This website aims to list and count the known extant species of the world grouped by how they are related to one another through evolution. The Species Accounts website is a work in progress. Currently, about 11.0% of described extant species are listed and the remainder have their place held as described below in the Introduction. Contact us for more information.
Compiled by: Stephen Gene Sullivan, Ph.D., M.D.
Contributors: Christine Metlen, B.F.A. (Amphibia, Anura, Squamata, Sauria, Serpentes)
Photography: Joel Metlen, B.F.A.
Photography: Joel Metlen, B.F.A.
Web Page Design: Elizabeth Ann Sullivan, B.A., M.A.
Learn about the definitions and methods used for the Species Account website.
Go directly to the list of species organized by group.
This phylogenetic list of described extant species of the world is called SPECIES ACCOUNTS because its purpose is to list and count the number of species in each group known to be related to each other through evolution.
The definition of species used is the most liberal and relies on the species definition used by experts in the study of each taxonomic group of organisms. In birds, species are usually clearly delineated by breeding groups. In some corals, which exhibit extensive hybridization and a reticular rather than dichotomous pattern of evolution, species definition may be one of convenience. In such cases, species may have to be defined by relying on recognizable groupings of physical, functional or other traits, while realizing that species so defined may exist along a seamless cline of organisms. Species definition is particularly difficult with viruses and bacteria.
Only extant species are listed and counted; extinct species are not included.
Only described species are listed. Experts in some taxa estimate that the actual number of species existing today may in some cases be up to 1000 times as many as those described.
This is a phylogenetic list, not a classification. The names used of species, genus, family or higher grouping rely on the opinions of experts in each taxonomic group. Species are grouped, listed and counted solely on the basis of their closest relationships in evolution regardless of their formal classification. The structure of the list therefore takes the form of a family tree with each species shown in relation to its closest relatives.
Among the over 1 million described extant species the detailed relationships in evolution are seldom fully known. Several rules are therefore used in preparing this list. One would like to insure that each group of species listed was monophyletic at each level of the family tree. For a group to be monophyletic, two conditions must be met: first, all species in the group must have evolved from one single ancestor; second, all descendants of that ancestor must be represented in the group. If either criterion is not met, the group is considered a paraphyletic group.
When considering the evolutionary relationships among all known species, the second criterion is seldom met since the relationships of many species are not precisely known. For this reason this list requires that the first criteria be met, that is, that all species in a group descended from a single ancestor, but allows the possibility that other species or groups separately listed may actually belong in that group.
The most conservative opinion accepted by most experts in a given taxon is used. In this way error is minimized. A newly described species or group, if its relationships were not known, would be placed by itself at the lowest branch on the tree where knowledge of its evolutionary relationships was certain. With further knowledge this branch would be moved further up the tree to its proper place.
This convention might be summarized as ‘errors toward the base of the tree’. An example is the placement of the coelacanth, Latimeria chalumnae. Latimeria is currently placed at the base of the branch containing all the Jawed Vertebrates until such time as its position further up the tree is understood.
The position of a species or group at the base of the tree or at a ‘low branch’ does not necessarily imply early separation from other groups in evolutionary time but may mean that its relationships are not more clearly defined. An example of this is the various groups of viruses which are placed at the base of the tree.
SPECIES ACCOUNTS is a work in progress. When a species
name is not yet available, its place on the list is held in one of two
ways. In a short list, the species may be given a temporary number.
An example is the genus Theligonum which contains 3 species. Theligonum
cynocrambe is named and space is held for the other 2 as ‘Theligonum
Currently, about 11.0% of described extant species are listed and the remainder have their place held as described above. Help with this project is welcomed.
Abbreviations used: sp species (singular)
spp species (plural)
Click here to go directly to: SPECIES LISTS
Please send comments, corrections, or lists of names to be included by regular mail to: Stephen Gene Sullivan, Ph.D., M.D., 533 East 13th Street, New York, NY 10009, USA.
GLOBAL BIODIVERSITY INFORMATION FACILITY
NATIONAL CENTER FOR BIOTECHNOLOGY INFORMATION TAXONOMY BROWSER
LIST OF BACTERIAL NAMES WITH STANDING IN NOMENCLATURE
THE INTERNATIONAL PLANT NAMES INDEX
INTERNATIONAL LEGUME DATABASE & INFORMATION SERVICE
PHYLUM CTENOPHORA: LIST OF ALL VALID SPECIES NAMES
A PRELIMINARY CHECKLIST OF THE FLAT BARK BEETLES OF THE WORLD
DR. BILLIE J. SWALLA (Deuterostomia and Tunicata)
CHRIS CAMERON’S HOME PAGE (Hemichordata)
LIVINGUNDERWORLD - AMPHIBIAN INFORMATION RESOURCE
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MOLECULAR PHYLOGENY OF THE PROTOCHORDATES: CHORDATE EVOLUTION. L. Zeng and B. J. Swalla. CAN. J. ZOOL. (83): 24-33, 2005.
FISHES OF THE WORLD. Third Edition. J. S. Nelson.
John Wiley, New York, 1994.
WALKER’S MAMMALS OF THE WORLD. Sixth Edition. 2 Vols. R. M. Nowak. Johns Hopkins University Press, Baltimore, 1999.