In biology, phylogenetics is the study of the evolutionary history and relationships among or within groups of organisms. These relationships are determined by phylogenetic inference methods that focus on observed heritable traits, such as DNA sequences, protein amino acid sequences, or morphology. The result of such an analysis is a phylogenetic tree—a diagram containing a hypothesis of relationships that reflects the evolutionary history of a group of organisms.
A cladogram is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to descendants, nor does it show how much they have changed, so many differing evolutionary trees can be consistent with the same cladogram. A cladogram uses lines that branch off in different directions ending at a clade, a group of organisms with a last common ancestor. There are many shapes of cladograms but they all have lines that branch off from other lines. The lines can be traced back to where they branch off. These branching off points represent a hypothetical ancestor which can be inferred to exhibit the traits shared among the terminal taxa above it. This hypothetical ancestor might then provide clues about the order of evolution of various features, adaptation, and other evolutionary narratives about ancestors. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational phylogenetics are now very commonly used in the generation of cladograms, either on their own or in combination with morphology.
In cladistics or phylogenetics, an outgroup is a more distantly related group of organisms that serves as a reference group when determining the evolutionary relationships of the ingroup, the set of organisms under study, and is distinct from sociological outgroups. The outgroup is used as a point of comparison for the ingroup and specifically allows for the phylogeny to be rooted. Because the polarity (direction) of character change can be determined only on a rooted phylogeny, the choice of outgroup is essential for understanding the evolution of traits along a phylogeny.
Gelsemiaceae is a family of flowering plants, belonging to the order Gentianales. The family contains only three genera: Gelsemium, Mostuea and Pteleocarpa. Gelsemium has three species, one native to Southeast Asia and southern China and two native to Central America, Mexico, and the southeastern United States. The eight species of Mostuea are native to tropical areas of South America, Africa, and Madagascar. The two genera were formerly classified in the family Loganiaceae. Pteleocarpa was originally placed in Boraginaceae or in its own family Pteleocarpaceae, but it is most closely related to Gelsemiaceae with which it shares significant characters.
In phylogenetics, long branch attraction (LBA) is a form of systematic error whereby distantly related lineages are incorrectly inferred to be closely related. LBA arises when the amount of molecular or morphological change accumulated within a lineage is sufficient to cause that lineage to appear similar to another long-branched lineage, solely because they have both undergone a large amount of change, rather than because they are related by descent. Such bias is more common when the overall divergence of some taxa results in long branches within a phylogeny. Long branches are often attracted to the base of a phylogenetic tree, because the lineage included to represent an outgroup is often also long-branched. The frequency of true LBA is unclear and often debated, and some authors view it as untestable and therefore irrelevant to empirical phylogenetic inference. Although often viewed as a failing of parsimony-based methodology, LBA could in principle result from a variety of scenarios and be inferred under multiple analytical paradigms.
Tetrapulmonata is a non-ranked supra-ordinal clade of arachnids. It is composed of the extant orders Uropygi, Schizomida, Amblypygi and Araneae (spiders). It is the only supra-ordinal group of arachnids that is strongly supported in molecular phylogenetic studies. Two extinct orders are also placed in this clade, Haptopoda and Uraraneida. In 2016, a newly described fossil arachnid, Idmonarachne, was also included in the Tetrapulmonata; as of March 2016 it has not been assigned to an order.
Harvestmen (Opiliones) are an order of arachnids often confused with spiders, though the two orders are not closely related. Research on harvestman phylogeny is in a state of flux. While some families are clearly monophyletic, that is share a common ancestor, others are not, and the relationships between families are often not well understood.
Three-taxon analysis is a cladistic based method of phylogenetic reconstruction. Introduced by Nelson and Platnick in 1991 to reconstruct organisms' phylogeny, this method can also be applied to biogeographic areas. It attempts to reconstruct complex phylogenetic trees by breaking the problem down into simpler chunks. Rather than try to resolve the relationships of all X taxa at once, it considers taxa 3 at a time. It is relatively easy to generate three-taxon statements (3is); that is, statements of the form "A and B are more closely related to one another than to C". Once each group of three taxa has been considered, the method constructs a tree that is consistent with as many three-item statements as possible.
Kirk J. Fitzhugh is the curator at the Natural History Museum of Los Angeles County, a position he has held since 1990. His research focuses on the systematics of polychaetes and on the philosophical foundations of evolutionary theory. Fitzhugh is a critic of DNA barcoding methods as a technical substitute for systematics. He attends Willi Hennig Society meetings where he has argued that "synapomorphy as evidence does not meet the scientific standard of independence...a particularly serious challenge to phylogenetic systematics, because it denies that the most severely tested and least disconfirmed cladogram can also maximize explanatory power." His graduate supervisor was V. A. Funk, from the U.S. National Herbarium, National Museum of Natural History, Smithsonian Institution MRC. He completed his doctoral thesis on Systematics and phylogeny of Sabellid polychaetes in 1988 while he was a research scientist at the LA County museum He married a lawyer named Nancy E. Gold in 1989.
Panorpida or Mecopterida is a proposed superorder of Endopterygota. The conjectured monophyly of the Panorpida is historically based on morphological evidence, namely the reduction or loss of the ovipositor and several internal characteristics, including a muscle connecting a pleuron and the first axillary sclerite at the base of the wing, various features of the larval maxilla and labium, and basal fusion of CuP and A1 veins in the hind wings. The monophyly of the Panorpida is supported by recent molecular data.
Gonzalo Giribet is a Spanish-American invertebrate zoologist and Alexander Agassiz Professor of zoology working on systematics and biogeography at the Museum of Comparative Zoology in Harvard University. He is a past president of the International Society for Invertebrate Morphology, of the Willi Hennig Society, and vice-president of the Sociedad Española de Malacología.
Theromaster is a genus of armoured harvestmen in the family Cladonychiidae. There are at least two described species in Theromaster, found in the eastern United States.
Travunioidea is a superfamily of armoured harvestmen in the order Opiliones. There are 4 families and more than 70 described species in Travunioidea.
Speleonychia is a genus of armoured harvestmen in the family Cladonychiidae. There is at least one described species in Speleonychia, S. sengeri. It is found in Washington state.
Joel Lester Cracraft, is an American paleontologist and ornithologist. He received a PhD in 1969 from Columbia University.
Arbasus is a genus of armoured harvestmen in the family Cladonychiidae. There is one described species in Arbasus, A. caecus. It is found in the Pyrenees of southern France.
Buemarinoa is a genus of armoured harvestmen in the family Cladonychiidae. There is one described species in Buemarinoa, B. patrizii, found in Sardinia, Italy.
Izunonychus is a genus of harvestman in the family Paranonychidae. There is one described species in Izunonychus, I. ohruii, endemic to Japan.
Kainonychus is a genus of harvestman in the family Paranonychidae. There is one described species in Kainonychus, K. akamai, endemic to Japan.
Nippononychus is a genus of harvestman in the family Paranonychidae. There is one described species in Nippononychus, N. japonicus, endemic to Japan.
