Frog Evolution

Published: 2019-09-03 00:00:00
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The frog family has lived for millions of years. Amphibians are the descendants of the fish species. Moreover, they have been classified as the first successful group of amphibians to walk on land. Due to their small sizes, these organisms are rarely noticed by human beings. They have been found to demonstrate some unique characteristics in their natural life. Thus, with the many years, they have lived there is the need to understand the key factors or features that have contributed to their successful evolution. Therefore, this study will discuss their natural history, evolution, and the morphological factors that have led to their successful existence on earth throughout history.

Frogs are members of the amphibian class of Chordata. In biology, they have classified under the Anura order a Greek word that means tail-less. These organisms fall in the same class as salamanders and toads. Frogs are cold-blooded vertebrates. However, amphibians differ from other vertebrates in that their young ones are hatched and live under water. Also, these tadpoles breathe using gills which eventually disappear as they undergo a metamorphosis to become adults when they can use their lungs (Urry et al., 2011). Adult frogs have four legs, but the hind ones are longer. Also, they have short bodies, protruding eyes, tail-less, and webbed feet. Frogs have a well developed voice unlike the other two species in the amphibian order. In the amphibian category frogs are the most numerous in number, extensively diverse, and are found in almost all habitats globally.

Frogs can be located in the terrestrial niches, arboreal, aquatic areas, and all continents except Antarctica. The tropical rainforests are where the greatest diversity of frogs can be found. In overall there are at least 5250 species of frogs within 33 families. The classes with the richest species are the Hylidae, Ranidae, and Leptodactylidae. Most frogs live either on land or water. On land frogs move through jumping or climbing. Anurans lay their eggs in pond, puddles, or lakes. Their larvae are called tadpoles which breathe using the gills where they live and develop under water until they mature (Maan & Cummings, 2012). Some adult frogs mostly eat plants, but the biggest number primarily follows a carnivorous modular. Frogs eat arthropods, gastropods, and annelids. Anurans are mainly recognized through their calls which are often heard at night particularly in the mating season. Frogs are crucial to the commercial sector, ecological, cultural values, and scientific studies. In the environmental sector, they contribute to developing an integrated food chain both in the terrestrial and aquatic eco-system. In the commercial section, they are used as a source of food. Scientist uses frogs to educate students especially in the anatomy classes where they are used as model organisms. In adding to cultural values frogs are used as examples during folklores and fairy tales during story telling.

Frogs are as ancient as 190 million years. While today amphibians are small animals in the old years, they were the most dominant animals on land. Some of them took crocodile-like sizes thus terrorizing smaller animals. This is because they were the apex predators in the swampy ecosystems then. Frogs developed from lungfish and used their lungs to get out of the water and comfortably live on dry land (Urry et al., 2011). Due to the warmth of earth then more and more water systems were drying up thus frogs had to find a way of surviving on land. As a result of decreased food supplies, frogs learnt to eat insects a thing that they still eat to date.

For anurans to evolve successfully throughout history, their morphology has greatly contributed to their ability to survive through the earths harsh ecosystem that has sometimes led to the extinction of many organisms. All vertebrates share a common feature that is the notochord. A notochord is a flexible rod that runs along an animals length that contributes to its locomotive capabilities. Also, there are the pharyngeal slits which are openings found between the throat and the outside of the animal (Maan & Cummings, 2012). These slits are mostly used for gaseous exchange. Vertebrates also have a dorsal nerve cord which runs from the brain to the muscles of an organism within the body. Also, vertebrates possess a post-anal tail which is lost in adulthood for some of the organisms. Another chordate characteristic is a well-developed heart within a closed circulatory system. Therefore, the morphology of a frog that has ensured it successful evolution will be evaluated against the above features associated with all chordates.

The locomotive morphology of a frog has successfully contributed to its development in all history. The feet or legs of a frog vary this consideration in all anuran species due to the areas in which they live. Some frogs live on dry land, in trees, in burrows, or in water. For a frog to survive in their ecosystems, they have to move very fast to either catch prey or escape their predators. Due to the musculoskeletal morphology, they have acquired from their ancestor's frogs have been able to become proficient jumpers. A frogs tibia, tarsal, and fibula are interconnected to form a single but adamant bone (Yamamoto & Vernier, 2014). Moreover, the forelegs of a frog are constituted by a radius and ulna which act as the shock absorbers whenever it lands. Its hind limbs are elongated and longer thus allowing the frog to push against the ground ensuring that they can borrow force from the ground with each jump.

