Science, Tech, Math › Animals & Nature The 19 Smallest Dinosaurs and Prehistoric Animals Many Tiny Species Were Ancestors of Massive Jurassic Giants Share Flipboard Email Print MirageC / Getty Images Animals & Nature Dinosaurs Basics Paleontologists Carnivores Dinosaurs & Birds Herbivores Marine Reptiles Prehistoric Mammals Amphibians Birds Habitat Profiles Mammals Reptiles Wildlife Conservation Insects Marine Life Forestry Evolution View More By Bob Strauss Science Writer B.S., Cornell University Bob Strauss is a science writer and the author of several books, including "The Big Book of What, How and Why" and "A Field Guide to the Dinosaurs of North America." our editorial process Bob Strauss Updated July 03, 2019 Museums are filled with gargantuan skeletons of dinosaurs and Ice Age animals that dwarf modern day species. It can come as a surprise, therefore, that there were many tiny reptiles, amphibians, and mammals living alongside Tyrannosaurus Rex and Triceratops. In a way, it's much more difficult to identify the smallest, sometimes cutest dinosaurs (and prehistoric animals) than the biggest ones—after all, a tiny, foot-long reptile might easily have been the juvenile of a much larger species, but there's no mistaking the evidence for a 100-ton behemoth. Some tiny prehistoric creatures, however, are absolutely unique. 01 of 19 Smallest Raptor: Microraptor (Two Pounds) Emily Willoughby/Wikimedia Commons/CC BY 2.5 With its feathers and four primitive wings (one pair each on its forearms and hind legs), the early Cretaceous Microraptor might easily have been mistaken for a bizarrely mutated pigeon. This was, however, a genuine raptor, in the same family as Velociraptor and Deinonychus, albeit one that only measured about two feet from head to tail and weighed only a few pounds. Befitting its tiny size, paleontologists believe that Microraptor subsisted on a diet of insects. 02 of 19 Smallest Tyrannosaur: Dilong (25 Pounds) Elena Duvernay/Stocktrek Images / Getty Images The king of the dinosaurs, Tyrannosaurus Rex, measured 40 feet from head to tail and weighed 7 or 8 tons—but its fellow tyrannosaur Dilong, which lived over 60 million years earlier, tipped the scales at 25 pounds, an object lesson in how plus-sized creatures tend to evolve from wee ancestors. Even more remarkably, the eastern Asian Dilong was covered with feathers—a hint that even the mighty T. Rex may have sported plumage at some stage of its life cycle. 03 of 19 Smallest Sauropod: Europasaurus (2,000 Pounds) MR1805 / Getty Images When most people think of sauropods, they picture huge, house-sized plant-eaters like Diplodocus and Apatosaurus, some of which approached 100 tons in weight and stretched 50 yards from head to tail. Europasaurus, though, wasn't much bigger than a modern ox, only about 10 feet long and less than 2,000 pounds. The explanation is that this late Jurassic dinosaur lived on a small island cut off from the European mainland, like its equally tiny titanosaur cousin Magyarosaurus. 04 of 19 Smallest Horned, Frilled Dinosaur: Aquilops (Three Pounds) Nobumichi Tamura/Stocktrek Images / Getty Images The three-pound Aquilops was a true outlier on the ceratopsian family tree: whereas most ancestral horned and frilled dinosaurs hailed from Asia, Aquilops was discovered in North America, in sediments dating to the middle Cretaceous period (about 110 million years ago). You wouldn't know to look at it, but the descendants of Aquilops, millions of years down the line, were multi-ton plant-eaters like Triceratops and Styracosaurus that could successfully fend off an attack by a hungry T. Rex. 05 of 19 Smallest Armored Dinosaur: Minmi (500 Pounds) Getty Images/DEA PICTURE LIBRARY You couldn't ask for a better name for a tiny dinosaur than Minmi—even if this early Cretaceous ankylosaur was named after Australia's Minmi Crossing and not the infamous "Mini-Me" from the "Austin Powers" movies. The 500-pound Minmi may not seem especially small until you compare it to later, multi-ton ankylosaurs like Ankylosaurus and Euoplocephalus—and judging by the wee size of its brain cavity, it was every bit as dumb as (or even dumber than) its more famous descendants. 