Paleozoic Era: Silurian Period 

444–419 Ma

The Silurian: expansion of fishes

Compared to almost all the other periods in geologic time, the Silurian is short at less than 25 million years in duration. Indeed, only the Neogene is shorter at approximately 20 million years, and there are even several Epochs, as subdivisions of Periods, that are longer than the Silurian. Nevertheless, there were still numerous amazing evolutionary firsts in this almost narrowest of time windows. One of the most important is very likely the Silurian-Devonian Terrestrial Revolution, where not only did vascular plants emerge and colonize land (building from the earlier spore-based evidence of primitive land plants in the Ordovician), but several other organisms made their ways into terrestrial environments. These included fungi and three important groups of arthropods: the arachnids (spiders, scorpions, and friends), the myriapods (centipedes and millipedes), and the largest clade of arthropods, the hexapods (insects). With high atmospheric carbon dioxide, these terrestrial plants an animals enjoyed a warm climate, as opposed to the cooling at the end of the Ordovician, though storms may have been amplified as evidenced by extensive coquina deposits of broken shell hash. Here, we have shown some simple Prototaxites-like trunk fungi, which could reach 1-meter widths and heights of 8 meters (26 feet), colonizing the shoreline in the distance. Underwater, the Silurian Period is known for the diversification and expansion of the fishes, shown here with the heavily armored placoderm Qilinyu (left) and bony-armored but jawless Cephalaspis (right) both searching for meals on the seafloor, as well as the eel-like Jamoytius swimming above. In the foreground are a snail and starfish making a home on the tabulate "chain coral", Halysites. Finally, the large predator in the water column is again a giant eurypterid, Pterygotus. Although this species could reach to almost 2 meters long, some of its most closely related kin could reach over 2.5 meters in length (over 8 feet!).