Although a frog is tail-less during metamorphosis, its tail vertebrae become attached to the pelvis. Therefore, whenever a frog jumps it does so with both the energy and force of the body and the legs together. Further, all frogs have been endorsed with webbed feet. However, the type of lifestyle a frog lives determines the extents to which the webs are available. For instance, the fully aquatic frogs have completely webbed toes. Those in the arboreal species are either webbed halfway or quarterly considering that their toes are only used to grip smooth and vertical surfaces. On the other hand, small toe pads and tiny webbing characterize the dry land frogs. However, the ground dwellers have very muscular and strong hind limbs than all the other frogs. The burrowing frogs are also acquitted a toe extension which is primarily meant to assist in burrowing. Frogs also have a strange characteristic where they can grow back a leg especially in their tadpole stage (Urry et al., 2011). This development is often established if a predator eats a tadpoles foot. In most cases it can grow back its leg or not nonetheless, in both instances, a frog still survives with the three remaining limbs. A parasitic flatworm is often responsible for causing a rearrangement to occur in the limb bud cells of a frog leading to the growth of one foot of two.

The frogs skin has a morphological feature that allows it to act as a respiratory organ, absorb water, and control its body temperature. Along the head and it is back an anuran has a lot of glands. From these glands, a toxic substance is produced. The substance exuded is sticky and as a result, the frog becomes slippery thus protecting it from its predators. Due to the stickiness of this substance the frogs skin keep its moisture and it becomes protected from getting moulds and other bacteria. The frogs skin acts as a respiratory organ because of its permeability to both gases and water. Lots of blood vessels extensively characterize its skins surface. Therefore, whenever it goes into aquatic environments, the skin absorbs oxygen directly into the blood vessels from the water.

While on land a frog breathes through the buccal pumping process. Although the lungs are also used in exchanging air, some frogs lack them altogether due the environment they live. Besides, the permeable skins that anurans have they also have a specially structured heart. The heart of a frog is divided into three chambers with the atria, ventricles, the aorta and arteries performing particular functions. While separate atriums bring in oxygenated and deoxygenated blood into the blood, only one ventricle pumps both blood streams into the appropriate vessels (Yamamoto & Vernier, 2014). However, the aorta transports oxygenated blood while the pulmonary artery is responsible for passing the deoxygenated one. Nonetheless, despite one ventricle giving both types of blood, some narrowed cavities minimize the possibility of them mixing. Due to the presence of a well-structured heart that ensures higher metabolic activity a frog is often found to be more active among all the other amphibians.

A frogs brain, nerves, and spinal cord demonstrates the extent to which anurans nervous system is extensively structured. Most parts of a frogs brain are partly similar to those of human beings. In the brain of an anuran, there is the pineal body, optic lobes, cerebral hemispheres, the medulla oblongata, and a cerebellum. Although a frogs cerebrum is quite smaller than that of humans it still actually implements the function of controlling its posture and ensuring proper muscular coordination (Yamamoto & Vernier, 2014). On the other hand, the medulla oblongata acts as the central regulator of its digestive systems, any automatic functions, and the respiration functionality in anurans. As per the nerve transition, a frog only has ten pairs unlike other vertebrates including the birds, reptiles and mammals who have twelve of them. The ten pairs found in the cranial nerves ensure to transmit information from the outside environment, and it goes directly into the brain. Also, the spinal nerves in their ten pairs provide to send extreme information from the outside environment into the brain through the vertebral cord.

From this study, it has been demonstrated that the frog family exhibits unique characteristics unlike all the other amphibian species on earth. It is clear that they can adapt to all conditions, have well-structured reproduction modes, are diverse, have an adaptable eating behaviorism, and are extremely crucial to all their adaptations. Amphibians can be studied and are still in existence due to the morphological advantages they have been endorsed. Anurans can exist due to their abilities to live in different environments with their locomotive capabilities, well defined respiratory systems, a specially structured heart, and an extremely alert nervous system. However, despite frogs being able to evolve and survive for all these years, they are slowly becoming extinct due the changes in the environment.

References

Maan, M. E., & Cummings, M. E. (2012). Poison frog colors are honest signals of toxicity,

particularly for bird predators. The American Naturalist, 179(1), E1-E14.

Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2011). Campbell

biology (p. 379). Boston: Pearson.

Yamamoto, K., & Vernier, P. (2014). The evolution of dopamine systems in chordates. Adaptive

Function and Brain Evolution.

sheldon

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