Did humans evolve from reptiles

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  1. Why whales are thought to have legs
    1. The physical changes of the whale over time.
    2. Jurassic period flora and fauna
    3. Forelimbs and hind limbs

Why whales are thought to have legs

The specific uses of forelimbs may be analogous if they evolved from different forelimb substructures, such as the flippers of turtles and dolphins, and the wings of birds and bats.[2] The specific uses of the forelimbs may be analogous if they evolved from different forelimb substructures, such as the flippers of turtles and dolphins, and the wings of birds and bats.[2

Musteloid carnivores that have an arboreal lifestyle usually have long, thin bones in the forelimbs, allowing them better movement and flexibility. Semi-fossorial and aquatic mustelids usually have short, stout forelimb long bones to withstand the effort of digging and swimming.[5] The forelimbs of the forelimbs are short and stout.

Tetrapods were initially understood to have first evolved five digits as an ancestral feature, which were later reduced or specialized for a number of uses. Some animals retained "primitive" forelimbs, such as pentadactyl (five-toed) reptiles and primates. This has largely been retained, but it is possible that the earliest tetrapods or "fishapods" had more than five toes. Stephen Jay Gould cast doubt on this in his 1991 essay "Eight (Or Fewer) Little Piggies."[8] In his 1991 essay "Eight (Or Fewer) Little Piggies."[8

The physical changes of the whale over time.

Female Nile crocodiles lay their eggs in a buried nest, and open it when they hear squeaks coming from it. The sex of the young depends on the temperature of the nest, not genetics.Photo by Michael NicholsSeptember 5, 2010

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The oceans, especially those that formed new, shallow inland, were teeming with abundant life. At the top of the food chain were long-necked plesiosaurs, giant marine crocodiles, sharks and rays. Fish-like ichthyosaurs, squid-like cephalopods and ammonoids with their spiral-shaped shells. Coral reefs grew in the warm waters and sponges, snails and mollusks grew without difficulty. Plankton floated free, microscopic and could make part of the ocean red.

On land, dinosaurs were literally making their mark. The herbivorous sauropod Brachiosaurus stood 16 meters tall, was about 26 meters long and weighed more than 80 tons. Diplodocus, another sauropod, was about 27 meters long. The sheer size of these dinosaurs may have deterred the Allosaurus, a hulking, carnivorous dinosaur that walked on two powerful legs, from attacking them. But Allosaurus and other fleet-footed carnivores, such as coelurosaurs, might have been successful a time or two. Other prey could be the huge armored stegosaurs.

Jurassic period flora and fauna

In fact, says Terrie Williams, "this could be a game changer in the way we think about the evolution of all marine mammals." Williams works at the University of California, Santa Cruz, and although she studies how the environment affects organisms' bodies, she was not involved in this research.

To survive in the cold oceans, mammals must have evolved ways to regulate their body temperature. Williams believes this is probably one of the clearest pieces of evidence that explains "this is how they do it."

Oxygen consumption is an indicator of how much heat cells produce. The researchers compared that rate of oxygen consumption in otters with that seen in other animals. They studied humans, elephant seals, and even Iditarod (ay-dítarod) sled dogs. (The Iditarod is a very long dog sled race in Alaska.) Sea otters don't have as much oxygen consumption.

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Sea otters don't have as much blubber or a large body as other marine mammals to survive in the frigid ocean temperatures. But their high metabolism helps them stay warm in the waves.T. WRIGHT (Image obtained under USFWS MARINE MAMMAL PERMIT NO. MA-043219 to R. DAVIS)

Forelimbs and hind limbs

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