Tetrapod

Tetrapod

Illustration of various tetrapods.

Tetrapods are a superclass of animals that includes all vertebrates with four limbs. This group encompasses a wide range of species, including amphibians, reptiles, birds, and mammals. The term "tetrapod" is derived from the Greek words "tetra," meaning four, and "pous," meaning foot.

Evolutionary History

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Phylogenetic tree of tetrapods.

Tetrapods evolved from lobe-finned fish during the late Devonian period, approximately 360 million years ago. This transition from aquatic to terrestrial life was a significant evolutionary step, allowing vertebrates to exploit new ecological niches on land. The earliest known tetrapods were primarily aquatic, but over time, they adapted to terrestrial environments.

Characteristics

Tetrapods are characterized by the presence of four limbs, although some species have lost one or more limbs through evolution. For example, snakes and some lizards have evolved to be limbless. Tetrapods typically have a skeleton that supports their body on land, and they possess lungs for breathing air.

Diversity

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Biodiversity of tetrapods over time.

Tetrapods are incredibly diverse, with over 30,000 species. They are divided into four major groups:

• Amphibians: This group includes frogs, toads, salamanders, and caecilians. Amphibians are known for their life cycle, which includes an aquatic larval stage and a terrestrial adult stage.

• Reptiles: Reptiles include turtles, crocodilians, lizards, and snakes. They are characterized by their scaly skin and typically lay eggs with leathery shells.

• Birds: Birds are warm-blooded tetrapods with feathers and wings. They are highly adapted for flight, although some species are flightless.

• Mammals: Mammals are warm-blooded tetrapods with hair or fur. They are distinguished by their ability to produce milk to feed their young.

Examples of Tetrapods

A Northern leopard frog (Lithobates pipiens).

• The Northern leopard frog (Lithobates pipiens) is a common amphibian found in North America.

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A Florida box turtle (Terrapene carolina bauri).

• The Florida box turtle (Terrapene carolina bauri) is a terrestrial reptile native to the southeastern United States.

A house sparrow (Passer domesticus).

• The house sparrow (Passer domesticus) is a small bird commonly found in urban areas worldwide.

A squirrel, a common mammal.

• Squirrels are small to medium-sized rodents found in many parts of the world.

Historical Context

Systema Naturae by Carl Linnaeus, 1735.

The classification of tetrapods has evolved over time. The Swedish botanist Carl Linnaeus was one of the first to classify animals in a systematic way in his work Systema Naturae (1735). Since then, the understanding of tetrapod relationships has been refined through the study of fossils and genetics.

Related Pages

• Vertebrate
• Amphibian
• Reptile
• Bird
• Mammal
• Evolution of tetrapods