06 of 19 Smallest Duck-Billed Dinosaur: Tethyshadros (800 Pounds) Wikimedia Commons/Tethyshadros.JPG: Ghedoghedo The second example on this list of "insular dwarfism"—that is, the tendency of animals confined to island habitats to evolve to modest proportions—the 800-pound Tethyshadros was a fraction of the size of most hadrosaurs, or duck-billed dinosaurs, which usually weighed two or three tons. On an unrelated note, Tethyshadros is only the second dinosaur ever to be discovered in modern-day Italy, much of which was submerged under the Tethys Sea during the late Cretaceous period. 07 of 19 Smallest Ornithopod Dinosaur: Gasparinisaura (25 Pounds) FunkMonk (Michael B. H.)/Wikimedia Commons/CC BY GNU 1.2 Since many ornithopods—the two-legged, plant-eating dinosaurs ancestral to hadrosaurs—were slight in stature, it can be a tricky matter to identify the smallest member of the breed. But a good candidate would be the 25-pound Gasparinisaura, one of the few ornithopods to have lived in South America, where either scant plant life or the exigencies of predator-prey relationships downscaled its body plan. (By the way, Gasparinisaura is also one of the few dinosaurs to be named after the female of the species.) 08 of 19 Smallest Titanosaur Dinosaur: Magyarosaurus (2,000 Pounds) Getty Images/DEA PICTURE LIBRARY Yet another insular dinosaur was the Magyarosaurus, classified as a titanosaur—the family of lightly armored sauropods best represented by 100-ton monsters like Argentinosaurus and Futalognkosaurus. Because it was restricted to an island habitat, though, Magyarosaurus weighed only a single ton. Some paleontologists believe this titanosaur plunged its neck under the surface of swamps and fed on aquatic vegetation! 09 of 19 Smallest Pterosaur: Nemicolopterus (A Few Ounces) AFP/Getty Images / Getty Images In February of 2008, paleontologists in China discovered the type fossil of Nemicolopterus, the tiniest flying reptile yet identified, with a wingspan of only 10 inches and a weight of a few ounces. Oddly enough, this pigeon-sized pterosaur may have occupied the same branch of evolution that gave rise to the enormous Quetzalcoatlus 50 million years later. 10 of 19 Smallest Marine Reptile: Cartorhynchus (Five Pounds) Fossilized paddle of an ichthyosaur. Getty Images/SINCLAIR STAMMERS/SCIENCE PHOTO LIBRARY A few million years after the Permian-Triassic extinction—the deadliest mass extinction in the history of life on earth—marine life had yet to fully recover. A survivor of this period was Cartorhynchus, an ichthyosaur ("fish lizard") that only weighed five pounds but was still one of the largest marine reptiles of the early Triassic period. You wouldn't have known to look at it, but the descendants of Cartorhynchus, millions of years down the line, included the enormous, 30-ton ichthyosaur Shonisaurus. 11 of 19 Smallest Prehistoric Crocodile: Bernissartia (10 Pounds) Wikimedia Commons/Ghedoghedo Crocodiles—which evolved from the same archosaurs that spawned the dinosaurs—were thick on the ground during the Mesozoic Era, making it difficult to identify the smallest member of the breed. But a good candidate would be Bernissartia, an early Cretaceous crocodile about the size of a house cat. As tiny as it was, Bernissartia sported all the classic crocodilian features (narrow snout, knobby armor, etc.), making it looked like a scaled-down version of later behemoths like Sarcosuchus. 12 of 19 Smallest Prehistoric Shark: Falcatus (One Pound) Wikimedia Commons/Smokeybjb Sharks have a deep evolutionary history, predating mammals, dinosaurs, and pretty much all terrestrial vertebrates. To date, the smallest identified prehistoric shark is Falcatus, a tiny, bug-eyed menace the males of which were equipped with sharp spines jutting out of their heads (which seem to have been used, rather painfully, for mating purposes). Needless to say, Falcatus was a far cry from true undersea giants like Megalodon, which it preceded by a whopping 300 million years. 