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Evolutionary processes give rise to diversity at every level of biological organization, from kingdoms to species, and individual organisms and molecules, such as DNA and proteins. The similarities between all present day organisms imply a common ancestor from which all known species, living and extinct, have diverged.
The idea of a tree of life arose from ancient notions of a ladder-like progression from lower into higher forms of life (such as in the Great Chain of Being).Early representations of "branching" phylogenetic trees include a "paleontological chart" showing the geological relationships among plants and animals in the book Elementary Geology, by Edward Hitchcock (first edition: 1840).
In biology, phylogenetics (/ ˌ f aɪ l oʊ dʒ ə ˈ n ɛ t ɪ k s,-l ə-/) [1] [2] [3] is the study of the evolutionary history of life using genetics, which is known as phylogenetic inference. It establishes the relationship between organisms with the empirical data and observed heritable traits of DNA sequences, protein amino acid sequences ...
Most of the current species have changed in size and so adapted to the climatic changes during the last ice age (see Bergmann's Rule). The further identification of fossil specimens as part of a "chronospecies" relies on additional similarities that more strongly indicate a specific relationship with a known species.
In 1941, a committee chaired by Horace E. Wood II compiled a list of 19 "provincial ages" for North America, later called North American Land Mammal Ages (NMLAs). An example of an NMLA is the Rancholabrean, named after the Rancho La Brea fossil site. One of its characteristic fossils is the bison, which first appears in the Rancholabrean. [7]
There are numerous species of cichlids that demonstrate dramatic variations in morphology. Given the right circumstances, and enough time, evolution leads to the emergence of new species. Scientists have struggled to find a precise and all-inclusive definition of species. Ernst Mayr defined a species as a population or group of populations ...
Smilodon, the best known of the sabre-toothed cats, appears. c. 2.4 Ma – The Amazon River takes its present shape in South America. c. 2.0–1.5 Ma – The basin of the Congo River acquires its present shape. c. 1.9 Ma – Oldest known Homo erectus fossils. This species might be evolved some time before, up to c. 2 Ma ago.
They first appeared in the fossil record around 66 million years ago, soon after the Cretaceous–Paleogene extinction event that eliminated about three-quarters of plant and animal species on Earth, including most dinosaurs. [25] [26] One of the last Plesiadapiformes is Carpolestes simpsoni, having grasping digits but not forward-facing eyes ...