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Terrestrial Vertebrates

Stegocephalians: Tetrapods and other digit-bearing vertebrates

Michel Laurin
The Devonian terrestrial choanates Acanthostega and Ichthyostega
taxon links [down<--]Sarcopterygii [up-->]Amniota extinct icon extinct icon [up-->]Solenodonsaurus [up-->]Living Amphibians extinct icon Monophyly Uncertain extinct icon extinct icon extinct icon extinct icon extinct icon extinct icon [up-->]Seymouriamorpha extinct icon extinct icon extinct icon extinct icon [up-->]Temnospondyli extinct icon extinct icon [up-->]Baphetidae extinct icon [up-->]Crassigyrinus extinct icon extinct icon extinct icon [up-->]Ichthyostega extinct icon [up-->]Acanthostega extinct icon extinct icon extinct icon Interpreting the tree
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Modified from Carroll (1995), Laurin and Reisz (1997), and Laurin (1998a-c). The position of Whatcheeria follows Lombard and Bolt (1995). The position of the poorly known Devonian taxa (those in which the presence of digits is uncertain: Elginerpeton, Metaxygnathus, Ventastega, and Hynerpeton) follows Ahlberg (1998). Temnospondyls are often thought to be early amphibians. However, notice that in this phylogeny, they are not closely related to lissamphibians.

Containing group: Sarcopterygii


This page discusses terrestrial vertebrates and other vertebrates that bear limbs with digits rather than fins. The muscular limb characteristic of this clade generally has well-defined joints and digits (fingers and toes) and is called a chiridium. This group includes about 21100 extant species and a probably much greater number of extinct species. Tetrapods are only one of the several groups of chiridium-bearing vertebrates (see the section on classification below).

Terrestrial vertebrates have a worldwide distribution. The earliest members of this group were moderately large (1-2.5 m body length). The oldest known skeletal remains of terrestrial vertebrates were found in the Upper Devonian of East Greenland (Clack, 1994). The presence of Lower to Middle Devonian trackways in Australia has led to suggestions that this group may have originated in the Lower Devonian, at least 400 million years ago (Warren et al., 1986), but digits are not visible in these impressions, so these trackways may have been left by other sarcopterygians.

The largest group of terrestrial vertebrates is Tetrapoda (see the section "Classification of Terrestrial Vertebrates", below). Tetrapoda means "four feet", and the group was so-named as its members primitively had four limbs, as opposed to fins. This taxon includes about 3000 extant species of amphibians (frogs, salamanders, and caecilians) and approximately 18100 extant species of amniotes (mammals, reptiles, and birds). The number of extinct species of tetrapods is of course unknown, but about half of the currently known species of tetrapods are extinct (Carroll, 1988).

Tetrapods originated no later than the Mississippian (about 350 million years ago), the period from which the oldest known relatives of living amphibians are known. Relatives of amniotes must have been present at that time, but they have not been found so far. The fossil previously reported (Smithson et al., 1994; Carroll, 1995) as an early Mississippian amniote or anthracosaur (Westlothiana) is probably either a stem-tetrapod or an early amphibian (Laurin, 1998a). Stegocephalians (see section on classification below for a definition of this group) originated no later than the Upper Devonian.

Tetrapods range from 9.8 mm (in the frog Psyllophryne didactyla) to 30 m (in the blue whale) in overall length. They have a worldwide distribution and inhabit all major habitats. Most are terrestrial, but several have returned to the aquatic environment in which our distant ancestors lived. Aquatic tetrapods include various salamanders (sirenids, cryptobranchids, proteids, etc.), frogs (pipids), some caecilians (typhlonectids), leatherback turtles, sea snakes, pinnipeds (seals and walruses), and whales. Some tetrapods are capable of flight (birds and bats), while others glide, such as flying squirrels, dermopterans (sometimes called "flying lemurs", even though they are not primates), and the flying dragons (Draco volans).

The page Life History of stegocephalians contains information on this complex topic.

The main breathing organ of most stegocephalians is the lung, but other respiratory organs exist in many groups. More detail is available on the Breathing in stegocephalians page.

Many stegocephalians have a tympanum for hearing high-frequence, air-borne sounds, and a lateral-line organ is found in many aquatic amphibians. For more information, see the Hearing in stegocephalians page.


