AMPHIBIA - CLASSIFICATION 1. Labyrinthodontia.—Amphibiawith a roofed skull, a lower jaw consisting of at least eight bones on each side and vertebrae consisting of neural arches and intercentra in all forms, with pleurocentra in addition in most.
The Labyrinthodontia are divided into three suborders, or grades : Embolomeri, Rachitomi and Stereospondyli. The first is from the Lower Carboniferous to Permian, the second, from the Permian and Triassic, and the last, from the Triassic. The skele tal organization of these groups has been discussed above. A de tailed classification has been given by Watson.
2. Phyllospondylia.—Small,very highly specialized Am phibia with a roofed skull, palate with very widely open interptery goid vacuities, coracoid and pubis not ossified ; ventral armour of small round scutes. Branchiosauridae. Carboniferous and Lower Permian.
3. Lepospondylia.---SmallAmphibia with roofed skull and lepospondylous vertebrae. Nectridia, Diplocaulidae, Aistopodidae. Carboniferous and Permian.
4. Gymnophiona.—Recentworm-like Amphibia without limbs and with a very short tail; male with an intromittent copu latory organ. Tropicopolitan, excepting Madagascar. Apparently evolved from the Lepospondylia, but fossil annectant forms lack ing. Nineteen genera are recognized.
5. Caudata.—Salamandersand newts (qq.v.) are readily dis tinguished from other living Amphibia by their four limbs and tail. They are grouped into five suborders and eight families. The latter may be briefly characterized here.
(I). Hynobiidae.—A small group of Asiatic land salamanders distinguished from ambystonids, which they resemble externally, in having the angular free, premaxillary spines short not separat ing nasals and in practising external fertilization. There are five genera, but only Hynobiius has a wide range.
(2) . Cryptobrancliidae.--Two genera of semi-larval salaman ders of large size directly evolved from the hynobiids, and differ ing in retaining a few larval characters in the adult. Crypto branchus (q.v.) of eastern United States is more larval than the Japanese-Chinese Megalobatrachus.
(3). Arnbystomidae.—A family of common American sala manders distinguished from salamandrids by their short pre vomers and amphicoelous vertebrae, and differing from hynobiids in their fused angulars, long premaxillary spines and internal fertilization. The family includes three American genera, of which only Ambystoma with eleven species is well known.
(4). Salarandridae.—A varied group of aquatic forms, such as the newts, and terrestrial species, such as Salamandra, with vomerine teeth extending back as a series on each side of the parasphenoid and with the vertebrae opisthocoelous. The primi tive salamandrids are large, rough-skinned newts, having a bony, fronto-squamosal arch, high neural spines, and long ribs. The more specialized forms show a reduction of these elements and also of the maxillaries, pterygoids and basi-hyals. The Sala mandridae are found in North America, Eurasia and North Africa.
(5) . Amphiumidae.—Afamily including only the genus Amphiuma. The large "Congo Eel" or Conger is a semi-larval type derived from the salamandrids and agreeing with them in most important characters. It possesses lungs, a bony pterygoid, a posterior process from each prevomer and premaxillary spines elongated to separate the nasals.
(6). Pletliodontidae.—A large group of salamanders abun dant in America and including both aquatic and terrestrial forms, with a pterygoid that remains cartilaginous throughout life and with vomerine teeth carried back by processes during ontogeny to form one or two dentigerous patches over the parasphenoid. All plethodontids are lungless and possess a naso-labial groove to assist in freeing the nostril from water.
(7) . Proteidae.—A group of permanently larval salamanders of unknown ancestry including only the European Proteus (q.v.) and American Necturus. Lungs are present, but the ypsiloid apparatus is absent. The pubo-ischium has a distinctive form, being long and pointed anteriorly. Proteus is a blind and pig mentless cave form while Necturus, represented by two species, is an active stream or pond dweller.
(8) . Sirenidae.—Long-bodied Siren (q.v.) and Pseudobranchus of south-eastern United States form a group which agrees with the very young larvae of other families in possessing only the anterior appendages and in lacking many later ontogenetic de velopments of the skull. They differ when adult from the young of other families in possessing reduced pterygoids, a separate ossification of the coracoid and a well-developed Jacobson's organ. Their relationships to the other families of Caudata is unknown.
