Determining the largest prehistoric animal is complex, as the answer depends on whether the creature lived on land, in the sea, or flew in the air. While the Mesozoic Era, the “Age of Reptiles,” produced many famous giants, massive animals have existed throughout Earth’s deep history. Defining “largest” requires using different metrics, such as total body mass or maximum length. Ultimately, the biggest creatures ever to inhabit the planet are found in the ocean, where buoyancy supports their immense weight.
The Challenge of Measuring Prehistoric Giants
Paleontologists face significant hurdles when attempting to determine the size of long-extinct animals because the fossil record is inherently incomplete. Most specimens consist of only partial skeletons, requiring scientists to rely on indirect methods to estimate the full size of a creature. One primary technique involves skeletal reconstruction, where existing bones are scaled up and arranged based on known relationships in modern, related animals.
The two major metrics used for size estimation are total length and estimated mass. Total length is often easier to estimate from a chain of vertebrae, but mass is considered a better indicator of how truly massive an animal was. Mass estimates rely on volumetric modeling, where researchers create a three-dimensional model and calculate the volume of space it would have occupied, then multiplying that volume by an estimated density. Due to the fragmentary nature of many finds, these mass estimates can vary considerably, leading to ongoing scientific debate.
Contenders for Largest Land Animal
The undisputed champions of terrestrial size are the sauropods, the group of long-necked, four-legged herbivorous dinosaurs that dominated the Mesozoic Era. Within this group, the Titanosaurs grew to staggering proportions, far exceeding the size of any land animal alive today. The leading contenders for the title of most massive land animal are the South American species Argentinosaurus and Patagotitan mayorum.
Argentinosaurus, known from fragmentary remains including massive vertebrae and a femur, is estimated to have weighed between 65 and 110 metric tons and reached lengths of up to 40 meters (130 feet). The sheer size of its bones suggests a body mass that dwarfs the largest modern land animal, the African bush elephant, which weighs up to about six tons. However, the incomplete nature of its fossil material means its size remains subject to wide-ranging interpretations.
Patagotitan mayorum is known from a more complete set of fossils, allowing for a more robust size calculation. Estimates for Patagotitan generally place its weight at around 50 to 77 metric tons and its length at about 37 meters (121 feet). Although some initial studies suggested it was the largest, later comparisons indicate that Argentinosaurus may have had a larger torso and therefore a higher overall mass.
Colossal Creatures of the Ancient Oceans
The largest animals of all time, prehistoric or otherwise, have always been marine species, a phenomenon enabled by the buoyant support of water. The ancient oceans were home to several colossal creatures that rivaled the modern Blue Whale, the largest animal currently known. The extinct megatoothed shark, Otodus megalodon, reigned as a formidable apex predator from about 23 to 3.6 million years ago.
Megalodon is primarily known from its massive, seven-inch-long teeth. Estimates suggest it could reach lengths of 15 to 20 meters (50 to 66 feet) and weigh between 50 and 100 metric tons. This size made it considerably larger than the largest modern Great White Shark and placed it in the same size class as some of the larger prehistoric marine reptiles.
The largest marine reptiles, the ichthyosaurs, may have held the record for sheer length among prehistoric ocean dwellers. Recent discoveries of jawbone fragments belonging to Ichthyotitan severnensis suggest this “giant fish lizard” may have reached an astonishing length of 26 to 35 meters (85 to 115 feet). This length puts it in direct competition with the longest Blue Whales, which can reach up to 33 meters (108 feet) and a maximum recorded weight of 190 metric tons. Although a definitive weight for Ichthyotitan is not yet available, its bulky body shape suggests it may have rivaled the Blue Whale in mass.
The Largest Flying Animals
The category of largest flying animals is dominated by the giant pterosaurs, a group of winged reptiles that lived alongside the dinosaurs. The physical constraints of powered flight, where lift must overcome weight, placed a strict upper limit on the size that flying animals could attain. The largest of these aerial giants was Quetzalcoatlus northropi, a member of the Azhdarchid family.
Quetzalcoatlus is estimated to have had a wingspan of approximately 10 to 11 meters (33 to 36 feet), roughly the size of a small airplane. When standing on the ground, this pterosaur was tall, with a shoulder height of about 3 meters (10 feet), allowing its head to reach a height comparable to a modern giraffe. Despite its enormous size, its skeleton was lightweight, featuring thin, hollow bones to facilitate flight. Weight estimates typically range around 200 to 250 kilograms (440 to 550 pounds). This combination of huge wingspan and relatively low weight makes Quetzalcoatlus the largest creature known to have achieved sustained flight.