Stegocephalians have an extensive fossil record (Carroll, 1988). Phylogenetic studies have revealed several derived characteristics (synapomorphies) of stegocephalians:

Loss of several cranial bones.
In panderichthyids (the group of sarcopterygians most closely related to stegocephalians), the skull was rigidly linked to the shoulder girdle by several bones that disappeared early in the evolution of terrestrial vertebrates. The loss of these bones also allowed the appearance of a mobile neck that allows the head to be moved relative to the trunk. This decoupling allows the head to remain relatively stable while walking.
Loss of the opercular bones that cover the gill chamber in bony fishes.
The operculum was no longer needed in early choanates because they had lost the internal gills of their early ancestors. However, the operculum may have disappeared before the internal gills (Coates and Clack, 1991).
A reduction of the notochord and a rigid spine.
The vertebral centra of osteolepiforms are thin and surround the notochord (a rigid rod present in all chordates and that persists in man as the intervertebral disks) without constricting it greatly. In stegocephalians, the centra are thick and they constrict the notochord. Special articulatory surfaces (the zygapophyses) link the neural arches to each other.
A shorter notochord that does not extend into the braincase.
The notochord of osteolepiforms extended up to the vicinity of the pituitary.
Four muscular limbs with discrete digits (fingers and toes).
Osteolepiforms had fleshy fins with elements homologous to the humerus, radius, ulna, intermedium, ulnare, femur, tibia, fibula, and fibulare, but the homology of more distal limb elements is uncertain, and no digits were present.
A sacral rib connecting the axial skeleton (the spine) to the pelvic girdle (the hip).
This allows the weight of the body of tetrapods to be transmitted to the hind limb. There was no bony connection between the pelvic girdle of osteolepiforms and their axial skeleton.
The loss of dermal fin rays (the modified scales that support the fins).
This simply represents the elimination of a structure that was no longer needed and may even have been harmful on land.

These characters did not appear simultaneously and suddenly. The oldest known stegocephalians, such as Ichthyostega and Acanthostega, possess intermediate conditions for some of these characters and lack others. For instance, Ichthyostega retained a subopercular, a bone that was part of the opercular complex that covered the gill chamber of osteolepiforms. Acanthostega retained an anocleithrum, which is one of the elements that linked the shoulder girdle to the skull in osteolepiforms (Coates and Clack, 1991). The notochord of Ichthyostega and Acanthostega extended deeply into the braincase, and most of its caudal vertebrae lacked zygapophyses (Jarvik, 1952). The connection between the sacral rib and the pelvic girdle of Acanthostega was still poorly defined. Finally, both Ichthyostega and Acanthostega retain lepidotrichia in the tail, indicating that these taxa still had a caudal fin.

The previous list includes only skeletal characters because all the earliest groups of stegocephalians are extinct, and soft anatomical characters can only be studied in extant taxa. The following characters are found in tetrapods, but not in other extant vertebrates:

A layer of dead, horny cells that reduces evaporative water loss.
This layer is present in amniotes and in most lissamphibians.
A well-developed muscular tongue with glands.
However, some lissamphibians have only a primary tongue, like fishes. A primary tongue is simply a fleshy fold on the floor of the mouth that lacks intrinsic muscles and with limited mobility.
A parathyroid gland involved in controlling the level of calcium in the blood.
A Harderian gland located anterior to the eye.
This gland secretes an oily liquid that lubricates the eye.
A vomeronasal (Jacobson's) organ.
This olfactory organ is located in the palate and is probably used to smell the food in the mouth.
The loss of the internal gills.
The external gills present in many aquatic and larval lissamphibians are new structures and are not homologous with the internal gills of fishes.

It is difficult to determine exactly when these characters appeared because they are not preserved in fossils, except for indirect clues about the internal gills, and the closest known relatives of tetrapods are extinct. However, these characters are not found in lungfishes (the closest extant relatives of tetrapods). Acanthostega, a Devonian stegocephalian, still had internal gills (Coates and Clack, 1991), but no other stegocephalian is known to have had them. Therefore, internal gills were probably lost early in the evolution of stegocephalians, in the Devonian or the Mississippian (about 360 million years ago), and no tetrapod ever had internal gills.

