ichthyostega amphibian

The tox­ins are isolated as the bufogin and bufotalin. Ichthyostega was an early tetrapod genus that lived at the end of the Upper Devonian period, 374 - 359 million years ago. Because they possess many features which are cer­tainly amphibian or lead towards amphibia.

The poison of Dendrobates acts on the ner­vous system.

It was one of the first tetrapods in the fossil record.

The most primitive amphibians, known the Ichthyostegid whose components of vertebrae have the similarity to the crossopterygians. The members of Panderichthyidae were crocodile-like fishes with fins instead of limbs. The venous system of the urodeles represents a tran­sitional stage between the fish and the anurans. Figure 7.53 shows the phylogenetic tree of the amphibians.

The portion of the conus next to ventricle is called pylangium while the distal part is designated as synangium.

The transition from aquatic to terrestrial life causes the shortening of the vertebral column. The earliest well-known amphibian, Ichthyostega, was found in Late Devonian deposits in Greenland, dating back about 363 million years. If you would In water, the eyes were adapted for short­sighted vision but on land long-sighted vision becomes necessary.

The living amphibians exhibit diverse structural adaptation.

These trabeculae are best deve­loped in the walls of auricles. Biting teeth are present in adult Ceratophrys ornata.

The early amphibians must have fulfilled the basic requirements for living on land by making the following modifications: (a) Partial loss of armours although present in some earliest amphibia, e.g., Stegocephalians. The auricles are completely separated by a complete inter-auricular septum. creatures evolved legs, shelled eggs, and the ability to breath through The most dramatic and widely accepted event to note in amphibian evolution is the transformation of the crossopterygian paddles into amphibian limbs. The eggs are discharged into the body cavity. The RBC of Proteus measures about 58 pm in diameter. It has not quite adapted fully to land, so it can only emerge near the shore. For the attachment of the muscles the girdle became expanded into plates consisting of dif­ferent characteristic pieces. The larval amphibians respire in water by the gills. Ichthyostega is considered to be one of the important transitional links between marine and fully terrestrial vertebrates. In per-ennibranchiate urodeles, the lungs are simple saccular organs and the hydrostatic function is predominant.

(i) The skin becomes suited for terrestrial life to resist desiccation. The dipnoans exhibit too many specialised features and such a specialised group cannot possibly hold the ancestry of another group of animals. 7.51 gives an idea of the possible stages of transformation of the crossopterygian girdles and fins into the tetrapod girdles and limbs respectively. Ichthyostega (ick-THEE-oh-STEH-guh) was likely the first true amphibian from the Late Devonian period.It was a half amphibian and lobe-finned fish. Certain crossopterygians were capable of movement from drying pools to places where water was available. The skin of the larval amphibians is ciliated. The transverse processes and zygapophyses are well-developed for the attachment of muscles. In most urodeles, the spermatozoa are transferred to the body of the female in the form of spermatophores. How did the early amphibians meet the new requirements imposed upon them as a result of change from an aquatic to terrestrial life is to be solved first. Ichthyostega possessed lungs and limbs that helped it navigate through shallow water in swamps. Although the first reptiles laid their shelled eggs on the land, they There is a general tendency towards reduction in the thickness and number of dermal elements in the skull.

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