Ghost lineage
As a ghost lineage ( German as " ghost line " ) lineages are in the paleontology and phylogeny refers not directly detected their presence in a given time period ( or stratigraphic unit ), but has been made available only indirectly. The concept and the term dates back to the paleontologist Mark Norell. For the duration of a given line is also used by "ghost range" spoken similarly. Ghost lineages are inherently problematic because they each correspond to an additional auxiliary hypothesis. Your recourse in the research, however, is inevitable in some areas. The hypothesis in the interpretation of the data is generally preferred that has less or at least shorter ghost lineages result - in practice - according to Occam's razor.
Ghost lineages arise due to a number of different methods and theoretical derivations. Most of them are based on that same problem, eg the age or relationships of a particular group of organisms, different and independent methods are used. Different age estimates are based primarily on absolute dated fossils, using the methods of molecular clock derived age estimates or from the cladistic analysis of the phylogenetic relationships of a group -developed sequences of splitting events evolutionary lineages.
Interpolations
The simplest case of the generation of ghost lineages stems directly from the incompleteness of the fossil record. If a particular taxon (one species, a genus or higher taxonomic unit ) found in a reservoir of a geological era and in another that has a differing therefrom age, the taxon must also exist in the intervening time. In paleontology, the application of this obvious principle is often referred to as "range through method ". Just a taxon can be detected in both fossil and living ( tart or even extant ). A prominent example is the coelacanth, which are only in the fossil record until the Cretaceous period and up to the present-day equivalents have a gap of more than 70 million years ago.
Phylogenetic branches
While based on interpolation ghost lineages only fill the length of life of a taxon virtually, they can also be extended over the area beyond fossil documented by the use of phylogenetic branching pattern (or cladograms ). In the extreme case, as the age groups are evaluated, of which no fossil found. The method is based on the application of Kladogrammen in the context of phylogenetic systematics or cladistics. This is based on original features, the various members of the group due to common inheritance from an ancestral species have in common ( the so-called autapomorphies ) opened up the topology and order of cladogenesis. This may be, although fossils may be used also be carried out only with living species. Since all living species have a common ancestry, new taxa can arise only by the fact that existing change their shape and characteristics and eventually split into several new taxa. Two related lines that have been created by the splitting of such a lineage, must be equal to each other necessarily old. Is now about fossils dated by the age of one of these lines is known, the other line must be at least as old. Extension of this method is naturally not possible on the oldest fossil of the oldest line addition.
Molecular Clocks
In addition to the dating of fossils the age of a lineage of which can be independently determined by the method of molecular clock. This is estimated by the difference between two DNA sequences and an average mutation rate of the age of the branching. After neutral theory of molecular evolution the sequence alteration should be proportional to the elapsed time approximately, so that knowledge of the rate of change of age would be read off directly. In practice, this method is often difficult, because the mutation rate depending on the group and sequence often varies significantly and the age of the clades is thus misjudged. The calibration of the respective molecular clocks have a reference of fossils or Tektonikereignissen is therefore complicated and has a strong influence on the length as calculated ghost lineages.
Applications
In addition to the direct estimate of the age of evolutionary lineages are ghost lineages, for example, uses this to determine the biodiversity of flora and fauna of earlier eras. This is as good fossil documented only for a handful of deposits that they could be read with some reliability directly from the Fossilberericht. If you want to find out if, for example, in a particular era the number of species increased or decreased if a particular geological event could have been related to an adaptive radiation or whether an alleged mass extinction was real or feigned only by accidents of tradition, it is necessary to reconstruct the Artbestand the corresponding epoch. To that effect the ghost lineages are included, otherwise the number of species would massively underestimated.
Problems
Since ghost lineages by definition only indirectly identified constructs are based all hypotheses that are based on their existence, in a critical way that the hypotheses underlying the design are correct. If a fossil dated wrong, a cladogram constructed incorrectly, a molecular clock calibrated wrong, are thereby extensive ghost lineages generated, which coincides ( shadowy ) existence with the use of correct methods in itself. Fossils can be dated incorrectly or, more often, poorly preserved or incomplete fossils in error or are allocated from wishful thinking to a known line. The age correctly dated and associated fossils must necessarily always the age of the lineage underestimate ( because it is not just their first representatives will have been fossilized ). On the other hand, there are serious indications that the method of molecular clock overestimated the age of lineages in most cases. In addition, this method is based on the calibration of critical branching events that dated fossil wrong both as well as could be phylogenetically misinterpreted (see ).