Classification of Terrestrial Vertebrates

In the past, most terrestrial choanates were included in Tetrapoda (Gaffney, 1979). Recently, Tetrapoda was formally defined as a crown-group (Gauthier et al., 1989). A crown-group is a clade that includes the last common ancestor of two or more extant taxa, and all its descendants. In this case, Tetrapoda was defined as the clade that includes the last common ancestor of lissamphibians and amniotes, and all its descendants. 

According to Gauthier et al. (1989), Tetrapoda included most known fossil terrestrial vertebrates because temnospondyls were thought to be the stem-group of amphibians, whereas embolomeres, gephyrostegids, and seymouriamorphs were thought to be more closely related to amniotes than to lissamphibians. Therefore, only a few very early terrestrial vertebrates, such as Ichthyostega and Acanthostega, were excluded from Tetrapoda.

The choanate phylogeny presented here suggests that temnospondyls, embolomeres, gephyrostegids, and seymouriamorphs are not part of the crown-group. If it is accurate, these taxa are not tetrapods and the origin of the "tetrapod limb" predates the origin of Tetrapoda. In the first versions of this page, all sarcopterygians bearing digits were simply called terrestrial vertebrates because no formal phylogenetic taxonomy of this whole clade had been proposed. Such a taxonomy was recently published (Laurin, 1998a). The taxon Stegocephali (that included for a long time all the vertebrates bearing a chiridium, except for lissamphibians and amniotes) was defined as all choanates more closely related to Temnospondyli than to Panderichthys (the closest relative of tetrapods known to have retained paired fins). Therefore, Stegocephali includes all taxa that bear digits, and a few (Elginerpeton, Metaxygnathus, Ventastega, and Hynerpeton) that may retain paired fins. Contrary to the old usage of this term, Stegocephali now refers to a clade. The term stegocephalian will be used below because it does not convey the hypothetical and probably somewhat erroneous interpretation that all digit-bearing vertebrates are terrestrial. As explained below, the earliest members of that clade were probably primitively aquatic.

Note about the node marked Amphibia: Others restrict the name Amphibia to descendents of the most recent common ancestor of extant amphibians (the terminal taxon Living Amphibians in this tree). The author prefers the usage indicated in the tree above, and the definition of Amphibia as all tetrapods more closely related to extant amphibians than to amniotes has historical precedence (Laurin, 1998a), but the second usage has been fairly widespread and cannot be ignored. In this page, the term Amphibia always refers to the node indicated in the tree above, and extant amphibians are referred to as lissamphibians.

Note about the node marked Tetrapoda: Others expand the use of this name to include all vertebrates that possess limbs with digits (Laurin and Anderson, 2004). However, in this page, Tetrapoda always refers to the node indicated in the tree above.

Discussion of Phylogenetic Relationships

The phylogeny of stegocephalians is controversial. All systematists agree that extant amphibians form a monophyletic group (Lissamphibia) that is closely related to amniotes, but the origin of lissamphibians and amniotes is controversial. Laurin and Reisz (1997, 1999), Laurin (1998a, b), and Vallin and Laurin (2004) suggest that lepospondyls are the stem-group of amphibians, and that diadectomorphs are more closely related to amniotes than to lissamphibians. Consequently, many groups of Paleozoic stegocephalians, such as temnospondyls and seymouriamorphs, are not closely related to amniotes or to lissamphibians:

     ====================== Ichthyostega
| =================== Loxommatidae
| |
| | ================ Temnospondyli
| | |
| | | ============= Embolomeri
| | | |
=====| | | | ========== Seymouriamorpha
===| | | |
===| | | ==== Lissamphibia (frogs, salamanders, and caecilians)
===| | ===|
===| | |||| Lepospondyli
| ==== Diadectomorpha
==== Amniota (mammals, reptiles, and birds)

However, most early studies and a few recent ones have suggested that lissamphibians are derived from temnospondyls, and that diadectomorphs, seymouriamorphs, and embolomeres are more closely related to amniotes than to lissamphibians (Bolt, 1969; Gaffney, 1979; Gauthier et al., 1988, 1989; Milner, 1988, 1993; Panchen and Smithson, 1988; Trueb and Cloutier, 1991; Lombard and Sumida, 1992; Ruta et al., 2003a, b). Lepospondyls have often been viewed as a paraphyletic group that included early relatives of temnospondyls and lissamphibians. Therefore, most known stegocephalians were viewed as related to either lissamphibians or amniotes. Only Ichthyostega and other Devonian taxa (Acanthostega, Tulerpeton) were not believed to be on one of these two main evolutionary lineages:

     =================== Ichthyostega
| ========== Lissamphibia (frogs, salamanders, and caecilians)
| ===|
| ===| |||||||||| Temnospondyli
| | |
| | ||||||||||||| Lepospondyli
| |
=====| | ============= Loxommatidae
===| |
| | ========== Embolomeri
| | |
===| | ======= Seymouriamorpha
===| |
===| ==== Diadectomorpha
==== Amniota (mammals, reptiles, and birds)

Additional discussion and more detailed phylogenies can be found on the Phylogeny of stegocephalians page.

Origin of Stegocephalians

Several scenarios have been proposed to explain the origin of the chiridium and why vertebrates ventured onto dry land. A theory found in most popular books is that the arid climate that was once thought to have prevailed in the Devonian had forced our sarcopterygian ancestors to crawl out of seasonally drying ponds to reach larger, deeper bodies of water (Romer, 1933). However, a problem with this scenario is that the Devonian is no longer viewed as having been seasonally dry. Furthermore, recent studies on functional morphology suggest that the limbs may have evolved to allow our early ancestors to walk at the bottom of shallow ponds or swamps (Edwards, 1989). Discovery of fairly complete specimens of the Devonian choanate Acanthostega (Coates and Clack, 1990) confirms that its limbs were poorly suited to walk on dry land (Zimmer, 1995). The inferred presence of internal gills in Acanthostega also confirms that this animal was still mainly aquatic (Coates and Clack, 1991). The transition from the aquatic to the terrestrial environment appears to have taken longer than previously thought.

Early Evolution of the Limbs

The presence of five fingers and toes has generally been believed to be primitive for tetrapods and to have been the highest number of digits that our early ancestors had. Five digits were probably present in the earliest tetrapods, but not in the earliest stegocephalians. Recent discoveries have demonstrated that the earliest stegocephalians had more digits; Acanthostega had eight fingers, Ichthyostega had seven toes, and Tulerpeton had six fingers (Lebedev, 1986; Gould, 1991). These "extra" digits were quickly lost, however, because no post-Devonian stegocephalian is known to have had more than five digits.

Coates (1991, 1996) suggested that the pentadactyl condition arose twice (at least in the fore limb) because in his proposed phylogenies, the Devonian polydactylous stegocephalian Tulerpeton was believed to be more closely related to amniotes than to lissamphibians. Therefore, he argued that the reduction from a polydactyl to a pentadactyl condition occurred convergently in anthracosaurs (amniotes and their extinct relatives) and in amphibians (although the pentadactyl condition in amphibians is only know from a few specimens; most lissamphibians have only four digits in the manus). However, reanalysis of these data, and incorporation of Tulerpeton into a data matrix that incorporates more taxa suggests that the pentadactyl condition appeared only once, and well before the divergence between amphibians and anthracosaurs (Laurin, 1998c). This conclusion results from the placement of Tulerpeton in a more basal position in the phylogeny, outside the clade that includes all post-Devonian (and all pentadactyl) taxa.

Four Devonian taxa tentatively included in the tree presented above are known from fragmentary remains. The fragmentary nature of the remains of these genera precludes a confident assessment of their affinities, although Coates (1996) and Ahlberg (1998) have suggested that they are more closely related to tetrapods than to panderichthyids (the closest known relatives of tetrapods known to have retained paired fins). These problematic taxa include Elginerpeton (Ahlberg, 1995), Ventastega (Ahlberg et al., 1994), Metaxygnathus (Campbell and Bell, 1977), and Hynerpeton (Daeschler et al., 1994). Their appendicular skeleton is poorly (or not) known, so they may have retained fins. Only further discoveries of more complete specimens will solve this question.


Ahlberg P. E. 1995. Elginerpeton pancheni and the earliest tetrapod clade. Nature 373: 420-425.

Ahlberg P. E. 1998. Postcranial stem tetrapod remains from the Devonian of Scat Craig, Morayshire, Scotland. Zoological Journal of the Linnean Society 122: 99-141.

