Body inflatable; body covered with well-developed sharp spines (in some species the spines erect only when body is inflated); two fused teeth in jaws (parrotlike); premaxillae and dentaries completely fused to opposite member at midline.
Adults inhabit inshore waters while the young are pelagic. Six genera, Allomycterus, Chilomycterus, Cyclichthys, Diodon, Lophodiodon, and Tragulichthys, with 19 species (J. M. Leis in Carpenter and Niem, 2001).
Family MOLIDAE (511)—molas. Marine; tropical and subtropical; Atlantic, Indian, and Pacific.
Two fused teeth in jaws; no spines in dorsal or anal fins; no caudal peduncle; caudal fin lost, posterior end of body reduced to a leathery flap or pseudocaudal (clavus); two minute nostrils on each side; lateral line absent; no swim bladder; 16-18 vertebrae.
Johnson and Britz (2005) tested the hypothesis that the clavus is 1) a highly modified caudal fin, or 2) formed by highly modified elements of the dorsal and anal fins. Based on ontogenetic evidence, they concluded that the latter is correct, that it is formed by modified elements of the dorsal and anal fin, and that the caudal fin is lost in molids (see also Britz and Johnson, 2005).
The major locomotory thrust is provided by the powerful dorsal and anal fins. It has been estimated that up to 300 million eggs can be produced by Mola mola (the Ocean Sunfish), probably making it the most fecund fish species. Molas feed extensively on jellyfishes. Maximum length over 2 m with weights up to 1,000 kg. Fossils include the Eocene Eomola. Santini and Tyler (2002b) gave a phylogeny of this family. Also known as ocean sunfishes.
Three genera and four species: Masturus lanceolatus (recognized in Mola by some), Mola mola, Mola ramsayi, and Ranzania laevis (P. Parenti, 2003).
Class SARCOPTERYGII—lobe-finned fishes and tetrapods
The Sarcopterygii, as used here, form the monophyletic taxon that includes the remaining group of vertebrates. It includes several fish groups, both recent and fossil, and the tetrapods. All the included fishes are thus more closely related to mammals and other tetrapods than they are to other fishes. The closest sister group to the tetrapods among living fishes is probably the lungfishes (versus the coelacanths), although there are differing theories. In the past, the term Sarcopterygii has been variously used; some workers used it to include only fishes conventionally called crossopterygians and dipnoans (the lobe-finned fishes). I use the term to include also the tetrapods as have many earlier authors (e.g., see Nelson, 1994). Synapomorphies recognized by M.-M. Chang in 1991 for this group include enamel on the teeth.
In an exciting find, Zhu and Yu (2002) described a fossil sarcopterygian fish from the Lower Devonian of China, Styloichthys, that showed characteristics suggesting it might be close to the last common ancestor of tetrapods and lungfish. It appears to bridge the morphological gap between stem-group sarcoptery-gians (Psarolepis and Achoania, described in 1999 and 2001, respectively, by M. Zhu and coauthors) and basal tetrapodomorphs/basal dipnomorphs. The description of these possible links between what are recognized in classification as major breaks (e.g., with Psarolepis combining features of actinopterygians and sarcopterygians) provides very valuable information.
Some earlier views of relationships between crossopterygians, lungfishes, and tetrapods were given in Nelson (1994). The present classification of the nontetrapods is largely from Cloutier and Ahlberg (1996). Much information on this group is in Long (1995), Janvier (1996), Maisey (1996), Schultze and Cloutier (1996), Ahlberg (2001), and Clack (2002).
The Sarcopterygii are recognized here with two subclasses, having about 26,742 species, of which eight are fishes.
Subclass COELACANTHIMORPHA (Actinistia)
Order COELACANTHIFORMES (61)—coelacanths. Caudal fin diphycer-cal, consisting of three lobes; external nostrils, no choana; branchiostegals absent; lepidotrichia never branched; lepidotrichia in tail equal to number of radials or somewhat more numerous; anterior dorsal fin in front of center of body. Maximum length about 1.8 m, in Latimeria chalumnae.
The order is recognized with nine families (Cloutier and Ahlberg, 1996), eight with only fossil members, and one with fossil members and the living species. Much of the classification of Cloutier and Ahlberg (1996) is based on the 1993 study of H.-P. Schultze. There is a good fossil record of this group from the Upper Devonian to the Upper Cretaceous. The majority of species were marine, but some were freshwater. Forey (1998) gave extensive information on this order.
