Largest prehistoric animals
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The largest prehistoric organisms include both vertebrate and invertebrate species. Many 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 mostly conjecture because soft tissue was rarely fossilized. Generally the size of extinct species was subject to energetic and biomechanical constraints.
- 1 Vertebrates
- 1.1 Mammals (Mammalia)
- 1.1.1 Monotremes (Monotremata)
- 1.1.2 Even-toed ungulates (Artiodactyla)
- 1.1.3 Marsupials (Marsupialia)
- 1.1.4 Carnivores (Carnivora)
- 1.1.5 Armadillos, glyptodonts and pampatheres (Cingulata)
- 1.1.6 Hedgehogs, gymnures, shrews, and moles (Erinaceomorpha and Soricomorpha)
- 1.1.7 Rabbits, hares, and pikas (Lagomorpha)
- 1.1.8 Cimolestids (Cimolesta)
- 1.1.9 Odd-toed ungulates (Perissodactyla)
- 1.1.10 Anteaters and sloths (Pilosa)
- 1.1.11 Primates (Primates)
- 1.1.12 Elephants, mammoths, and mastodons (Proboscidea)
- 1.1.13 Rodents (Rodentia)
- 1.1.14 Astrapotherians (Astrapotheria)
- 1.1.15 Arsinoitheres (Arsinoitheriidae)
- 1.1.16 Condylarths (Condylarthra)
- 1.1.17 Dinoceratans (Dinocerata)
- 1.1.18 Desmostylians (Desmostylia)
- 1.1.19 Litopterns (Litopterna)
- 1.1.20 Notoungulates (Notoungulata)
- 1.1.21 Oxyaenids (Oxyaenidae)
- 1.1.22 Hyaenodontids (Hyaenodontidae)
- 1.1.23 Mesonychids (Mesonychia)
- 1.2 Non-mammal synapsids (Synapsida)
- 1.3 Reptiles (Reptilia)
- 1.3.1 Crocodiles and relatives (Crocodylomorpha)
- 1.3.2 Lizards and snakes (Squamata)
- 1.3.3 Plesiosaurs
- 1.3.4 Ichthyosaurs (Ichthyosauria)
- 1.3.5 Turtles and tortoises (Testudines)
- 1.3.6 Pareiasaurs (Pareiasauridae)
- 1.3.7 Phytosaurs (Phytosauria)
- 1.3.8 Pterosaurs (Pterosauria)
- 1.4 Non-avian dinosaurs (Dinosauria)
- 1.5 Birds (Aves)
- 1.5.1 Waterfowl (Anseriformes)
- 1.5.2 Storks and allies (Ciconiiformes)
- 1.5.3 Hesperornithines (Hesperornithes)
- 1.5.4 Diatrymas (Gastornithiformes)
- 1.5.5 Teratorns (Teratornithidae)
- 1.5.6 Phorusrhacids (Phorusrhacidae)
- 1.5.7 Accipitriforms (Accipitriformes)
- 1.5.8 Gamebirds (Galliformes)
- 1.5.9 Songbirds (Passeriformes)
- 1.5.10 Cormorants and allies (Pelecaniformes)
- 1.5.11 Bony-toothed birds (Odontopterygiformes)
- 1.5.12 Woodpeckers and allies (Piciformes)
- 1.5.13 Parrots (Psittaciformes)
- 1.5.14 Penguins (Sphenisciformes)
- 1.5.15 Owls (Strigiformes)
- 1.6 Amphibians (Amphibia)
- 1.7 Lobe-finned fish (Sarcopterygii)
- 1.8 Ray-finned fish (Actinopterygii)
- 1.9 Cartilaginous fish (Chondrichthyes)
- 1.10 Placoderms (Placodermi)
- 1.1 Mammals (Mammalia)
- 2 Arthropods (Arthropoda)
- 2.1 Dinocaridida
- 2.2 Chelicerata
- 2.3 Myriapoda
- 2.4 Trilobitomorpha
- 2.5 Insects (Insecta)
- 3 Molluscs (Mollusca)
- 4 See also
- 5 References
The largest-known monotreme (egg-laying mammal) ever was the extinct long-beaked echidna species known as Zaglossus hacketti, known from a couple of bones found in Western Australia. It was the size of a sheep, weighing probably up to 30 kg (66 lb).
