FIGURE 1. Map of Mexico with approximate locations for reported records of Lower Kimmeridgian ataxioceratin ammonites mentioned in text, with reference to Mexican states. Light brown (Oaxaca state). Black star (town of Tlaxiaco at the surroundings of which Schneidia lopeztichai [Cantú-Chapa] was found). Red dots (north-to-south surface records reported and illustrated by López-Caballero, 2009 from Coahuila; Villaseñor, 1991 and Villaseñor et al., 2000, 2015 from Zacatecas; Cantú-Chapa, 1984 and Jiménez-López, 2011 from San Luis Potosí; and Cantú-Chapa, 1991 from Oaxaca). Green triangle (subsurface record reported and illustrated from Veracruz by Cantú-Chapa, 2001). Purple square (subsurface records reported without illustration by Cantú-Chapa, 1969, 1971).

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FIGURE 2. 1 - Type of Ataxioceras ( Ataxioceras ) lopeztichae as illustrated by Cantú-Chapa (1991), and re-interpreted as Schneidia lopeztichai (Cantú-Chapa); reproduced with permission of the Revista Mexicana de Ciencias Geológicas. 2 - Ribbing pattern of Schneidia lopeztichai (Cantú-Chapa) obtained from computer image-analysis showing sculpture relief according to the degree of shading (dark to light for higher to lower relief) and white for inter-ribs and depressed spaces.

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FIGURE 3. Bivariate plot of ribbing curves for Schneidia lussasense (Atrops, 1982), Schneidia lopeztichai (Cantú-Chapa, 1991) and involute “species” assigned to genus Ataxioceras by Wegele (1929), Schneid (1944), and Geyer (1961). Mainly phragmocones of nominal “species” of Ataxioceras, revised or not after their original interpretation (green). Taxa synonymous of Schneidia lussasense according to Atrops, 1982 (blue). Schneidia lopeztichai (Cantú-Chapa) (red). Schneidia lussasense from SE France in Atrops, 1982 (orange). Note less number of nominal species than in Figure 4 because of unidentified precise data about shell diameter. Dubious interpretation for small specimen below 40-50 mm (*). See text for comparative analyses.

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FIGURE 4. Bivariate plot of primary ribs' crowding vs. coiling degree for Schneidia lussasense (Atrops, 1982; ammonite species in his synonymy list included), Schneidia lopeztichai (Cantú-Chapa, 1991), and involute “species” assigned to genus Ataxioceras by Wegele (1929), Schneid (1944), and Geyer (1961). Colours and asterisk as in Figure 3. Original measurements separated up to 3%-5% from those obtained from the illustrations of the specimens referred (squares). See text for comparative analyses.

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FIGURE 5. Adapertural structures in microconchiate Schneidia, Ataxioceras and Parataxioceras drafted from different authors as indicated: 1 - Schneidia lussasense Atrops (= Ataxioceras [Atax.] subinvolutum [Siemiradzki] in Geyer, 1961, pl 10, fig. 6). 2 - Schneidia lussasense (= Atax. [Schn.] lussasense in Atrops, 1982, pl. 21, fig. 6). 3 - Schneidia lopeztichai (= Atax. [Atax.] lopeztichae in Cantú-Chapa, 1991, fig. 2). 4 - Atax. lothari (Oppel) morphotype lothari Oppel [m] (Moliner, 2009, fig. 2.5 d). 5 - Atax. (Parataxioceras) hyppolytense (Atrops, 1982, pl. 7, fig. 7). 6 - Atax. (Paratax.) hyppolytense (Atrops, 1982, pl. 8, fig. 6). 7 - Atax. (Paratax.) lothari lothari (Oppel) (Atrops, 1982, pl. 42, fig.4). 8 - Atax. (Paratax.) pseudolothari (Geyer, 1961, pl. 16, fig. 6). 9 - Atax. (Paratax.) evolutum (Atrops, 1982, pl.4, fig. 5). 10 - Atax. (Paratax.) planulatum (Quenstedt) (Geyer, 1961, pl. 14, fig. 2). 11 - Atax. (Paratax.) planulatum (Quenstedt) (Atrops, 1982, pl. 43, fig. 6). 12 - Atax. (Paratax.) oppeli (Geyer, 1961, pl. 16, fig. 5). 13 - Atax. (Paratax.) oppeli (Geyer, 1961, pl. 14, fig. 2). 14 - Atax. (Paratax.) pseudoeffrenatum Wegele (Geyer, 1961, pl. 16, fig. 1).

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