Ceratosphinctes (Ammonitina, Kimmeridgian)

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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’ammonites 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).

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 of the finding of Ceratosphinctes. Fig. 1. Localisation géographique et cadre géologique de la région étudiée (modifié de Suter, 1990), avec l’astérisque pour préciser la récolte in situ de Ceratosphinctes. ● (i) Smooth nucleus and inner whorls characterise early on- Suture lines are better preserved in the larger IGM 6118 togeny in both specimens, up to 4.3 mm in IGM 6118 and (holotype) than in the smaller IGM 6119 (paratype), and no up to 4.4 mm in IGM 6119. crowding of preserved suture lines is identifiable. Fig. 4 shows ● (ii) Sudden development of external and widely separated the suture line obtained from the holotype (IGM 6118) at swellings initiates tuberculation on the periphery of the 25.8 mm, in which the frilling of major elements is well pre- flanks in half-a-whorl (four tubercles), extending to served. The lateral lobe is parallel to the coiling direction, deep 5.2 mm in IGM 6118. This phase is unknown in IGM and well developed, but clearly shallower than the ventral lobe, 619, which shows rib-like subtle undulations of flanks, se- a feature typical for C. rachistrophus (Gemmellaro, 1872: Pl. parated by narrow spaces, between 4.4 and 5.8 mm. 7, Fig. 6; reproduction in Ziegler, 1959: Fig. 4c). However, ● (iii) Rib-like and slightly prominent undulations of shell, poor preservation of the deeper part of the ventral lobe impedes separated by narrower spaces, develop from the middle part its precise reproduction, for both of the accessory lobes in this of the flanks towards shell periphery to connect with spiny, part and the ventral saddle. Moreover, reliable observation of more densely packed marginal tubercles, between 5.2 and the umbilical lobe is not possible due to cancellation by spiny 7.9 mm in IGM 6118. Equivalent sculpture appears in prolongation of the external tubercle from the preceding whorl. IGM 6119 between 5.8 and probably 10 mm. This sculptur- A significant, distinctive feature is the wide first lateral saddle, al phase determined the occurrence of six tubercles per half- which shows asymmetry forced by a greater, subdivided ven- a-whorl in both specimens. tral (external) branch. ● (iv) From 7.9 mm onwards in IGM 6118, and probably from Comparative analysis: The bizarre, cryptic taxon Cerato- 10 but clearly identified at 12 mm in IGM 6119, crescent ribs sphinctes has been considered to include two species, namely connecting larger, external tubercles, and reaching the line of septenarius Quenstedt and rachistrophus Gemmellaro. This is whorl-overlapping with the precedent whorl. This ontogenetic the classical interpretation, even in recent revisions (Schlampp, phase determined the characteristic ornamentation in Cerato- 1991; Schlegelmilch, 1994; Cecca, 2002). However, an alter- sphinctes. In this latter ontogenetic phase, the number of tuber- native hypothesis has been introduced by Schweigert et al. cles per-half-a-whorl is six-to-seven in IGM 6118 and poten- (2002), who envisaged a conspecific relationship (i.e. synony- tially five in IGM 6119 (lacking fragment of shell). Between my) between these two taxa, with no arguments to support this these typical crescent-tuberculated ribs, two to three rather rur- interpretation. siradiate and adorally, slightly concave ribs exist, which eva- At the present state of knowledge, the real separation be- nesce before connecting to the lower part of the flank. tween septenarius and rachistrophus at the species level remains an open question. However, clear, well-established mor- Throughout the ontogeny, the ventral region is slightly con- phological differences between these species are shell size and vex, smoothed and subtly elevated just above the siphuncle in sculpture, the latter rather poorly understood at present (see IGM 6118, in which slightly and adorally convex, subtle ven- below). In fact, apart from shell size and the difficulty in re- tral ribs have been observed at 22.6 mm. The typical, adoral cognising whether the nucleus is sculptured or really smooth projection of rib-like extensions from the tubercles increases (see above), the single most relevant morphological difference, progressively with shell size, and this feature is better ex- apparent from the precise observations made by Cecca (2002), pressed when the typical sculptural phase (iv), diagnostic for seems to be the absence of tuberculation before development of Ceratosphinctes, is accomplished. typical crescent-tuberculated ribs in the smaller German spe- 258 F. Olóriz, A.B. Villaseñor / Geobios 39 (2006) 255–266

