In the Atlantic Coastal Plain, a day's processing of Late Cretaceous sediments with the intention of capturing small (1-6mm) matrix, results in two or more weeks of off-site processing. The 1-2mm fraction will likely include more than one small rostral spine and a good number of Ptychotrygon teeth. While the oral teeth can be readily identified to genus, the rostral spines lack a clear published record.

The only carefully bulk-sampled Cretaceous material I have is derived from a Wayne Co,, NC Castle Hayne Fm. (Middle Eocene) locale which yields an excellent reworked Late Cretaceous fauna (which appears to include both Tar Heel Fm / Campanian and Peedee Fm / Maastrichtian; this topic is discussed in greater detail on the Black Creek fauna page). The care taken in the collection of this sample rendered it more useful for discussion purposes than less carefully collected sites.

Six specimens (from that sample) are included for discussion purposes and will be referred to at this time as 'types'. Manning (pers com 2007) noted that all are primitive sclerorhynchids; "the more derived ones get larger, elongate the crown, lose the anterior ridges, get dorso-ventrally flattened, and sometimes develop posterior barbs." Terminology will generally follow Deynat & Séret (1996).

  • Type A1 (Fig. ). The most simplified design includes a tall conical peduncle (neck) above splayed (varying degrees) roots. The cusp is much reduced, posteriorly directed and dorsoventrally compressed. The basal margin of the anterior face bears multiple ridges, two of which extend well apically. The anterior face is flat medially and no distinct carina (cutting-edge) is apparent. A design similar to this was included by Manning & Dockery(1992:, pl. 7, fig. 2) as a Ptychotrygon triangularis (REUSS 1844) rostral denticle.
    Manning (pers. com. 2007) in reviewing Figure noted it was, "the most typical P. triangularis rostral denticle, one from the middle of the rostrum. None of these are exactly well-seated on either side of the edge of the rostrum, and it doesn't look like it'd take much to brush them off."
    This rostral spine-design will be referred to on this page as P. vermiculata CAPPETTA 1975, the East Coast Campanian-Maastrichtian designation for the tooth-design referred to by Manning as P. triangularis.2

  • Type A2 (Fig. & ). This design differs from the type A1 by the more greatly splayed roots and a cusp which is only compressed apically. Other aspects of the cusp are nearly identical to the type A1 and likely reflect a positional variation of a spine positioned posterior to the type A1.
    In viewing these specimens, Manning (pers. com. 2007) noted, "Besides the presence of a slight anterior carina in these two, they're also more derived than either A1 or A3 in the reduction of the anterior ridges to little short ridges at the base of each crown. More derived sclerorhynchid rostral denticles lose them entirely...from the reduction of the crown to a conical stub, I'd suggest [they] are posterior rostral denticles."
  • Type A3 (Fig. ). This design differs from the type A2 by its shorter peduncle, greatly splayed roots and more slender posterior crown cusp. Other aspects of the cusp are nearly identical to the type A2 and likely represent a more posterior positional variation of the type A2. Welton & Farish (1993: 140) & Hartstein et al (1999: plate 2, fig 30) included this design as Ischyrhiza cf avonicola ESTES 1964.3
    Manning (pers. com. 2007) noted that this specimen was, "a fairly close match for the rostral denticle of I. "avonicola" in Welton & Farish (1993), which to me is P. triangularis (the type of I. "avonicola" is Late Maastrichtian, has a longer crown, and I interpret it as a far-posterior rostral denticle of I. m. mira)."
  • Type B (Fig. ). Although the crown includes multiple basal ridges as seen in type A2 spines, two of these (dorsal and ventral) form a nearly complete transverse carina. In addition, the posterior margin of the cusp (lateral perspective) is more inflated and the peduncle 'pinched' apically.
    Manning (pers. com. 2007) notes, "... Ptychotrygon triangularis, even though the roots are mostly worn off... the anterior ridges of the crown have been reduced to just the base, making most of the crown smooth. Why there should be dorsal and ventral carina, with a flat anterior edge, I haven't a clue. This seems to me a unique derived character of this individual rostral denticle... doesn't seem very functional ... The anterior carina in more derived sclerorhynchid rostral denticles is usually dead-center on the anterior edge of the crown, ... I might also note that type B also doesn't have a dorsoventrally-compressed crown base, as in A1..."
    Based on both the similarities and differences of this rostral spine-design, it will be referred to as Ptychotrygon sp on the website.

  • Type C (Fig. ). A striking difference with this spine is the cusp-design -- the multiple basal ridges are lacking and an anterior (albeit skewed) carina is present. This specimen compares very well with the I. cf avonicola rostral spine figured in Cappetta & Case (1975: 30, fig 8 e-g) and probably that in Becker et al (2004: 787, fig 5 a-d).
    In viewing this specimen, Manning (pers. com. 2007) noted, "this is a rather progressive rostral. denticle., compared to the others on the page ... The crown is considerably more derived in having a strong anterior carina, and in having lost the primitive-type anterior ridges"; he deemed the type C as a possible positional variation of P. triangularis. He went on to note that "the crown of this rostral denticle is rather like that of the "I. avonicola" (P. triangularis) in Becker, Chamberlain, and Wolf (2006, fig. 4-1 to -4). ...in the Turonian Ischyrhiza mira schneideri primitive rostral denticles have, like I. mira mira posterior rostral denticles and Ptychotrygon ones, been identified in the literature as I. 'avonicola'."
    As this denticle-design has been attributed to I. cf avonicola by other authors and it clearly differs from the type A & B cusp-design ("more derived") it will be attributed on the website to "I. cf avonicola" at this time.

