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A rectangular timetree of vertebrates Timetree-rect.png
A rectangular timetree of vertebrates
A spiral timetree Spiral timetree.jpg
A spiral timetree

A timetree is a phylogenetic tree scaled to time. [3] It shows the evolutionary relationships of a group of organisms in a temporal framework. [3]

Therefore, if living organisms are represented, the branch length between the base of the tree and all leafs (e.g., species) is identical because the same time has elapsed, although extinct organisms can be shown in a timetree. [4]

As with a phylogenetic tree, timetrees can be drawn in different shapes: rectangular, circular, [3] or even spiral. [2] The only figure in Darwin's On the Origin of Species , [5] one of the earliest printed evolutionary trees, is a hypothetical timetree. Because the fossil record has always been tightly linked to the geologic record, evolutionary trees of extinct organisms are typically illustrated as timetrees. [6]


In the past, timetrees were sometimes called "chronograms," [7] but that term has been criticized because it is imprecise, referring to any graph that shows time, and not indicating that evolutionary relationships are involved. [3] The first use of the single word "timetree," in the context of an evolutionary tree scaled to time, was in 2001. [8]

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<span class="mw-page-title-main">Clade</span> Group of a common ancestor and all descendants

A clade, also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, the equivalent Latin term cladus is sometimes used in taxonomical literature.

<span class="mw-page-title-main">Evolution</span> Change in the heritable characteristics of biological populations

In biology, evolution is the change in heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation tends to exist within any given population as a result of genetic mutation and recombination. Evolution occurs when evolutionary processes such as natural selection and genetic drift act on this variation, resulting in certain characteristics becoming more common or more rare within a population. The evolutionary pressures that determine whether a characteristic is common or rare within a population constantly change, resulting in a change in heritable characteristics arising over successive generations. It is this process of evolution that has given rise to biodiversity at every level of biological organisation, including the levels of species, individual organisms, and molecules.

<span class="mw-page-title-main">Paleontology</span> Study of life before 11,700 years ago

Paleontology, also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch. It includes the study of fossils to classify organisms and study their interactions with each other and their environments. Paleontological observations have been documented as far back as the 5th century BC. The science became established in the 18th century as a result of Georges Cuvier's work on comparative anatomy, and developed rapidly in the 19th century. The term has been used since 1822 formed from Greek παλαιός, ὄν, and λόγος.

Zoology is the branch of biology that studies the animal kingdom, including the structure, embryology, evolution, classification, habits, and distribution of all animals, both living and extinct, and how they interact with their ecosystems. The term is derived from Ancient Greek ζῷον, zōion ('animal'), and λόγος, logos.

<span class="mw-page-title-main">Phylogenetic tree</span> Branching diagram of evolutionary relationships between organisms

A phylogenetic tree is a branching diagram or a tree showing the evolutionary relationships among various biological species or other entities based upon similarities and differences in their physical or genetic characteristics. All life on Earth is part of a single phylogenetic tree, indicating common ancestry.

<span class="mw-page-title-main">Molecular clock</span> Technique to deduce the time in prehistory when two or more life forms diverged

The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleotide sequences for DNA, RNA, or amino acid sequences for proteins. The benchmarks for determining the mutation rate are often fossil or archaeological dates. The molecular clock was first tested in 1962 on the hemoglobin protein variants of various animals, and is commonly used in molecular evolution to estimate times of speciation or radiation. It is sometimes called a gene clock or an evolutionary clock.

<span class="mw-page-title-main">Evolutionary biology</span> Study of the processes that produced the diversity of life

Evolutionary biology is the subfield of biology that studies the evolutionary processes that produced the diversity of life on Earth. It is also defined as the study of the history of life forms on Earth. Evolution holds that all species are related and gradually change over generations. In a population, the genetic variations affect the phenotypes of an organism. These changes in the phenotypes will be an advantage to some organisms, which will then be passed onto their offspring. Some examples of evolution in species over many generations are the peppered moth and flightless birds. In the 1930s, the discipline of evolutionary biology emerged through what Julian Huxley called the modern synthesis of understanding, from previously unrelated fields of biological research, such as genetics and ecology, systematics, and paleontology.