(i ). Liopelmidae. — Primitive frogs with amphicoelous verte brae and two pairs of ribs ; a fam ily including only Liopelma of New Zealand and Ascaphus of north-western United States. The latter is remarkable in possessing an extension of the cloaca in the male to form a "tail." This appendage is apparently used in copulation as fertilization is in ternal (fig. 6).
( 2 ) . Discoglossidae.—Primitive Old World frogs having opistho coelous vertebrae, three pairs of ribs, sacral vertebra free with bi convex centrum. The family in cludes only two European, one Eurasian and one Philippine genus.
(3). Pipidae.—Aquatic Salien tia which have lost the tongue and movable eyelids (except Pseudhymenocliirus which retains a lower eyelid) . Ribs are free in the larva, but ankylose to the diapophyses on metamorphosis. Various fusions occur in the vertebral column, the presacral verte brae numbering five to seven. The sacrum is fused to the coccyx (rarely free with a single condyle). The pectoral girdle is partly or wholly firmisternal, the cartilages never broadly overlap as in the Discoglossidae. The family includes the Surinam toad (q.v.) .
(4)• Pelobatidae.—Salientia without ribs at any stage of de velopment, sacral vertebrae procoelous, ankylosed to coccyx or if free with only a single articular condyle for the latter ; presacral vertebrae eight, either uniformly procoelous or with free inter vertebral discs (interdorsals). The Pelobatidae agree with bufo nids in the arciferal pectoral girdle and dilated sacral diapophyses; they differ from them in their single coccygeal condyle and primi tive musculature. The family includes the spade-foot toads and certain forest frogs of the Seychelles, south-eastern Asia and the East Indies.
(5) . Palaeobatrachidae.—Fossil frogs from the Jurassic, Oli gocene and Miocene formations of Europe. They are procoelous, arciferal forms differing from the Pelobatidae in having a double condyle on the coccyx and in having the sacrum formed of two or three slightly dilated precoccygeal vertebrae. In limb proportions the Palaeobatracbidae approach the Pipidae and it is highly prob able that the species were thoroughly aquatic.
(6). Bufonidae.—A dominant family of true toads (q.v.) and neotropical "frogs" having a uniformly procoelous vertebral col umn and a double condyle to the coccyx (rarely fused to sacrum). They are arciferal and resemble the Pelobatidae in many charac ters, but differ in musculature and coccygeal articulation. The toothed bufonids are frequently designated as Cystignathidae or Leptodactylidae. They are more primitive than the toothless genera, but as they have given rise to toothless bufonids in dif ferent parts of the world, it makes a more natural system to group both together as a single family.
(7) . Hylidae.—Bufonids with an intercalary cartilage or bone between the last two phalanges of each digit and usually with claw-shaped terminal phalanges. They are procoelous and usually with dilated sacral diapophyses. Most, but not all, are tree-frogs (q.v.) and a few, such as Acris, are semi-aquatic. There are 15 genera of hylids. All of these, save Hyla (including Hylella and Nyctimystes), are confined to the neotropical region.
(8). Brachycephalidae.—A large group of small neotropical toads recently shown to be closely allied to the Bufonidae and to have no relationship to the Ranidae or Brevicipitidae with which they were formerly confused; procoelous forms with the two halves of the pectoral girdle partly or wholly fused in the mid-line.
(9). Ranidae.—Firmisternal frogs (q.v.) with cylindrical or slightly dilated sacral diapophyses, digits without intercalary car tilages, sacral vertebra convex anteriorly, the eighth vertebra biconcave and preceded by seven procoelous vertebrae. Ranids are primarily Old World frogs, only one genus, Rana, reaching Amer ica. Africa seems to have been a centre of differentiation for the family, the greatest diversity of type occurring there.
(io). Polypedatidae.—Ranids with cylindrical sacral dia pophyses and intercalary cartilages between the two last pha langes of each digit. The Polypedatidae are tropical tree-frogs of the Old World.
(I I) . Brevicipitidae.—A group of toads closely related to the ranids and differing chiefly in the more dilated sacral diapophyses. The more specialized forms have lost their teeth and all the ventral elements of the shoulder girdle save the coracoids. The family is cosmopolitan. Brevicipitids in the Asiatic, East Indian, and Malagasy regions seem to have run through independently on series of structural changes, of ten parallel in the three regions.