What are tetrapods and their evolution?
Introduction:
Tetrapods are members of the super-class of Tetrapoda. This class includes all animals that contain all animals having backbone i.e. limbed vertebrates. Tetrapods include the following classes:
Amphibia (amphibians)
Reptilia (reptiles)
Aves (birds)
Mammalia (mammals)
And also their ancestors emerged almost during the Devonian Period, 397 million years ago.
Characteristics:
In a natural evolutionary way, all tetrapods are particularly limbed fishes because their maximum vertebrate ancestor is fish. All tetrapods have a variety of morphological characteristics. The characteristics they share are a pair of bones including the forelimbs ulna and radius and hind limbs the tibia and fibula, fenestra ovalis in the opening of the skull in the middle of the ear, a stapes which is the ear bone, and many other skeletal characteristics. Indeed, the earlier tetrapods also have special physiological, behavioral, and soft anatomical segments; however, only skeletal features are conserved in the fossil record and thus are used for classification.
There is an almost universal accord that tetrapods arose someplace from Sarcopterygii within the fleshy-finned or lobed-finned fishes. Still, it is not totally confirmed that sarcopterygians are the ancestors of tetrapods. The main problem in deciding tetrapod ancestry originates from the incapacity to determine finally which traits are ancestral and which characteristics and traits emerged after one group diverged from another one.
skull sharing many characteristics of early tetrapods. Fossil elements of V. curonica which contained parts of a pelvis, an upper shoulder girdle, and a brain case, were excavated 365 million years ago in Latvia. However, tetrapods appeared much earlier, as demonstrated by fossil imprints almost 397 million years ago.
Classification:
Kingdom: Animalia
Phylum: Chordata
Clade:Eotetrapodiformes
Clade:Elpistostegalia
Clade: Stegocephalia
Superclass:Tetrapoda
Evolution:
The evolution of tetrapods started when tetrapods evolved from lobe-finned fishes in the Devonian period almost 400 million years ago. Most of the species of tetrapods are today terrestrial little proof from history supports the hypothesis that any of the primitive tetrapods could move on land because their limbs don't have harbored their cores off the ground and the known trackways do not imply they pulled their abdomens around. Presumably, the paths were made by animals walking along the bases of shallow bodies of water. The specific aquatic antecedents of the tetrapods and the method by which land colonization appeared are still unclear. And these are the main topics of dynamic research and discussion among paleontologists in present times.
Many amphibians of today's time are semi-aquatic, spending the initial stage of their lives like tadpoles as fishes do. Many groups of tetrapods, like the snakes and cetaceans(dolphins and whales, etc), lost some or almost all their limbs. Moreover, many tetrapods have been born to fully aquatic or partially aquatic lives in the entire history of the group and their modern examples of fully aquatic tetrapods enclose cetaceans and sirenians.
Researches and fossil records explain that the first returns to an aquatic lifestyle may have occurred in the early Carboniferous Period whereas returns to other lifestyles occurred in the recent Cenozoic Era like in pinnipeds, cetaceans, and many other modern amphibians.
The change in body plan from breathing in air and steering in water to a body plan promoting the animal to drag on land is one of the most deeply known evolutionary changes. Many relating fossils which finds at the end of the 20th century connected with improved phylogenetic analysis help to better understand the history of evolution from water to land and the emergence of tetrapods.
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