Ahlberg P. E., E. Luksevics, & O. Lebedev. 1994. The first tetrapod finds from the Devonian (Upper Famennian) of Latvia. Philosophical Transactions of the Royal Society B 343: 303-328.

Bolt, J. R. 1969. Lissamphibian Origins: Possible Protolissamphibian from the Lower Permian of Oklahoma. Science 166: 888-891.

Campbell K. S. W. & M. W. Bell. 1977. A primitive amphibian from the Late Devonian of New South Wales. Alcheringa 1: 369381.

Carroll, R. L. 1988. Vertebrate Paleontology and Evolution. New York: W. H. Freeman and Company.

Carroll, R. L. 1995. Problems of the phylogenetic analysis of Paleozoic choanates. Bulletin du Muséum national d'Histoire naturelle de Paris 4ème série 17: 389-445.

Clack, J. A. 1994. Earliest known tetrapod braincase and the evolution of the stapes and fenestra ovalis. Nature 369: 392-394.

Coates M. 1991. New palaeontological contributions to limb ontogeny and phylogeny. In: J. R. Hinchcliffe (ed.) Developmental Patterning of the Vertebrate Limb 325-337. New York: Plenum Press.

Coates M. I. 1996. The Devonian tetrapod Acanthostega gunnari Jarvik: postcranial anatomy, basal tetrapod interrelationships and patterns of skeletal evolution. Transactions of the Royal Society of Edinburgh 87: 363-421.

Coates, M. I. & J. A. Clack. 1990. Polydactyly in the earliest known tetrapod limbs. Nature 347: 66-69.

Coates, M. I. & J. A. Clack. 1991. Fish-like gills and breathing in the earliest known tetrapod. Nature 352: 234-236.

Daeschler E. B., N. H. Shubin, K. S. Thomson, & W. W. Amaral. 1994. A Devonian tetrapod from North America. Science 265: 639-642.

Edwards, J. 1989. Two perspectives on the evolution of the tetrapod limb. The American Zoologist 29: 235-254.

Gaffney, E. S. 1979. Tetrapod monophyly: a phylogenetic analysis. Bulletin of the Carnegie Museum of Natural History 13: 92-105.

Gauthier, J., A. G. Kluge, & T. Rowe. 1988. The early evolution of the Amniota. In M. J. Benton (ed.) The phylogeny and classification of the tetrapods, Volume 1: amphibians, reptiles, birds: 103-155. Oxford: Clarendon Press.

Gauthier, J., D. C. Cannatella, K. De Queiroz, A. G. Kluge, & T. Rowe. 1989. Tetrapod phylogeny. In B. Fernholm, K. Bremer, and H. Jornvall (eds.) The Hierarchy of Life: 337-353. New York: Elsevier Science Publishers B. V. (Biomedical Division).

Gould, S. J. Eight (or fewer) little piggies. Natural History, January 1991, 22-29.

Jarvik, E. 1952. On the fish-like tail in the ichthyostegid stegocephalians with descriptions of a new stegocephalian and a new crossopterygian from the Upper Devonian of East Greenland. Meddelelser om Grønland 114: 1-90.

Laurin M. 1998a. The importance of global parsimony and historical bias in understanding tetrapod evolution. Part I-systematics, middle ear evolution, and jaw suspension. Annales des Sciences Naturelles, Zoologie, Paris, 13e Série 19: 1-42.

Laurin M. 1998b. The importance of global parsimony and historical bias in understanding tetrapod evolution. Part II-vertebral centrum, costal ventilation, and paedomorphosis. Annales des Sciences Naturelles, Zoologie, Paris, 13e Série 19: 99-114.

Laurin M. 1998c. A reevaluation of the origin of pentadactyly. Evolution 52: 1476-1482.

Laurin M. & J. S. Anderson. 2004. Meaning of the name Tetrapoda in the scientific literature: an exchange. Systematic Biology 53: 68-80.

Laurin, M. & R. R. Reisz. 1997. A new perspective on tetrapod phylogeny. In S. Sumida and K. Martin (eds.) Amniotes Origins: Completing the Transition to Land: 9-59. London: Academic Press.

