Dinosaur size

Size is an important aspect of dinosaur paleontology, of interest to both the general public and professional scientists. Dinosaurs show some of the most extreme variations in size of any land animal group, ranging from tiny hummingbirds, which can weigh as little as two grams, to the extinct titanosaurs, which could weigh as much as .

The latest evidence suggests that dinosaurs' average size varied through the Triassic, early Jurassic, late Jurassic and Cretaceous periods, and dinosaurs probably only became widespread during the early or mid Jurassic. Predatory theropod dinosaurs, which occupied most terrestrial carnivore niches during the Mesozoic, most often fall into the category when sorted by estimated weight into categories based on order of magnitude, whereas recent predatory carnivoran mammals peak in the range of . The mode of Mesozoic dinosaur body masses is between one and ten metric tonnes. This contrasts sharply with the size of Cenozoic mammals, estimated by the National Museum of Natural History as about .

Size estimation

Scientists will probably never be certain of the largest and smallest dinosaurs. This is because only a small fraction of animals ever fossilize, and most of these remains will either never be uncovered, or will be unintentionally destroyed as a result of human activity. Of the specimens that are recovered, few are even relatively complete skeletons, and impressions of skin and other soft tissues are rarely discovered. Rebuilding a complete skeleton by comparing the size and morphology of bones to those of similar, better-known species is an inexact art (though governed by some established allometric trends), and reconstructing the muscles and other organs of the living animal is, at best, a process of educated guesswork, and never perfect. Mass estimates for dinosaurs are much more variable than length estimates given the lack of soft tissue preservation in the fossilization process. Modern mass estimation is often done with the laser scan skeleton technique that puts a "virtual" skin over the known or implied skeleton, but the limitations inherent in previous mass estimation techniques remain.

Sauropodomorphs

Sauropodomorph size is difficult to estimate given their usually fragmentary state of preservation. Sauropods are often preserved without their tails, so the margin of error in overall length estimates is high. Mass is calculated using the cube of the length, so for species in which the length is particularly uncertain, the weight is even more so. Estimates that are particularly uncertain (due to very fragmentary or lost material) are preceded by a question mark. Each number represents the highest estimate of a given research paper. One large sauropod, '' Maraapunisaurus fragillimus'', was based on particularly scant remains that have been lost since their description by paleontologists in 1878. Analysis of the illustrations included in the original report suggested that ''M. fragillimus'' may have been the largest land animal of all time, possibly weighing and measuring between long. One later analysis of the surviving evidence, and the biological plausibility of such a large land animal, suggested that the enormous size of this animal was an over-estimate due partly to typographical errors in the original report. This would later be challenged by a different study, which argued Cope's measurements were genuine and there's no basis for assuming typographical errors. The study, however, also reclassified the species and correspondingly gave a much lower length estimate of and a mass of . This in itself would later be disputed as being too small for an animal of such size, with some believing it to be even larger at around and weighing around .

Generally, the giant sauropods can be divided into two categories: the shorter but stockier and more massive forms (mainly titanosaurs and some brachiosaurids), and the longer but slenderer and more light-weight forms (mainly diplodocids).

Because different methods of estimation sometimes give conflicting results, mass estimates for sauropods can vary widely causing disagreement among scientists over the accurate number. For example, the titanosaur ''Dreadnoughtus'' was originally estimated to weigh 59.3 tonnes by the allometric scaling of limb-bone proportions, whereas more recent estimates, based on three-dimensional reconstructions, yield a much smaller figure of 22.1–38.2 tonnes.

The sauropods were the longest and heaviest dinosaurs. For much of the dinosaur era, the smallest sauropods were larger than almost anything else in their habitat, and the largest were an order of magnitude more massive than anything else known to have walked the Earth since. Giant prehistoric mammals such as ''Paraceratherium'' and ''Palaeoloxodon'' (the largest land mammals ever discovered) were dwarfed by the giant sauropods, and only modern whales approach or surpass them in weight, though they live in the oceans. There are several proposed advantages for the large size of sauropods, including protection from predation, reduction of energy use, and longevity, but it may be that the most important advantage was dietary. Large animals are more efficient at digestion than small animals, because food spends more time in their digestive systems. This also permits them to subsist on food with lower nutritive value than smaller animals. Sauropod remains are mostly found in rock formations interpreted as dry or seasonally dry, and the ability to eat large quantities of low-nutrient browse would have been advantageous in such environments.Carpenter, K. (2006). "Biggest of the big: a critical re-evaluation of the mega-sauropod ''Amphicoelias fragillimus''." In Foster, J.R. and Lucas, S.G., eds., 2006, ''Paleontology and Geology of the Upper Jurassic Morrison Formation.'' New Mexico Museum of Natural History and Science Bulletin 36: 131–138.

