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The placental lineage containing living manatees and dugongs. fossils with substantial weight-bearing limbs document earlier stages of its aquatic transition.

Geographic coexistence at a stated scale. fossils from one deposit may still represent different times or habitats.

A Cretaceous fossil hagfish preserving evidence of specialized soft-tissue anatomy, including slime-producing structures.

A specified crown group together with its stem group. fossil occurrences must be assigned at the correct level before they are used for fossil calibration.

A fossil with a combination of ancestral and derived characters informative about an evolutionary transition. It need not be the direct ancestor of a named living group.

A member of the turtle lineage, whose shell and skull underwent substantial modification. Molecular and fossil evidence support a diapsid origin, with living turtles commonly recovered as sister to archosaurs.