After hundreds of millions of years being largely restricted to the oceans, terrestrial ecosystems were well-established by the beginning of the Carboniferous Period. Primeval forests were rapidly crawling further inland, pumping oxygen into the air through photosynthesis.
Despite the mass extinction of marine life towards the end of the Devonian, the period that preceded the Carboniferous, terrestrial ecosystems were booming. The first amphibians evolved from fish, insects formed from arthropods, and the first primitive trees formed the basis of land-based biomes.
The Carboniferous period saw the highest oxygen levels ever known, the largest insects and arachnids and climate change on truly unprecedented levels. It’s a time known for its incredibly volatile nature, where pretty much everything that lived was vying for dominance in a lush rainforest world.
Highlights of the Carboniferous
- Diversification of insects and arachnids
- Highest ever oxygen levels
- Evolution of the first reptiles
- Climate change leads to rainforest collapse
Vast Swamp Forests Span a Tropical World
The Carboniferous Period inherited the ancient terrestrial ecosystems responsible for the greening of the land during the late Devonian. Like the period that preceded it, the Lower Carboniferous world was much warmer than it is today, and oxygen levels were rising rapidly as early vascular plants crept across the land. The poles were free of permanent ice. Sea levels also remained high, but the oceans were a very different place after catastrophic marine extinctions destroyed most of the world’s coral reefs during the Devonian.
Despite the devastating effects of the Late Devonian Extinction, marine life quickly recovered throughout the warm seas. Where huge armoured monster like dunkleosteus had once ruled, sharks were now the apex predators of the vast Panthalassic Ocean. Among these were the stethacanthids, characterised by their bizarre anvil-shaped crests in place of dorsal fins. Among its contemporaries were the falcatids, males of which had dorsal fins like bayonets, and helicoprionids, sharks with dental arrangements like circular saws.
As life recovered in the Early Carboniferous oceans, vast swathes of swamp forest colonised freshwater regions. Creating lush rainforests across equatorial regions and far beyond. Swampy rainforests covered millions of square miles of land. Their rapid and unhindered evolution continued to pump vast amounts of oxygen into the air, thus changing the course of evolution.
Amphibians Join Terrestrial Ecosystems
Terrestrial animals had yet to evolve to large sizes, which is the reason why plant life managed to evolve unhindered with so little to prey upon it. Nonetheless, the Early Carboniferous saw the continued development of true amphibians. Which continued to grow throughout the Period, eventually leading to giants like the eryops.
Later in the Carboniferous, the very first reptiles evolved. Among the earliest of them was hylonomus, whose name means ‘forest dweller’. In terms of appearance, it was akin to a gecko, albeit much larger.
Photosynthesis Leads to Supersized Bugs
Not since the Great Oxygenation Event of 2.3 billion years ago did oxygen have such a profound effect on the evolution of life on Earth as it did during the Carboniferous. With the unprecedented greening of the land came rapidly rising oxygen levels, peaking at up to 35% during the period. Humans may have trouble adapting to such an oxygen-rich atmosphere today, since we’re used to breathing an atmosphere consisting of only 21% oxygen. However, it was this record high that allowed arthropods to evolve to monstrous proportions.
First among the terrifying Carboniferous creatures were giant scorpoions. Theseast would have been among the largest terrestrial predators of the Viséan Age in which it lived, likely preying among upon small tetrapods. Among its contemporaries was the equally freakishly large arthropleura, the largest known terrestrial invertebrate of all time. Where the first land-dwelling animal had been a tiny millipede during the Late Silurian, arthropleura had grown into a 7.5-foot-long (2.3 metre) abomination. Nonetheless, despite popular belief, this monster millipede was neither venomous nor predatory, and was instead content with gorging on the vast amount of greenery that existed throughout the Carboniferous.
Although the first flying insects likely evolved during the Devonian Period, it was not until the Late Carboniferous that they really took off, and they certainly did so in style: Meganeura was a prehistoric dragonfly with a wingspan of 26 inches (65 cm), and one of the largest flying insects that ever lived.
As oxygen levels spiralled out of control, it wasn’t just giant bugs that were the horrors of the time. Forest fires would have also been rife, since such high levels of oxygen would allow even damp biomass to catch alight easily. In other words, everything on Earth was a whole lot more flammable, likely to the extent that the sky would have had a bruised reddish tint to it, owing to the ubiquity of forest fires.
The Carboniferous began as a hot and humid world of ever-rising oxygen levels only to end with glaciations transforming the climate and redefining the course of evolution. Although the end of the period was not marked by a major extinction event as many other periods are, a great deal of species disappeared as icy deserts crept up from the South Pole into far higher latitudes. Next week, we’ll be exploring the continuation of this time of extreme climate change during the Permian Period, the last of the Palaeozoic periods and a time that ended with the near complete annhiliation of all life on Earth.
The largest trees in history grow including Yggdrasil, elder treants tend the land creating great forests.