    North Carolina Conclusion

    This short webpage presents a myriad of possibilities regarding what is known and unknown about these 'lateral rostral denticles' (spines) and which interpretation(s) might be followed. I see three distinct types, grouped them accordingly and mapped them to the (oral) teeth of an appropriate taxon.
    Earl viewed them as primitive sclerorhynchid rostral denticles of a single taxon (Ptychotrygon triangularis) that reflected varying morphological states and would say (Manning pers. com. 2007), "as a sclerorhynchid rostral denticle, A1 is of an exceedingly primitive type (although derived relative to a placoid scale) - very small in size, with an elongate base with very short root flanges, a very short crown maintaining the anterior ridges, and with the conical crown strongly posteriorly-recurved, and coming to a sharp posterior point. The more derived variants (some simply juveniles, or ones from the anterior or posterior ends of the rostrum) reduce or lose the anterior ridges, reduce the posterior tip of the crown, and add anterior carinae"

    Texas comments

    Amongst Welton & Farish (1993), Case & Cappetta (1997) and Cappetta & Case (1999) numerous sclerorhynchid rostral spines have been reported from the Late Cretaceous of Texas; interestingly, the above Types A & B are not included. Despite numerous Ptychotrygon oral tooth-designs spanning the Cenomanian-Maastrichtian they reported, these authors did not associate rostral denticles with any of them. Welton & Farish (1993:140) included the Type C spine as Ischyrhiza avonicola. Case & Cappetta (1997:148, Pl. 11 fig. 5) erected Ischyrhiza monasterica for I. avonicola-type spines with elongated cusps; they associated no oral teeth with them.

    Acknowledgements

    Earl Manning played a significant role in this webpage by sharing his observations and experience. We failed to agree on terminology and the appropriate specific names to be employed; but came to overall similar conclusions from very different directions.

    Footnotes

      1.   In discussing this topic with Manning (pers com 2007), he refers to an Estes (1964. p. 14) statement, "Arambourg and Bertin (1958) synonymized Arambourg's (1935) genus Ganopristis with Sclerorhynchus and changed the subfamily name Ganopristinae to Sclerorhynchinae [they were incorrectly in the Fam. Pristidae then, where Estes had them - EM]. The I.C.Z.N. Copenhagen Decisions [1953, p. 36, par. 54 (1) (a)] rule against changing the name of a family-group taxon in the event that the type genus is synonymized. Thus the latter subfamily name must be rejected and Ganopristinae restored."
    I completely agree with Estes on this, and add that, again according to ICZN rules, a subfamily is in the family-group, so Cappetta (1974) was wrong to claim (Cappetta, 1987, p. 146) that he was the author of the Family Sclerorhynchidae, simply by raising it to family rank. Cappetta (1987, p. 148) actually considers Ganopristis valid. The authorship should thus be: Family Ganopristidae Arambourg, 1935 (=Sclerorhynchinae Arambourg & Bertin, 1958).
      2.   The P. vermiculata vs triangularis determination is possibly a lumper vs splitter issue with P. vermiculata perhaps representing a sub-set (chronospecies) of a broader triangularis definition.
      3.   The I. cf avonicola oral tooth-design depicted in Cappetta & Case (1975) is very close to the design included as Ptychotrygon sp A on this website. It is beyond the scope of this paper or the knowledge of this author to argue the proper placement of either.


    Cited References

    Becker, M., Chamberlain, J. and Terry, D., 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, Chamberlain, J and Wolf, G., 2006. Chondrichthyans from the Arkadelphia Formation (Upper Cretaceous: Upper Maastrichtian) of Hot Spring County, Arkansas. Journal of Paleontology; 80:4; pp 700-716.
    Cappetta, H. 1975. Ptychotrygon vermiculata n. sp., sélacien nouveau du Campanien du New Jersey. Comptes Rendus Sommaires de la Société Géologique de France 17:164-166.
    Cappetta, H. and Case, G., 1975. Contribution à l'étude des sélaciens du groupe Monmouth (Campanien - Maestrichtian) du New Jersey. Palaeontographica Abteilung A, 151:1-46.
    Cappetta, H. and Case, G., 1999. Additions aux faunes de sélaciens du Crétacé du Texas (Albien supérieur-Campanien). Palaeoichthyologica, 9, 5-111.
    Case, G. R., and H. Cappetta. 1997. A new selachian fauna from the late Maastrichtian of Texas. Muünchener Geowissenschaften Abhandungen 34:131-189.
    Deynat, P and Séret, B., 1996. Le revêtement cutané des raies, I - Morphologie et arrangement des denticules cutanés. Ann. Sci. Natn., Zoologie, 17(2):65-83.
    Estes, R. 1964. Fossil Vertebrates from the Late Cretaceous Lance Formation, Eastern Wyoming. University of California Publications in Geologic Sciences 49:1-187.
    Hartstein, E., Decina, L. and Keil, R., 1999. A Late Cretaceous (Severn Formation) Vertebrate Assemblage from Bowie, Maryland. The Mosasaur, Vol 6, Delaware Valley Paleontological Society. pp 17-23.
    Manning, E, and Dockery III, D, 1992. A guide to the Frankstown vertebrate fossil locality (Upper Cretaceous), Prentiss County, Mississippi. Mississippi Dept. of Env. Qual., Office of Geology, Circular 4, 43 p., 12 pls.
    Welton, B. and Farish, R., 1993. The Collector's Guide to Fossil Sharks and Rays from the Cretaceous of Texas. Before Time, Texas. 204 pp.

     

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