Fig. 2. 1–6. Ceratosphinctes rachistrophus amatitlaensis nov. subsp. 1, 2. IGM 6118, holotype, imprint (impression) showing details of sculpture in internal whorls, × 2 and × 1, respectively. 3, 6. IGM 6118, holotype, phragmocone showing four ontogenetic phases, as mentioned in text (i. smooth nucleus; ii. external and widely separated swellings; iii. rib-like and slightly prominent undulations; iv. crescent ribs connecting larger, external tubercles), × 1 and × 2, respectively. 4, 5. IGM 6119, paratype, internal mould showing part of the body chamber and three ontogenetic phases (i. smooth nucleus; iii. rib-like and slightly prominent undulations; iv. crescent ribs connecting larger, external tubercles), × 1 and × 2, respectively. Black scale-bars = 1 cm. F. Olóriz, A.B. Villaseñor / Geobios 39 (2006) 255–266 259

Fig. 3. Diagram showing graphic relationships between umbilical width and shell diameter (in mm). Data from the Betic Cordillera and north-west Sicily specimens (Olóriz, 1975; Cecca, 2002, respectively). Fig. 3. Diagramme de la variation de la largeur de l’ombilic par rapport au diamètre (en millimètres). Individus de la Cordillère Bétique et de Sicile (Olóriz, 1975 ; Cecca, 2002, respectivement). ported, according to data in the papers listed below), the known material for this species is still extremely scarce compared with other components of the ammonite assemblages in which it is registered (Gemmellaro, 1872, 1878, 1882; Nicolis and Parona, 1885; Ziegler, 1959; Geyer, 1963; Wendt, 1965, 1971; Geys- sant, 1966; Bourrouilh and Geyssant, 1968; Olóriz, 1975, 1978; Caracuel, 1996; Cecca, 2002; Martire et al., 2002; this paper for the new subspecies). The usual inadequate preservation, especially of the inner whorls, together with the fact that described specimens of C. rachistrophus are of different shell-sizes, prevents conclusive interpretation of intra-species diversity at present. Although sculptural phase (iv) is typical in C. rachistrophus, Fig. 4. Suture line taken from the holotype, IGM 6118, at 25.8 mm. Grey as well as in the less well-known septenarius, slight variation shading for tubercle related structures. has been identified in coiling and/or sculpture in the Gemmel- Fig. 4. Ligne cloisonnaire de l’holotype IGM 6118, à 25,8 mm. En grisé structures liées aux tubercules. laro species (Bourrouilh and Geyssant, 1968; Olóriz, 1975; Cecca, 2002; this paper). In addition, Ceratosphinctes sp. 1 cies. This feature could be interpreted in two, opposite ways: described by Olóriz (1978: p. 202) is a juvenile, most probably (i) invalidating the assertion made by Schweigert et al. (2002); incomplete specimen (no sutures preserved), which impedes its and (ii) as the phenotype expression of sexual dimorphism (a precise interpretation. Data provided by Cecca (2002), on the possibility envisaged by Schlampp, 1991), thus reinforcing the original material of rachistrophus studied by Gemmellaro, in- interpretation made by Schweigert et al. (2002). Unfortunately, dicate limitations of Gemmellaro’s interpretation of inner- neither a precise biohorizon-stratigraphy nor co-occurrence of whorl sculpture. In fact, the exclusive fine ribbing in the lecto- the two species exists to provide empirical support to address type, erected by Cecca (2002), below a shell size of 30–35 mm this problem. In addition, palaeobiogeography establishes a was misinterpreted by Gemmellaro (as stated by Cecca, 2002), fairly distinct separation of these two species, reported by and tuberculation really exists at least at a shell size of 20 mm Quenstedt (1858) and Gemmellaro (1872). The former, which in the Sicilian material (paralectotype in Cecca, 2002). In con- is type species of Ceratosphinctes, is smaller and restricted to trast, exclusive Nebrodites-like ribbing characterises sculpture epicontinental, or even scantier, northernmost records. below 25 mm in the smaller Ceratosphinctes septenarius Although the record of the larger species rachistrophus is more (Quenstedt), whereas typical crescent-tuberculated ribs are ex- abundant (at least 11 specimens and fragments have been re- clusive at greater diameters.

