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 . Cotylorhynchus hancocki is also large, with an estimated length and weight of at least and more than .
Edaphosaurids (Edaphosauridae)
The largest edaphosaurids were Lupeosaurus at long and Edaphosaurus, which could reach even more than in length. With weights of and respectively.
Sphenacodontids (Sphenacodontidae) The biggest carnivorous synapsid of the Early Permian was Dimetrodon, which could reach and . 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 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 long, tall, and 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 in length, possibly up to and more than in weight for adult specimens.
Dinocephalians (Dinocephalia)
Perhaps the largest known dinocephalian was the titanosuchid Jonkeria truculenta, with volumetric models suggesting it could have weighed . Tapinocaninus pamelae was slightly smaller, volumetric models suggesting it weighed .Romano, M., & Rubidge, B. (2019). First 3D reconstruction and volumetric body mass estimate of the tapinocephalid dinocephalian Tapinocaninus pamelae (Synapsida: Therapsida). Historical Biology, 33(4), 498–505. https://doi.org/10.1080/08912963.2019.1640219 The largest carnivorous non-mammalian synapsids was the anteosaurid Anteosaurus, which was long, and weighed .van Valkenburgh, Blaire; Jenkins, Ian (2002). "Evolutionary Patterns in the History of Permo-Triassic and Cenozoic synapsid predators". Paleontological Society Papers 8: 267–288. Fully grown Titanophoneus from the same family had skull lengths measuring at least .
Gorgonopsians (Gorgonopsia)
Inostrancevia latifrons is the largest known gorgonopsian, with a skull length of more than , a total length approaching and a mass of . Rubidgea atrox is the largest African gorgonopsian, with skull of nearly long. Other large gorgonopsians include Dinogorgon with skull of ~ long, Leontosaurus with skull of almost long, and Sycosaurus with skull of ~ long.
Therocephalians (Therocephalia)
The largest whaitsiid, as well as the largest therocephalian, was Megawhaitsia, which had an estimated skull length of . Other large whaitsiids include Therigonathus , with adults having a skull length of . The largest known scylacosaurid was Julognathus, with an estimated skull length of . Other large scylacosaurids include Glanosuchus, the largest skulls were noted to have measured . The largest lycosuchid therocephalian may have been “Scymnosaurus major”, with an estimated skull length of . It was thought that “Scymnosaurus” was similar in size to a modern hyena. Another large lycosuchid was Simorhinella with the an estimated skull length of ~. Gorynychus sundyrensis was a large basal therocephalian with an estimated skull length of .
Non-mammalian cynodonts (Cynodontia) The largest known non-mammalian cynodont, as well as the largest member of Cynognathia, is Scalenodontoides, a traversodontid, which had a maximum skull length of approximately based on a fragmentary specimen. Paceyodon davidi was the largest of morganucodontans, cynodonts close to mammals. It is known by a right lower molariform in length, which is bigger than molariforms of all other morganucodontans. The largest known docodont was Castorocauda, almost in length.
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 and an estimated mass of . With such parameters it surpassed in size several small theropod dinosaurs of the Early Cretaceous. Gobiconodon was also a large mammal, it weighed , had a skull of in length, and had in presacral body length.
Multituberculates (Multituberculata) The largest multituberculate, Taeniolabis taoensis is the largest non-therian mammal known, at a weight possibly exceeding .
Monotremes (Monotremata)
The largest known monotreme (egg-laying mammal) ever was the extinct long-beaked echidna species known as Murrayglossus hacketti, known from a couple of bones found in Western Australia. It was the size of a sheep, weighing probably up to . The largest known ornithorhynchid is Obdurodon tharalkooschild. Kollikodon ritchiei was likely the largest monotreme in the Mesozoic. Its body length could be up to a .
Metatherians (Metatheria)
The largest sparassodont, as well as the largest non-marsupial metatherian and carnivorous metatherian, was Proborhyaena gigantea, which is estimated to have weighed weigh . Thylacosmilids have also been noted to have reached large sizes among sparassodonts. Thylacosmilus atrox was estimated to have weighed depending on the regressions used. Pampaluctor was noted to have been larger than Thylacosmilus, weighing . Australohyaena is another large metatherian, weighing up to . Stagodontid mammal Didelphodon was one of the largest Mesozoic metatherians and all Cretaceous mammals. Its skull could reach over in length and a weight of complete animal was .
