The extant family of sawfishes () inhabits warm shallow marine waters worldwide. Despite their shark-like form, they are batoids. Extinct "sawfish" material, particularly their rostral spines, are a common component of a day's collecting in the Late Cretaceous of the western North Atlantic. If greater effort is expended by saving the finer gravel for closer scrutiny, the investment will return oral teeth as well. Unlike the modern which have rostral spines imbedded in sockets of hardened cartilage, the sclerorhynchid's were skin-mounted on the snout (Bigelow & Schroeder 1953). In describing these modified dermal denticles, Cappetta (1987: 150) referred to the cusps as "caps" and their bases, as peduncles". According to Cappetta, Ischyrhiza is known only from oral (to 7 mm in width) and rostral (to 6 cm in height) teeth found in Upper Cretaceous sediments of Europe, Africa and the Americas. Manning (pers. comm. 2007) noted that associated "rostral denticles" and vertebral centra of I. mira are now known from the Early Campanian of Alabama; the centra are circular and relatively thin.

Ischyrhiza mira LEIDY 1856. Two of the rostral spines illustrated in Figure (b & c) are rather typical complete specimens of I. mira. The cap is rather erect or lingually inclined (weakly) and laterally compressed - the enameloid is smooth. A strong cutting edge usually remains on the upper posterior edge (convex portion) of the cap. The peduncle is massive, expanding basally; depressions along the basal lateral face create a finger-like appearance. In the Late Cretaceous of the East/Gulf Coast and Interor Sea of North America, this taxon is widespread and often quite common. Some of the earlier and more recent reports include:

  • Leidy (1856a: 221) described Onchosaurus mirus from the Campanian "Green Sand" of New Jersey and (1856b: 256) Ischyrhiza antiqua (Emmons collection) from North Carolina.
  • Emmons (1858: 225) included as I. antiqua from the "Miocene" of the Neuse River (likely Campanian) in North Carolina.
  • Leidy (1860:120) synonimized I. antiqua with mira and added South Carolina & Mississippi to its range.
  • Leriche (1942) described Raja texana for I. mira oral teeth from the Maastrichtian of Texas.
  • McNulty & Slaughter (1962) reported I. mira present in Turonian through Maastrichtian sediments of Texas.
  • Case (1979: 850) reported a rostral spine from the Peedee Fm. (Maastrichtian) of North Carolina.
  • Williamson et al (1989: 241) included I. mira in the Santonian of New Mexico.
  • Case et al (2001:93, pl 6, fig 126-132) reported I. mira based on oral teeth and rostral denticles from the Santonian of Georgia. In this paper they also erected I. georgiensis for a rostral denticle design with a striated cap. Elasmo.com deems the spine-design distinct from other described examples but not convinced it should be included as Ischyrhiza.
  • Beker et al (2004) I. mira from the Fox Hills Fm. (Maastrichtian) of South Dakota.
  • Kriwet (2004) wrote that using cladistic principles and phylogenic analysis, appeared to represent a sister group to the Pristiformes and proposed the order Sclerorhynchiformes.
  • Manning (2006) reported I. mira as present in Late Santonian through Late Maastrichtian deposits in Mississippi.
  • Beker (2006: 707) included I. mira in the Arkadelphia Fm. fauna (Maastrichtian) of Arkansas.
  • Bourdon et al (2011: 35) reported as Ischyrhiza aff I. mira, rostral spines and oral teeth from the Point Lookout Fm. (E-M Santonian) of New Mexico. They noted the unusually small size and presence of low ridges on some of the teeth (Figs. - below)
  • Hamm & Cicimurri (2011: 118) included as Ischyrhiza schneideri, isolated rostral spines from the Atco Formation (Early Coniacian) of Texas.

    The oral teeth of I. mira are small but aesthetically pleasing. Depending on functional position the teeth may be laterally elongated (Fig. b) or compressed (Fig. )). Although somewhat similar to the nurse shark design, these teeth, when complete, can be readily differentiated by their complete nutrient groove and broad labial root lobe width.

    "Ischyrhiza" avonicola ESTES 1964 has been reported from the Campanian and/or Maastrichtian of Wyoming (Estes 1964), New Jersey (Cappetta & Case 1975), Delaware (Lauginiger 1984), Texas (Welton & Farish 1993), Maryland (Hartstein et all 1999), South Dakota (Becker, et al 2004, and others) and Mississippi (Manning 2006).
    Most reports of this taxon include only rostral spines. Recent (2007) collecting in North Carolina yielded a spine (Fig. ) which compares well with Cappetta & Case (1975: 30, fig 8). Manning (2006) suggested that some of the rostral denticles attributed to Ischyrhiza might belong with Ptychotrygon (I think it better to say a ptychotrygonid).

    Ischyrhiza monasterica CASE & CAPPETTA, 1997 was erected for Maastrichtian rostral spines from Texas that were similar to those of I. avonicola but more gracile and elongated. This rostral design has only been reported from the Kemp Clay of Texas, but the below Mississippi specimen (Fig. ) suggests a wider distribution.