One of the tallest and heaviest dinosaurs known from good skeletons is '' Giraffatitan brancai'' (previously classified as a species of ''Brachiosaurus''). Its remains were discovered in Tanzania between 1907 and 1912. Bones from several similar-sized individuals were incorporated into the skeleton now mounted and on display at the Museum für Naturkunde Berlin; this mount is tall and long, and would have belonged to an animal that weighed between . One of the longest complete dinosaurs is the ''Diplodocus'', which was discovered in Wyoming in the United States and displayed in Pittsburgh's Carnegie Natural History Museum in 1907.

There were larger dinosaurs, but knowledge of them is based entirely on a small number of fragmentary fossils. Most of the largest herbivorous specimens on record were discovered in the 1970s or later, and include the massive titanosaur ''Argentinosaurus huinculensis'', which is the largest dinosaur known from uncontroversial and relatively substantial evidence, estimated to have been and long. Some of the longest sauropods were those with exceptionally long, whip-like tails, such as the ''Diplodocus hallorum'' (formerly ''Seismosaurus'') and the ''Barosaurus''.

In 2014, the fossilized remains of a previously unknown species of sauropod were discovered in Argentina. The titanosaur, named ''Patagotitan mayorum'', was estimated to have been around long weighing around , larger than any other previously found sauropod. The specimens found were remarkably complete, significantly more so than previous titanosaurs. It since been suggested that ''Patagotitan'' was not necessarily larger than ''Argentinosaurus'' and ''Puertasaurus''. In 2019, ''Patagotitan'' was estimated to have been long and massive.

The largest of non-sauropod sauropodomorphs was ''Euskelosaurus''. It reached in length and in weight. Another large sauropodomorph ''Yunnanosaurus youngi'' reached long.

Theropods

''Tyrannosaurus'' was for many decades the largest and best-known theropod to the general public. Since its discovery, however, a number of other giant carnivorous dinosaurs have been described, including ''Spinosaurus'', ''Carcharodontosaurus'', and ''Giganotosaurus''. These large theropod dinosaurs are estimated to rival or even exceeded ''Tyrannosaurus rex'' in size, though more recent studies and reconstructions show that ''Tyrannosaurus'', although shorter, was the bulkier animal overall. Specimens such as Sue and Scotty are both estimated to be the most massive theropods known to science. There is still no clear explanation for exactly why these animals grew so bulky and heavy compared to the land predators that came before and after them.

The largest extant theropod is the common ostrich, up to tall and weighs between .

The smallest non-avialan theropod known from adult specimens may be ''Anchiornis huxleyi'', at in weight and in length.Xu, X., Zhao, Q., Norell, M., Sullivan, C., Hone, D., Erickson, G., Wang, X., Han, F. and Guo, Y. (2009). "A new feathered maniraptoran dinosaur fossil that fills a morphological gap in avian origin." ''Chinese Science Bulletin'', 6 pages, accepted November 15, 2008. However, some studies suggest that ''Anchiornis'' was actually an avialan. The smallest dinosaur known from adult specimens which is definitely not an avialan is '' Parvicursor remotus'', at and measuring long. However, in 2022 its holotype was recognized as a juvenile individual. Among living dinosaurs, the bee hummingbird (''Mellisuga helenae'') is smallest at and long.Conservation International (Content Partner); Mark McGinley (Topic Editor). 2008. "Biological diversity in the Caribbean Islands." In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth May 3, 2007; Last revised August 22, 2008; Retrieved November 9, 2009].
>

Recent theories propose that theropod body size shrank continuously over the past 50 million years, from an average of down to , as they eventually evolved into modern birds. This is based on evidence that theropods were the only dinosaurs to get continuously smaller, and that their skeletons changed four times faster than those of most other dinosaur species.

See also

*Largest prehistoric animals
*Megafauna
* Pterosaur size

References

External links

*

The Biggest Carnivore: Dinosaur History Rewritten
* ( Dinosaur size#References)

"Dinosaur records"
Czech article by Vladimír Socha; ''DinosaurusBlog.com'', August 1, 2016

{{DEFAULTSORT:Dinosaur Size
Animal size
Dinosaur paleobiology