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Amphibians have soft bodies with thin skins, and lack claws, defensive armour, or spines. Nevertheless, they have evolved various defence mechanisms to keep themselves alive. The first line of defence in salamanders and frogs is the mucous secretion that they produce. This keeps their skin moist and makes them slippery and difficult to grip.
The vertebral column, also known as the spinal column, spine or backbone, is the core part of the axial skeleton in vertebrate animals.The vertebral column is the defining and eponymous characteristic of the vertebrate endoskeleton, where the notochord (an elastic collagen-wrapped glycoprotein rod) found in all chordates has been replaced by a segmented series of mineralized irregular bones ...
Like Panderichthys, the humerus of Acanthostega is flattened dorso-ventrally, the intermedium terminates level with the radius, and the endoskeleton can be divided into stylopodium, zeugopodium and autopodium segments. [3] Similar to Eusthenopteron, the radials do not articulate with the radius on the distal end. [3]
The cell cycle, or cell-division cycle, is the sequential series of events that take place in a cell that causes it to divide into two daughter cells. These events include the growth of the cell, duplication of its DNA ( DNA replication ) and some of its organelles , and subsequently the partitioning of its cytoplasm, chromosomes and other ...
Scientists found that members of the new species are smaller than their offshore common bottlenose counterparts, eat different fish and have spines adapted to navigating the tight spaces of rivers ...
Early in development, deuterostome embryos undergo radial cleavage during cell division, while many protostomes (the Spiralia) undergo spiral cleavage. [143] Animals from both groups possess a complete digestive tract, but in protostomes the first opening of the embryonic gut develops into the mouth, and the anus forms secondarily.
The hemipenis is the intromittent organ of Squamata, [4] which is the second largest order of vertebrates with over 9,000 species distributed around the world. They differ from the intromittent organs of most other amniotes such as mammals, archosaurs and turtles that have a single genital tubercle, as squamates have the paired genitalia remaining separate. [5]
The largest living amphibian is the 1.8 m (5 ft 11 in) South China giant salamander (Andrias sligoi), but this is dwarfed by prehistoric temnospondyls such as Mastodonsaurus which could reach up to 6 m (20 ft) in length. The study of amphibians is called batrachology, while the study of both reptiles and amphibians is called herpetology.