A transitional fossil is a fossilized organism that shows traits typical of both an ancestral group and its descendant group, representing an intermediate form in the evolutionary transition between two major lineages. These fossils help illustrate how major groups are related and how certain features evolved over time. Key points
- Definition: A fossil with characteristics linking an ancestral form to a later, derived form.
- Purpose: Provides evidence for evolutionary change and the continuum of variation across lineages.
- Common examples: Archaeopteryx (dinosaurs to birds), early tetrapods showing limb and neck features bridging fish and land-dwelling vertebrates, and various early mammal-like reptiles showing traits of both groups.
- Caution about ancestry: A transitional fossil is not necessarily a direct ancestor of a later species; it is a snapshot within a continuum that helps model evolutionary relationships.
- Concept origin: The idea underpins Darwinian evolution and the interpretation of the fossil record as a mosaic of gradual changes rather than a set of completely distinct, abrupt jumps.
If you’d like, I can pull together a few well-supported examples with brief descriptions of the key features that mark their transitional status.