<span class="mw-page-title-main">Osteostraci</span> Extinct class of jawless fishes

The class Osteostraci is an extinct taxon of bony-armored jawless fish, termed "ostracoderms", that lived in what is now North America, Europe and Russia from the Middle Silurian to Late Devonian.

<span class="mw-page-title-main">Evidence of common descent</span> Common ancestor evolutionary evidence

Evidence of common descent of living organisms has been discovered by scientists researching in a variety of disciplines over many decades, demonstrating that all life on Earth comes from a single ancestor. This forms an important part of the evidence on which evolutionary theory rests, demonstrates that evolution does occur, and illustrates the processes that created Earth's biodiversity. It supports the modern evolutionary synthesis—the current scientific theory that explains how and why life changes over time. Evolutionary biologists document evidence of common descent, all the way back to the last universal common ancestor, by developing testable predictions, testing hypotheses, and constructing theories that illustrate and describe its causes.

The tree of life or universal tree of life is a metaphor, model and research tool used to explore the evolution of life and describe the relationships between organisms, both living and extinct, as described in a famous passage in Charles Darwin's On the Origin of Species (1859).

The affinities of all the beings of the same class have sometimes been represented by a great tree. I believe this simile largely speaks the truth.

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Terrabacteria is a taxon containing approximately two-thirds of prokaryote species, including those in the gram positive phyla as well as the phyla "Cyanobacteria", Chloroflexota, and Deinococcota.

<span class="mw-page-title-main">Ghost lineage</span> Phylogenetic lineage that is inferred to exist but has no fossil record

A ghost lineage is a hypothesized ancestor in a species lineage that has left no fossil evidence yet can be inferred to exist because of gaps in the fossil record or genomic evidence. The process of determining a ghost lineage relies on fossilized evidence before and after the hypothetical existence of the lineage and extrapolating relationships between organisms based on phylogenetic analysis. Ghost lineages assume unseen diversity in the fossil record and serve as predictions for what the fossil record could eventually yield; these hypotheses can be tested by unearthing new fossils or running phylogenetic analyses.

<span class="mw-page-title-main">TimeTree</span>

TimeTree is a free public database developed by S. Blair Hedges and Sudhir Kumar, now at Temple University, for presenting times of divergence in the tree of life.. The basic concept has been to produce and present a community consensus of the timetree of life from published studies, and allow easy access to that information on the web or mobile device. The database permits searching for average node times between two species or higher taxa, viewing a timeline from the perspective of a taxon, which shows all divergences back to the origin of life, and building a timetree of a chosen taxon or user-submitted group of taxa. TimeTree has been used in public education to conceptualize the evolution of life, such as in high school settings. David Attenborough's Emmy Award-winning film and television program Rise of Animals used Hedges and Kumar's circular timetree of life, generated from the TimeTree database, as a framework for the production. The timetree was brought to life using animated computer-generated imagery in scenes every 10 minutes during the 2-hour movie. The original development of TimeTree, by Hedges and Kumar, dates to the late 1990s, with initial support from NASA Astrobiology Institute. Since then, it has been supported by additional grants from NASA, and by NSF and NIH. The current version (v5) was released in 2022 and contains data from 4,075 studies and 137,306 species.

<span class="mw-page-title-main">Hydrobacteria</span>

Hydrobacteria is a taxon containing approximately one-third of prokaryote species, mostly gram-negative bacteria and their relatives. It was found to be the closest relative of an even larger group of Bacteria, Terrabacteria, which are mostly gram positive bacteria. The name Hydrobacteria refers to the moist environment inferred for the common ancestor of those species. In contrast, species of Terrabacteria possess adaptations for life on land.

