The Earliest Crown Mammals
The crown group mammals, sometimes called 'true mammals', are the extant mammals and their relatives back to their last common ancestor. This part of the story introduces new complications, since the crown group are the only group that still has living members, enabling both anatomical and DNA analysis:
- One has to distinguish between extinct groups and those that have living representatives.
- One often feels compelled to try to explain the evolution of features that do not appear in fossils. This endeavor often involves Molecular phylogenetics, a technique that has become popular since the mid-1980s, but is still often controversial because of its assumptions, especially about the reliability of the molecular clock.
Read more about this topic: Evolution Of Mammals
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—Henry David Thoreau (1817–1862)