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Tuesday, May 12, 2009

Science Fact -- Is shark a mammal?


A Port Jackson Shark's Egg
Is shark a mammal?
Answer from WikiAnswers: They are not mammals! They are cartilaginous fish. Like most fish they breathe through gills and are cold blooded creatures.
Is shark an oviparous or viviparous animal?
Answer fom Wikipedia: It depends on the species. There are three ways in which shark pups are born.
Oviparity: Some sharks lay eggs. In most of these species, the developing embryo is protected by an egg case with the consistency of leather. Oviparous sharks include the horn shark, catshark, Port Jackson shark(As shown in the picture above), and swellshark.

Vivipaity: These sharks maintain a placental link to the developing young, more analogous to mammalian gestation than that of other fishes. Hammerheads, the requiem sharks, and smoothhounds fall into this category.
Ovoviviparity: Most sharks utilize this method. The young are nouished by the yolk of their egg and by fluids secreted by glands in the walls of the oviduct. The eggs hatch within the oviduct, and the young continue to be nourished by the remnants of the yolk and the oviduct's fluids. The whale shark is now considered to be in this category after long having been classified as oviparous.
I was really shocked when I first knew that sharks do lay eggs. I know that whale is the only mammal in the sea but I never want to know how a shark's egg looks like. =.=" After I saw the picture of the shark's egg, I was really like oh my God~ How special it is! I told Jacqueline about this and she was shocked too. After that, my niece showed me her science paper. The question asked them to classify the oviparous and viviparous animals. Her teacher's answer is viviparous and my niece's answer is wrong. But I did see a picture of shark's egg before! It means that sharks do lay eggs! Then I tried to search for information on the internet and I found the answers. Amazing huh? So keep in your mind, shark is not mammal but fish. There are three ways in which shark pups are born, depending on the species! =)

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