<span class="mw-page-title-main">Outline of evolution</span>

The following outline is provided as an overview of and topical guide to evolution:

<span class="mw-page-title-main">Reticulate evolution</span> Merging of lineages

Reticulate evolution, or network evolution is the origination of a lineage through the partial merging of two ancestor lineages, leading to relationships better described by a phylogenetic network than a bifurcating tree. Reticulate patterns can be found in the phylogenetic reconstructions of biodiversity lineages obtained by comparing the characteristics of organisms. Reticulation processes can potentially be convergent and divergent at the same time. Reticulate evolution indicates the lack of independence between two evolutionary lineages. Reticulation affects survival, fitness and speciation rates of species. 

<span class="mw-page-title-main">Stephen Blair Hedges</span> Professor of evolutionary biology

Stephen Blair Hedges is Laura H. Carnell Professor of Science and director of the Center for Biodiversity at Temple University where he researches the tree of life and leads conservation efforts in Haiti and elsewhere. He co-founded Haiti National Trust.

Triumph of the Vertebrates is a 2013 British documentary film by David Attenborough. It is about the evolution of vertebrates. The first part is From the Seas to the Skies, while the second part is Dawn of the Mammals. The film uses a circular timetree of life generated by scientists S. Blair Hedges and Sudhir Kumar, from their TimeTree database, as a temporal framework for the production. The timetree was brought to life using animated computer-generated imagery in scenes every 10 minutes during the 2-hour movie. The circular timetree was published by Hedges and Kumar in 2009 and Hedges was consulted during production of the film.

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The Amerophidia, also known as amerophidian snakes, are a superfamily of snakes that contains two families: Aniliidae and the boa-like Tropidophiidae.

<span class="mw-page-title-main">Afrophidia</span> Clade of snakes comprising large and venomous species

Afrophidia is a clade of alethinophidian snakes comprising the groups Henophidia and Caenophidia, essentially making up the snakes people commonly associate with. The name refers to the deep split between Afrophidia and their sister taxon, Amerophidia, which originated in South American origin, and the afrophidians was recently hypothesized to represent a vicariant event of the breakup of Gondwanan South America and Africa.


  1. Hedges SB (2009). Vertebrates (Vertebrata). in The Timetree of Life, SB Hedges and S Kumar, Eds. (New York: Oxford University Press, 2009) P. 310 ISBN   0199535035
  2. 1 2 Hedges, SB; Marin, J; Suleski, M; Paymer, M (2015). "Tree of Life Reveals Clock-Like Speciation and Diversification" (PDF). Mol. Biol. Evol. 32 (4): 835–845. doi:10.1093/molbev/msv037. PMC   4379413 . PMID   25739733.
  3. 1 2 3 4 Hedges SB; Kumar S (2009). Discovering the timetree of life. in The Timetree of Life, SB Hedges and S Kumar, Eds. (New York: Oxford University Press, 2009) P. 3-18 ISBN   0199535035
  4. Marjanović, David; Laurin, Michel (2014-07-04). "An updated paleontological timetree of lissamphibians, with comments on the anatomy of Jurassic crown-group salamanders (Urodela)". Historical Biology. 26 (4): 535–550. doi:10.1080/08912963.2013.797972. ISSN   0891-2963. S2CID   84581331.
  5. Darwin C (1859). On the origin of species by means of natural selection. (London: John Murray).
  6. Benton MJ (2014). Vertebrate paleontology. Oxford, UK: Wiley-Blackwell. ISBN   978-111840755-4
  7. Wikström, Niklas; Savolainen, Vincent; Chase, Mark W. (2001-11-07). "Evolution of the angiosperms: calibrating the family tree". Proceedings of the Royal Society of London B: Biological Sciences. 268 (1482): 2211–2220. doi:10.1098/rspb.2001.1782. ISSN   0962-8452. PMC   1088868 . PMID   11674868.
  8. Hedges SB (2001). Molecular evidence for the early history of living vertebrates. Pp. 119-134 in P. E. Ahlberg (Ed.) Major events in early vertebrate evolution: palaeontology, phylogeny, genetics and development. London: Taylor and Francis. doi : 10.1201/b12434