• Weird Nature

Theories And Explanations Why Prehistoric Animals Were So Big

Everyone knows that prehistoric animals were huge, but does anyone know why? Prehistoric gigantism doesn't just apply to dinosaurs or wooly mammoths; many animals that still roam the earth today were terrifyingly massive thousands of years ago.

The massive size of prehistoric species has been studied for many years. Scientists have many theories as to what was different back then that allowed these giant creatures to thrive. Out of the many reasons why dinosaurs were so big, some of them may surprise you. Does laying eggs help animals grow larger? Does that mean humans could be giants if we laid eggs? Are only cold-blooded creatures huge? Did sauropods have long necks for the same reasons giraffes do? Check out this list to find out all the possible reasons why prehistoric creatures were so big. 

  • Photo: Charles R. Knight / Wikimedia Commons / Public domain

    Larger Animals Are Less Vulnerable To Predators

    It seems fairly logical that the larger an animal is, the less vulnerable to predators they become. When it comes to dinosaurs, herbivores were massive, therefore carnivorous species had to become larger, too, to keep up their spot at the top of the food chain. 

    Herbivores, like Sauropods, grew larger to protect themselves from predators, but they did so for many other reasons as well. Their large bodies and long necks allowed them to reach more foliage for sustenance.

    Carnivores, like Theropods, evolved to keep up with the size of the herbivores. This maintained the natural order of the food chain as dinosaurs continued to evolve. 

  • Photo: epSos.de / Wikimedia Commons / CC-BY 2.0

    In Extreme Climates, A Large Body Can Keep An Animal’s Temperature Regulated

    Humans are warm-blooded, along with all other mammals. This means we are capable of maintaining a constant body temperature in a vast array of climates and temperatures. But for a long time, many scientists theorized that dinosaurs, like reptiles, were cold-blooded, meaning they took on the temperature of their surroundings.

    According to that theory, many large dinosaurs, especially Sauropods, who were the largest herbivores, grew larger to keep them cool. The more surface area, the more room they had to cool off, which helped them regulate their body temperature in hot climates. This might also explain the theory of meteors and ice ages leading to the mass extinction of dinosaurs. Intense changes in temperature are disastrous for cold-blooded creatures.

    That theory, however, was thrown into question after some scientists theorized dinosaurs were warm-blooded. The theory was further supported when researchers analyzed the chemistry of dinosaur eggshells in early 2020 and discovered the composition correlated with temperatures warmer than the environment, suggesting dinosaurs may have had warm blood like birds rather than reptilian cold blood.

    But that doesn't necessarily upend the theory that size could have helped regulate animal body temperatures in extreme climates. Even in warm-blooded animals, the large frame helped retain heat in cold environments.

  • Photo: J. Smith / Wikimedia Commons / Public domain

    A Larger Body Could Have Helped Prehistoric Animals Digest Extremely Tough Foliage

    When we look back on prehistoric animals, herbivores were usually the largest. Sauropods, including Brontosaurus, had incredibly long necks and tails, along with massive bodies. Their long necks allowed them to reach more foliage, and their size enabled them to have long and intricate digestive systems.

    The only way herbivores were able to sustain their diet of foliage was through their long digestive process, which allowed them to break down the toughest leafy greens and get all the nutrients they needed to nourish them. 

  • Photo: Charles R. Knight / Wikimedia Commons / Public domain

    The Higher Oxygen Content In The Prehistoric Atmosphere Could Better Support Large Animals

    Through decades of archaeological research, scientists have been able to pinpoint the disparity in oxygen content over time. In prehistoric times, it's estimated that the oxygen content in the atmosphere was 30%, whereas today, our oxygen content is around 20%. That difference could have allowed animals to grow larger, faster. 

    This explains why so many species were larger in prehistoric times. Insects and invertebrates especially benefited from this boost in oxygen, which helped them both grow large and avoid extinction. Some scientists believe that because of the higher oxygen content, cockroaches were able to become the size of house cats.