    Selected References

    Becker, M., J. Chamberlain, and D. Terry, 2004. Chondrichthyans from the Fairpoint Member of the Fox Hills Formation (Maastrichtian), Meade County, South Dakota. Journal of Vertebrate Paleontology, 24(4):780-793,
    Becker, M, J. Chamberlain, and G. Wolf, 2006. Chondrichthyans from the Arkadelphia Formation (Upper Cretaceous: Upper Maastrichtian) of Hot Spring County, Arkansas. Journal of Paleontology; 80:4; pp 700-716.
    Bigelow, H. and W. Schroeder, 1953. Part 2. Sawfishes, Guitarfishes, Skates and Rays; Chimaeroids in; Fishes of the western North Atlantic. Sears Foundation for Marine Research, Yale University, New Haven.
    Bourdon, J., Wright, K., Lucas, S.G., Spielmann, J.A. and Pence, R., 2011. Selachians from the Upper Cretaceous (Santonian) Hosta Tongue of the Point Lookout Sandstone, central New Mexico. New Mex. Mus. Nat. His. and Sc., Bulletin 52; 54pp.
    Cappetta, H., 1987. Chondrichthyes II. Mesozoic and Cenozoic Elasmobranchii. In: Handbook of Paleoichthyologie, vol. 3b, Gustav Fischer Verleg, Stuttgart, 193 pp.
    Cappetta, H. & G. Case, 1975. Contribution à l'étude des sélaciens du groupe Monmouth (Campanien - Maestrichtian) du New Jersey. Palaeontographica Abteilung A, 151:1-46.
    Case, G., 1979. Cretaceous Selachians from the Peedee Formation (Late Maestrichtian) of Duplin County, North Carolina, Brimleyana, Vol 2, pp 77-89.
    Case, G. and H. Cappetta. 1997. A new selachian fauna from the late Maastrichtian of Texas. Muünchener Geowissenschaften Abhandungen 34:131-189.
    Case, G, D. Schwimmer, P. Borodin and J. Leggett, 2001. A new selachian fauna from the Eutaw Formation (Upper Cretaceous/Early to Middlew Santonian) of Chattahoochee County, Georgia. Palaeontographica Abt. A, 261:83-102.
    Emmons, E., 1858. Agriculture of the eastern counties; together with descriptions of the fossils of the marl beds. Report, North Carolina Geol. Surv. Printed by H.D. Turner, Raleigh, xvi + 314pp.
    Estes, R. 1964. Fossil Vertebrates from the Late Cretaceous Lance Formation, Eastern Wyoming. University of California Publications in Geologic Sciences 49:1-187.
    Hamm, S.A. and D.J. Cicimurri, 2011. Early Coniacian (Late Cretaceous) selachian fauna from the basal Atco Formation, Lower Austin Group, north central Texas; Paludicola [Rochester Institute of Vertebrate Paleontology] 8(3):107-127.
    Hartstein, E., L. Decina and R. Keil, 1999. A Late Cretaceous (Severn Formation) Vertebrate Assemblage from Bowie, Maryland. The Mosasaur, VI:17-23.
    Kriwet, J., 2004. The systematic position of the Cretaceous sclerorhynchid sawfishes (Elasmobranchii, Pristorajea) In: Mezozoic Fishes 3 - Systematics , Palaeoenvironments and Biodiversity. Arratia & Tintori (eds.); Pfeil, Germany. pp 57-73.
    Lauginiger, E. 1984. An upper Campanian vertebrate fauna from the Chesapeake and Delaware Canal, Delaware. The Mosasaur 2:141-149.
    Leidy, J., 1856. Notices of remains of extinct vertebrated animals discovered by Professor E. Emmons. Proc. Acad. Nat. Sci. Philadelphia, 8:255-256.
    Leidy, J., 1860. Description of vertebrate fossils. In: Holmes, F., Post-Pleiocene Fossils of South Carolina. Charleston:Russell and Jones, pp 99-122.
    Leriche, M., 1942. Contribution à l'étude des faunes ichthyologiques marines des terrains Tertiaires de la Plaine Côtière Atlantique et du centre des Etats Unis. Mémoire de la Société Géologique de France, Paris, new series, 43:1-111.
    Manning, E., 2006. Late Campanian vertebrate fauna of the Frankstown site, Prentiss County, Mississippi; systematics, paleoecology, taphonomy, sequence stratigraphy. Unpub. PhD dissertation, Tulane Univ., New Orleans, xvii+419 p., 16 pls.
    McNulty, C. and B. Slaughter, 1962. A new sawfish from the Woodbine Formation (Cretaceous) of Texas. Copeia 1962: 775-777.
    Schwimmer, D., 1986. Late Cretaceous fossils from the Blufftown Formation (Campanian) in western Georgia. The Mosasaur. Delaware Valeey Paleontological Society. pp 109-119.
    Welton, B. and R. Farish, 1993. The Collector's Guide to Fossil Sharks and Rays from the Cretaceous of Texas. Before Time, Texas. 204 pp.
    Williamson, T.E., Lucas, S.G. and Pence, R., 1989. Selachians from the Hosta Tongue of the Point Lookout Sandstone (Upper Cretaceous, Santonian), central New Mexico: New Mexico Geological Society, Guidebook 40, p. 239-245.

     

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