Marsupials (Marsupialia)
The largest known marsupial, and the largest metatherian, is the extinct Diprotodon, about long, standing tall and weighing up to . Fellow vombatiform Palorchestes azael was similar in length being around , with body mass estimates indicating it could exceed . The largest known carnivorous marsupial was Thylacoleo carnifex. Measurements taken from a number of specimens show they averaged in weight. The largest known koala is the giant koala (Phascolarctos stirtoni) which has an estimated weight of , which is the same weight as a large contemporary male koala. The largest ever member of the Tasmanian devil genus was Sarcophilus laniarius which were around 15% larger and 50% heavier than modern devils.Owen and Pemberton, p. 35. The largest known kangaroo was an as yet unnamed species of Macropus, estimated to weigh , larger than the largest known specimen of Procoptodon, which could grow up to and weigh . Some species from the genus Sthenurus were similar in size or a bit larger than the extant grey kangaroo (Macropus giganteus). The largest ever tree kangaroo, Bohra, had an estimated body mass of . The largest potoroid ever recorded was Borungaboodie, which was nearly 30% bigger than the largest living species and weighed up to . The largest member of the Thylacinidae is Thylacinus megiriani, which is somewhat reasonably larger than the Tasmanian wolf (Thylacinus cynocephalus), and bigger than its fellow Miocene relative Thylacinus potens, usually being 57.3 kilograms in weight.
Non-placental eutherians
Cimolestans (Cimolesta) The largest known panodont, as well as cimolestan, was Coryphodon, high at the shoulder, long and up to of mass. Barylambda was also a huge mammal, at . 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 in body mass. Psittacotherium, which appeared two million years later, reached .
Leptictids (Leptictida) The largest leptictid ever discovered is Leptictidium tobieni from the Middle Eocene of Germany. It had a skull long, head with trunk long, and tail long. Close European relatives from the same family Pseudorhyncocyonidae had skulls of 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)
The largest known land-dwelling artiodactyl was Hippopotamus antiquus, estimated to be 14.1 ft (4.3 m) in length and in weight. However, volumetric models suggests it was slightly smaller, weighing . While Hippopotamus gorgops estimated to have weighed over , other experts consider it to be smaller than Hippopotamus antiquus. Daeodon and Paraentelodon were the largest-known entelodonts that ever lived, at long and high at the shoulder. The Andrewsarchus from the Eocene of Inner Mongolia had a skull about long.
The largest bovine and bovid was possibly Bison latifrons. It reached a weight from to possibly , in length, shoulder height of , and had horns that spanned . The African giant buffalo (Syncerus antiquus) may have rivaled Bison latifrons in size. It reached weight from to , measured in length from muzzle to the end of the tail, in height at the withers, in height at the hindquarters, and the distance between the tips of its horns was as large as . The African Pelorovis reached in weight and had bony cores of the horns about long. The North American Bison antiquus reached up to long, tall, weight of , and horn span of . Aside from local populations and subspecies of extant species, such as the gaur population in Sri Lanka, European bison in British Isles, Caucasian wisent and Carpathian wisent, the largest modern extinct bovid is aurochs (Bos primigenius) with an average height at the shoulders of in bulls and in cows, while aurochs populations in Hungary had bulls reaching . The kouprey (Bos sauveli), reaching in shoulder height, has existed since the Middle Pleistocene and is also considered to be possibly extinct. The long-legged Megalotragus is possibly the largest known alcelaphine bovid, bigger than the extant wildebeest. The tips of horns of M. priscus were located at a distance of about from each other.
The extinct cervid Irish elk (Megaloceros giganteus) reached over in height, in mass and could have antlers spanning up to across, about twice the maximum span for a moose's antlers. The giant moose (Cervalces latifrons) reached high and was twice as heavy as the Irish elk but its antler span at was smaller than that of Megaloceros. North American stag-moose (Cervalces scotti) reached in length and a weight of . The largest known giraffid is the Sivatherium, with a body weight of upto . The largest protoceratid was Synthetoceras, it reached long and in mass. The largest known wild suid to ever exist was Kubanochoerus gigas, having measured up to and stood around tall at the shoulder.. tesorosnaturales.es Megalochoerus could be similar in size, possibly weighing or .