先史時代の海の恐怖

In this class, we will learn about some of the largest and strangest ocean animals to have ever lived, while exploring geologic time along the way!

Day 1: Introduction and Paleozoic Era. We will start in the Cambrian period, over 500 million years ago, with Anomalocaris. This shrimp-like creature is smaller than a person, but for its time it was gigantic! Moving forward into the Ordovician period, we will meet a new class of apex predators: the shelled, tentacled nautiloids, like Endoceras. In the following Silurian period, we will meet a new order of life: the eurypterids, or sea scorpions, which became some of the largest arthropods to have ever lived! Fish and their close cousins have been around since the Early Cambrian, but the first apex predator fish may have been Dunkleosteus. This Late Devonian armored fish grew to nearly 9 m (30 ft) long and had jaws built for cracking shells and bone. In the Carboniferous period, shark-like fish diversify dramatically; to see some of the largest, such as Orthacanthus, we will take a detour, leaving the ocean to visit freshwater! Carboniferous marine fish are much smaller, but make up for it with their strangeness; one of the oddest is Stethacanthus, which has a large "brush" on its back. Less is known about the marine life of the Permian period--most of those fossils are likely still below the oceans--but we do have fossils from another exceedingly strange cartilaginous fish: the Early Permian Helicoprion, famous for its spiral "tooth whorl."

Day 2: Mesozoic and Cenozoic Eras. The end of the Permian was marked by the most devastating mass extinction, which wiped out over 80% of all ocean life. This allowed for the evolution of new groups of marine reptiles. The first to reach enormous sizes in the Triassic period were the Ichthyosaurs. These dolphin-like "fish lizards'' were likely all carnivorous, and some reached enormous sizes! The first plesiosaurs lived near the end of the Triassic, but in the Jurassic period they diversified and grew much larger. The final well-known group of Mesozoic marine reptiles, the mosasaurs, lived only during the Cretaceous period, but included some of the most fearsome predators the seas have ever known. The Mesozoic era ended with another mass extinction, wiping out the last of these marine reptiles. The mammals followed their lead, though, and soon a new group came to dominate the seas: whales and dolphins! The Paleogene period was dominated by one of the first of the giant whales: Basilosaurus. In the Neogene period, about 9 million years ago, another giant whale, Livyatan, reigned as an apex predator. Livyatan was not the only giant carnivore of its time though; it shared the oceans with a similarly large shark, the fearsome, whale-eating megalodon!