The First Animals

By | September 9, 2016

Fossils tell us that animal life began about 600 million years ago. The first animals lived in darkness, rooted to the seabed, and had simple, soft bodies shaped like disks or leaves, with which they gathered nutritious chemicals or particles in the water. These strange beings seem to have had no legs, no heads, no mouths, no sense organs, and no internal organs.

First life

Stromatolites

Living stromatolites in Shark Bay, Australia

For nearly nine-tenths of the Earth’s history, there were no animals or plants. During most of this early era, called the Precambrian period, the only life forms were microscopic single cells. Some grew in colonies on the sea floor, building up over time to form cushion-shaped mounds of rock – “stromatolites” – that still form today.


CHARNIA (CHAR-nee-a)

charnia-3

ANCHOR: Some fossil of Charnia have a stem with a disk at the base. These disks, buried in the sandy seabed, may have been anchors that held Charnia fixed in place while the feathery top waved about in the current.


Discovered by a schoolboy in 1957, Charnia caused a sensation because it came from rocks thought far too old to contain animal fossils. It had a feather-shaped body and lived rooted to the seafloor by a stem, perhaps feeding on microbes filtered out of the water. Its main body was made of rows of branches that gave it a striped, quilted appearance. Some experts think its body might have housed algae that made it green and allowed it to gather energy from sunlight (photosynthesis).

Fossil location: England, Australia, Canada, Russia

Habitat: Seafloor

Length: 6 in–6. ft (0.15–2 m)


Spriggina (sprig-EEN-a)

spriggina-fossils

SEGMENTS: Fossils show that Spriggina’s body was made of segments. Most fossils are curved in different ways, suggesting it had a flexible body.


Spriggina may have been one of the very first animals with a front and back end. It may even have had a head with eyes and mouth, suggesting it was one of the first predators to exist. Some scientists think it may have been an early trilobite. Others liken it to worms.

When: 550 million years ago (Late Precambrian)

Fossil: location Australia, Russia

Habitat: Seafloor

Length: 1. in (3 cm)


Dickinsonia (dickin-SO-nee-a)

 dickinsonia

Dickinsonia fossils are usually oval, with what look like segments extending from a central groove. Hundreds of fossils have been found, with a huge variety of sizes.


One of most baffling Ediacaran fossils is Dickinsonia—a flat, round organism that appears to have had distinct front and back ends but no head, mouth, or gut. Studies suggest Dickinsonia lived fixed to the seafloor, perhaps absorbing food through its base.

When: 560–555 million years ago (Precambrian)

Fossil location: Australia, Russia

Habitat: Seafloor

Length: 3⁄8–39 in (1–100 cm)


Cyclomedusa (cy-clo-med-OO-sa)

cyclomedusa


Mysterious Cyclomedusa was originally mistaken for a jellyfish because of its circular shape, but neighboring fossils are often misshapen, as though growing around each other on the seafloor. Some scientists think Cyclomedusa was just a colony of microbes or the anchor for the stalk of a bigger creature.

When: 670 million years ago (Precambrian)

Fossil location: Australia, Russia, China, Mexico, Canada, British Isles, Norway

Habitat: Seafloor

Length: 1–12 in (2.5–30 cm) across


Parvancorina (PAR-van-coe-REE-na)

parvancorina

 


Parvancorina had a shield-shaped front end that may have been a head and that faced into the current when it was alive. It also had a central ridge flanked by what look like segments. Many fossils have a well-preserved shape, suggesting that its body had a hardened outer casing.

When: 558–555 million years ago (Precambrian)

Fossil location: Australia, Russia

Habitat: Seafloor

Length: 3⁄8–1 in (1–2.5 cm)


DID YOU KNOW…?

In 1946, a scientist named Reg Sprigg was eating a packed lunch in the Ediacara Hills of Australia when he spotted what looked like jellyfish fossils in the rocks. He’d discovered something amazing: the oldest animal fossils in the world. One was named Spriggina, after him, and all the fossils from the period are now called Ediacaran fossils.

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