Fig. 2. 1–6. Ceratosphinctes rachistrophus amatitlaensis nov. subsp. 1, 2. IGM 6118, holotype, empreinte montrant l’ornementation des tours internes, × 2 et × 1, respectivement. 3, 6. IGM 6118, holotype, phragmocône montrant les quatre phases ontogéniques (i. nucléus lisse ; ii. tubercules externes nettement espacés ; iii. faibles ondulations côteformes ; iv. côtes crescentiformes avec tubercules externes forts), × 1 et × 2, respectivement. 4, 5. IGM 6119, paratype, moule interne montrant une partie de la loge et trois phases ontogéniques (i. nucléus lisse ; iii. faibles ondulations côteformes ; iv. côtes crescentiformes avec tubercules externes forts), × 1 et × 2, respectivement. Échelles en noir = 1 cm. 260 F. Olóriz, A.B. Villaseñor / Geobios 39 (2006) 255–266

Fig. 5. 1–3. Orthaspidoceras of the uhlandi (Oppel) – ziegleri Checa group, IGM 6120, lateral, frontal and ventral views. 4. Idoceras of the durangense- neohispanicum-bösei group Burckhardt, IGM 6121. 5. Idoceras of the balderum Burckhart non Oppel – lorioli Burckhardt group, IGM 6122. 6–9. Ochetoceras cf. neohispanicum Burckhardt, IGM 6123-6126, respectively. 10, 11. Sutneria of the cyclodorsata (Moesch) group, lateral and ventral views, IGM 6127. 12. Taramelliceras sp., IGM 6128a. 13. Taramelliceras of the compsum (Oppel) group, IGM 6129. 14. Aulacomyella sp. IGM 6128b. All specimens at natural size (black scale-bars = 1 cm). F. Olóriz, A.B. Villaseñor / Geobios 39 (2006) 255–266 261

Table 1 cimens, given that the latter are preserved as internal moulds— Dimensions of C. rachistrophus amatitlaensis nov. subsp. (in mm) i.e. without preservation of an epigenised shell that would fa- Mensurations de C. rachistrophus amatitlaensis nov. subsp. (en millimètres). vour recognition of delicate structures. The significantly wide Specimen DUHWU/DH/D first lateral saddle observed in the Mexican holotype IGM IGM 6118 36.8 15.5 12 0.59 0.25 62.2 6118 cannot be used conclusively as a distinctive trait versus 26.3 11.5 0.24 47.9 0.55 European-African specimens, since no sutures are known other 17.2 8.3 0.27 29.8 0.57 than that of the Gemmellaro paralectotype (Cecca, 2002) and 14.8 6.4 0.24 25.8 0.57 the more eroded one identified in the Majorcan specimen de- 10.9 5.7 6.4 0.58 0.25 22.1 scribed by Bourrouilh and Geyssant (1968). In fact, both of 10.8 5 0.26 18.8 0.57 these specimens are preserved as internal moulds and, there- 9.4 4.4 5.8 0.53 0.24 17.7 fore, comparative simplification of preserved sutures might be 7.8 3.6 0.24 14.5 0.53 expected. Whatever the real importance of the wide first lateral 7.1 3.5 0.27 12.6 0.56 saddle in the Mexican holotype, its different morphology could 6.1 2.9 0.27 10.7 0.57 be interpreted as reinforcing the taxonomic interpretation pro- 5.1 2.4 0.25 9.4 0.54 posed below. 4.4 2.2 0.27 8 0.55 In accordance with the above, we interpret the Mexican spe- 3.7 1.7 0.25 6.8 0.54 cimens described as belonging to the same morphospace as 3.1 1.4 0.23 6 0.51 rachistrophus, first identified by Gemmellaro (1872). The most 2.3 1.2 0.23 5.1 0.45 significant differences of Mexican specimens versus this west- 1.4 3.2 0.43 Tethyan species seem to be the lower degree of coiling during IGM 6119 the early ontogeny and the earlier appearance of tuberculation, 25.2 15.3 6 4.6 0.60 0.23 other sculptural traits being of secondary value and difficult 19.5 11.2 4.3 0.57 0.22 evaluation according to existing material at the same shell size 15.1 8.6 3.5 0.56 0.23 (eight tubercles in the Gemmellaro type versus six in the Mex- 11.6 6.8 2.6 0.58 0.22 ican specimens). However, precise evaluation of coiling below 8.8 5.2 2 0.59 0.22 20 mm is not possible in the Gemmellaro types (Cecca, 2002), 8.2 4.5 1.7 0.54 0.20 and no published information from other Tethyan specimens 7.2 3.8 1.4 0.52 0.19 serves this purpose. Given the limited comparison with the 5.9 3.1 1.2 0.52 0.20 paralectotype of rachistrophus (Gemmellaro, 1872: Pl. 7, 4.8 2.6 0.8 0.54 0.16 Fig. 6), we prefer not to make a conclusive interpretation of D: diameter; U: umbilical diameter; H: whorl-height; W: whorl-width; U/D: the differences observed in the incomplete sutural pattern