Lungfish

Lungfish (Dipnoi) are recognized as living fossils whose evolutionary history dates back to the early Devonian (泥盆纪). Their close phylogenetic relationship with tetrapods is supported by recent studies (reviewed in Brinkmann et al., 2004). Extant lungfish include six species

Morphology The early members of the lungfish were generally long, with a thick, lumpy scale, a lobed, ankylosis, and a higher degree of cranial ossification.Visible evolutionary trends include reduced ossification, a shorter head area and a shorter body, and a reappearance of the dorsal fin. The scales are thin and circular scales.

Lung Lungfish have a highly specialized respiratory system. They have a distinct feature that their lungs are connected to the larynx and pharynx without a trachea.The lungs of lungfish are subdivided into numerous smaller air sacs, maximizing the surface area available for gas exchange. Most extant lungfish species have two lungs, with the exception of the Australian lungfish, which only has one. The lungs of lungfish are homologous to the lungs of tetrapods. As in tetrapods and bichirs, the lungs extend from the ventral surface of the esophagus and gut.

The teeth of the lungfish are very special, showing two large, thick plates with the tip of their teeth pointing forward, and the lungfish use it to smash the crustaceans of underwater animals.

Adaptation In summer, the lungfish, when they are dry, often hide in the mud for summer sleep until the rainy season comes. This is an adaptation of the lungfish to a bad environment. This helps the lungfish to escape the dry environment and promote ethnic reproduction.

Differences Lungfish in soft tissue structure, morphological, physiological and behavioral aspects, there are many characters with modern amphibians close to and different from other living fish, such as the Americas lungfish has a double lung connected with glottis and esophagus, gills and gills vascular degeneration, heart has two Chambers, one receives blood from the lungs, arterial cone valve will blood from the lungs is separated from the blood from the gills.The mouth of a lungfish communicates with the nasal cavity, which is different from other fish.

Recently, scientists have been studying the formation of lungfish bones and found that the formation of lungfish bones is similar to that of the early human limbs. Leave the body recently is a bone, and then the two bones, there are some small branches at the top of the bone, these small branches extend outward again what we call the fins are formed, and the bones of the fin looks like human finger or toe.

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