Even-toed ungulates (Artiodactyla)
- The largest-known artiodactyl was Hippopotamus gorgops with a length of 4.3 m (14 ft) and a height of 2.1 m (6 ft 11 in). Bison latifrons reached a shoulder height of 2.5 m (8 ft 2 in), and had horns that spanned over 2 m (6 ft 7 in). The largest extinct bovid is Aurochs (Bos primigenius) with an average height at the shoulders of 155–180 cm (61–71 in) in bulls and 135–155 cm (53–61 in) in cows, while aurochs populations in Hungary had bulls reaching 155–160 cm (61–63 in).
- The largest-known camel that ever lived was the Syrian camel. It was 3 m (9.8 ft) at the shoulder and 4.0 m (13 ft) tall. Gigantocamelus and Titanotylopus from North America, both possibly reached 2,485.6 kg (5,480 lb) and a shoulder height of over 3.4 m (11 ft).
- Daeodon was the largest-known entelodont that ever lived, at 3.7 m (12 ft) long and 2.1 m (7 ft) at the shoulder. The largest-known wild suid to ever exist was Kubanochoerus gigas, having measured up to 550 kg (1,210 lb) and stood more than 1.3 m (4 ft 3 in) tall at the shoulder.
- The extinct Irish elk (Megaloceros giganteus) and the stag-moose (Cervalces scotti) were of similar size to the Alaskan moose. However, the Irish elk could have antlers spanning up to 4.3 m (14 ft) across, about twice the maximum span for a moose's antlers. Cervalces latifrons was twice as heavy as the Irish elk but its antlers were smaller.
- The largest-known extinct marsupial was Diprotodon, about 3 m (9.8 ft) long, standing 2 m (6 ft 7 in) tall and weighing up to 2,786 kg (6,142 lb).
- The two largest-known carnivorous marsupials were the marsupial lion and Thylacosmilus (larger than the Tasmanian tiger), both about 1.8 m (6 ft) long and weighing 100–160 kg (220–350 lb). The largest-known kangaroo ever was Procoptodon, which could grow to 3 m (10 ft) and weigh 230 kg (510 lb). Some species from the genus Sthenurus were similar in size as well.
- The largest palorchestids Palorchestes was almost as large as a horse, being around 2.5 m (8 ft 2 in) in length with a weight of about 200 kg (440 lb), and had four powerful legs.
- The largest terrestrial known carnivoran and the largest-known bear as well as the largest-known mammalian land-predator of all time was Arctotherium angustidens or the South American short-faced bears. A humerus of A. angustidens from Buenos Aires indicate that the large males could have weighed 1,588–1,749 kg (3,501–3,856 lb) and standing at least 3.4 m (11 ft) tall on the hind-limbs.
- The largest viverrid known to have existed is Viverra leakeyi, which was around the size of a wolf or small leopard at 41 kg (90 lb).
- The heaviest known felids are the Ngangdong tiger (Panthera tigris soloensis), with the largest specimen weighing up to 470 kg (1,040 lb) , the American lion (Panthera leo atrox or P. atrox), weighing up to 420 kg (930 lb) and saber-toothed cats Amphimachairodus Kabir and Smilodon populator, with the males possibly reaching 350–490 kg (770–1,080 lb) and 220–400 kg (490–880 lb) respectively. 
- The largest known wolf species is the dire wolf (Canis dirus) 1.5 m (4 ft 11 in) in length and weighed between 50 and 110 kg (110 and 243 lb). The largest canid of all time was Epicyon haydeni, which stood 0.94 m (37 in) tall at the shoulder. The largest bear-dog was a species of Pseudocyon weighing around 773 kg (1,704 lb), representing a very large individual.
- The largest-known mustelid to ever exist was likely the giant otter, Enhydriodon. It exceeded 3 m (9.8 ft) in length, and would have weighed in at around 200 kg (440 lb), much larger than any other known mustelid, living or extinct. There were other giant otters, like Siamogale, at around 50 kg (110 lb) and Megalenhydris, which was larger than a modern-day giant river otter. Another large-bodied mustelid was the superficially cat-like Ekorus from Africa, about the size of a leopard and filling a similar ecological niche before big cats came to the continent. Megalictis was thought to be around the size of a black bear according to old estimates. Newer estimates, however, significantly downgrade its size, although, at a maximum weight more than twice that of a wolverine, it is larger than most (if not all) living mustelids.
- The largest known fossil hyena is Pachycrocuta, estimated at 190 kg (420 lb). The closely related percrocutid feliform, Dinocrocuta, was even bigger, 240 kg (530 lb).