re- umbilicus/diameter ratio; H/D: whorl-height/diameter ratio. D : diamètre ; U : largeur de l’ombilic ; H : hauteur du tour ; W ; épaisseur du cognised. Thus, the specimens described from the surroundings tour ; U/D : rapport entre la largeur de l’ombilic et le diamètre ; H/D : rapport of Amatitla (San Luis Potosí, Mexico) could be interpreted as a entre la hauteur du tour et le diamètre. local variation of the Gemmellaro species or, alternatively, as a new taxon at the species level. Following our previous treat- In the Mexican specimens described, the interpretation of ment of new findings of Tethyan-related taxa in Mexico ontogenetic differences in sculpture can be summarised as fol- (Olóriz and Villaseñor, 1999; Olóriz et al., 2000; Villaseñor lows: sculptural phase (ii) in the holotype IGM 6118 clearly et al., 2003), we favour their present interpretation as a local represents an abrupt phenotype deviation, given that phases subspecies—i.e. C. rachistrophus amatitlaensis nov. subsp. (i) and (iii) are equivalent in the specimens described. Due to (see below arguments other than morphology to support this the clear morphological deviation it produces, without relevant interpretation). effect either on the final diameter of sculptural phase (i) or on Comparison of the Mexican specimens described with later ontogeny in either of these specimens, phase (ii) in holo- C. septenarius (Quenstedt) reveals a lack of the smooth shell type IGM 6118 could represent early, episodic innovation. In during early ontogeny in the German species (poor preserva- contrast, the slight, differential diameter for turnover of phase tion?), which developed a more complete, Nebrodites-like rib- (iii) by phase (iv) among the specimens described could repre- bing on the flanks, before establishing the typical sculpture for sent heterochrony in the timing of phenotype expression. How- Ceratosphinctes related to crescent-tuberculated ribs. ever, incomplete preservation impedes the identification of the precise heterochrony-type. These morphological differences 3. Biostratigraphic interpretation well adapt intra-species diversity. In addition, ribbing in the spaces between tubercles cannot be conclusively taken as a The specimens described were gathered from two silty lime- typical sculptural feature in Mexican versus Euro-African spe- stone beds, together with mostly incomplete remains of Sutner-

Fig. 5. 1–3. Orthaspidoceras groupe uhlandi (Oppel) – ziegleri Checa, IGM 6120, vues latérale, frontale et ventrale. 4. Idoceras du groupe morphologique durangense-neohispanicum-bösei Burckhardt, IGM 6121. 5. Idoceras du groupe morphologique balderum Burckhart non Oppel – lorioli Burckhardt, IGM 6122. 6– 9. Ochetoceras cf. neohispanicum Burckhardt, IGM 6123-6126, respectivement. 10, 11. Sutneria groupe cyclodorsata (Moesch), vues latérale et ventrale, IGM 6127. 12. Taramelliceras sp., IGM 6128a. 13. Taramelliceras du groupe compsum (Oppel), IGM 6129. 14. Aulacomyella sp. IGM 6128b. Toutes les illustrations en vraie grandeur (échelles en noir = 1 cm). 262 F. Olóriz, A.B. Villaseñor / Geobios 39 (2006) 255–266

Fig. 6. Dispersion pattern for genus Ceratosphinctes. Palaeogeography according to data from López-Ramos (1983); Salvador (1991); Cecca et al. (1993); Marton and Buffler (1999); Aurell et al. (2002); Olóriz et al. (2003). B: Betic Cordillera (Subbetic Zone and Intermediate Units, southern Spain), IB: Iberian Basin s. Salas and Casas (1993) (Sa Montenegrelo, north-eastern Spain), Ma: Majorca (Balearic Archipelago, Spain), PR: Moroccan Pre-rift (Morocco), SA: Schwabian Alps (southern Germany), Si: north-western Sicily (Trapanese Domain, Italy), VA: Venetian Alps (northern Italy). Data taken from: B (Olóriz, 1975, 1978; Caracuel, 1996); IB (Geyer, 1963); Ma (Bourrouilh and Geyssant, 1968); PR (Geyssant, 1966); SA (Quenstedt, 1858, 1887–1888; Engel, 1908; Ziegler, 1959; Schlampp, 1991; Schlegelmilch, 1994); Si (Gemmellaro, 1872, 1878, 1882; Wendt, 1965, 1971; Cecca, 2002; Martire et al., 2002). Fig. 6. Schéma de répartition paléobiogéographique du genre Ceratosphinctes. Paléogéographie d’après López-Ramos (1983) ; Salvador (1991) ; Cecca et