A ghost lineage is a hypothesized ancestor in a species lineage that has left no fossil evidence, but can still be inferred to exist or have existed because of gaps in the fossil record or genomic evidence.
Ghost lineages and Lazarus taxon are related concepts, as both stem from gaps in the fossil record.
Name
In 1992, an article stated: "These additional entities are taxa groups that are predicted to occur by the internal branching structure of phylogenetic trees.... I refer to these as ghost lineages because they are invisible to the fossil record."
Phylogenetic trees constructed based on fossil records and Darwin's theory of evolution often give an indication that species with similar phenotypes existed, although its fossil has not been discovered.
It is important to note that ghost lineages and ghost taxa are not the same. A ghost lineage is a one direct connection between the descendant and the ancestor, whereas a ghost taxon has many split descendants.
Examples
When looking back at extinct organisms, there are some groups of organisms (or lineages) that have gaps in their fossil records. These organisms or species may be closely related to one another, but there are no traces in the fossil records or sediment beds that might shed some light on their origins. Biologists may infer the existence of ghost lineages by examining sequential
stratigraphic units in the fossil record.
Fossils can then be mapped onto
and range charts to assess which lineages are missing in the fossil record.
A classic example is the
coelacanth, a type of fish related to the
and to primitive
. Coelacanths have been around for the past 80 million years but have failed to leave any fossils. The reason for this is their environment, which is deep water near volcanic islands; therefore, these sediments are hard to get to, giving these coelacanths an 80 million year gap or ghost lineage.
Another ghost lineage was that of the
theropods, a ghost lineage now reduced considerably due to the discovery of
Tachiraptor.
Duration and diversification
The duration between distinct fossils can be measured and used to derive information about the evolutionary history of a species. A study conducted in 1998 showed that a correlation exists between the diversification of a species and the duration of its ghost lineage; namely that a shorter ghost lineage implies that there will be greater species diversification.
Genetic evidence
Genetic evidence has revealed
in many species, including modern bonobos and chimpanzees,
allopolyploid frogs, polyploid
parthenogenetic crayfish, a variety of plants, and humans.
A study comparing the genomes of 69 modern bonobos and chimpanzees found between 0.94.2% of gene flow from ancient bonobos and an archaic great ape lineage to modern bonobos, allowing researchers to reconstruct 4.8% of this ghost population's genome.
Furthermore, previous models for European ancestry suggested that European populations descended from two ancient populations, but genetic evidence now suggests that a third ghost population, the Ancient North Eurasians, has also contributed to European ancestry.
See also