The largest cingulate known is Doedicurus, at 3.8 m (12 ft) long and reaching a mass of approximately 1,910 to 2,370 kg (2.11 to 2.61 short tons) Glyptodon easily topped 3.3 m (11 ft) and 2 t (2.2 short tons).
Hedgehogs, gymnures, shrews, and moles (Erinaceomorpha and Soricomorpha)
The largest-known animal of this group was Deinogalerix, measuring up to 60 cm (24 in) in total length, with a skull up to 20 cm (7.9 in) long. It occupied the same ecological niche as dogs and cats today.
Rabbits, hares, and pikas (Lagomorpha)
The largest-known prehistoric lagomorph is Minorcan giant lagomorph (Nuralagus rex) at 23 kg (51 lb).
Odd-toed ungulates (Perissodactyla)
- The largest-known perissodactyl, and the second largest land mammal (see Palaeoloxodon namadicus) of all time was Paraceratherium. The largest individual known was estimated at 4.8 m (15.7 ft) tall at the shoulders, 7.4 m (24.3 ft) in length from nose to rump, and 17 t (18.7 short tons) in weight.
- Some prehistoric horned rhinos also grew to large sizes. The giant woolly rhino Elasmotherium reached 6 m (20 ft) long and 2 m (6 ft 7 in) high. The largest prehistoric horse was Equus giganteus of North America. It was estimated to grow to more than 1,250 kg (1.38 short tons) and 2 m (6 ft 7 in) at the shoulders.
- The largest-known pilosan ever was Megatherium, a ground sloth with an estimated average weight of 3.8 t (4.2 short tons) and a height of 6 m (20 ft) which is close to the size of the African bush elephant. Several other sloths grew to large sizes as well, such as Eremotherium, but none as large as Megatherium.
- The largest-known primate of all time was Gigantopithecus blackii, standing 3 m (9.8 ft) tall and weighing 540 kg (1,200 lb).
- The largest-known old world monkey, the prehistoric baboon Dinopithecus grew even larger than modern Mandrills, weighing as much as a grown man.
- Some prehistoric prosimians grew to huge sizes as well. Archaeoindris was a 1.5-metre-long (4.9 ft) lemur that lived in Madagascar and weighed 200 kg (440 lb), as large as a silverback gorilla. Megaladapis is another large extinct lemur at 1.3 to 1.5 m (4 ft 3 in to 4 ft 11 in) in length.
Elephants, mammoths, and mastodons (Proboscidea)
- The largest-known land mammal ever was a proboscidean called Palaeoloxodon namadicus which weighed about 22 t (24.3 short tons), and was about 5.2 m (17.1 ft) tall at the shoulder. The largest individuals of the steppe mammoth of Eurasia (Mammuthus trogontherii) estimated to reach 4.5 m (14.8 ft) at the shoulders and 14.3 t (15.8 short tons) in weight.
- Some other enormous proboscideans include the southern mammoth (Mammuthus meridionalis), the Columbian mammoth (Mammuthus columbi), and Deinotherium.
- Josephoartigasia monesi was the largest-known rodent of all time, approximately 3 m (9.8 ft) long and 1.5 m (4 ft 11 in) tall and weighing an estimated 1 t (1.1 short tons).
- Before the discovery of Josephoartigasia monesi, another giant rodent was known, Phoberomys insolita, but it was known from only a few fragments, so its real size is unknown. A slightly smaller relative, Phoberomys pattersoni, was found, which was 3 m (9.8 ft) long and weighed 320 kg (700 lb).
- The largest beaver was the giant beaver of North America. It grew over 2.4 m (8 ft) in length and weighed roughly 60 to 100 kg (130 to 220 lb), also making it one of the largest rodents to ever exist.
The largest-known condylarth is Phenacodus. It was 1.5 m (4 ft 11 in) long and weighted up to 56 kg (123 lb).
The largest notoungulate known of complete remains is Toxodon. It was about 2.7 m (8 ft 10 in) in body length, and about 1.5 m (4 ft 11 in) high at the shoulder and resembled a heavy rhinoceros. Although is not complete, the preserved fossils suggests that Mixotoxodon were the most massive member of the group, with a weight about 3.8 t (4.2 short tons).
The plant-eating dinocephalian Tapinocephalus probably was the largest-known of all non-mammal synapsids, at 4 m (13 ft) and 2,000 kg (4,400 lb). Among the largest carnivorous synapsids was the therapsid Anteosaurus, which was 5–6 m (16–20 ft) long, and weighed 500–600 kg (1,100–1,300 lb).
