Dentition consisting of a few large permanent grinding tooth plates (selachianlike anterior teeth may also be present); palatoquadrate fused to neurocra-nium (holostyly); dorsal fin spine usually present. This diagnosis is very imperfect; some assumed members are known only from isolated tooth plates.
fOrder PSAMMODONTIFORMES. Position uncertain. Known only from isolated tooth plates. One family, Psammodontidae (e.g., Archaeobatis, Lagarodus, and Psammodus) (Stahl, 1999; Elliott et al., 2004). Upper Devonian to Lower Carboniferous.
fOrder COPODONTIFORMES. Position uncertain. Known only from tooth plates. One family, Copodontidae (e.g., Copodus) (Stahl, 1999). Carboniferous.
Of the following taxa, Grogan and Lund (2004) suggested that chon-drenchelyiforms and menaspiforms are sister taxa as are cochliodontiforms and chimaeriforms, with all four being sister to the squalorajiforms, and all five taxa being placed in the Cochliodontomorpha.
fOrder SQUALORAJIFORMES. Body depressed. One family, Squalorajidae, and one genus, Squaloraja (Stahl, 1999). Lower Jurassic. Stahl (1999) recognized this taxon as one of four suborders of Chimaeriformes and sequenced it between the Echinochimaeroidei and Myriacanthoidei.
fOrder CHONDRENCHELYIFORMES. Body elongate, biserial pectoral fin, and long lower jaw. One family, Chondrenchelyidae (e.g., Chondrenchelys, Harpagofututor, and Platyxystrodus) (Stahl, 1999). Lower Carboniferous.
fOrder MENASPIFORMES. Three families, Deltoptychiidae, with
Deltoptychius, Menaspidae, with Menaspis, and Traquairiidae, with Traquairius (Stahl, 1999). Lower Carboniferous (Mississippian) to Upper Permian.
fOrder COCHLIODONTIFORMES. Known primarily from teeth and tooth plates. Two families, Cochliodontidae (e.g., Cochliodus, Deltodus, Poecilodus, and
Sandalodus) and Psephodontidae (with Psephodus) (Stahl, 1999). Upper Devonian to Permian.
Order CHIMAERIFORMES (3)—chimaeras. Three families, six genera, and 33 species. Stahl (1999) recognized four suborders of chimaeriforms; her Squalorajoidei are recognized here as more basal following Grogan and Lund (2004).
fSuborder Echinochimaeroidei. Position uncertain. One family, Echinochimaeridae, with one genus, Echinochimaera. Mississippian. Differs from the chimaeroids in having a dermal cranial armor of denticles, placoid squamation, a tuberculated first dorsal spine, and no frontal clasper in males (Lund, 1986; Stahl, 1999).
fSuborder Myriacanthoidei. Two families, Chimaeropsidae, with one genus, Chimaeropsis, and Myriacanthidae (e.g., Acanthorhina, Agkistracanthus, Halonodon, and Myriacanthus) (Stahl, 1999). Upper Triassic to Jurassic.
Suborder Chimaeroidei (chimaeras). Two dorsal fins, the first erectile, with short base, and preceded by an erectile spine, the second nonerectile, low, and with long base; mouth inferior. In living forms, at least, fertilization is internal; the deposited egg is encased in a brown horny capsule. Water for breathing is chiefly taken in through the nostrils. Maximum length about 1.5 m.
Six extant genera with about 33 species (listed in Compagno, 2005; Didier, 2004, with several undescribed species). Lower Jurassic to present. Fossil taxa, all in the extant families, are given with the families.
Didier (1995), in a phylogenetic analysis of living taxa based on morphological characters, gave synapomorphic characters for the higher taxa and reviewed ideas on the origin of the Holocephali.
Superfamily Callorhinchoidea (Callorhynchoidea)
Family CALLORHINCHIDAE (Callorhynchidae) (5)—plownose chimaeras. Marine, continental and insular shelves and uppermost slopes; Southern Hemisphere (e.g., off southern South America, New Zealand, southern Australia, southern Africa).
Snout with elongate, flexible, hooklike process; lateral line canals closed; eyes small; tail heterocercal. Egg capsule large, ovoid (typically 27 cm X 13 cm), with wide, ribbed lateral web.
Fossil Callorhinchidae (earliest in Jurassic) include: Brachymylus, Ischyodus, and Pachymylus, with Edaphodon placed in its own subfamily, Edaphodontinae, by Stahl (1999), with possibly also in this family the Jurassic Eomanodon and Ganodus. In addition, fossils of the genus Callorhinchus are known from the Eocene of Antarctica (Kriwet and Ga'zdzicki, 2003).
One genus, Callorhinchus, with three species (Didier, 1995, 1998, 2004). Change in orthography of family name to conform with generic name (Eschmeyer, 1998).
Family RHINOCHIMAERIDAE (6)—longnose chimaeras. Marine, deep oceanic, continental and insular slopes; Atlantic, Indian, and Pacific.
Snout long, fleshy, and pointed, not hooklike; lateral line canals are open grooves; tail diphycercal; anal fin separated from caudal in Neoharriotta and joined with it in the other genera. Egg capsule ovoid (pear-like) (typically 15 cm x 6 cm), with ribbed lateral web.
Fossil Rhinochimaeridae (earliest in Jurassic) include Amylodon and Elasmodus.
Three genera, Harriotta (2), Neoharriotta (3), and Rhinochimaera (3), with about eight species (Compagno et al., 1990; Didier, 1995, 2004; Didier and Stehmann, 1996; Didier and Nakaya, 1999). Didier (1995, 2004) placed Harriotta and Neoharriotta, with thick tooth plates, in the subfamily Harriottinae, and Rhinochimaera, with smooth, thin tooth plates in the subfamily Rhinochimaerinae.
Family CHIMAERIDAE (7)—shortnose chimaeras or ratfishes. Marine; Atlantic and Pacific.
Snout (rostrum) short, fleshy, and rounded; lateral line canals are open grooves with those on snout widened; tail diphycercal. Egg capsule relatively small (typically 17 cm x 2.5 cm), spindle-shaped with distinct dorsal keel and
little or no lateral web. A poison gland is associated with the dorsal spine, and the venom is painful to humans. Maximum total length about 1.4 m, attained in Chimaera lignaria, probably the largest extant chimaeroid.
Fossil Chimaeridae (earliest in Cretaceous), include Belgorodon. In addition, fossils of the genus Chimaera are known from the Late Cretaceous and Eocene of Antarctica (Stahl, 1999; Stahl and Chatterjee, 1999).
Two genera, Chimaera (with a notch separating the anal fin from the caudal fin) and Hydrolagus (with anal fin joined to caudal fin), and about 22 species. Chimaera has seven species that occur in the northern Atlantic, off South Africa, Japan and northern China, Australia, and New Zealand, whereas Hydrolagus has about 16 species that occur primarily in the northern and southwestern Atlantic, off South Africa, and in many areas in the Pacific (e.g., southern Alaska to southern California, Japan, Australia, and New Zealand) (Didier, 1995, 1998, 2002, 2004; Soto and Vooren, 2004). Most species are in the western Pacific offJapan and New Zealand. The allocation of some species to the above genera on the basis of the anal fin character is subject to change (Hardy and Stehmann, 1990; Didier, 2004). Several undescribed species are known from Australia and New Zealand (Didier, 1998, 2002, 2004; Compagno, 2005).
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