Discover how the extinction of dinosaurs paved the way for the rise of megafauna. Photo: Sam TsangWhat comes to mind when you think of the prehistoric world? For many, it is dinosaurs, the fierce and powerful stars of the Mesozoic era, which spanned from about 251 to 66 million years ago. However, there were also 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 usually weighed over 44kg. Some of them resemble larger versions of their living relatives.
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 dinosaurs died out, mammals evolved into many different shapes 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 elephants like the Deinotherium and mammoths, the enormous deer Megaloceros and the giant ground sloth Megatherium (see graphic).
Why did mammals grow so big? Scientists believe that mammals evolved to fill the vacant ecological niches after the mass extinction that wiped out dinosaurs. Freed from competition with the dinosaurs, the mammals 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 observing the ecological relationships between extinct species based on fossil records is challenging.
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Vanished giants
At the end of the Pleistocene epoch, 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 their demise could have been because climate change affected their food sources or humans had excessively hunted them.
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 crucial to 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?