STEG'OCEPHA'LIA (Neo-Lat. nom. pl., from Gk. o-7-1-yeo, strgrin, to cover + KecpaX7i, kephale, head). The name proposed by Cope to designate a well-defined order of fossil amphibia, found in strata from the Lower Carboniferous to the Upper Trias. They are distinguished from other amphibians by a dermal armor of overlap ping bony scales which usually protects the ven tral. and in some cases the dorsal surface. The group is important as representing the earliest and most primitive tetrapoda or four-footed vertebrates adapted to at least partial land-liv tore of the group, consists chiefly of bony scales, arranged in regular rows on the ventral surface, but scattered or wanting on other portions of the body. Three large plates, one median and two paired, on the pectoral region. represent the interelaviele and the clavicles. The skull, of flattened triangular form, is characterized by a solid roof of paired plates of dermal hone, and the cranial roof is always pierced by five open ings— the paired nares and orbits, and the median opening for the pineal body. which may have served as a The teeth are simple hol low cones in the smaller Paleozoic but in inany of the later types the dentine and cement exhibit a system of extremely compli cated folds — hence the name Labyrin- ; thodontia often ap plied to these forms. The vertebral column presents widely divergent conditions in dif ferent types. as regards the nature and degree of ossification of the eentra. As a rule the Paleozoic genera have the notochord largely persistent, the vertebral column thus remain ing permanently in the larval condition, while the large Triassic labyrinthodonts have well developed centra. The limbs are known for but few forms, and in these they do not differ remarkably from those of modern urodeles. The bind foot is always pentadactyl, hut in the fore foot (except in Keraterpeton, Melanerpeton, and a few related forms) the number is reduced to four, the fifth or outer digit probably being the one lacking. In any attempt to trace the phylo genetic relationships of vertebrate classes the Stegocephalia are of the greatest importance, since it is in this group only with its solid skull roof, that we find on the one hand a close ap proximation to the Paleozoic bony fishes, and on the other to the most generalized Permian rep tiles, the Cotylosauria. See REPTILE.
ing habits, and breathing by means of lungs. The majority of stegocephalians are salamander like or o lizard like in form, with a long tail, flattened head, and two pairs of limbs. The presence of gills in the young and grooves for sensory mucous canals on the skull-bones of some forms proves an aquatic habit. A carnivorous diet is indicated by the conical pointed teeth.
The dermal armor, the most distinctive fen The classification is as follows: A.—Suborder Leptospondyli. Small animals, usually salaman driform, occurring in the Carboniferous and Per mian. The suborder is divided into three fain ilies: (1) l;ranchiosauritL•e; (2) Nicrosaurithe; Aistopodidle, the serpent-like footless forms. Dolichosoma, which attained a length of three feet, and Uphiderpeton are the best known forms. B.—Subo,der Ganocephala or Temnospondyli. The most familiar type is _trehrgosourus Decheni from the Lower Permian of Germany, a species Nvhich attained a length of fora• feet. Cricotus and Eryops, from the North American Permian, measure ten feet, and are the largest American amphibia.
C.—Suborder Lahyrinthod out ia or Stereo spondyli. The true labyrinthodonts are clearly differentiated by the form of the teeth, which have the dentine in folded in a more or less com plicated manner. and by the vertthisa•. which are completely ossified, with biconcave centra some tiuu•s perforated for the passage of the con stricted notochord. A few genera occur in the Carboniferous and Permian, hut the maximum development of the group is attained in the Trias, chiefly of Europe. The genera Labyrin thodon, Capitosaurus, Trematosaurus, and Mas todonsaurus, from the European Trias, are all enormous animals, the last-named, with a skull four• feet in length, being the largest amphibian known. Consult: Woodward, Vertebrate Pahr ontology (London, 1808) ; Zittel, Text-book of Pa /won t uloNt 1 )