While not all dinosaurs were the massive beasts that we often think of today, even the earliest dinosaurs of the Triassic period were a force to be reckoned with. Scientists believe that the closest known relative of the earliest dinosaurs was the Nyasasaurus—an omnivore, approximately 10 feet long, 3 feet tall, and 135 pounds. Despite its relatively short stature, this creature had to be strong and fast enough to catch the occasional prey.
It’s hard to imagine the fleshy, furry mammals of the Triassic period and beyond surviving with early dinosaurs. But based on our current knowledge of these animals, we know that they did. The real question is, how did mammals live alongside dinosaurs in the Mesozoic era, and how did they survive to make the 5,400 mammalian species that modern science has identified?
The Origin of Mammals
For scientists to classify an animal as a mammal, it must—at the very least—have the ability to produce milk and feed its offspring. Although the exact origin of mammals remains unknown, we do know that their earliest-known relatives likely existed at the end of the Triassic or the beginning of the Jurassic period.
These early mammals were known as cynodonts. Most of these early mammals never evolved to grow past the size of dogs, and the environmental pressures of dinosaurs only caused them to grow smaller. This is why, during the end of the Jurassic and throughout the Cretaceous period, most mammals were the size of rats.
How They Existed Alongside Dinosaurs
If the mammals that lived alongside dinosaurs were so small, how did any of them survive past the Mesozoic era to evolve into the mammals that we know today? The answer lies in the beauty of evolution.
The smaller an animal, the less food it needs in relation to its size, and the easier it becomes to hide and run. This leads to less competition and fewer encounters with predators. As more time passed, early mammals evolved to become almost entirely nocturnal, and some would eventually master the arboreal lifestyle of living in the trees.
While scientists believe that some bird-like dinosaurs could climb, these dinosaurs never mastered living in trees as early placental mammals did. Additionally, most dinosaurs were diurnal, but the ones that did eat at night were typically herbivores; it was the carnivores that usually hunted during the day. All these factors together allowed mammals to survive and evolve into a plethora of different species.
After the K-T Event
The K-T event—also called the Cretaceous-Tertiary Mass Extinction event—wiped out approximately three-quarters of the planet’s species 66 million years ago. This marked the end of the Mesozoic era and the start of the Cenozoic era. The new lack of competition and environmental pressures the dinosaurs once posed allowed mammals to evolve and ascend the food chain. They quickly became bigger, faster, and stronger, which eventually allowed them to prioritize brains over brawn. Today, we have an extensive array of mammals varying widely in size and intelligence.
Though the dinosaurs of the Triassic, Jurassic, and Cretaceous are long gone, Creative Beast Studio is dedicated to remembering their strength and influence through our quality, highly detailed figures. From the mighty Tyrannosaurus rex to the small but fierce Troodons, our Beasts of the Mesozoic era collection has all of your favorites.