Transitional fossil that share a more recent common ancestor with one another than they do with other groups. There are a few exceptional cases, such as some marine plankton microfossils, where the fossil record is complete enough to suggest with confidence that certain fossils represent a population that was actually ancestral to a later population of a different species. But, in general, transitional fossils are considered to have features that illustrate the transitional anatomical features of actual common ancestors of different taxa, rather than to "be" actual ancestors. "Archaeopteryx" is a genus of theropod dinosaur closely related to the birds. Since the
Specimens of Archaeopteryx Tischlinger & Unwin (2004), who reclassified it as part of the sternum, albeit minimally ossified (mostly cartilagenous). This supports the idea that the Berlin "Archaeopteryx" was not a full-grown individual at the time of its death, and instead represents an immature animal. The pelvis of the Berlin specimen was considered by Dames to be markedly different from that of the London specimen, which was a major point in favor of his assigning a new species to the Berlin "Archaeopteryx", "siemensii", after its generous donor. Other researchers, however, disputed this difference, claiming it could be entirely accounted for by deformation of