See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/268149743 On the Relationships of the Petalodontiformes (Chondrichthyes) Article in Paleontological Journal · December 2014 DOI: 10.1134/S0031030114090081 CITATIONS READS 3 257 3 authors, including: Richard Lund Eileen Grogan Saint Joseph's University, Philadelphia, United… Saint Joseph's University (PA, USA) 71 PUBLICATIONS 975 CITATIONS 39 PUBLICATIONS 376 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: Upper Mississipian Fishes From the Bear Gulch Limestone View project Chondrichthyan evolution View project All content following this page was uploaded by Eileen Grogan on 05 January 2015. The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the original document and are linked to publications on ResearchGate, letting you access and read them immediately. ISSN 00310301, Paleontological Journal, 2014, Vol. 48, No. 9, pp. 1015–1029. © Pleiades Publishing, Ltd., 2014. On the Relationships of the Petalodontiformes (Chondrichthyes)1 R. Lunda, b, c, E. D. Grogana, b, c, and M. Fatha aBiology Department, Saint Joseph’s University, 5600 City Avenue, Philadelphia PA 19131 bCarnegie Museum of Natural History 4400 Forbes Avenue, Pittsburgh, PA 15213 cAcademy of Natural Sciences in Philadelphia 1900 Benjamin Franklin Parkway, Philadelphia, PA 19103 email: [email protected] Received February 21, 2012 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. Fissodusstyle teeth are found as the lower median tooth position of most heterodont dentitions, with a Ctenoptychiuslike upper anterior tooth or teeth, accompanied by lateral upper and lower teeth of Janassalike 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 dentitionbased 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. Keywords: Petalodontiformes, petalodont dentitions, heterodonty, Fissodus, Janassa, Petalorhynchus, Missis sippian DOI: 10.1134/S0031030114090081 INTRODUCTION1 MATERIALS AND METHODS A petalodont tooth has been distinguished from Imaging and Measurements similar teeth as consisting of a distinct labially situated Specimens were digitally scanned at original size, crown with a Iingually extended heel, and a root that in RGB color, and with resolution up to 6400 ppi using originates below the lingual edge of the heel (e.g. an Epson Perfection V500 color flatbed scanner. Newberry and Worthen, 1866; Lund, 1989), resulting Images were corrected for color casts, levels (white in a sigmoid tooth profile. Teeth with these properties and black points), brightness and contrast with Corel were originally included in a Family Petalodontidae by Paint Shop Pro X2, rendered into black and white and Newberry and Worthen (1866), but the systematic reduced to the resolution required for publication. level of this group has gradually been elevated to an Drawings were prepared with Adobe Illustrator CS4, Order (Patterson, 1965) to accommodate the accumu from drawings rendered with a microscope drawing lated increase in primarily toothbased taxa. Whole tube, as well as prepared from overlays of scanned fos and partial dentitions are rare, and specimens that dis sil images. Original drawings based upon studies made play additional cranial or postcranial information are for Lund (1989) were also digitized into scanned rarer still. However, reexamination of previously images. Anatomical measurements were made using described taxa and the recovery of new specimens the guide and measurement tools in Adobe Illustrator. from the Serpukhovian (Upper Mississippian) of Montana, USA, now make it possible to attempt a characterbased phylogenetic analysis of the known Terminology petalodont dentitions. In the following pages, formal taxonomic names 1 The article is published in the original. are italicized, but names used to describe particular 1015 1016 LUND et al. (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) Fig. 1. Teeth of the Fissodus form. All teeth drawn to same scale. (a) Netsepoye hawesi, lingual view, CM 46092; (b, c) “Fissodus”, CM 62709 A and B; (d) “Ctenoptychius” (Janassa) korni, from Brandt, 1996, Fig. 4b; (e) “Ctenoptychius” (Janassa) korni, from Brandt, 1996, Fig. 4c; (f) “Ctenoptychius” (Janassa) korni, from Brandt, 1996, Fig. 6b; (g) Siksika ottae, MV 6199, from Lund, 1989, Fig. 12; (h, i) Fissodus bifidus, from St. John and Worthen, 1875, Pl. XIII, Figs. 1, 2, in labial (h) and lingual (i) views; (j) Fissodopsis robustus sp. nov., CM 62710; (k) “Fissodus”, CM 48824. tooth forms that are not, or may not be restricted to a in Peripristis semicircularis (Newberry and Worthen, single taxon are not italicized. 1866) or Siksika ottae (Lund, 1989). Heterodonty is prevalent among the known petal A Janassalike tooth displays a low crown, which odont dentitions, but is not present in all the taxa. As varies from a horizontal to a slightly peaked profile several of the known specimens with dentitions are that is smooth to denticulate, the absence of a basin, small and some are probably juveniles or subadults, and an extended heel approximating a perpendicular neither ontogenetic addition of tooth positions nor to the crown, with several strong ridges, and a promi ontogenetic heterodonty can be excluded. In addition, nent root. the denticulate condition described for some teeth A Fissoduslike tooth displays a high acuminate may simply reflect the unworn state of unerupted or and somewhat trenchant bifid crown, with the crown recently erupted teeth, but since this cannot be deter edge smooth to slightly cuspidate, no basin, a conspic mined on the basis of available material and the char uous heel with few to several weak to strong ridges, and acter has been repeatedly used in older literature, the a long narrow root. character state has been included in our analysis. Three basic tooth forms are variably displayed in the several petalodont dentitions, Petaloduslike, Phylogenetic Analyses Ctenoptychiuslike, and Janassalike (Plate 7). A Fis Cladistic analyses were performed with the pro soduslike form is also present as an apparent lower gram TNT (Goloboff et al., 2008) upon two matrixes median tooth in the dentitions of several different taxa (matrix Chon58). The first matrix contains 122 char (Fig. 1). There is no evidence to support any of these acters and 61 taxa and includes a theoretical zero tooth forms as the plesiomorphous petalodont condi based outgroup as well as placoderm, acanthodian and tion for an entire dentition. osteichthyan outgroups. The second matrix is com A Petaloduslike tooth displays a crown that varies prised of the available morphological and dentition from high to low and acuminate to low acuminate, characters of the Petalodontiformes, and contains with the crown edge not trenchant and smooth to 34 characters and 15 taxa including a zerobased out lightly denticulate, with a slight basin, a minor heel, group as well as Gregorius rexi (Lund and Grogan, and few, low basal ridges. 2004a) and two Bear Gulch Limestone species related A Ctenoptychiuslike tooth displays a high crown to Chomatodus. that is acuminate to sharply acuminate and trenchant, Institutional abbreviations. CM, Carnegie with the crown edge denticulate to cuspidate, and a Museum of Natural History, Pittsburgh, Pennsylva heel with a conspicuous basin and few, strong basal nia, USA; FMNH, Field Museum of Natural History, ridges. The crown may be proximodistally straight, as Chicago, Illinois, USA; MV, University of Montana in Belantsea montana, or proximodistally curved, as Geological Museum, Missoula, Montana, USA. PALEONTOLOGICAL JOURNAL Vol. 48 No. 9 2014 ON THE RELATIONSHIPS OF THE PETALODONTIFORMES (CHONDRICHTHYES) 1017 SYSTEMATIC PALEONTOLOGY to the median sagittal plane) of the lateral teeth is CLASS CHONDRICHTHYES small (1.5 mm wide) and has a slightly peaked crown HUXLEY, 1880 and a rectangular heel. The distal tooth is wider than its neighbor (1.9 mm) is and has a horizontal slightly SUBCLASS EUCHONDROCEPHALI LUND ET GROGAN 1997B denticulate crown and