Megafauna: Giants of the Post-Dinosaur Era
Published on 18 February 2025
What comes to mind when you think of the prehistoric world? For many, it's dinosaurs, the fierce, powerful stars of the Mesozoic era, which spanned from about 251 to 66 million years ago. However, there were other incredible prehistoric animals.
After the extinction of the dinosaurs during the Cretaceous mass extinction (the fifth mass extinction) about 66 million years ago, a new era of "megafauna" emerged. These were large animals that weigh over 44 kilograms. Some of them resemble larger versions of their living relatives. The 3-metre tall terror bird, the over-10-metre long megalodon, and the shaggy woolly mammoth are a few well-known species to name.
The Rise of Mammals
The earliest known mammals first appeared about 225 to 200 million years ago during the late Triassic period. This was about the same time that the earliest dinosaurs first showed up.
Early mammals were small, about the size of rats and badgers. This is because dinosaurs were the top predators at that time, posing challenges for mammals to gain their sizes. After the total wipe out of non-avian dinosaurs, mammals evolved into many different forms and sizes as they filled the empty spaces left by the dinosaurs during the Cenozoic era. This period is also called the "Age of Mammals".
During the Oligocene epoch about 33.9 to 23 million years ago, most mammals remained small, but one giant, Paraceratherium, stood out. This enormous rhino stretching over eight metres long and weighing as much as five elephants was one of the largest land mammals ever to roam the Earth.
Over time, more giant mammals emerged, including relatives of modern felines like Smilodon, as well as the enormous deer Megaloceros and the giant kangaroo Procoptodon.
Why did mammals grow so big? Scientists believe that after the mass extinction that wiped out dinosaurs, mammals evolved to fill the vacant ecological niches. Freed from competition with the dinosaurs, they diversified into a wide range of sizes, diets, and lifestyles.
One hypothesis suggests that mammals co-evolved with plants. Following the fifth mass extinction, flowering plants and grasses underwent significant diversification. This likely led to the creation of new ecological opportunities and abundant food sources, which fuelled the diversification of mammals into various large species, each adapted to specific habitats.
However, finding strong evidence for the co-evolution of plants and megafauna is difficult, as it is challenging to observe the ecological relationships between extinct species based on fossil records.
Vanished Giants
At the end of the Pleistocene around 12,000 to 11,000 years ago, many megafauna species went extinct. Scientists are still trying to understand why this extinction event occurred. Some suggest that climate change affecting food sources or the excessive hunting by humans could have led to their demise.
However, it is interesting to note that many smaller relatives of these extinct giants survived and continue to thrive today. This suggests that body size may have been a crucial factor in their survival and evolution.
Today, we live alongside large animals like elephants, Komodo dragons and ostriches. Why do you think they survived while others perished?
