Anagenesis:
Most anthropologists agree that A. anamensis is the ancestor of the later species A. afarensis. It is both slightly older and slightly more ape-like.
However, Melillo and her colleagues are now questioning the standard story for how A. anamensis gave rise to A. afarensis, which is widely thought to have been our ancestor.
Many believe this happened by anagenesis. “That’s when one species is evolving and gradually wholesale turns into another species,” says Melillo. “You just see some trends in time, and all of a sudden there’s no more of the ancestral species and we only find the descendant species.” The transition from A. anamensis to A. afarensis has been “one of the strongest cases for anagenesis in the fossil record”, she says. [“We’ve finally found a skull from one of our most important ancestors,” Michael Marshall, NewScientist (7 September 2019)]
I wonder how many species which leave appreciable clues in the fossil records are not geographically dispersed, or, is there a strong link between geographical dispersion and a presence in the fossil record, or is it just the luck of the draw?
I’m thinking it depends on the ecological needs of the species. If the needs are not of an environment which results in a high percentage of fossilization, then your species may not ever be found and studied.
Take that as you may.
