. Intermediate and transitional forms: the possible morphologies of predicted common ancestors All fossilized animals found should conform to the standard phylogenetic tree. If all organisms are united by descent from a common ancestor, then there is one single true historical phylogeny for all organisms. Similarly, there is one single true historical genealogy for any individual human. It directly follows that if there is a unique universal phylogeny, then all organisms, both past and present, fit in that phylogeny uniquely. Since the standard phylogenetic tree is the best approximation of the true historical phylogeny, we expect that all fossilized animals should conform to the standard phylogenetic tree within the error of our scientific methods. Every node shared between two branches in a phylogeny or cladogram represents a predicted common ancestor; thus there are ~29 common ancestors predicted from the tree shown in Figure 1 . Our standard tree shows that the bird grouping is most closely related to the reptilian grouping,
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