabs and allies (Xiphosura)

Chasmataspidids (Chasmataspidida)

The largest chasmataspidids were the Ordovician Hoplitaspis at 29 cm in length and similar in size range Chasmataspis.

Eurypterids (Eurypterida)

Arachnids (Arachnida)

Artiopods (Artiopoda)

Retifacies probably reached up to 55 cm. Tegopelte is another one example of large non-trilobite artiopod, reached 280 mm long and was the largest of the Burgess Shale bilaterians, surpassing all other benthic organisms by at least twice.

Trilobites (Trilobita)

Some of trilobites exceeded 60 cm in length. A nearly complete specimen of Isotelus rex from Manitoba attained a length over 70 cm, and an Ogyginus forteyi from Portugal was almost as long. Fragments of trilobites suggest even larger record sizes. An isolated pygidium of Hungioides bohemicus implies that the full animal was 90 cm long.

Myriapods (Myriapoda)

The largest known myriapod by far was Arthropleura. Measuring 2.5 m long and 50 cm wide. Some specimens could have been even larger, up to 2.63 m in length and 50 kg in weight.

Non-hexapod crustaceans (Crustacea)

Cycloids (Cyclida)

The largest cyclid was Opolanka decorosa, the Late Triassic Halicyne-like cycloid which reached over 6 cm across the carapace.

Remipedes (Remipedia)

Tesnusocaris had body length at least 9.5 cm, larger than every living remipedes which could reach up to 4.5 cm.

Insects (Insecta)

Sawflies, wasps, bees, ants and allies (Hymenoptera)

Fleas (Siphonaptera)

The largest known in Siphonaptera was probably Pseudopulex magnus, growing to 22.8 mm in length.

Earwigs (Dermaptera)

Extinct as recently as after 1967 and also submitted as the Holocene subfossils, the Saint Helena giant earwig (Labidura herculeana, with synonym Labidura loveridgei) reached 84 mm in length including forceps 34 mm long.

Chresmodidae

Chresmodidae had long specialized legs like of the modern Gerridae family. One of the Chresmodidae, Chresmoda obscura, could have reached a size of about 19 cm.

Beetles (Coleoptera)

One of the largest known fossil beetles in the superfamily Scarabaeoidea is Protognathinus spielbergi. It had total length including mandibles about 5.5 cm. The largest fossil scarabaeid was Oryctoantiquus borealis with an estimated body length of 5 cm.

Titanopterans (Titanoptera)

Related to modern orthopterans, titanopterans from the Triassic period were much larger. The wingspan of Gigatitan vulgaris was up to 40 cm. Clatrotitan andersoni also reached a huge size, having a forewing 13.8 cm long.

Antlions and related net-winged insects (Neuroptera)

Makarkinia adamsi from the Crato Formation is estimated to have the longest forewings of any neuropteran species, estimated at 160 mm.

Cockroaches, termites, mantises and allies (Dictyoptera)

Dragonflies, damselflies and griffinflies (Odonatoptera)

Mayflies (Ephemeroptera)

Palaeodictyoptera

The largest known palaeodictyopteran was Mazothairos, with an estimated wingspan of up to 22 in. If a subcircular wing known from Piesberg Quarry belongs to a palaeodictyopteran, it possibly had single wing length at least 30 cm.

Archaeognatha (jumping bristletails) and other wingless primitive insects

Arrow worms (Chaetognatha)

The Cambrian stem-chaetognathan Timorebestia koprii had reached up to 20 cm in body length and 30 cm including the antennae. Capinatator had a third of length, about 10 cm, but it is not considered as stem member and still had length similar to the largest modern arrow worms.

Ringed worms (Annelida)

Websteroprion is the largest known fossil eunicidan annelid, with estimated length ranges 0.42 - 8.3 m, however comparison with closely related extant taxa indicates length around 1 - 2 m. It also had the biggest scolecodonts of any prehistoric polychaete, up to 13.2 mm in length and possibly larger.

Molluscs (Mollusca)

Snails and slugs (Gastropoda)

Bivalves (Bivalvia)

Tusk shells (Scaphopoda)

Cephalopods (Cephalopoda)

Nautiloids (Nautiloidea)

The largest and longest known of nautiloids was Endoceras giganteum with a shell length of 5.73 m. There is a record of individual whose shell length had reached 9.14 m, but it is doubtful.

Ammonites (Ammonoidea)

The largest known ammonite was Parapuzosia seppenradensis. A partial fossil specimen found in Germany had a shell diameter of 1.95 m, but the living chamber was incomplete, so the estimated shell diameter was probably about 3.5 m and weighed about 705 kg when it was alive. However, a later study estimates shell diameter up to around 2 m.

Belemnites (Belemnoidea)

The largest known belemnite was Megateuthis gigantea, reaching about 50 and 700 mm in maximum diameter and length of rostrum, respectively.

Squids, octopuses, cuttlefishes and allies (Neocoleoidea)

Brachiopods (Brachiopoda)

The largest brachiopod ever evolved was Striatifera striata from Akkermanovka Quarry, Russia, with height up to 0.5 m. Another huge brachiopod was the Carboniferous Gigantoproductus giganteus, with shell width from 30 cm to over 35 cm. Titanaria costellata had large and long shell 35 - 36 cm in width, nearly as large as Gigantoproductus.

Hyoliths (Hyolitha)

The largest hyolith is Macrotheca almgreeni, with length about 50 cm.

Cnidarians (Cnidaria)

Jellyfishes and allies (Medusozoa)

The largest fossil jellyfish is Cambrian Cordubia gigantea, with diameter of 88 cm. Specimens from the Cambrian of Wisconsin reached 70 cm in length.

Vendobionts (Vendobionta)

Petalonamids (Petalonamae)

Longest specimens of Trepassia wardae (also known as Charnia wardi) reached 185 cm in length. Charnia masoni is known from specimens as small as only 1 cm, up to the largest specimens of 66 cm in length.

Proarticulata

Dickinsonia tenuis reached 1.4 m in length, that makes it one of the largest precambrian organisms.

Sponges (Porifera)

The largest known Permian sponge Gigantospongia had diameter up to 2.5 m.

Sources