13 of 19 Smallest Prehistoric Amphibian: Triadobatrachus (A Few Ounces) Triadobatrachus, re-examined by CT scan. Wikimedia Commons/Eduardo Ascarrunz; Jean-Claude Rage; Pierre Legreneur; Michel Laurin Believe it or not, shortly after they evolved hundreds of millions of years ago, amphibians were the largest land-dwelling animals on earth—until their pride of place was usurped by even bigger prehistoric reptiles. One of the smallest amphibians yet identified, a mere tadpole compared to giants like Mastodonsaurus, was Triadobatrachus, the "triple frog," which inhabited the swamps of Madagascar during the early Triassic period and likely lay at the root of the frog and toad evolutionary tree. 14 of 19 Smallest Prehistoric Bird: Ibermesornis (A Few Ounces) Nobumichi Tamura/Stocktrek Images / Getty Images Pound for pound, the birds of the Cretaceous period weren't any bigger than their modern counterparts (for the simple reason that a dinosaur-sized pigeon would immediately plummet out of the sky). Even by this standard, though, Iberomesornis was unusually small, only about the size of a finch or sparrow—and you'd have to take a close look at this bird to discern its basal anatomy, including a single claw on each wing and a set of jagged teeth embedded in its tiny jaws. 15 of 19 Smallest Prehistoric Mammal: Hadrocodium (Two Grams) As a general rule, the mammals of the Mesozoic Era were some of the smallest vertebrates on earth—the better to keep out of the way of the giant dinosaurs, pterosaurs, and crocodiles with which they shared their habitat. Not only was the early Jurassic Hadrocodium incredibly tiny—only about an inch long and two grams—but it's represented in the fossil record by a single, exquisitely preserved skull, which hints (ironically) at a bigger-than-usual brain compared to the size of its body. 16 of 19 Smallest Prehistoric Elephant: The Dwarf Elephant (500 Pounds) Ninjatacoshell/Wikimedia Commons/CC BY 3.0 Just like some dinosaur species, many mammals developed in isolated circumstances during the Cenozoic Era. What we call the Dwarf Elephant included scaled-down, quarter-ton species of Mammoths, Mastodons and modern elephants, all of which lived on various Mediterranean islands during the Pleistocene epoch. 17 of 19 Smallest Prehistoric Marsupial: The Pig-Footed Bandicoot (A Few Ounces) duncan1890 / Getty Images For every Australian behemoth like the Giant Wombat or the Giant Short-Faced Kangaroo, there were a bewildering variety of tiny pouched mammals. While there's no consensus as to which was the smallest, one good possibility is the Pig-Footed Bandicoot, a long-nosed, spindly-legged, two-ounce furball that hopped across the plains of Australia until the modern era, when it was crowded out by the arrival of European settlers and their pets. 18 of 19 Smallest Prehistoric Dog: Leptocyon (Five Pounds) Wikimedia Commons/Mariomassone The evolutionary lineage of modern canines goes back 40 million years, including both plus-sized breeds (like Borophagus and the Dire Wolf) and comparatively runty genera like Leptocyon, the "slender dog." The amazing thing about the five-pound Leptocyon is that various species of this canid persisted for almost 25 million years, making it one of the most successful predatory mammals of Oligocene and Miocene North America. 19 of 19 Smallest Prehistoric Primate: Archicebus (A Few Ounces) Wikimedia Commons/Mat Severson As with many other animals on this list, it's not a straightforward matter to identify the smallest prehistoric primate: after all, the vast majority of Mesozoic and early Cenozoic mammals were mouse-sized. Archicebus, though, is as good a choice as any: this tiny, tree-dwelling primate only weighed a few ounces, and it seems to have been ancestral to modern apes, monkeys, lemurs, and humans (though some paleontologists disagree).