Crocodiles and relatives (Crocodylomorpha)
- The largest-known crocodylomorph is likely Sarcosuchus imperator at 12 m (39 ft) long and weighing 8 t (8.8 short tons).
- Some close contenders in size are Deinosuchus estimated at around 12 m (39 ft), and Purussaurus estimated at 11–13 m (36–43 ft) in length. Another large crocodilian is Rhamphosuchus, estimated at 8–11 m (26–36 ft) in length.
- The largest terrestrial sebecid crocodylomorph is Barinasuchus, from the Miocene of South America, which reached 9 m (30 ft) long.
- The largest-known rauisuchian is Fasolasuchus tenax, which measured an estimated 8–10 metres. It is both the largest rauisuchian known to science, and the largest non-dinosaurian terrestrial predator ever discovered.
- Giant mosasaurs are the largest-known animals within this group. The largest-known mosasaur is likely Mosasaurus hoffmanni, estimated at 17.6 m (58 ft) in length. Another giant mosasaur is Tylosaurus, estimated at 10–14 m (33–46 ft) in length. Another large mosasaur is Hainosaurus bernardi (could be synonymous to Tylosaurus). It was once estimated at 17 and 15 m (56 and 49 ft) in length, but later estimates put it at around 12.2 m (40 ft).
- The largest-known prehistoric snake is Titanoboa cerrejonensis, estimated at 12.8 m (42 ft) in length and 1,135 kg (2,502 lb) in weight. Another known very large fossil snake is Gigantophis garstini, estimated at around 9.3–10.7 m (31–35 ft) in length. A close rival in size to Gigantophis is a fossil snake, Palaeophis colossaeus, which may have been around 9 m (30 ft) in length.
- The largest-known land lizard is probably Megalania at 7 m (23 ft) in length. However, maximum size of this animal is subject to debate.
There is much controversy over the largest-known of these reptiles. Fossil remains of a pliosaur nicknamed as Predator X have been discovered and excavated from Norway in 2008. This pliosaur has been estimated at 15 m (49 ft) in length and 45 t (50 short tons) in weight. However, in 2002, a team of paleontologists in Mexico discovered the remains of a pliosaur nicknamed as Monster of Aramberri, which is also estimated at 15 m (49 ft) in length. This species is, however, claimed to be a juvenile and has been attacked by a larger pliosaur. Some media sources claimed that Monster of Aramberri was a Liopleurodon but its species is unconfirmed thus far. Another very large pliosaur was Pliosaurus macromerus, known from a single 2.8-metre-long (9.2 ft) incomplete mandible. It may have reached 18 m (59 ft), assuming the skull was about 17% of the total body length.
The largest-known ichthyosaur was Shastasaurus sikanniensis at 21 m (69 ft) in length. In April 2018, paleontologists announced the discovery of a previously unknown ichthyosaur that may have reached lengths of 26 m (85 ft)- 30 m (100 feet long) making it one of the largest animals known, rivaling the Blue Whale in size. 
Turtles and tortoises (Testudines)
- The largest-known turtle ever was Archelon ischyros at 4 m (13 ft) long, 4.9 m (16 ft) wide and 2,200 kg (4,900 lb). The next largest was Protostega at 3 m (9.8 ft). The second largest seems to be Stupendemys, with an estimated total carapace length of more than 3.3 m (11 ft) and weight of up to 1,814–2,268 kg (3,999–5,000 lb). Carbonemys cofrinii has a shell that measures about 1.72 m (5 ft 8 in) and was estimated to weigh 916 kg (2,019 lb).
- Two tortoises share the title of largest-known ever tortoise: Meiolania at 2.4 m (8 ft) long and well over 0.91 t (1 short ton), and Colossochelys atlas at 2.4 to 2.7 m (8 to 9 ft)and weighing over 450 kg (0.5 short tons).
The largest-known is Scutosaurus, up to 3 m (9.8 ft) in length, with bony armor, and a number of spikes decorating its skull.
- The largest-known pterosaur was Quetzalcoatlus northropi, at 127 kg (280 lb) and with a wingspan of 12 m (39 ft). Another close contender is Hatzegopteryx, also with a wingspan of 12 m (39 ft). This estimate is based on a skull 3 m (9.8 ft) long.
- Yet another possible contender for the title is Tropeognathus, which had a 9-metre (30 ft) wingspan.
