Develop a detailed, illustrated or illuminated overview of what paleontologists

Question

Develop a detailed, illustrated or illuminated overview of what paleontologists have discovered regarding the origin and evolutionary history of the mammalian order Cetacea (whales and dolphins). Include a phylogeny with indohyus, Pakicetus, Ambulocetus, Rhodocetus, Durodon, and the modern Odontocetes toothed whales and dolphins) Mysticetes (baleen whales). Discuss evidence from the double pulley astragalus found in Indohyus and pakicetus, that whales are descended from ancient artiodactyls(even toed ungulates) and therefore belong to the artiodactyl clade. Explain the significance of the thick, dense involucrum found in Pakicetus (a synapomorphy found in all whales). Finally, discuss the fossil evidence for the progressive reduction eventual loss of hind legs by ancestral whales as well as the isotopic evidence for the timing of the adaptive shift by ancestral whales from fresh water to marine habits.

Explanation / Answer

Answer- Order Cetacea include distinct groups of dolphins and whales. Pakicetus was the first fossil of Cetacean recovered from Pakistan in the Early Paleocene Epouch (55.8-49 million year). It was extinct groups of Amphibian its length was about the 1-2m.it shape was resembled from Land drwaling animals with 4 functionally long legs with long snout. It was carnivorous in nature. Ambulocetus was early cetacean, it has large feet for swimming adaptations and short limbs. Ambulocatus was transition fossil it represent how whales derived from land dwelling animals. they were capable for walk and also lack external ears. there is presence of long snout their skull was like hippopotamous. Indohyus is small chevrotarin like organism.it is omnivorous in nature. its was like domestic cat.bone were hippos that helps in reducing the buoyancy and helps in stay in underwater.

there are 2group of cetacean.mysticetus (baleen whales) and odontocetus (tooth whales).

Involucrum in pekicetus is associated with detecting the sounds in underwater by using skull vibration, Involucrum amplifies these soundwaves. with the help of Involucrum pekisetus able to hear the sound underwater.it indicate relationship between raoellids and the whales and by we can determine that raoellids are direct ancestor of whales.

there is also presnce of double pulley astragalus in Indohyus and Pekicetus. astragalus is ankle bone in hindlimb. double pulley gives greater flexibility to foot and also increase the springiness of of lower hindlimb.

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