Evolution
Squamates are a monophyletic sister group to the tuatara. The squamates and tuatara together are a sister group to crocodiles and birds, the extant archosaurs. Squamate fossils first appear in the middle Jurassic period, but a mitochondrial phylogeny suggests they evolved in the late Permian. The evolutionary relationships within the squamates are not yet completely worked out, with the relationship of snakes to other groups being most problematic. From morphological data, iguanid lizards have been thought to have diverged from other squamates very early, but recent molecular phylogenies, both from mitochondrial and nuclear DNA, do not support this early divergence. Because snakes have faster molecular clocks than other squamates, and few early snake and snake ancestor fossils have been found, resolving the relationship between snakes and other squamate groups is difficult.
Read more about this topic: Squamata
Famous quotes containing the word evolution:
“By contrast with history, evolution is an unconscious process. Another, and perhaps a better way of putting it would be to say that evolution is a natural process, history a human one.... Insofar as we treat man as a part of nature—for instance in a biological survey of evolution—we are precisely not treating him as a historical being. As a historically developing being, he is set over against nature, both as a knower and as a doer.”
—Owen Barfield (b. 1898)
“Analyze theory-building how we will, we all must start in the middle. Our conceptual firsts are middle-sized, middle-distanced objects, and our introduction to them and to everything comes midway in the cultural evolution of the race.”
—Willard Van Orman Quine (b. 1908)
“Like Freud, Jung believes that the human mind contains archaic remnants, residues of the long history and evolution of mankind. In the unconscious, primordial “universally human images” lie dormant. Those primordial images are the most ancient, universal and “deep” thoughts of mankind. Since they embody feelings as much as thought, they are properly “thought feelings.” Where Freud postulates a mass psyche, Jung postulates a collective psyche.”
—Patrick Mullahy (b. 1912)