- First fossils of animals that could walk on land were found in a place called Willie’s Hole in Scotland.
- The first creature believed to have walked on land is known as Ichthyostega.
- The first mammals appeared during the Mesozoic era and were tiny creatures that lived their lives in constant fear of dinosaurs.
The first animals that walked on land were called tetrapods. It is believed that the first tetrapods walked the parts of our planet where Scotland is situated today. Fossils of four-legged animals were found near Chirnside in Scotland, in a place called Willie’s Hole. These remains were believed to be from almost 400 million years ago, the time when animals with backbones started making the transition from sea to land.
After a more thorough examination in Willie’s Hole in 2015, five new fossil species were found, and these are considered to be the earliest known animals that walked on land. Once they stepped foot on land, tetrapods were divided into two groups, the ancestors of reptiles, birds, and mammals, and the ancestors of amphibians. This would mean that in a weird way, all mammals have evolved from Scotland.
The First Mammals
The first mammals evolved at the end of the Triassic period, and they arose from a population of therapsids. Therapsids are most easily described as “mammal-like reptiles” that were extinct during the Jurassic period. However, some of them evolved and developed traits such as fur and warm-blooded metabolisms, which were then developed further in the upcoming periods. It is hard to distinguish between the last therapsids and the first mammals ultimately.
However, certain vertebrates that lived in this period can prove to be the missing links between them. Ignoring the details that can be considered insignificant for our article, the first mammals appeared in the Mesozoic era, and they were considerably smaller than most mammals today. Only a few of them were larger than mice, and because of the dominance of dinosaurs, they were forced to feed on plants and hide during the day.
The Mesozoic Tetrapods
During this period, another group started to develop itself, called the diapsids. From this group, a large number of animals we know today developed, such as turtles, crocodiles, and dinosaurs. Their appearance did not happen until the Jurassic part of the Mesozoic period. This, however, marks the time where we can start to recognize the animals that roamed the surface.
Although dinosaurs are no more, they should be well known to anyone reading this. Turtles and crocodiles are still all over the planet, so they should not need a special introduction either. Another essential thing started happening during this period as well; the first mammals appeared.
Permian Period Tetrapods
During this period, two more groups were developed, the sauropsids and the synapsids. The synapsids are considered to be the most important animals of this period. They shared most of their characteristics with the previously mentioned animals. At the end of this period, a large scale extinction event happened, and multiple species were completely wiped out. Various groups that were previously large in numbers were either severely reduced or died out entirely.
Carboniferous Period Tetrapods
During this period, tetrapods began having a standardized number of digits (fingers) on their hands and feet. The number was never more than five, and all of the lineages with more than five digits started dying out. Later on, these tetrapods divided into two groups.
The first one is the temnospondyls, from which the modern amphibians originated, and the other group is the anthracosaurus, which later on gave birth to reptiles and mammals. The members of the first group are believed to have needed to return to the sea to lay eggs. The eggs laid by the other group had a membrane that allowed them to develop on land normally.
The first creature that most scientists consider to have walked on land is today known as Ichthyostega. However, this creature did not just waltz gracefully out of the sea onto the shore and continued running. No, it most likely hauled itself out on its front limbs. The process probably resembled walking on crutches.
At first, it was believed that the creature walked similarly to a salamander, however recent findings have proven otherwise. Ichthyostega resembled a mudskipper fish more than a lizard. Since the environment during this time had extraordinarily wet and dry periods, the animal needed to be able to swim and walk. Ichthystega was living during the Paleozoic period.