versión On-line ISSN 2007-2902
Rev. mex. cienc. geol vol.25 no.2 México ago. 2008
Comment on "The oldest stratigraphic record of the Late Cretaceous shark Ptychodus mortoni Agassiz, from Vallecillo, Nuevo León, northeastern Mexico" by BlancoPiñón et al, Rev. Mex. Cienc. Geol. (2007), 24, 2530
Comentario a "El registro estratigráfico más antiguo del tiburón del Cretácico Tardío Ptychodus mortoni Agassiz, de Valdecillo, Nuevo León, noreste de México" por BlancoPiñón et al., Rev. Mex. Cienc. Geol. (2007), 24, 2530
Wolfgang Stinnesbeck1,2,*, José Guadalupe LópezOliva3, Eberhard Frey4, Christina Ifrim4, and Samuel Giersch4
1 GeologischPaläontologisches Institut, Universität Heidelberg, Im Neuenheimer Feld 234, D69120 Heidelberg, Germany;
2 Former address: Institut für Regionale Geologie, Universität Karlsruhe, Kaiserslr. 12, 76131 Karlsruhe, Germany. * Slinnesbeck@uniheidelberg.de
3 Facultad de Ciencias de la Tierra, Hacienda de Guadalupe, Carretera a Cerro Prieto Km. 10.5, 67700 Linares, N.L., México.
4 Staatliches Museum für Naturkunde, Erbprinzenstr. 13, 76133 Karlsruhe, Germany.
We believe the article by BlancoPiñón et al. (2007) contains severe formal and scientific errors which, to our view, should be revised according to international scientific rules.
The specimen presented by BlancoPiñón et al. (2007) belongs to the type collection of the FCT at Linares. Its correct acronym is UANLFCTVC 341 (VC for Vallecillo) or UANLFCTR (R for reptiles). FCT alone is incorrect and does not allow the identification of the specimen.
Specimen UANLFCTVC341 originates from the Vallecillo area and was discovered in 1995 by one of us (WS) in the collection of the small museum at Vallecillo. The specimen lacks any finding data. Based on the black colour, the high carbonate content as well as the imperfect cleavage of the host rock, it appears to us that the specimen does not originate from the platy limestone member but from the monotonous sediment sequence of black marlstone and limestone overlying the Vallecillo Member. These sediments are widely known from northeastern Mexico as the Agua Nueva Formation. In the Vallecillo area, the unit clearly overlies the platy limestone and is stratigraphically younger. In consequence, the Ptychodus specimen discussed here must also result from stratigraphic levels younger than the Vallecillo limestone (Ifrim, 2006).
BlancoPiñón et al. (2007) refer to the presence of Watinoceras coloradoense (see also BlancoPiñón et al., 2005, where the authors refer to Arkell et al., 1978 for the biostratigraphic assignation of UANLFCTVC341). In fact, the Treatise of Invertebrate Paleontology on Mesozoic ammonoidea was published by Arkell et al. in 1957, and is an overview on generic level only. A more recent volume of the "Treatise" exclusively on Cretaceous ammonites was published by Wright et al. (1996). However, these monographs are entirely taxonomic and do not refer to the stratigraphic significance of W. coloradoense and the dating by BlancoPiñón et al. is thus invalid. W. coloradoense was unknown from the Vallecillo deposits, between 1998 and 2003, when BlancoPiñón studied the site (BlancoPiñón, 2003). Later publications, by Buchy et al. (2005) and Ifrim et al. (2005) refer to W. color adoensis, but they are ignored by BlancoPiñón et al. (2007).
W. coloradoensis does not occur in the black limestone beds of the Agua Nueva Formation. At Vallecillo, this species is restricted to lower part of the platy limestone member, with its last occurrence at least 3 m below the transition into the Agua Nueva Formation s.s. (Ifrim, 2006, Ifrim and Stinnesbeck, 2007). A cooccurrence of Watinoceras and UANLFCTVC341 is thus highly unlikely.
BlancoPiñón et al. (2007, p.28) also mention Spathites and Collignoniceras as representatives of the Vallecillo Member of platy limestones. These genera, however, are representatives of the middle Turonian and not the early Turonian assemblage. In case of cooccurrence with UANLFCTVC341, this specimen would thus be of middle Turonian and not early Turonian age. The stratigraphic occurrence of Ptychodus mortoni at Vallecillo would then be in line with other localities in NE Mexico (e.g., Peyotes, Coahuila and Xilitla, San Luis Potosí), arguing against the title of their contribution ("The oldest record of..."). In consequence, the argumentation of BlancoPiñón et al. (2007) regarding the age of UANLFCTVC341 is incorrect in all aspects. A detailed taxonomic description and biostratigraphic distribution of the ammonites of the Vallecillo Member was recently published by Ifrim (2006) and Ifrim and Stinnesbeck (2007) and is now available.
Other references to the work of our research group are also omitted by BlancoPiñón et al. (2007). For instance, the relationship between the formation of the platy limestone and the latest Cenomanian global oceanic anoxic event (OAE 2) was established by Ifrim et al. (2005), and it was specified by Ifrim (2006). It was not Jacobs et al. (2005) who established the presence of a plesiopedal mosasaur as part of the Vallecillo fossil assemblage, even though these authors briefly mention the existence of this fossil. The detailed taxonomic description of the specimen by Buchy et al. (2005), published in the same volume of the Nederlands Journal of Geosciences, however, was not cited. BlancoPiñón et al. (2007) also omit the record of P. mortoni from the El Rosario quarry, Coahuila, described by Stinnesbeck et al. (2005). This specimen is there precisely dated to early Coniacian age but is not included in the stratigraphic range chart given by BlancoPiñón et al. (2007).
BlancoPiñón et al. (2007) conclude that Ptychodus and other vertebrates with buttonshaped teeth are necessarily durophagous. We believe that this conclusion is erroneous. Studies on the gastric contents of extant pycnodont fishes (e.g., Sparassius) demonstrated that these fishes are omnivorous and well able to prey on fishes and other food items (Ifrim et al, 2005).
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