Non-avian dinosaurs (Dinosauria)
- A mega-sauropod, Amphicoelias fragillimus, is a contender for the largest-known dinosaur in history. It has been estimated at 58 m (190 ft) in length and 122,400 kg (269,800 lb) in weight. Unfortunately, the fossil remains of this dinosaur have been lost.
- Barosaurus lentus may have been the largest sauropod and largest dinosaur yet discovered. Originally thought to reach only 27 m (89 ft), a massive cervical vertebra has been recently attributed to this species, suggesting maximum length of 50 m (160 ft) and masses of up to 100 t (110 short tons).
- Other huge sauropods include Argentinosaurus, Alamosaurus, and Puertasaurus with estimated lengths of 30–33 m (98–108 ft) and weights of 50–80 t (55–88 short tons). Giant sauropods like Supersaurus, Sauroposeidon, and Diplodocus probably rivaled them in length but not weight.
Many large sauropods are still unnamed and may rival the current record holders.
- The "Archbishop", a large brachiosaur that was discovered in 1930. The animal was reported to get a scientific paper published by the end of 2016.
- "Brachiosaurus" nougaredi, is yet another large brachiosaur from Early Cretaceous North Africa. The remains have been lost, but the sacrum drawing remains. They suggest a sacrum of almost 5 ft (2 m) long, making it the largest dinosaur sacrum discovered so far.
- In 2010, the femur of a large sauropod was discovered in France. The femur suggests an animal that grew to immense sizes.
- In 2014, the nearly complete skeletons of 7 titanosaurs were discovered. The skeletons were massive and possibly exceeded Argentinosaurus in size. The skeletons also belonged to sub-adults, suggesting they got much larger.
- The largest theropod as well as the largest terrestrial (or possibly semi-aquatic) predator yet known is Spinosaurus aegyptiacus, with the largest specimen known estimated at 12.6–18 m (41–59 ft) in length and around 7–20.9 t (8–23 short tons) in weight.
- Other large theropods were Giganotosaurus carolinii, and Tyrannosaurus rex, whose largest specimens known estimated at 13.2 m (43 ft) and 12.3 m (40 ft) in length, respectively. Some other notable giant theropods (e.g. Carcharodontosaurus, Acrocanthosaurus, and Mapusaurus) may also have rivaled them in size.
Armoured dinosaurs (Thyreophora)
The largest-known thyreophoran was Ankylosaurus at 9 m (30 ft) in length and 6 t (6.6 short tons) in weight. Stegosaurus was also 9 m (30 ft) long but around 5 t (5.5 short tons) tonnes in weight.
The very largest-known ornithopods, like Shantungosaurus were as heavy as medium-sized sauropods at up to 23 t (25 short tons) The largest is probably Shantungosaurus at 16.5 m (54 ft) in length.
The largest-known birds of all time might have been the elephant birds of Madagascar. Of almost the same size was the Australian Dromornis stirtoni. Both were about 3 m (9.8 ft) tall. The elephant birds were up to 400 kg (880 lb) and Dromornis stirtoni was up to 500 kg (1,100 lb) in weight. The tallest bird ever was the giant moa (Dinornis maximus) at 3.6 m (12 ft) tall.
The largest-known flight-capable bird was Argentavis magnificens which a wingspan of 8.3 m (27 ft), and a body weight of 110 kg (240 lb).
Storks and allies (Ciconiiformes)
The largest-known of the hesperornithines was Canadaga arctica at 1.5 m (5 ft) long.
The largest-known teratorn and the largest flying bird ever was Argentavis. The immense bird had a wingspan estimated up to 8.3 m (27 ft) and a weight up to 110 kg (240 lb). It was as high as an adult human when standing.
The largest-known-ever gruiform and largest phorusrhacid or "terror bird" (highly predatory, flightless birds of South America) was Brontornis, which was about 175 cm (69 in) tall at the shoulder, could raise its head 2.8 m (9 ft 2 in) above the ground and could have weighed as much as 400 kg (880 lb). The immense phorushacid Kelenken stood 3–3.2 m (9.8–10.5 ft) tall with a skull 710 mm (28 in) long (460 mm [18 in] of which was beak), had the largest head of any known bird. The largest North American phorusrhacid is Titanis, which is about 2.5 m (8 ft 2 in) tall, as tall as a forest elephant.
The largest-known bird of prey ever was the enormous Haast's eagle (Harpagornis moorei), with a wingspan of 2.6 to 3 m (8 ft 6 in to 9 ft 10 in), relatively short for their size. Total length was probably up to 1.4 m (4 ft 7 in) in female and they weighed about 10 to 15 kg (22 to 33 lb). The largest extinct Titanohierax was a giant hawk about 8 kilograms that lived in the Antilles, where it was among the top predators.
