Animals colonized the continental interior in the late Silurian or early Devonian, with insects likely being the first. The evolution of wings allowed insects to travel inland, provided there was sufficient food in the form of plants. Colonization of the continental interior occurred around the same time as vascular plants evolved, with fossil examples being Cooksonia and Baragwanathia. Insects existed on earth in small numbers for tens of millions of years, but they don’t appear in large numbers in the fossil record until the late Carboniferous. The first tetrapods, such as Acanthostega, began taking their first steps on land about 360 million years ago.
Animals first colonized the continental interior in the late Silurian or early Devonian, around the same time that extensive terrestrial fossils appear. The first animals to colonize the continental interior were probably insects. Surprisingly, the earliest known fossil insect, Rhyniognatha hirsti, estimated to be 396-407 million years old, had already evolved wings, which would have allowed it to travel inland, provided there was sufficient food in the form of plants.
Colonization of the continental interior probably occurred around the same time as vascular plants evolved, about 425 million years ago, with fossil examples being Cooksonia (northern hemisphere) and Baragwanathia (Australia). Prior to this, the terrestrial flora consisted mainly of bryophytes (mosses, etc.) which had to be found in very humid, usually coastal areas to survive.
Of course, life could have spread to the continental interior via rivers, but in this ancient era, due to a lack of land plants, most rivers had a braided rather than meandering structure, making them less hospitable to humans. animals. Once vascular plants really started working, they shaped rivers into a more unified flow, bringing in algae and small aquatic animals. The insects that first made footsteps on land would have been similar to modern-day bristletails, an evolutionary relic that has changed little since it first emerged in the Devonian.
Insects have existed on earth in small numbers for tens of millions of years, but they don’t appear in large numbers in the fossil record until the late Carboniferous, about 330 million years ago, when the first true forests began to grow. It’s entirely possible that insects existed before this, but didn’t reliably fossilize due to a variety of reasons.
Meanwhile, the first tetrapods, such as Acanthostega, began taking their first steps on land about 360 million years ago. For tens of millions of years they remained on shorelines and in the muddy marshes where they were common at the time. But around 340 million years ago, some amphibians evolved a tough membrane around their eggs, which allowed them to be laid on land, creating the first reptiles, which resembled small lizards. These animals would have been among the first non-insects to colonize the continental interior, now filled with nutrient-rich forests.
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