Life 2

Life : 3 Beginning of Life – BURNT SIENNA

On  By burnt

575 million years ago

Strange life forms known as the Ediacarans appear around this time and persist for about 33 million years.

570 million years ago

A small group breaks away from the main group of deuterostomes, known as the Ambulacraria. This group eventually becomes the echinoderms (starfish, brittle stars and their relatives) and two worm-like families called the hemichordates and Xenoturbellida.

Another echinoderm, the sea lily, is thought to be the “missing link” between vertebrates (animals with backbones) and invertebrates (animals without backbones), a split that occurred around this time.

565 million years ago

Fossilised animal trails suggest that some animals are moving under their own power.

540 million years ago

As the first chordates – animals that have a backbone, or at least a primitive version of it – emerge among the deuterostomes, a surprising cousin branches off.

The sea squirts (tunicates) begin their history as tadpole-like chordates, but metamorphose partway through their lives into bottom-dwelling filter feeders that look rather like a bag of seawater anchored to a rock. Their larvae still look like tadpoles today, revealing their close relationship to backboned animals.

535 million years ago

The Cambrian explosion begins, with many new body layouts appearing on the scene – though the seeming rapidity of the appearance of new life forms may simply be an illusion caused by a lack of older fossils.

530 million years ago

The first true vertebrate – an animal with a backbone – appears. It probably evolves from a jawless fish that has a notochord, a stiff rod of cartilage, instead of a true backbone. The first vertebrate is probably quite like a lamprey, hagfish or lancelet.

Around the same time, the first clear fossils of trilobites appear. These invertebrates, which look like oversized woodlice and grow to 70 centimetres in length, proliferate in the oceans for the next 200 million years.

520 million years ago

Conodonts, another contender for the title of “earliest vertebrate“, appear. They probably look like eels.

500 million years ago

Fossil evidence shows that animals were exploring the land at this time. The first animals to do so were probably euthycarcinoids – thought to be the missing link between insects and crustaceans. Nectocaris pteryx, thought to be the oldest known ancestor of the cephalopods – the group that includes squid – lives around this time.

489 million years ago

The Great Ordovician Biodiversification Event begins, leading to a great increase in diversity. Within each of the major groups of animals and plants, many new varieties appear.

465 million years ago

Plants begin colonising the land.

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