Browsing by Author "Baskin, Jonathan N."
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Item The caudal skeleton of the catfishes, order Siluriformes. American Museum novitates ; no. 2398(New York, N.Y. : American Museum of Natural History, 1969) Lundberg, John G.; Baskin, Jonathan N."To achieve a better understanding of the evolution of catfishes, comparative studies of single character complexes throughout the entire order is believed to be a rewarding approach. A survey of the caudal skeleton of the Siluriformes reveals 10 basic features which, taken together, distinguish catfishes from other fishes. Of these the most diagnostic are: 1) bases of hypurals 3 and 4 fused with a distinct U[subscript]2 chordacentrum in the young and with a usually reduced second ural centrum in the adults; 2) a secondary hypurapophysis; 3) principal rays of the caudal fin fewer than 10+9, with upper principal rays equal to, or fewer than, the lower rays. Within the Siluriformes four features of the caudal skeleton are found to exhibit group specific patterns of variation and trends from primitive to advanced conditions, and may thus be useful in determining relationships: 1. In the trend from the primitive condition of six separate hypurals to the most advanced condition of complete fusion of caudal elements, various groups have reached different structural levels. In this process the sixth hypural is lost. 2. The trend toward elaboration of the sites of caudal muscle origin (hypurapophysis and secondary hypurapophysis) has involved the formation and elaboration of shelves from originally distinct projections, and a subsequent dorsal shift of these sites. 3. While the most primitive principal caudal fin ray number in siluriforms is 9+9, most groups have 8+9. The trend toward a reduction of principal rays always involves loss of an upper ray before loss of a lower so that upper principal rays are never more numerous than lower ones. 4. A separate U[subscript]2 chordacentrum is present in the young of all Ostariophysi except the Loricariidae, Plotosidae, and probably the Chacidae. In the adults of the majority of catfishes a reduced second ural centrum fused with one or more hypurals lies in the cavity on the posterior face of the compound centrum, PU[subscript]1+ U[subscript]l. In some groups the second ural centrum fuses to the compound centrum. In the Loricariidae and Plotosidae the second ural centrum is fused with PU[subscript]1+U[subscript]l, in early development. A separate, well-developed second ural autocentrum occurs in some members of four specialized and unrelated families. This is interpreted as independent redevelopment of a presumedly primitive pre-ostariophysan condition. The advanced conditions of each of these four features of the caudal skeleton tend to occur together in forms which are also regarded as advanced in most other parts of their anatomy. The primitive character states of these features tend to be retained together in a number of families, i.e. Diplomystidae, Ictaluridae, Bagridae, Cranoglanididae, Schilbeidae, Pangasiidae, and Cetopsidae. Advanced features in the caudal skeleton indicate a relationship between the Clariidae and Heteropneustidae, the Doradidae and Auchenipteridae, the Loricariidae, Astroblepidae, and Callichthyidae, and the Plotosidae and Chacidae. The siluriform caudal skeleton shares many features with that of the cypriniforms but it is consistently more advanced. The ostariophysan caudal skeleton is similar to that of the clupeoids, but it resembles the caudal skeleton of the Gonorynchiformes more closely than that of any other group"--P. 45-46.Item New and noteworthy Venezuelan glanapterygine catfishes (Siluriformes, Trichomycteridae), with discussion of their biogeography and psammophily. American Museum novitates ; no. 3496(New York, NY : American Museum of Natural History, 2005) Schaefer, Scott Allen, 1958-; Provenzano, Francisco.; Pinna, Mário C. C.; Baskin, Jonathan N.Four new species of the trichomycterid subfamily Glanapteryginae are described from the Río Orinoco basin of Venezuela. Two new species each in Pygidianops Myers 1944 and Typhlobelus Myers 1944 represent the first documented occurrence of these genera in Venezuela, and for Pygidianops the first occurrence outside the Río Negro basin. The new species were captured from sand-bottom habitats in two disparate locations in the Orinoco River basin and display a remarkable suite of reductive features, such as loss of eyes, fins, and pigment, and reductions or absence of laterosensory canals and odontodes. Pygidianops cuao, n.sp. from the Río Cuao, a clear-water tributary of the upper Orinoco River, is diagnosed from its congeners by the presence of diminutive eyes and a triangular skin flap at the corner of the mouth. Pygidianops magoi, n.sp., known from near the delta of the Orinoco River, is diagnosed from its congeners by the absence of pectoral and anal fins, presence of four laterosensory pores, and nine or ten caudal-fin rays. Typhlobelus guacamaya, n.sp. from the Río Cuao is diagnosed relative to its congeners by the presence of three branchiostegal rays, posterior naris absent, lack of pleural ribs, and is further distinguished from both T. ternetzi and T. macromycterus by the absence of eyes and from T. lundbergi by the presence of three laterosensory canal pores. Typhlobelus lundbergi, n.sp. from the lower Orinoco is diagnosed by the presence of four laterosensory canal pores and further distinguished from T. ternetzi and T. macromycterus by the absence of eyes. We review the characters useful in diagnoses of Pygidianops and Typhlobelus among trichomycterid catfishes and discuss morphological patterns in the diversification of the Glanapteryginae. Species of Pygidianops and Typhlobelus are known only from the rivers draining the Guyana and Brazilian shields, yet within these areas they occupy all major water types. Such broad ecological range suggests that the geographic distribution of species of these two genera are not limited by water type. That observation, plus their common occurrence in the ubiquitous shallow sand-bottom habitats of the larger rivers of the shield regions of northern South America, indicate that species of Pygidianops and Typhlobelus may be expected to occur throughout the entire Amazon and Orinoco basins. The evolution of habitat preference in glanapterygines seems to follow a trend toward increased specialization for interstitial environments. The degree of psammophilic adaptation in species of Pygidianops and Typhlobelus is remarkable, without parallel in siluriforms and perhaps in any other freshwater fishes. We describe the physical characteristics of the sand and review the suite of morphological specializations for life in interstitial sand that are shared by these species, such as loss or reduction of certain structures and presence in these species of paired metapleural keels along the ventral edges of the abdomen formed by a long ridge of stiffened integument, underlain by well-differentiated medial infracarinalis muscles, that are superficially similar to the metapleural folds of sand-dwelling cephalochordates and other interstitial organisms.