This tree diagram shows the relationships between several groups of organisms.
The root of the current tree connects the organisms featured in this tree to their containing group and the rest of the Tree of Life. The basal branching point in the tree represents the ancestor of the other groups in the tree. This ancestor diversified over time into several descendent subgroups, which are represented as internal nodes and terminal taxa to the right.
You can click on the root to travel down the Tree of Life all the way to the root of all Life, and you can click on the names of descendent subgroups to travel up the Tree of Life all the way to individual species.close box
Phylogenetic relationships of extant taxonomic families are from Larson and Dimmick (1993). Phylogenetic positions of four extinct families (Batrachosauroididae, Karauridae, Prosirenidae and Scapherpetontidae) are unknown because fossil remains are not sufficient for a confident phylogenetic analysis (see Estes, 1981).
Salamanders are amphibians of the order Caudata (also called Urodela). This taxon includes the newts, a group of rough-skinned species in the salamander family Salamandridae. Salamanders are distinguished from other amphibians (frogs and caecilians) most obviously by the presence of a tail in all larvae, juveniles and adults, and by having limbs set at right angles to the body with forelimbs and hindlimbs of approximately equal size (except in the family Sirenidae, which lacks hindlimbs). Salamanders are distinguished from frogs and caecilians also by numerous characteristics of their skeleton and musculature (see "Characteristics of Salamanders" below).
Many salamanders have a biphasic life cycle containing an aquatic larval form with external gills, and a metamorphosed terrestrial adult form that breathes by lungs and/or through moist skin. Some species lack metamorphosis and retain a larval appearance throughout their life, whereas other species lack the aquatic larval stage and hatch on land as terrestrial forms that resemble miniature adults. The general association of lungs with terrestrial animals and gills with aquatic ones is not universally true among salamanders; terrestrial plethodontid salamanders lack lungs and breathe through the skin, whereas aquatic adult amphiumas lack gills and use lungs to breathe. Salamanders are carnivorous in the larval, juvenile and adult stages of their life cycles; they prey mainly on small arthropods.
Most salamanders are relatively small for vertebrates, usually less than 15 cm long, although the aquatic cryptobranchid salamanders of the genus Andrias may exceed 1.5 m in length.
Salamanders inhabit nearly all northern temperate regions of the world where moist and cool habitats occur. The greatest phylogenetic diversity of salamanders is in North America where representatives of 9 of the 10 extant taxonomic families occur. Lungless salamanders of the family Plethodontidae occur also in tropical areas of Central and South America. Terrestrial salamanders are usually found on the forest floor under rocks or logs, from which they emerge at night to feed. Aquatic forms live on the bottoms of streams or ponds, often under stones. Salamanders are usually seasonal in their activity and are easily found only during their active season, which differs among species.
Salamanders are unusual among animals in having very large amounts of DNA in their nuclear genomes (reviewed by Morescalchi, 1975; Larson, 1984; Raff and Kaufman, 1983:314). Genome size measured as C-value (mass of DNA in a haploid, unreplicated nucleus) ranges from approximately 15-90 pg. in salamanders (Morescalchi, 1975) and shows substantial variation within some genera, such as Plethodon; for comparison, the C-value for humans is approximately 3 pg. Much of this DNA is repetitive and may constitute retrotransposons (Marracci et al., 1996). Large genomes may limit rates of differentiation during development (Sessions and Larson, 1987).
See Duellman and Trueb (1985) for detailed coverage of the biology of salamanders, and Estes (1981) for detailed coverage of fossil salamanders. Recent reviews are available on specific aspects of salamander biology, including parental care of eggs (Nussbaum, 1985; Crump, 1995), developmental rates of eggs (Nussbaum, 1985), territoriality and aggressive behavior (Mathis et al., 1995), and mating (Halliday and Tejedo, 1995; Sullivan et al., 1995).
In addition to presence of a tail and usually two pairs of limbs of approximately equal size, salamanders are distinguished from other amphibians by a combination of several technical features of the skeleton and musculature. These include (1) absence of an otic notch and middle ear, (2) presence of a large footplate and short stylus on the columella in most taxa, (3) absence of postorbital, postparietal, tabular, supratemporal, jugal, quadratojugal (present in Karauridae), supraoccipital, basioccipital and ectopterygoid bones, (4) presence of ribs, (5) presence of true teeth on both jaws, (6) gill slits and external gills in aquatic larvae (when present), (7) origin of the adductor mandibulae internus superficialis muscle on the top and back of the skull (except Karauridae) and small size of the levator mandibulae posterior. See Duellman and Trueb (1986) for further coverage of these characters.