al. (1993) ; Marton et Buffler (1999) ; Aurell et al. (2002) ; Olóriz et al. (2003). B : Chaîne Bétique (Zone Subbétique et Unités Intermédiaires, Espagne méridionale), IB: Basin Ibérique s. Salas and Casas (1993) (Sa Montenegrelo, nord-est Espagne), Ma : Majorque (Iles Baléares, Espagne), PR : Chaîne prérifaine (Maroc), SA : Jura Souabe (Allemagne méridionale), Si : nord-ouest de la Sicile (Domaine Trapanese, Italie), VA : Alpes Vénitiennes (Italie du Nord). Données de : B (Olóriz, 1975, 1978 ; Caracuel, 1996) ; IB (Geyer, 1963) ; Ma (Bourrouilh et Geyssant, 1968) ; PR (Geyssant, 1966) ; SA (Quenstedt, 1858, 1887–1888 ; Engel, 1908 ; Ziegler, 1959 ; Schlampp, 1991 ; Schlegelmilch, 1994) ; Si (Gemmellaro, 1872, 1878, 1882 ; Wendt, 1965, 1971 ; Cecca, 2002 ; Martire et al., 2002). ia of the cyclodorsata (Moesch) group, Glochiceras or Lingu- Majorca (e.g. Geyer, 1963; Bourrouilh and Geyssant, 1968). laticeras sp., Orthaspidoceras of the uhlandi (Oppel) – ziegleri Our interpretation agrees with all previous ones based on Checa groups, Taramelliceras sp., Taramelliceras of the comp- west-Tethyan records (citations above) of C. rachistrophus sum (Oppel) group (some fragmented individuals being identi- (Gemmellaro), and differs slightly from the comparatively re- cal to Oppelia (Neumayria) flexuosa costata Burckhardt non strictive age assumption made by Cecca (2002) in his recent Quenstedt), Ochetoceras cf. neohispanicum Burckhardt, and revision of the Gemmellaro types. In addition, the registered Idoceras of the durangense-neohispanicum-bösei Burckhardt ammonite assemblage, Ceratosphinctes included, and the bios- and balderum Burckhardt non Oppel – lorioli Burckhardt mor- tratigraphic interpretations proposed by Villaseñor et al. phological plexus (Fig. 5(1-13)). On this basis, and following (2000), reinforce each other to improve the updated biostrati- Geyer (1963), Bourrouilh and Geyssant (1968, which reinter- graphy for Kimmeridgian deposits in Mexico. preted data in Nicolis and Parona, 1885; Geyssant, 1966; According to the above, the genus Ceratosphinctes can be Wendt, 1965), Olóriz (1975, 1978), Caracuel (1996) and Villa- confirmed as a precise age-marker within the Kimmeridgian, señor et al. (2000), a late-Early to early-Late Kimmeridgian age and its proven large biogeographic range provides a useful reference for long-distance biostratigraphic correlation below the is envisaged for C. rachistrophus amatitlaensis nov. subsp. ammonite biozone level. Therefore, its biostratigraphic interpretation as belonging to stratigraphic horizons close to the Lower/Upper Kimmeridgian 4. Palaeobiogeographic interpretation boundary (twofold division) in the Taman Fm. is favoured. In addition, this interpretation places the stratigraphic interval ty- The wide biogeographic range of the genus Ceratosphinctes pical for Mexican Ceratosphinctes in close relation to the con- is illustrated by the dispersion pattern shown in Fig. 6. Such a densed section assumed to be related to the latest Early Kim- dispersion pattern (s. Amstrong, 1977; Dingle, 1996; Olóriz, meridgian maximum flooding in Iberia (Marques et al., 1991). 1988 for extended treatment; Olóriz et al., 2000 for application The latter agrees with the record of C. rachistrophus (Gemmel- to Upper Jurassic ammonites in Mexico) implies great diffi- laro) from condensed (comparatively nodular) horizons inter- culty in interpreting the underlying biogeographical dynamics calated in extended hemipelagites in north-eastern Iberia and (dispersal s. Amstrong, 1977; Brown and Gibson, 1983; Din- F. Olóriz, A.B. Villaseñor / Geobios 39 (2006) 255–266 263 gle, 1996; Olóriz, 1988 for extended treatment, and Olóriz et Concerning ecological conditions, palaeogeography and real., 2000 for application to Upper Jurassic ammonites in Mex- gional geology indicate epicontinental environments develop- ico) when the case study refers to a rare taxon with a presum- ing on the southern palaeomargin of the North-American Plate ably small population size —i.e. Ceratosphinctes. In fact, the (e.g. Enos, 1983; Scott, 1984; Olóriz et al., 2003), a situation main combined feature in such a