Early Jurassic

The Early Jurassic Epoch is the first part of the Jurassic Period, a long time ago. It started right after the Triassic–Jurassic extinction event, which happened 201.3 million years ago, and lasted until the beginning of the Middle Jurassic about 174.7 million years ago. During this time, Earth looked quite different from today. The continents were moving, and many new kinds of plants and animals were beginning to appear.

Some important rocks from this time, especially those formed in the ocean, are found in Europe and are called "Lias". People in the 19th century used this name to talk about the whole Early Jurassic period. In southern Germany, rocks from this age are known as the Black Jurassic. These rocks help scientists understand what the world was like millions of years ago and how life has changed over time. The Early Jurassic was a time when many new species evolved and the planet was shaping up to look more like what we know today.

Origin of the name Lias

The name "Lias" has two possible origins. One idea is that a geologist heard it from an English quarryman who said the word "layers" in a special way. Another idea is that sailors from Cornish towns like Bude would bring rocks from places like the Vale of Glamorgan. These rocks came from limestone quarries along the coast. The sailors called these rock layers "laiyers" or "lias". The word "leac" in Gaelic also means "flat stone".

Geology

The Early Jurassic Epoch marks the beginning of the Jurassic Period, starting right after the Triassic-Jurassic extinction event about 201.3 million years ago. It ended around 174.7 million years ago when the Middle Jurassic began.

In the United Kingdom, especially around the coast, there are many rocks from this time. The area known as the Jurassic Coast in Dorset is famous for its cliffs and layers of clay, limestone, and siltstone. These rocks were studied by Mary Anning, a pioneer in fossil discovery, near Lyme Regis. The cliffs show repeating layers formed when a desert from the late Triassic period was covered by the sea.

Life

During the Early Jurassic, many sea creatures called ammonoids, which had nearly disappeared at the end of the Triassic period, reappeared in many new shapes and patterns. These ammonites changed quickly and their shells are often found as fossils, making them useful for scientists to study this time period.

This was also an important time for sea reptiles. Existing ichthyosaurs and plesiosaurs continued to thrive, while new types such as Ichthyosaurus and Temnodontosaurus appeared among ichthyosaurs, and Eurycleidus, Macroplata, and Rhomaleosaurus among plesiosaurs. Later in the Early Jurassic, new kinds of sea "crocodiles" called thalattosuchians showed up, along with new genera of ichthyosaurs and plesiosaurs. On land, many new dinosaurs appeared, including heterodontosaurids, dilophosaurus, scelidosaurs, stegosaurs, and tetanurans, joining groups that had survived from the Triassic like coelophysoids, prosauropods, and sauropods. Small carnivorous crocodilians, new pterosaurs, early mammals, tritylodont synapsids, lizard-like sphenodonts, and early lissamphibians also lived during this time.