Salamanders comprise the order Caudata (Urodela) of the Class Amphibia, phylum Chordata. Living salamanders are divided taxonomically into ten taxonomic families based upon phylogeny and anatomical features: Ambystomatidae (mole salamanders), Amphiumidae (amphiumas), Cryptobranchidae (hellbenders), Dicamptodontidae (Pacific giant salamanders), Hynobiidae, Plethodontidae (lungless salamanders), Proteidae (mudpuppies), Rhyacotritonidae (torrent salamanders), Salamandridae (true salamanders and newts) and Sirenidae (sirens). Some extinct species known only from fossils are grouped into the families Batrachosauroididae, Karauridae, Prosirenidae and Scapherpetontidae. Each extant family of salamanders is described in more detail on further pages.
These families are grouped into four taxonomic suborders as follows: Cryptobranchoidea (Cryptobranchidae, Hynobiidae), Karauroidea (Karauridae), Salamandroidea (Ambystomatidae, Amphiumidae, Batrachosauroididae, Dicamptodontidae, Plethodontidae, Prosirenidae, Proteidae, Rhyacotritonidae, Salamandridae, Scapherpetontidae) and Sirenoidea (Sirenidae).
A few Mesozoic fossil salamanders (genera Comonecturoides, Galverpeton and Hylaeobatrachus, each containing a single species) have not been assigned to taxonomic families or suborders.
See Frost (1985), Duellman and Trueb (1986) and Duellman (1993) for further information on classification of salamanders.
Monophyly of each of the 10 extant salamander families is well established, with the exception of the Proteidae, a tentative grouping of two genera (Necturus and Proteus) that may not be closely related phylogenetically. Evidence for monophyly of the families is discussed on the separate Tree-of-Life pages devoted to each family. The phylogenetic relationships among the different families of salamanders have been very difficult to resolve (see reviews by Larson  and Larson and Dimmick ). The relationships presented here are based on an analysis of 209 phylogenetically informative characters (177 from aligned ribosomal RNA sequences, 20 from structures of the head and trunk, and 12 from anatomy of the cloaca). These relationships are partially confirmed by the mitochondrial DNA sequences of Titus and Larson (1995). Conflicting relationships are presented by Hedges and Maxson (1993) from mitochondrial DNA sequences, but resolution in that data set is poor with regard to the salamander families.
An advantage of the phylogenetic tree presented here is that it maintains monophyly of the salamanders having internal fertilization of eggs (extant families of the suborder Salamandroidea; mode of fertilization is not known for extinct salamanders of this suborder), which is strongly supported by the characters derived from cloacal anatomy (see Sever, 1991a, 1991b). Additional features of this tree that appear very well supported include (1) monophyly of the suborder Cryptobranchoidea (Cryptobranchidae plus Hynobiidae), (2) close relationship of Ambystomatidae and Dicamptodontidae as sister taxa, (3) monophyly of a group containing the Ambystomatidae, Dicamptodontidae and Salamandridae, (4) monophyly of a group containing the Ambystomatidae, Dicamptodontidae, Salamandridae and the proteid genus Necturus (position of the proteid genus Proteus is uncertain), and (5) a sister-group relationship of the Cryptobranchoidea and Salamandroidea.
Within the Salamandroidea, the Amphiumidae, Rhyacotritonidae and Plethodontidae each represent ancient phylogenetic divergences and have no close extant relatives. The weight of the phylogenetic evidence places the Amphiumidae and Plethodontidae as sister taxa, but this result is not statistically significant (see discussion by Larson  and Larson and Dimmick ). The exact placements of these three families relative to each other and to the branch containing the remaining salamandroid taxa are not well resolved and require further investigation. Because the arrangement shown here is the most parsimonious tree resulting from combined analysis of 209 molecular and morphological characters, it is recommended as the best current working hypothesis.
The phylogeny presented here indicates strongly that the salamanders that retain at least some aquatic larval characteristics throughout life (families Amphiumidae, Cryptobranchidae, Proteidae, Sirenidae and parts of the Ambystomatidae and Plethodontidae) do not form a monophyletic group. Evolutionary displacement of larval characteristics into the adult phase of the life cycle must have occurred independently numerous times in salamanders.
