The Silurian Expansion

The Silurian Expansion spans 443.8 to 419.2 MYA with the extreme climate changes almost forcing the evolutionary progress to come to a halt. After the mass ban in the end of the Ordovician expansion, the biodiversity was greatly decreased. This is one of the shorter expansion with less but still significant patches. As sea levels begin to rise, rivers and lake would overwhelm the coastal areas of supercontinent, Gondwana as well as the newly forming Euroamerica in the north, becoming habitats for larger life form. Earth’s atmosphere developed an effective ozone layer concentration. The climate were starting to stabilise to reduce periodic continental glaciations that contributes to significant rise in global sea level.

## Formation of the early forests

In 425 MYA, the plants specced into vascular tissues to allow them to have a more stable structure and grow to greater sizes as well as distribute water and nutrients throughout the plant to collect more sunlight for XP. Along the streams and rivers of solaria Gondwana and Euroamerica, the early plants spread out even father than their ancestors. Species like Cooksonia were some of the first to ponder this new strategy forming what could be called one of the first example of a forest biome. The Fungi kingdom was able to beat them for the record of the tallest organisms in the forests. The very first forest in the game were made up of giant tree trunk-like fungus named Prototaxites in 420 MYA. Fungal and plant life on land still had to stick close to the water.

## The Rise of Fish

Life in the ocean was on the slow road to recovery. The large Nautiloid predators were hit hard by the bans with a some surviving species like Sphooceras but they were less dominant, allowing more top predators to fill in. New types of coral and cranoids were introduced to open up new marine ecosystems.

Early true fishes started to branch into several different forms. Evolution of movable jaws allowed vertebrates to take advantage of all the different food sources that had previously only been available to arthropods and cephalopods. The Jawed fish (Agnatha) split into three distinct groups: the Cartilaginous fish, Bony fish, Armoured fish (Placodermi - partly external skeleton). Bony fish then splits into Ray-finned fish and Lobe-finned fish. Guiyu oneiros, the earliest lobe-finned fish dataminers currently know, had fins mounted to the pectoral and pelvic girdles to buff their range of motion for more efficient swimming. The most successful fish build was the Megamastax in this period, the biggest vertebrate (a meter long) at the time.

Ever since the Cambrian explosion, the Arthropods have been major competitors for dominance in the world’s ocean. Unlike other factions, Trilobites were still making a resurgence at the time. Eurypterid (Sea Scorpions) began to take the apex predator role. The eurypterids would split into two different body plan and playstyles - Stylonurina (smaller, scavengers) and Eurypterina (active hunters with big arms). Most common Eurypterina was the Eurypterus (95% of the sea scorpion fossils found from this time). The 3 meter long Jaekelopterus were the apex predators of the Silurian with giant grasping claws.

## Animals on land

The end of the Silurian was not as devastating as most other patches with gradual continental changes. The rise of temperature in the climate caused there to be no ice at all in the poles. A few groups of small arthropods have managed to transition into living on land with first terrestrial pioneers being millipedes and possibly, cousins of the sea scorpions.