The largest-known in this group was a giant flightless Sylviornis, a bird 1.70 m (5 ft 7 in) long and weighing up to about 30 kg (66 lb).
The largest-known songbird is the extinct giant grosbeak (Chloridops regiskongi) at 280 mm (11 in) long.
Cormorants and allies (Pelecaniformes)
The largest-known cormorant was the spectacled cormorant of the North Pacific (Phalacrocorax perspicillatus), which became extinct around 1850, was larger still, averaging around 6.4 kg (14 lb) and 1.15 m (3 ft 9 in).
Bony-toothed birds (Odontopterygiformes)
The largest-known in this 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 5.5–6 m (18–20 ft) and stood about 1.2 m (3 ft 11 in) 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 560 mm (22 in). The largest woodpecker confirmed to be extant is the great slaty woodpecker (Mulleripicus pulverulentus).
The largest-known parrot is the extinct Norfolk Island kaka (Nestor productus), about 38 cm (15 in) long.
The largest-known penguin of all time was Anthropornis nordenskjoeldi of New Zealand and Antarctica. It stood 1.7 m (5 ft 7 in) in height and was 90 kg (200 lb) in weight. Similar in size were the New Zealand giant penguin (Pachydyptes pondeorsus) with a height of 1.4 to 1.6 m (4 ft 7 in to 5 ft 3 in) and weighing possibly around 80 to 100 kg (180 to 220 lb) and over, and Icadyptes salasi at 1.5 m (4 ft 11 in) tall.
The largest-known frog ever was a yet unnamed species frog that was about 58–59-centimetre-long (22.8–23.2 in).
The largest-known diacectid, Diadectes, was a heavily built animal, 1.5 to 3 m (4 ft 11 in to 9 ft 10 in) long, with thick vertebrae and ribs.
Lobe-finned fish (Sarcopterygii)
The largest-known of these was the 6–7 m (20–23 ft) long Rhizodus.
Ray-finned fish (Actinopterygii)
Cartilaginous fish (Chondrichthyes)
Mackerel sharks (Lamniformes)
An extinct megatoothed shark, C. megalodon is by far the biggest shark known. This giant shark reached a total length of more than 16 m (52 ft). C. megalodon may have approached a maximum of 20.3 m (67 ft) in total length and 103 t (114 short tons) in mass.
The largest-known symmoriid was Stethacanthus at 2 m (6 ft 7 in) long.
Another fairly large eugenedont is Parahelicoprion. The specimens suggest an animal that grew to the same size (12 m [39 ft]), but was much less slender and overall less heavy.
The largest-known hydontiformid is Ptychodus, which was about 9.8 m (32 ft) long.
There are two contenders for largest-known ever arachnid: Pulmonoscorpius kirktonensis and Brontoscorpio anglicus. Pulmonoscorpius was 70 cm (28 in) Brontoscorpio was 90 cm (35 in). The biggest difference is that Brontoscorpio was aquatic, and Pulmonoscorpius was terrestrial. Brontoscorpio is not to be confused with various Eurypterids: it was a true scorpion with a venomous stinger.
The largest-known myriapod by far was the giant Arthropleura. Measuring 2.5 m (8 ft 2 in) and 45 cm (18 in) wide, it was the largest-known terrestrial arthropod of all time. Like its modern-day relatives, Arthropleura would have likely sprayed hydrogen cyanide at potential predators, although its sheer size and tough exoskeleton protected it from attack.
Some of these extinct marine arthropods exceeded 60 cm (24 in) in length. A nearly complete specimen of Isotelus rex from Manitoba attained a length over 70 cm (28 in), 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 (35 in) long.
Sawflies, wasps, bees, ants and allies (Hymenoptera)
The largest-known of this order was Mazothairos, with a wingspan of up to 560 mm (22 in).
Snails and slugs (Gastropoda)
The largest-known ammonite was Parapuzosia seppenradensis. A partial fossil specimen found in Germany had a shell diameter of 1.95 m (6 ft 5 in), but the living chamber was incomplete, so the estimated shell diameter was probably about 2.55 m (8 ft 4 in) when it was alive.
The largest-known belemnite was Megateuthis gigantea with a guard of 46 cm (18 in) in length and an estimated total length 3 m (9.8 ft) long.
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