LYCOS RETRIEVER 
Cladistics: Cladograms
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Cladistics is a highly useful tool for palaeontologists. It enables them to achieve a far better understanding of the relationships between living things and how life on Earth evolved from simple beginnings. The relationship between, say, a dolphin and a weasel is not immediately clear and obvious, and Linnaean taxonomy helps very little with that. But a cladogram containing both those animals will reveal not only how they are related to each other, but ... through analysis of their shared derived traits, what their common ancestor might have been like, and what has happened to the rest of that ancestor's descendants.
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Extinct Species in Cladograms — Cladistics makes no distinction between extinct and non-extinct species,[7] and it is appropriate to include extinct species in the group of organisms being analyzed. Cladograms that are based on DNA/RNA generally do not include extinct species because DNA/RNA samples from extinct species are rare. Cladograms based on morphology, especially morphological characteristics that are preserved in fossils, are more likely to include extinct species.
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Cladistics is one way scientists classify organisms. A cladogram shows the nature of evolutionary relationships that may have occurred, similar to a family tree. You will make a cladogram in this activity.
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Cladistics can be defined as the study of the pathways of evolution. In other words, cladists are interested in such questions as: how many branches there are among a group of organisms; which branch connects to which other branch; and what is the branching sequence. A tree-like network that expresses such ancestor-descendant relationships is called a cladogram. Thus, a cladogram refers to the topology of a rooted phylogenetic tree.
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The debate over cladistics has largely been confined to seminar rooms and laboratories. Henry Gee brings it to the general public in this spirited look at how the science of palaeontology, that grand tour of what Gee calls Deep Time, is conducted. Replacing old family trees with "cladograms", Gee challenges long-accepted notions about the past (for example, the classification of Archaeopteryx, which walks like a duck and quacks like a duck but is accounted for as a dinosaur) and argues for a return to rigour in testing hypotheses. His book, although about difficult issues, is immediately accessible, and readers seeking to learn something about cladistics--which Gee believes is "a revolution in thought as profound as that of Darwinian evolution by natural selection"--are off to a fine start in these pages. --Gregory McNamee --This text refers to an out of print or unavailable edition of this title.
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One of the arguments in favor of cladistics is that it supports arbitrarily complex, arbitrarily deep trees. Especially when extinct species are considered (both known and unknown), the complexity and depth of the tree can be very large. Every single speciation event, including all the species that are now extinct, represents an additional fork on the hypothetical, complete cladogram representing the full tree of life. Fractals can be used to represent this notion of increasing detail: as a viewpoint zooms into the tree of life, the complexity remains virtually constant[28]. This great complexity of the tree, and the uncertainty associated with the complexity, are among the reasons that cladists cite for the attractiveness of cladistics over traditional taxonomy.
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Cladograms