Geobios 39 (2006) 255–266 http://france.elsevier.com/direct/GEOBIO/ Original article Ceratosphinctes (Ammonitina, Kimmeridgian) in Mexico: from rare but typical inhabitant of west-Tethyan epioceanic and epicontinental waters to a geographically widespread ammonite genus Ceratosphinctes (Ammonitina, Kimméridgien) au Mexique : de rare mais typique élément cantonné dans des eaux épiocéaniques et épicontinentales de l’ouest Téthysien à un genre d’ammonites avec un large range biogéographique Federico Olóriz a,*, Ana Bertha Villaseñor b a Departamento de Estratigrafía y Paleontología, Facultad de Ciencias, Universidad de Granada, Avenida Fuentenueva s/n, 18002 Granada, Spain b Departamento de Paleontología, Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, 04510 México DF, Mexico Received 27 April 2004; accepted 17 November 2004 Available online 26 January 2006 Abstract Two specimens of Ceratosphinctes represent the first record of this taxon in Mexico (Mexican Huasteca), and are interpreted as Cerato- sphinctes rachistrophus amatitlaensis nov. subsp. The subspecies level is used with biogeographic significance, most probably indicating incom- ing propagules and adaptation to local environmental requirements. Biostratigraphy, based on agreement of the composition of the ammonite assemblage that included C. rachistrophus amatitlaensis nov. subsp. and the previous interpretation of ammonite assemblages with Idoceras in Mexico by Villaseñor et al., indicates precise correlation with Tethyan records (uppermost-Lower to lowermost-Upper Kimmeridgian). The dispersion pattern available for Ceratosphinctes is interpreted as related to ecospace enlargement during the relative sea-level highstand of the late-Early Kimmeridgian. © 2006 Elsevier SAS. All rights reserved. Résumé Deux exemplaires de Ceratosphinctes représentent la première mention registre du taxon au Mexique (Huasteca mexicaine), et ont été inter- prété comme Ceratosphinctes rachistrophus amatitlaensis nov. subsp. Le niveau de sous-espèce est utilisé au sens biogéographique, indiquant probablement l’arrivée de propagules et leur adaptation à des conditions locales de l’environnement. L’interprétation biostratigraphique, fondée sur la composition des associations d’ammonites accompagnant C. rachistrophus amatitlaensis nov. subsp. et sur celle des associations d’ammo- nites avec Idoceras au Mexique par Villaseñor et al., indique la corrélation précise avec les enregistrements Téthysien (partie sommitale du Kimméridgien inférieur – partie basale du Kimméridgien supérieur). Le schéma de dispersion disponible pour Ceratosphinctes est considéré comme résultant de l’élargissement de l’espace écologique durant la montée relative du niveau marin vers la fin du Kimméridgien inferieur. © 2006 Elsevier SAS. All rights reserved. Keywords: Ammonites; Ceratosphinctes; Taphonomy; Biostratigraphy; Palaeobiogeography; Kimmeridgian; Mexico Mots clés : Ammonites ; Ceratosphinctes ; Taphonomie ; Biostratigraphie ; Paléobiogéographie ; Kimméridgien ; Mexique * Corresponding author. E-mail address: [email protected] (F. Olóriz). 0016-6995/$ - see front matter © 2006 Elsevier SAS. All rights reserved. doi:10.1016/j.geobios.2004.11.006 256 F. Olóriz, A.B. Villaseñor / Geobios 39 (2006) 255–266 1. Introduction Interpretation at both the family and subfamily levels has been classical from Ziegler (1959) to Cecca (2002), as has been The ammonite taxon Ceratosphinctes Ziegler (1959), which its interpretation as a subgenus of Simosphinctes. However, we is usually considered a subgenus of Simosphinctes Barthel now consider this hypothesis inconclusive. In fact, observa- (1957), but see Schweigert (1997), is a rare Ammonitina most tions made by the authors on inner whorls of Mexican Idoceras usually registered from Tethyan areas to date. In these areas, demonstrate a sculptural affinity with the subfamily Ataxiocer- Ceratosphinctes has been referred to the Gemmellaro species atinae (Olóriz, 2002 in Pavia and Cresta (Sci. Coords.); re- rachistrophus (Gemmellaro, 1872), which was identified in search in progress), rather than with evolutionary lineages de- epioceanic rather than epicontinental deposits (see Olóriz, rived from Passendorferiinae. Doubts also arise about the 1975, 1978 for extended references; Ziegler, 1981). In fact, proposal of subgenus-level relationships between Simo- records of this species reported from hemipelagic-shelf depos- sphinctes and Ceratosphinctes if the interpretation of dimorph- its were only provided by Geyer (1963) from northeastern Iber- ism made by Hantzpergue (1989), and later comments by ia (connecting area for Iberian and Catalan Coastal Ranges Schweigert (1997), apply to support their belonging to different showing palaeogeographic transition