Two living species.
tFamily MIGUASHAIIDAE. Miguashaia. Devonian.
tFamily DIPLOCERCIDAE. Diplocercides (synonym Nesides). Devonian and Lower Carboniferous.
tFamily HADRONECTORIDAE. Allenypterus, Hadronector, and Polyosteorhynchus.
tFamily RHABDODERMATIDAE. Paraphyletic. E.g., Caridosuctor and Rhabdoderma. Primarily Carboniferous.
tFamily LAUGIIDAE. Coccoderma and Laugia. Lower Triassic to Lower Cretaceous. tFamily WHITEIIDAE. Whiteia. Triassic.
tFamily COELACANTHIDAE. E.g., Axelia, Coelacanthus, and Wimania.
tFamily MAWSONIIDAE. E.g., Alcoveria, Axelrodichthys, Chinlea, Diplurus, Holophagus, and Mawsonia. Triassic and Jurassic.
Family LATIMERIIDAE (512)—gombessas or coelacanths. Marine; off southern Africa (Mozambique, Madagascar, and Comoros Archipelago) and Indonesia (Celebes Sea, north of Sulawesi).
The first living species, Latimeria chalumnae (Gombessa), a marine species known from South Africa, Comoros Archipelago, and off Mozambique, was formerly recognized as the sole extant member of the family Latimeriidae. Views that Latimeria is more closely related to Chondrichthyes than to bony fishes (based in part on similarities in the pituitary gland, presence of a rectal gland, and high blood levels of urea) are not considered probable.
The first specimen was trawled off East London, South Africa, in December 1938. This species is livebearing. Length of adults up to 1.8 m. There is much interest in the unusual head-standing behavior of L. chalumnae, filmed by Hans Fricke in his submersible at about 170-200 m depth (the species ranges between about 150-400 m). It also has an unusual mode of swimming, especially for a notochordal fish, in keeping the body rigid. It is the only living
chordate with an intracranial joint, also found in other coelacanths, porolepi-forms, and osteolepidiforms. As described by M.-M. Chang in a 1991 study discussing its phylogenetic importance, the intracranial joint is a plesiomorphic character of sarcopterygians with mobility reduced in porolepiforms and lost in dipnoans. This joint divides the neurocranium into an orbitosphenoid anterior half and an otico-occipital posterior half. It, with other joints, may allow the upper jaw to be elevated.
Events leading to the discovery of the second species (Latimeria menadoen-sis) began with the sighting by Mark and Arnaz Erdmann of a coelacanth in an Indonesian fish market in Manado, Sulawesi, on 18 September 1997, and the subsequent preservation of a second specimen on 30 July 1998. These events are documented in a 1999 issue of Environmental Biology of Fishes. The new species was described by Pouyaud et al. (1999).
Two species, Latimeria chalumnae and L. menadoensis. In addition to the two living species, there are Jurassic and Cretaceous genera, e.g., Holophagus, Libys, Macropoma, and Undina. All taxa recognized here in the family Latimeriidae were recognized in the Coelacanthidae in Nelson (1994). Reasons for splitting the two families are given in Cloutier and Ahlberg (1996).
This new term (Dipnotetrapodomorpha) in this edition is for the unnamed taxon of Onychodontida + Rhipidistia in Cloutier and Ahlberg (1996). The classification of the taxon has changed from that in Nelson (1994). It is now based primarily on Cloutier and Ahlberg (1996). An overview is presented below.
Subclass Dipnotetrapodomorpha, sister to subclass Coelacanthimorpha (Actinistia) Unranked 1a. Onychodontida Unranked 1b. Rhipidistia Unranked 2a. Dipnomorpha Superorder Porolepimorpha f Order Porolepiformes fSuperorder Dipterimorpha—several fossil families, paraphyletic. Superorder Ceratodontimorpha
Order Ceratodontiformes—two suborders with three extant families Unranked 2b. Tetrapodomorpha Unranked 3a. fRhizodontimorpha Unranked 3b. Osteolepidimorpha
Unranked 4a. Unnamed Osteolepidiformes + Elipistostegalia + Tetrapoda Order Osteolepidiformes Unranked 4b. Unnamed. Elipistostegalia + Tetrapoda fInfraclass Elipistostegalia Infraclass Tetrapoda
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