dispersion pattern is the re- that applied to Kimmeridgian times (Olóriz, 1987, 1992; Olóriz cord in widely separate areas within the context of a short-lived et al., 1990, 1997, 2003). Abundant benthos (bivalves) and the organism, as assumed from biostratigraphy. Moreover, an ad- absence of Phylloceratina and Lytoceratina (their rarity-to-ab- ditional limitation arises from the fact that no conclusive data sence being a general trait in the Mexican Upper Jurassic) re- exist about intra-species diversity or potential phenotypes for inforce this interpretation and, complementing taphonomy sexual dimorphs. In such a context, taphonomy, ecology and (above), point to depths in the order of tens of metres. This traits of the eco-sedimentary context are of special value for context accords with high endemism in Mexican shelves palaeobiogeographic interpretations. (Olóriz, 1987, 1992; Olóriz et al., 1990), but does not eliminate the possibility for open-sea influence during floodings, which Fossil remains showing traces of epigenised shell are com- would be supported by increasing ammonite diversity and/or mon in the fossiliferous horizons sampled, in which well-pre- the record of Tethyan-like phenotypes (Olóriz et al., 2000; Vil- served and densely packed bivalves (Aulacomyella, Fig. 5(14)) laseñor et al., 2003). Both these features apply to the described overwhelmingly dominate. Ammonites are usually incomplete, record of Ceratosphinctes. In fact, biostratigraphy (above) except for small individuals with lappets (Sutneria, glochicer- places this record in close relation with the well-known sea- atids), and the combination of hollow phragmocones together level highstand during latest-Early to earliest-Late Kimmerid- with body chambers preserved in volume or crushed is typical gian times (twofold division), an environmental scenario also evidence of rapid burial. The lack of size-selection of ammo- identified for Mexican shelves where minor floodings certainly nite carcasses, the melange of relatively heavy, sculptured car- occurred (during the late-Early and Late, but not latest, Kim- casses prone to sinking (Idoceras, Ceratosphintes) and com- meridgian, according to Olóriz et al., 1997, 1999, 2003; Villa- paratively inflated, smooth ones (aspidoceratids), the absence señor et al., 2000). of epibionts, and the preservation of delicate structures (fine As recently demonstrated for Mexico (Olóriz et al., 2000; crenulations, lirae, lappets), reinforce the interpretation of a Villaseñor et al., 2003), phenotypic deviation in ammonites short biostratinomic phase without traces of collision during might be envisaged for colonisers during floodings (i.e. Teth- floating (e.g. Wine, 2004) and sudden burial. Thus, the inter- yan-like ammonites), except for floated shells. Assuming lim- pretation of limited post-mortem transport applies to the am- ited information about intra-species diversity in Cerato- monite assemblage registered (an extended treatment of this sphinctes, this could be the case for the specimens described topic can be found in Chamberlain et al., 1981, among others, and, therefore, their interpretation as a local subspecies, which and in Olóriz et al., 1996 for Upper Jurassic cases, as well as in resulted from an enlarging ecospace for open-sea ammonite- Olóriz et al., 2000 for application to Upper Jurassic ammonite propagules (i.e. early ontogenetic phases up to the end of the assemblages in Mexico). Rapid burial and short time for sedi- neanic stage, but without allusion to founding population size; mentary infilling of neither corroded nor microbored carcasses for using this term in the latter sense see Berggren, 2004) and accord with common crushing during earliest diagenesis, but later growth (i.e. from the juvenile stage onwards in the onto- no fragmentation due to transport with sediment (e.g. Wine, geny) under ecological exigency to local adaptation under new 2004) has been identified. These conditions selectively affected environmental conditions. This interpretation agrees with ammonite propagules being the main dispersing stage in their life ammonites with narrow body chambers (Ochetoceras, Ido- cycles. Hence, the real occurrence of rare ammonites (i.e. bi- ceras), while wider ones (Sutneria, Orthaspidoceras) were pre- zarre records), such as Ceratosphinctes, can be expected to be served in volume. Thus, in situ decaying, narrow, soft bodies evidenced by rare records from separate areas, especially when impeded sedimentary infilling of phragmocones in narrow, fas- they are proven as components of compatible ammonite assem- ter-sinking, buried shells, whereas wider, empty carcasses only blages. In the case study, the composition of the ammonite permitted sedimentary infilling during the short time it oc- assemblage mentioned is in accordance with this approach curred in sediments rich in organic mater, which accords with and allows us to envisage the biogeographical dynamics under- high sedimentary rates. The fact that the body chamber of one lying the occurrence of Ceratosphinctes in the Mexican Huas- of the specimens of Ceratosphinctes described is not preserved teca. The extremely short time that seems to be evidenced cannot be conclusively interpreted in biostratinomic terms, due through Ceratosphinctes biostratigraphy elsewhere impedes to sampling limitations, which impeded the reliable evaluation any conclusive interpretation in terms of vicariance, since no of the degree of carcass completeness. On the basis of all the persistence during a time span after flooding (colonisation) can above, and recognising the limitations derived from non exis- be proved. However, neither a precise centre for dispersal nor tent data about water density (see Maeda and Seilacher, 1996 migratory routes can be demonstrated within a latitudinal zone for an extended treatment of this question), we assume that the north from the equator approximately 30° wide (Fig. 6). No ammonite assemblage registered basically shows an image of records from a similar latitudinal zone south from the equator autochthonous/parautochthonous populations belonging to a could be related to the scanty record of marine, outer-shelf late- local community. Early/early-Late Kimmeridgian deposits, at least for South 264 F. Olóriz, A.B. Villaseñor / Geobios 39 (2006) 255–266

America. In such a context, we envisage Ceratosphinctes as a References rare component of mainly outer-neritic and epioceanic waters during the latest-Early to earliest-Late Kimmeridgian. There- Amstrong, D.M., 1977. Dispersal vs. dispersion: process vs. pattern. Systema- fore, this genus was prone to enter more internal areas on tic Zoology 26, 210–211. shelves during relative sea-level highstands, when they oc- Atrops, F., 1982. La sous-famille des Ataxioceratinae (Ammonitina) dans le curred on epicontinental areas showing favourable conditions Kimméridgien inférieur du Sud-Est de la France; systématique, évolution, for the entry of ammonites belonging to open-sea populations chronostratigraphie des genres Orthosphinctes et Ataxioceras. Documents – included in local, off-shore communities, at least within a geo- des Laboratoires de Géologie de la Faculté des Sciences de Lyon 83, 1 463. graphical zone up to 30° north from the equator. Aurell, M., Meléndez, G., Olóriz, F., (Coords.), Bádenas, B., Caracuel, J., Gar- Given the case under study, the assumed separation or in- cía-Ramos, J.C., Goy, A., Linares, A., Quesada, S., Robles, S., Rodríguez- creasing distance between Ceratosphinctes individuals, without Tovar, F.J., Rosales, I., Sandoval, J., Suarez De Centi, C., Tavera, J.M., control by them (i.e. dispersal as considered above), is inter- Valenzuela, M., 2002. Jurassic. In: Gibbons, W., Moreno, T. (Eds.), The – preted as preceding disconnection (i.e. vicariancy) better than Geology of Spain. Geological Society, London, pp. 213 253. Bádenas, B., Aurell, M., 2001. Kimmeridgian palaeogeography and basin evo- related to ranging (s. Dingle, 1996) or to station keeping or lution of northeastern Iberia. Palaeogeography, Palaeoclimatology, Pa- home-range displacements (e.g. Kennedy, 1985). In fact, a par- laeoecology 168, 291–310. ticularly favourable case of “accidental” displacement (e.g. Barthel, K.W., 1957. 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