Janassa

Abstract: The Petalodontiformes are Upper Paleozoic marine euchondrocephalan chondrichthyans known primarily from isolated teeth. Few dentitions have been reported, among them that of the Permian Janassa bituminosa and “Janassa” korni and the Serpukhovian, Mississippian Belantsea montana, Obruchevodus griffithi, Netsepoye hawesi and Siksika ottae. A dentition has been reconstructed for the Pennsylvanian Petalodus ohioensis. New information on dentitions and postcranial morphology is now introduced for petalodont remains from the Bear Gulch Limestone of Montana (USA). These include N. hawesi, Petalorhynchus beargulchensis, several specimens bearing teeth of the Fissodus form, and a new genus and species, Fissodopsis robustus. Analysis of all material reveals dignathic heterodonty as prevalent among the Upper Mississippian petalodonts, with distinct regionalization resulting in large anterior and small lateral teeth. Fissodus-style teeth are found as the lower median tooth position of most heterodont dentitions, with a Ctenoptychius-like upper anterior tooth or teeth, accompanied by lateral upper and lower teeth of Janassa-like form. As heterodonty seems to have been the plesiomorphic condition not only in these petalodonts but for the Euchondrocephali as well, a model is proposed to explain the derived homodont conditions found in Petalodus (Hansen, 1985), Polyrhizodus (Lund, 1983), Belantsea (Lund, 1989), and J. bituminosa (Jaekel, 1899). The principally dentition-based cladistic analysis retains the previously erected families Petalodontidae, Belantseidae, and Janassidae, rejects the assignment of ”J.” korni to Janassa, and suggests a heterodont clade for the remaining taxa. Two new families are designated on the basis of these data, the Petalorhynchidae and the Obruchevodidae.

Abstract: The dentition of the Petalodont sharks is still very imperfectly known. It has hitherto been satisfactorily observed only in the highly-specialized Janassa bituminosa from the Upper Permian (Kupferschiefer and Marl Slate) of Germany and England. Nearly all the other species and genera are represented in collections merely by isolated teeth. It is, therefore, of interest to examine the comparatively well-preserved dentition of a new Lower Carboniferous Petalodont, which has been kindly lent to me by Dr. William Eagle Clarke, Keeper of the Natural History Department of the Royal Scottish Museum, Edinburgh. The specimen was obtained from the Calciferous Sandstone of Calderside, near East Kilbride (Lanarkshire), and was presented to the Royal Scottish Museum in 1892 by Mr. John B. Wise, of Glasgow. It was regarded by the late Dr. R. H. Traquair as belonging to a new species of Janassa , which he named J. wisei but it has not so far been described or discussed. The hard shale in which the two jaws are preserved has split along the plane of the mouth, so that the dentition of each is exposed from the oral aspect, as shown in Pl. I. Of the cartilages only fragments remain behind and partly below the teeth, especially in the wider of the two jaws (which is here regarded as the upper). Nearly all the teeth seem to be present in the narrower or supposed lower jaw; but some of the small anterior teeth are broken away from the front of the opposing jaw, and

Abstract: A new holomorphic petalodont from the Bear Gulch Limestone, Obruchevodus griffithi, is described and features of the related Netsepoye hawesi are reinterpreted. Comparison of these taxa with the holomorphic petalodonts Janassa bituminosa, Belantsea montana, and Siksika ottae provide insight into petalodont anatomical form and variation. All holomorphic material supports holostyly and nested, subcranial branchial arches. Teeth occur in families with linguo-labial replacement but alignment of most families relative to the jaw ramus results in a staggered tooth alignment between adjacent tooth families. Symphysial teeth are the exception to this pattern. Tooth retention is clearly indicated only in the homodont Janassa bituminosa. In contrast there is no evidence of tooth retention in examined petalodonts with a heterodont dentition. There is variation in styles of squamation among all forms; sexual dimorphism in scale development and distribution are suggested as well. Despite depressiform and compressiform conditions there is commonality in possession of a lobular, anteriorly extended and high aspect ratio pectoral fin, large pelvic fins, and absence of fin spines. Pectoral fins provide the primary means of locomotion. Variation in the ventral aspect of the pelvic girdle anatomy exists between that interpreted for Janassa and that documented by Obruchevodus and Netsepoye. Male claspers are long and highly flexible. Laterally compressed body forms display two dorsal fins (first being largest) that are variable in their vertical expanse along the length of the fin. Cranial anatomy shows some correspondence to general features of the Holocephali. Meckel’s cartilage is dorso-ventrally deep, as in extant chimaeroids, with contralaterals in symphysial fusion. Mandibular labial cartilages, when present, may be sexually dimorphic.

Abstract: The Petalodontiformes are Upper Paleozoic marine euchondrocephalan chondrichthyans known primarily from isolated teeth. Few dentitions have been reported, among them that of the Permian Janassa bituminosa and “Janassa” korni and the Serpukhovian, Mississippian Belantsea montana, Obruchevodus grif fithi, Netsepoye hawesi and Siksika ottae. A dentition has been reconstructed for the Pennsylvanian Petalodus ohioensis. New information on dentitions and postcranial morphology is now introduced for petalodont remains from the Bear Gulch Limestone of Montana (USA). These include N. hawesi, Petalorhynchus bear gulchensis, several specimens bearing teeth of the Fissodus form, and a new genus and species, Fissodopsis robustus. Analysis of all material reveals dignathic heterodonty as prevalent among the Upper Mississippian petalodonts, with distinct regionalization resulting in large anterior and small lateral teeth. Fissodus style teeth are found as the lower median tooth position of most heterodont dentitions, with a Ctenoptychius like upper anterior tooth or teeth, accompanied by lateral upper and lower teeth of Janassa like form. As hetero donty seems to have been the plesiomorphic condition not only in these petalodonts but for the Euchondro cephali as well, a model is proposed to explain the derived homodont conditions found in Petalodus (Hansen, 1985), Polyrhizodus (Lund, 1983), Belantsea (Lund, 1989), and J. bituminosa (Jaekel, 1899). The principally dentition based cladistic analysis retains the previously erected families Petalodontidae, Belantseidae, and Jan assidae, rejects the assignment of ”J.” korni to Janassa, and suggests a heterodont clade for the remaining taxa. Two new families are designated on the basis of these data, the Petalorhynchidae and the Obruchevodidae.