Passage into the Devonian

The Devonian Period, lasting from approximately 419.2 to 358.9 million years ago, was characterized by elevated temperatures and high sea levels. While today, oceans encompass about 71 percent of Earth's surface, during the Devonian, a staggering 85 percent was submerged, forming a vast aquatic landscape. This era, often referred to as the Age of Fishes, was marked by the emergence of numerous marine species, with fish reigning as the dominant animals. Yet, while these aquatic creatures flourished, some four-legged vertebrates began their quiet ascent onto land.

The transition from the Silurian to the Devonian is often overlooked in geological history. Although extinctions generally mark the boundaries of geological periods, the end of the Silurian saw only minor species loss, likely due to climatic shifts rather than catastrophic events. Nature's artistry here resembled a subtle touch-up rather than a complete overhaul, setting the stage for an explosion of new fish species throughout the Devonian.

At Sea

Most life forms during the Devonian thrived in the shallow seas and coastal regions. Evolution took advantage of the available resources, leading to a surge in armored and jawed fish species. The emergence of jaws prompted many species to develop protective features, resulting in a symbiotic relationship between predator and prey.

Midway through the Devonian, a new class of fish known as Chondrichthyes appeared. These early ancestors of sharks possessed cartilaginous skeletons and included species such as skates and rays.

Meanwhile, the Early Devonian saw the rise of ammonites, resembling modern nautilus. These ancient predators utilized their coiled shells for both defense and mobility, with their siphuncle allowing for buoyancy control in the water. Unfortunately, ammonites are no longer extant.

Perhaps the most fascinating evolution during this time was the emergence of the Rhipidistia, an extinct group of bony fish with lobe-finned structures. Their unique anatomy hinted at the potential evolution into the first tetrapods that would eventually venture onto land.

Life on the Move

Alongside the Rhipidistia, lungfish also emerged during the Devonian, capable of surviving prolonged periods out of water using atmospheric oxygen. While insects were likely the first land-dwelling creatures from the Silurian, the arrival of four-legged animals was imminent. By the end of the Devonian, these tetrapods, probably resembling early amphibians, were firmly establishing themselves on land.

Geological changes were also underway. The supercontinent Pangea was forming, with Laurasia and Gondwanaland gradually coming together. This convergence led to significant mountain-building events, resulting in the early Appalachian Mountains and the ongoing rise of the Caledonides in regions like Britain and Scandinavia.

The flourishing of life during the Devonian was the result of intricate interactions between climate, geology, and biology. A warm climate and high sea levels fostered long-lasting shallow seas, with extensive limestone and shale deposits forming in places like Utah. The period also witnessed some of the most significant coral reef formations in Earth's history.

As animal life advanced, plant life also experienced remarkable growth. The emergence of vascular plants and the first true trees had profound implications for Earth's ecological landscape, possibly influencing its history even more than the changes in animal life.

The Complete History of the Earth: Devonian Period - This video provides an in-depth look at the ecological and geological transformations during the Devonian, highlighting the era's significance in Earth's history.

Rooted in Earth history: the Devonian transition to a forested planet - Explore how the Devonian Period set the stage for Earth's transition to terrestrial ecosystems and the rise of forested landscapes.

(Next time — The rise of Devonian trees)

(The Forgotten Origins series is also available on ArcheanWeb)

ArcheanWeb

Sources:

Silurian Period (Source: Cal Poly Humboldt Natural History Museum)

Rhipidistia (Source: Britannica)

Devonian Period (Source: InfoPlease)

Devonian Period (Source: National Geographic)