Acanthostega

Acanthostega was an extinct animal that lived about 365 million years ago, during the late Devonian period.

It is considered one of the first vertebrates to have recognizable limbs, and a transitional form between lobe-finned fishes and land-dwelling tetrapods.

Acanthostega had a fish-like body, with scales, fins, and a long tail.

It also had internal gills that were covered by a flap of skin, and lungs that allowed it to breathe air.

However, it was not well adapted for walking on land, as its limbs were weak and lacked wrists, elbows, and ankles.

It had eight digits on each hand, and an unknown number on each foot, which were connected by webbing.

Its shoulder and forelimb were similar to those of fish, and its ribs were too short to support its chest out of water.

Acanthostega is thought to have lived in shallow freshwater habitats, such as rivers, lakes, and swamps.

It probably used its limbs to paddle in the water, or to grip onto aquatic plants.

It may have also crawled onto land for short periods of time, perhaps to escape predators or to find new food sources.

It fed on small animals, such as worms, insects, and crustaceans, using its sharp teeth and strong jaws.

Acanthostega is an important fossil for understanding the evolution of tetrapods, as it shows many features that are intermediate between fish and land animals.

It also reveals the diversity and experimentation that occurred during the Devonian period, when many different kinds of vertebrates with limbs emerged.

Acanthostega is closely related to another early tetrapod, Ichthyostega, which had more robust limbs and a stronger backbone.

Together, they represent the ancestors of all modern amphibians, reptiles, birds, and mammals.