As you might expect, the Oacian is among the longest living of all amphibians. And, thanks to its long life, its fossil evidence has provided a unique glimpse into the ancient world.
Life cycle
A frog’s life cycle varies from species to species. Some live in aquatic habitats and others are obligate breeders in standing water. However, all amphibians go through metamorphosis. The process includes cell growth, differentiation, and organogenesis.
Generally, the life cycle of an amphibian involves two phases: the larval stage and the adult phase. However, some animals go through an additional metamorphosis. For example, some species of toads go through a paedomorphic change that reduces their body size. This may also restrict their ability to disperse over land.
Many frogs rely on external fertilization. In this case, a male releases sperm over a female’s eggs. Both the sexes of a frog may be different colors or shapes, depending on the species.
Ectothermic
Ectothermic animals are characterized by a constant internal temperature that matches the surrounding environment. While some endotherms, like human beings, can cool themselves, ectotherms are unable to do so. This means they must gain heat from other sources, such as panting, sweating or changing their position.
Many ectotherms enter a state of torpor during the coldest months of the year. Torpor, or hibernation, lasts from days to years depending on the species. A common strategy used by ectotherms to survive the cold is to burrow into the ground. Other ectotherms seek out environments with cooler temperatures.
While many species of ectotherms have evolved to resist extreme temperatures, others have not. These include tropical lizards, which have not adapted to cold weather.
Skin
The skin of an amphibian represents a complex system, containing a diverse mix of molecules. Its functions include osmoregulation, respiration, and protection from environmental insults. However, this protective system is species-specific, meaning it depends on the biology of individual species. Understanding how the skin functions is essential to understanding amphibians.
Amphibians have evolved a variety of strategies to protect their skin against ultraviolet radiation (UV), oxidative stress, and other pathogenic insults. Some of these strategies involve enzymes and proteins, while others involve peptides. There are many different types of peptides in amphibian skin, and their effects vary according to the species.
One example is Cathelicidin-OA1, a cationic peptide that accelerates reepithelialization and granulation tissue formation. Although its antimicrobial activity is limited, its antioxidant potential is high. Another example is bombesin, which promotes proliferation in damaged tissue.
Lungs absorb limited amounts of oxygen
The ability to breathe in the air is an important part of amphibians’ existence. Their lungs, however, are much smaller than those of other land vertebrates, and they can only process a limited amount of air. That means that some species of amphibians are unable to breathe underwater, or need to use a special form of respiration to survive.
Air enters the amphibian’s lungs through the mouth and nose, and is then forced through the respiratory system. The lungs are a group of organs that are asymmetrically arranged. Some parts of the lungs are located near the head and mouth, while others are located in the chest.
Longest-living amphibian
One of the longest living amphibians on Earth is the common European toad, a member of the genus Pristimantis. Its body size varies from a diminutive 3.2 cm to a whopping 15.4 cm. The toad spends a great deal of time underground and digs tunnels to cool itself in hot summer months.
A frog’s life span is typically measured in years, but some are known to live for decades. The oldest known frog, Bufo bufo, lived for 36. While not as long as its namesake, the longest living frog in captivity is estimated to be 27 years old.
Amphibians have a complex reproductive cycle, involving the laying of eggs and the development of a larval stage. Some species have evolved to bypass the larval stage and complete development in their eggs.
Fossil evidence
Amphibians are considered transitional forms in biological evolution. Their origin is traced back to lobe-finned fish with lungs. Over millions of years, these animals became the dominant creatures on land. But now, scientists have found fossil evidence of the earliest amphibians. This is an important step forward in understanding the evolutionary origin of living amphibians.
The fossil record demonstrates that a number of different groups of animals emerged during the Permian period. Some of these were large, while others were small. A few of the animals, including Eryops megacephalus and Branchiosaurus, are known to have possessed external gills on the sides of their heads. Other species were adapted for both aquatic and terrestrial environments.
