Amphibians

By | September 9, 2016

Amphibians are animals that spend their lives partly in water and partly on land. They evolved from fish about 370 million years ago as fins slowly turned into fully formed legs that allowed them to walk on land.
Amphibians were the first four-legged animals (“tetrapods”) and the ancestors of all four-legged animals alive today, from frogs and mice to elephants and humans.

FAMILY FACT FILE

Key features
■ Four limbs with wrist and elbow joints
■ Distinct fingers and toes
■ Eggs laid in water
■ Fishlike larvae (babies)

When
Amphibians evolved from fish during the Devonian Period, 370–400 million years ago.

Ichthyostega (ICK-thee-oh-STAY-gah)

skeleton-of-ichthyostega

Ichthyostega skeleton


When: 370 million years ago (Late Devonian)

Fossil location: Greenland

Habitat: Shallow northern seas

Length: About 5 ft (1.5 m)

Ichthyostega’s head, body, and tail fin were like those of a fish, but it had webbed feet like a frog’s. It used lungs to breathe on land and had strong shoulder muscles that supported its weight out of water and helped it to crawl around. It hunted for fish and other prey in shallow pools.

Seymouria (see-MORE-ee-ah)

seymouria-fossil

Seymouria fossil


When: 290 million years ago (Early Permian)

Fossil location: USA, Germany

Habitat: Swamps of N. America and western Europe

Length: About 2 ft (60 cm)

For many years Seymouria was believed to have been an early reptile because it had sturdy legs and was well suited to life on land. However, scientists discovered that a close relative of Seymouria had external gills in early life, like a tadpole, which suggests Seymouria did too. Although adults lived on land, youngsters probably lived entirely in water. The adult males had thick skulls that may have been used to butt rivals in mating contests.

Phlegethontia (FLEH-geh-THON-tee-ah)

phlegethontia


When: 300 million years ago (Late Carboniferous to Early Permian)

Fossil location: USA, Czech Republic

Habitat: Swamps of N. America and western Europe

Length: About 3 ft (0.9 m)

Phlegethontia belonged to a group of amphibians that had evolved snakelike bodies and lost their legs. It had rows of small, spiked teeth similar to those found in some nonvenomous snakes.

Microbrachis (MY-crow-BRACK-iss)

microbrachis


When: 300 million years ago (Early Permian)

Fossil location: Czech Republic

Habitat: Swamps of eastern Europe

Length: Almost 6 in (15 cm)

Microbrachis looked like a tiny salamander with puny limbs. It had gills for breathing in water and probably swam like a fish, propelling itself forward by swishing its flattened tail from side to side. It\ seems to have spent most of its time in swamps, rivers, lakes, and ponds, where it hunted for prey such as small fish and shrimp.

Eryops (EH-ree-ops)

eryops

Eryops fossil specimen in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.


When: 295 million years ago (Early Permian)

Fossil location: N. America

Habitat: Swamps of N. America and western Europe

Length: About 6 ft (1.8 m)

One of the largest land animals of its time, Eryops looked like a fat crocodile. It had a long snout (its name means “drawn-out face”), and its huge, strong jaws were lined with sharp fangs. It couldn’t chew and so would have flung its head up and backward, tossing prey further into its mouth just as crocodiles and alligators do today. Eryops had sturdy limbs but moved slowly on land because of its bulky body and short legs.

Crassigyrinus (CRASS-ee-jih-RYE-nuss)

crassigyrinus


When: 350 million years ago (Early Carboniferous)

Fossil location: Scotland and USA

Habitat: Shallow waters of northern Europe

Length: About 5 ft (1.5 m)

This bizarre creature probably lived in water, since its tiny limbs would have made walking on land impossible. It was a large and powerful predator, with two rows of sharp teeth lining a huge mouth that it used to catch prey with a snapping motion. Large eyes suggest it could have hunted well in murky water, or perhaps at night.

Acanthostega (ah-CAN-tho-STAY-gah)

acanthostega


When: 365 million years ago (Late Devonian)

Fossil location: Greenland

Habitat: Northern rivers and swamps

Length: About 2 ft (0.6 m)

This is believed to have been the first tetrapod capable of briefly climbing out of water. It had lungs but also gills and is thought to have lived largely in shallow swamps. Unlike its fish relatives, Acanthostega had eight webbed digits on its forelimbs.

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