Carboniferous rainforest collapse

The Carboniferous rainforest collapse was an important change that happened about 305 million years ago during a time called the Carboniferous period. It took place at the end of the Moscovian and into the early Kasimovian stages of the Pennsylvanian.

This event changed the huge forests that grew in a place called the equatorial region of Euramerica, which included parts of Europe and North America. These forests, known as coal forests, were broken up into smaller, separate areas. This separation changed some plants and animals, and many of them disappeared forever.

Even after this collapse, forests that could make coal kept growing in many parts of the world, but they were not the same as before. Their size and what kinds of plants and animals lived there were very different.

Extinction patterns on land

The Carboniferous period had huge tropical rainforests in Euramerica. These forests were home to tall plants called lycopodiophyta and many animals like giant griffinflies, millipedes, blattopterans, smaller amphibians, and the first amniotes.

When the rainforests began to disappear, the plants and animals changed a lot. First, more ferns started to grow. Then, the big lycopsids suddenly died out, and tree ferns became more common. The rainforests broke into smaller pieces, and finally, they almost completely vanished. Because the rainforests were gone, many insects and amphibians disappeared. However, the ancestors of reptiles and mammals began to develop into many new types of species. This happened because each small area of surviving rainforest developed its own special group of plants and animals, a pattern known as endemism.

Biotic recovery and evolutionary consequences

Plants

When the wetlands broke apart, only a few small areas in Europe stayed safe for plants. But even these areas could not keep all the different kinds of plants that lived there before. By a certain time called the Asselian, many plant families that were common in the old tropical wetlands had disappeared.

Invertebrates

Some people think the Carboniferous rainforest collapse caused large insects and other animals like giant griffinflies and millipedes to go away. They believed that because there was less oxygen and fewer forests, these animals could not survive. But newer research shows that these animals probably did not live only in forests. We still find fossils of them after the rainforests disappeared, so the collapse and lower oxygen levels were not the main reasons they disappeared.

Vertebrates

The sudden change hurt many large animal groups. Amphibians were especially hard hit, while animals with eggs that could stay dry, like the first reptiles and mammal-like reptiles, did better because they were better suited to drier places.

Amphibians can survive cold by resting quietly, but this does not help them for long periods of dry weather. They need water to lay eggs, while animals with dry eggs can survive better in dry places. Because amphibians could not change easily to the new dry conditions, many of them disappeared. They also lost the scales their water-dwelling ancestors had and needed to keep their skin wet to breathe, while the new animals grew scales that helped them save water.

Reptiles and mammal-like reptiles moved into new places faster than amphibians and started eating different foods, like plants and meat, instead of just insects and fish. Reptile-like reptiles grew much bigger, and this kept happening until a big event later on, when their mammal-like descendants got smaller and started being active at night, though some reptile-like reptiles stayed big throughout a long time.

Possible causes

Atmosphere and climate

Scientists have many ideas about why the Carboniferous rainforest collapse happened, and some of these ideas include climate change. After a very cold time around 318 million years ago, the weather started changing often between very wet and very dry periods.

During the Carboniferous period, lots of coal formed because carbon was being taken away from the air. Then, around the middle of this time, things started getting drier, and animals and plants in the oceans and on land began to change quickly. We can see this in old soils, which show that the land became drier and more stable. The climate turned cooler and drier, which made it hard for rainforests to survive. The rainforests shrank and became scattered in small patches in wet valleys. The amount of carbon dioxide in the air also dropped to very low levels, and finally, rainforests were replaced by drier landscapes.

Volcanism

Studies show that a large area called the Skagerrak-Centered Large Igneous Province became active about 300 million years ago. A big eruption happened around 297 million years ago, which matches the time when the rainforests began to disappear. This eruption happened around the same time as the end of the Moskovian and start of the Kasimovian stages.

Geography

The Carboniferous rainforest collapse mainly affected the equatorial region of Euramerica, which includes Europe and North America. It did not impact the region of Cathaysia, which mostly corresponds to modern China. In Cathaysia, rainforests similar to those from the Carboniferous period continued until the end of the Permian period, around 252 million years ago.

Fossil sites

Many fossil sites around the world show us what happened during the Carboniferous rainforest collapse. Some important places include Hamilton, Kansas in the US, Jarrow in Tyne & Wear, UK, the former Linton Mine in Saline Township, Jefferson County, Ohio, the US, Nýřany in the Czech Republic, and Joggins, Nova Scotia in Canada.

The Joggins Fossil Cliffs along the Bay of Fundy in Nova Scotia is a special place with very well-preserved fossils. These cliffs were studied by Sir Charles Lyell in 1852. Later, in 1859, his friend William Dawson found the oldest known reptile-ancestor called Hylonomus lyelli. Since then, many more skeletons have been discovered there, including the oldest synapsid, Protoclepsydrops.