Evolution
Hair has its origins in the common ancestor of mammals, the Synapsids, or possibly a subclade, the Sphenacodontoidea, about 310 million years ago. It is currently unknown at what stage the synapsids acquired mammalian characteristics such as body hair and mammary glands, as the fossils only rarely provide direct evidence for soft tissues. An exceptionally well-preserved skull of Estemmenosuchus, a therapsid from the Upper Permian shows smooth, hairless skin with what appears to be glandular depressions. The oldest known fossil showing unambiguous imprints of hair is the Callovian (late middle Jurassic) Castorocauda, an early mammal. The more advanced therapsids could have had a combination of naked skin, whiskers and scutes. A full pelage likely did not evolve until the therapsid-mammal transition. The more advanced, smaller therapsids could have had a combination of hair and scutes, a combination still found in some modern mammals, such as rodents and the opossum.
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Famous quotes containing the word evolution:
“The more specific idea of evolution now reached is—a change from an indefinite, incoherent homogeneity to a definite, coherent heterogeneity, accompanying the dissipation of motion and integration of matter.”
—Herbert Spencer (1820–1903)
“The more specific idea of evolution now reached is—a change from an indefinite, incoherent homogeneity to a definite, coherent heterogeneity, accompanying the dissipation of motion and integration of matter.”
—Herbert Spencer (1820–1903)
“Historians will have to face the fact that natural selection determined the evolution of cultures in the same manner as it did that of species.”
—Konrad Lorenz (1903–1989)