Crump, M. L. 1995. Parental care. Pp. 518-567 in H. Heatwole (ed.) Amphibian Biology Volume 2: Social Behavior. Surrey, Beatty and Sons. NSW, Australia.
Duellman, W. E. 1993. Amphibian Species of the World: Additions and Corrections. Univ. of Kansas Printing Service. Lawrence, KS.
Duellman, W. E. and L. Trueb. 1986. Biology of Amphibians. McGraw-Hill, New York.
Estes, R. 1981. Gymnophiona, Caudata. Handbuch der Paläoherpetologie 2:1-115.
Frost, D. R. 1985. Amphibian Species of the World. Allen Press and the Association of Systematics Collections. Lawrence, KS.
Halliday, T. R. and M. Tejedo. 1995. Intrasexual selection and alternative mating behavior. Pp. 419-468 in H. Heatwole (ed.) Amphibian Biology Volume 2: Social Behavior. Surrey, Beatty and Sons. NSW, Australia.
Hedges, S. B. and L. R. Maxson. 1993. A molecular perspective on lissamphibian phylogeny. Herpetological Monographs 7:27-42.
Larson, A. 1984. Neontological inferences of evolutionary pattern and process in the salamander family Plethodontidae. Evolutionary Biology 17:119-217.
Larson, A. 1991. A molecular perspective on the evolutionary relationships of the salamander families. Evolutionary Biology 25:211-277.
Larson, A. and W. W. Dimmick. 1993. Phylogenetic relationships of the salamander families: A analysis of congruence among morphological and molecular characters. Herpetological Monographs 7:77-93.
Marracci, S., R. Batistoni, G. Pesole, L. Citti and I. Nardi. 1996. Gypsy/Ty3-like elements in the genome of the terrestrial salamander Hydromantes (Amphibia, Urodela). Journal of Molecular Evolution 43:584-593.
Mathis, A., R. G. Jaeger, W. H. Keen, P. H. Ducey, S. C. Walls and B. W. Buchanan. 1995. Aggression and Territoriality by Salamanders and a Comparison with the Territorial Behaviour of Frogs. Pp. 633-676 in H. Heatwole (ed.) Amphibian Biology Volume 2: Social Behavior. Surrey, Beatty and Sons. NSW, Australia.
Morescalchi, A. 1975. Chromosome evolution in the caudate Amphibia. Evolutionary Biology 8:339-387.
Nussbaum, R. A. 1985. The evolution of parental care in salamanders. Miscellaneous Publications, Museum of Zoology, University of Michigan 169:1-50.
Raff, R. A. and T. C. Kaufman. 1983. Embryos, Genes and Evolution. Macmillan Publishing Co., New York.
Sessions, S. K. and A. Larson. 1987. Developmental correlates of genome size in plethodontid salamanders and their implications for genome evolution. Evolution 41:1239-1251.
Sever, D. M. 1991a. Comparative anatomy and phylogeny of the cloacae of salamanders (Amphibia: Caudata). I. Evolution at the family level. Herpetologica 47:165-193.
Sever, D. M. 1991b. Comparative anatomy and phylogeny of the cloacae of salamanders (Amphibia: Caudata). II. Cryptobranchidae, Hynobiidae, and Sirenidae. Journal of Morphology 207:283-301.
Sullivan, B. K., M. J. Ryan and P. A. Verrell. 1995. Female choice and mating system structure. Pp. 469-517 in H. Heatwole (ed.) Amphibian Biology Volume 2: Social Behavior. Surrey, Beatty and Sons. NSW, Australia.
Titus, T. A. and A. Larson. 1995. A molecular phylogenetic perspective on the evolutionary radiation of the salamander family Salamandridae. Systematic Biology 44:125-151.
David Heyse, Todd Jackman, David Maddison, Frances Moffitt and Tom Titus contributed to the preparation of this Tree of Life page.
Department of Biology
St. Louis, MO 63130-4899, USA
Page copyright © 1996
Citing this page:
Larson, Allan. 1996. Caudata. Salamanders. Version 01 January 1996 (under construction). http://tolweb.org/Caudata/14939/1996.01.01 in The Tree of Life Web Project, http://tolweb.org/