Amphibians

Bullfrog

Scott Rando

Amphibians are a diverse group of vertebrates found on every continent expect Antarctica. There are more than 6,000 species living today. Different types of amphibians found in the Upper Delaware Region include frogs, toads, and salamanders. Though not found in the Upper Delaware Region, caecilians are another type of amphibian that live in tropical areas. Many amphibians can take advantage of aquatic and terrestrial habitats, although some may exclusively live in one habitat type. Similar to reptiles, amphibians are ectothermic or cold-blooded, meaning they do not generate their own body heat.

 

Red-spotted Newt (Terrestrial Red Eft Stage)

National Park Service

Amphibians are characterized by several features, including their unique skin and teeth. Their skin is especially thin, moist, and permeable to liquids and gases. Although many have lungs, they also perform cutaneous respiration, which means they breathe through their skin. Special glands keep the skin moist for gas exchange and decrease water loss. Some adult amphibians also have poison-producing glands in their skin that secrete toxins to deter or even kill predators. In the Upper Delaware Region, the American Toad, Pickerel Frog, and Red-spotted Newt all produce poison. However, none of these species are dangerous to humans. Amphibians also have bicuspid, pedicellate teeth, meaning that each tooth has two cusps, and the crown of the tooth sits on a tall base called the pedicel.

 

Red-spotted Newt (Aquatic Adult Stage)

National Park Service

Most amphibians have a bimodal lifestyle, meaning their lives have two distinct phases. Frogs and toads often hatch as aquatic tadpoles with no legs, a long tail, and gills. The tadpoles metamorphose into adults that are usually terrestrial and typically have legs and lungs. Salamanders often show direct development, meaning they hatch as tiny versions of the adults. Other amphibians show paedomorphosis, meaning that the adults retain some juvenile traits such as gills.

Amphibians are extremely sensitive to changes in their environment. When something alters their habitat like contamination or habitat destruction, they are often the first species to decline. Thus, they serve as important indicators of ecosystem health. Across the world, amphibian species are declining and threatened by extinction. Areas such as the Upper Delaware Scenic and Recreational River serve as important refuges for these species.