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Reptiles (Late Latin for creeping or crawling) do not have an aquatic larval stage, and in this way are unlike amphibians. Most reptiles are oviparous, although several species of squamates are viviparous , as were some extinct aquatic clades [ 25 ] — the fetus develops within the mother, contained in a placenta rather than an eggshell .
Today, the 5,500 species of living synapsids, known as the mammals, include both aquatic and flying species, and the largest animal ever known to have existed (the blue whale). Humans are synapsids, as well. Most mammals are viviparous and give birth to live young rather than laying eggs with the exception being the monotremes.
Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semiaquatic life in a marine environment. Only about 100 of the 12,000 extant reptile species and subspecies are classed as marine reptiles, including marine iguanas , sea snakes , sea turtles and saltwater crocodiles .
Scientists consider the blue whale, which grows up to 110 feet (33.5 meters) long, to be the largest known animal ever to exist on the planet. But it’s possible that the 202 million-year-old ...
For instance, descendants of the first reptiles include modern reptiles, mammals and birds; the agnathans have given rise to the jawed vertebrates; the bony fishes have given rise to the land vertebrates; a group of amphibians, the labyrinthodonts, have given rise to the reptiles (traditionally including the mammal-like synapsids), which in ...
Because of overhunting, the blue whale population has dropped from what biologists estimate was 200,000 in the 1800s to approximately 20,000 today. They are listed as endangered by the IUCN. Their ...
While today's blue whale has long held the title, scientists have dug up fossils from an ancient giant that could tip the scales. ... 13 vertebrae from the whale’s backbone, four ribs and a hip ...
Unlike amphibians, reptiles do not have an aquatic larval stage. Most reptiles are oviparous, although several species of squamates are viviparous, as were some extinct aquatic clades [6] – the fetus develops within the mother, using a (non-mammalian) placenta rather than contained in an eggshell. As amniotes, reptile eggs are surrounded by ...