between the Catalan Ba- families within Perisphinctoidea, although contradictory or in- sin and the north-eastern Iberian shelf throughout Oxfordian to conclusive interpretations exist of lineage relationships based Lower Kimmeridgian outer-ramp deposits; Salas, 1989; Salas on suture lines (e.g. Barthel, 1957; Ziegler, 1959; Schweigert, and Casas, 1993; Fernández-López et al., 1996; Bádenas and 1997). In addition, interpreted biostratigraphy for the respec- Aurell, 2001), and by Geyssant (1966) from north-western tive type-species tieringensis Fischer and close forms (e.g. Africa (Pre-rift, Morocco); Ziegler (1981) mentioned Algeria Fischer, 1913; Barthel, 1957; Ziegler, 1959; Schairer, 1976; probably taking as correct the citation made by Roman Keupp, 1977; Zeiss, 1981; Atrops, 1982; Hantzpergue, 1989; (1936) from the Tithonian. A single record from transitional, Schlampp, 1991; Schlegelmilch, 1994; Cariou et al., 1997), as slope areas between neritic-shelf and epioceanic environments well as for septenarius Quenstedt (e.g. Quenstedt, 1858, 1887– (ammonitico rosso and related facies) was observed by Bour- 1888; Ziegler, 1959; Schlampp, 1991; Schlegelmilch, 1994; rouilh and Geyssant (1968) at Majorca in the Balearic Archi- Cariou et al., 1997), indicates clearly unconnected stratigraphic pelago (north-western Serres de Llevant). All these records ranges. Thus, the taxonomic scheme presented above must be point to a latest-Early to earliest-Middle (threefold division) considered preliminary. Kimmeridgian age. Thus, Ceratosphinctes rachistrophus Ceratosphinctes rachistrophus amatitlaensis nov. subsp. (Gemmellaro) has been considered a rare, but rather precise (Figs. 2(1,6), 3 and 4i Table 1). age-marker in western Tethys, where records have been inter- Material: Two specimens, IGM 6118 (holotype) and IGM preted as revealing pronounced provincialism (e.g. Ziegler, 6119 (paratype), gathered from silty limestone beds belonging 1981). Outside the Tethys s.s., Ammonites septenarius to the Taman Fm., outcropping among dense covering by for- (Quenstedt, 1858), the type species of subgenus Cerato- est, jungle-like vegetation. National Palaeontological Collec- sphinctes according to Ziegler (1959), was reported from tion, housed in the Institute of Geology (UNAM), Mexico DF. southern Germany (Quenstedt, 1858, 1887–1888; Engel, Derivatio nominis: From the small village of Amatitla (San 1908; Schlampp, 1991; Schlegelmilch, 1994), a relatively Luis Potosí, Mexico). northern part of the Submediterranean province. Schweigert Location: 21°13.735′N–98°51.987′W (Garmin GPS12XL), et al. (2002) considered Ammonites rachistrophus, first de- in the surroundings of Amatitla (San Luis Potosí, Mexico). scribed in western Sicily (Gemmellaro, 1872), as synonymous Measurements: see Table 1. with A. septenarius (Quenstedt, 1858). Description: Specimen IGM 6118 (holotype) is 62.2 mm in The recent finding of Ceratosphinctes in the Mexican Huas- size, and completely chambered, while the smaller IGM 6119 teca (Fig. 1) supports the first report for this taxon in Mexico, (paratype) preserves part of the body-chamber between 23.5 documents a wider palaeobiogeographic range of this taxon, and 25.2 mm, and its present state is more fragmentary. The and contributes to both complete the interpretation of its pa- umbilicus is extremely evolute (0.43–0.6 in IGM 6118, and laeobiogeographic significance and support palaeobiogeo- 0.54–0.6 in IGM 6119), showing a constant coiling degree in graphic models envisaging Late Jurassic ammonite assem- both specimens (Fig. 3 and Table 1). The whorl-section is blages in Mexico as being submitted to episodic influences of ovate between tubercles, but trapezoidal with maximum width epioceanic, Tethyan ammonite assemblages (Olóriz, 1987, on the shell periphery, in coincidence with spiny and progres- 1992; Olóriz et al., 1990, 1997, 2000; Villaseñor et al., 2003). sively clearly divergent tubercles that are located just below the line of whorl-overlapping. No umbilical wall is identifiable, 2. Palaeontological description due to the slight curvature of flanks towards the line of whorl-overlapping. Family PERISPHINCTIDAE Steinmann and Doderlein The sculpture shows four ontogenetic phases (i–iv), the last 1890. of which is typical and well known for identification of this Subfamily IDOCERATINAE Spath 1924. taxon. The two Mexican specimens share three of these sculp- Genus Ceratosphinctes Ziegler 1959. tural phases (i), (iii) and (iv), but they differ in the transitional Type-species: A. septenarius Quenstedt 1858. phase (ii): F. Olóriz, A.B. Villaseñor / Geobios 39 (2006) 255–266 257 Fig. 1. Location and geologic sketch of the area explored (modified from Suter, 1990), with asterisk for precise placement