Laurin M. & R. R. Reisz. 1999. A new study of Solenodonsaurus janenschi, and a reconsideration of amniote origins and stegocephalian evolution. Canadian Journal of Earth Sciences 36: 1239-1255.

Lebedev, O. A. 1986. The first record of a Devonian tetrapod in the USSR. Doklady-Earth science sections 278: 220-222.

Lombard, R. E. & J. R. Bolt. 1995. A new primitive tetrapod, Whatcheeria deltae, from the Lower Carboniferous of Iowa. Palaeontology 38: 471-494.

Lombard, R. E. & S. S. Sumida. 1992. Recent progress in understanding early tetrapods. The American Zoologist 32: 609-622.

Milner, A. R. 1988. The relationships and origin of living amphibians. In M. J. Benton (ed.) The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds: 59-102. Oxford: Clarendon Press.

Milner, A. R. 1993. The Paleozoic relatives of lissamphibians. Herpetological Monographs 7: 8-27.

Nussbaum, R. A. 1977. Rhinatrematidae: A new family of caecilians (Amphibia: Gymnophiona). Occasional papers of the Museum of Zoology, University of Michigan 682: 1-30.

Panchen, A. L. & T. R. Smithson. 1988. The relationships of the earliest tetrapods. In M. J. Benton (ed.) The Phylogeny and Classification of the Tetrapods, Volume 1: Amphibians, Reptiles, Birds: 1-32. Oxford: Clarendon Press.

Romer, A. S. 1933. Vertebrate Paleontology. 1st ed., Chicago: University of Chicago Press.

Ruta M., M. I. Coates, & D. D. L. Quicke. 2003. Early tetrapod relationships revisited. Biological Reviews of the Cambridge Philosophical Society 78: 251-345.

Ruta M., J. E. Jeffery, & M. I. Coates. 2003. A supertree of early tetrapods. Proceedings of the Royal Society of London, Series B 270: 2507-2516.

Smithson, T. R., R. L. Carroll, A. L. Panchen, & S. M. Andrews. 1994. Westlothiana lizziae from the Viséan of East Kirkton, West Lothian,Scotland, and the amniote stem. Transactions of the Royal Society of Edinburgh 84: 383-412.

Trueb, L. & R. Cloutier. 1991. A phylogenetic investigation of the inter- and intrarelationships of the Lissamphibia (Amphibia: Temnospondyli). In H.-P. Schultze and L. Trueb (eds.) Origins of the higher groups of tetrapods-Controversy and Consensus: 223-313. Ithaca: Comstock Publishing Associates.

Vallin G. & M. Laurin. 2004. Cranial morphology and affinities of Microbrachis, and a reappraisal of the phylogeny and lifestyle of the first amphibians. Journal of Vertebrate Paleontology 24: 56-72.

Warren, A., R. Jupp, & B. Bolton 1986. Earliest tetrapod trackway. Alcheringa 10: 183-186.

Zimmer, C., Coming onto the land. Discover, June 1995, 118-127.

Information on the Internet

For a general introduction to tetrapods and their close relatives, try the Introduction to the Tetrapoda (UCMP, Berkeley)
Title Illustrations
Scientific Name Acanthostega gunnari and Ichthyostega
Comments The Devonian terrestrial choanates Acanthostega (bottom) and Ichthyostega (on the shore).
Reference first published in Discover Magazine
Creator Illustration by Alfred Kamajian
Specimen Condition Fossil -- Period: Devonian
Copyright © 1995 Alfred Kamajian
About This Page

I wish to thank Mr. John Hutchinson, Ms. Patricia Lai, and Mr. Matthew Marlowe who edited this page. I am indebted to Dr. David Maddison who provided invaluable help in formatting this page, in linking it with other pages on the Tree of Life, and whose numerous suggestions improved the presentation of this page.

Michel Laurin

"Evolution et adaptations des syst?mes ost?omusculaires"
Case 7077
Universit? Paris 7
Paris 75005

Correspondence regarding this page should be directed to Michel Laurin at

Citing this page:

Laurin, Michel. 2006. Terrestrial Vertebrates. Stegocephalians: Tetrapods and other digit-bearing vertebrates. Version 17 January 2006 (tol-reviewed). http://tolweb.org/Terrestrial_Vertebrates/14952/2006.01.17 in The Tree of Life Web Project, http://tolweb.org/

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