Monophyly - Wikipedia
What is the Difference Between Monophyletic vs Paraphyletic vs Polyphyletic. Explore Evolution's inaccurate diagram of polyphyletic relationships Therefore, in this diagram, A = monophyletic, B = paraphyletic, and C = polyphyletic. Phylogenetic tree with examples of monophyletic groups or clades circled. . the relationships among taxa, many previously paraphyletic or polyphyletic groups.
Gordon and Olson's point is far narrower than Explore Evolution presents it, and is marred by the authors' inexperience with the field. Even if the problems raised were valid when the paper was written, substantial new material has been found which clarifies many of the issues, and which has spawned new research.
Explore Evolution introduces this sidebar with a blatant error: Scientists have long thought that amphibians were a transitional form between aquatic and land-dwelling life forms. Because amphibians can live in both the water and on land.
Yet, the fossil record has revealed at least two problems with this idea. Explore Evolutionp. Fossil stem groups are very problematic for Linnaean ranks such as "class. May be reproduced freely for nonprofit educational purposes.
Monophyletic vs. Paraphyletic - What's the difference? | Ask Difference
Tetrapod crown groups with some fossil stem groups added, with an attempt made to map the Linnaean classes onto the stem groups. As discussed above, this use of the term is hopelessly mired in a way of categorizing life that does not incorporate evolutionary thinking, and has been rejected by biologists precisely because of its ambiguity.
For more on this shift in the way groups are named, see Appendix 2 and the figure at right. A traditional Linnaean classification would treat all the species in the area shaded pink as amphibians, while a modern classifications regard the amphibians as the major lineage branching off at the base of the phylogeny in the figure, and the species below that branch are regarded as "stem tetrapods," neither amphibians, reptiles, nor mammals. Similarly, the species before the split between reptiles and mammals are neither mammals nor reptiles, and are no longer referred to as "mammal-like reptiles," despite the use of that term in Explore Evolution.
This shift in terminology invalidates the first sentence of the sidebar since the transitional form would not have been an amphibian, but a stem tetrapod from before the main split shown in the figure above. This also helps clarify the first supposed problem raised by Explore Evolution. The authors cite a paper by Gordon and Olsen authors who are not phylogeneticists and used terminology vaguely.
When they make comments like, "no fossils are known that relate directly to the vertebrate transitions to land.
The tetrapods, however, share many traits with those fish, and treating these groups as totally separate is an inaccurate holdover from non-evolutionary classification schemes. Tetrapods are members of the same lineage as those fish, making the distinction Gordon and Olsen draw very ambiguous. The book with the paper by Gordon and Olsen was published inwith Everett Olson dying inmeaning these chapters were written well over 15 years ago. Paleontologists these days do not speak in terms of direct ancestors — i.
There are 2 problems with such a claim: We are more likely to find something like an 'aunt' or 'cousin' as opposed to a 'parent,' 'child' or 'grandparent'. In other words, paleontologists do not claim to find direct ancestors, but instead find what are referred to as collateral ancestors or sister groups.
Even if the common ancestor were included in the definition, Taxa C, D, F, and G would need to be included to make the group monophyletic.
With the advent of new methods in systematics, particularly methods that use DNA sequences to determine the relationships among taxa, many previously paraphyletic or polyphyletic groups have been reorganized or dissolved so that scientific classifications follow the principle of monophyly.
Outside of a historical context, is there any reason to continue to recognize or utilize groups that are paraphyletic or polyphyletic? For example, living land plant diversity is typically divided into four major groups in introductory biology or botany courses: Two of these groups, the bryophytes and ferns and fern allies, are paraphyletic.
Living gymnosperms are also traditionally considered paraphyletic, although results from molecular systematic studies have more recently suggested that living gymnosperms form a monophyletic group.Ch. 23 what types of groups can we form
Nevertheless, these four categories are convenient units to compare and contrast broad structural and life history features and trends in living land plants. The four major groups of land plants typically used to teach plant diversity at the introductory level.
The images show examples of plants from each major group. Moss top and liverworts bottom. A fern top and lycophytes bottom. A pine top and a cycad bottom. A passionflower top and a tulip poplar flower bottom.
All images by E. Major groups of land plants by E. Polyphyletic groupings of taxa are also sometimes still recognized and utilized. For example, the algae are a polyphyletic collection of eukaryotic organisms that have chloroplasts and, typically, the ability to photosynthesize. We now know that several unrelated groups of algae gained their chloroplasts when their distinct ancestors independently engulfed unicellular, photosynthetic organisms, in an evolutionary process involving endosymbiosis.
The three types of algae illustrated below are from unrelated groups that gained their chloroplasts independently. Examples of algae from three unrelated groups, each of which inherited its chloroplast from a distinct ancestor. This alga inherited its chloroplast from an ancestor that engulfed a cyanobacterium. This alga inherited its chloroplast from an ancestor that engulfed a unicellular red alga. This alga inherited its chloroplast from an ancestor that engulfed a unicellular green alga.
Fossils, Crown Groups, and Stem Groups Most phylogenetic analyses conducted by biologists exclusively feature modern extant species as terminal taxa. Adding fossil taxa to these analyses can have variable effects.
Polyphyletic vs. Monophyletic
In some cases, the fossil taxa will nest among the extant taxa; in fact, some fossil taxa are more closely related to a living species than the living species is to its closest extant relative. For example, all dinosaurs are more closely related to modern birds than birds are to their closest living relatives, the crocodiles!
In other cases, the fossil taxon will be located in a position basal to all of its living relatives. Crown groups and stem groups are illustrated on the tree below. In phylogenetic terminology, a crown group is a clade defined by extant species. It consists of the most recent shared common ancestor of all extant members of a clade, as well as all of the descendants of that common ancestor, whether they are still living or are extinct.
So, it is possible for fossil species to be members of a crown group.
A stem group is more closely related to its corresponding crown group than to the extant sister clade of the crown group. Example of a hypothetical phylogenetic tree with both crown group clades green and stem groups yellow.
All three of these great ape species are extant and belong to the crown group Hominidae, the great apes. Phylogenetic tree depicting the relationships between a gorilla, a chimpanzee, and a human Mary Anning; image public domain [ link ]. Does this mean that we evolved from chimpanzees?
Rather than evolving directly from chimps, we instead share a common ancestral species with chimps that probably lived around 7 million years ago it is represented by the node that connects the chimp and Mary Anning in the phylogenetic tree above. Our immediate evolutionary ancestor was a human species i. If that extinct species of human were still alive today, we would recognize it as our closest living relative, not the chimpanzee.