Fig. 2

Selected Upper Jurassic–Lower Cretaceous aptychi. Specimens figured at c, i, m, o. q–s are coated with ammonium chloride. a–n, q, s–u Praestriaptychus spp., a K952b, Kimmeridge Bay, Middle Volgian, Pallasiodes Zone; b K477, Kimmeridge Bay, Lower Volgian, Pectinatus Zone; c PMO225.170, Janusfjellet Mt, Upper Volgian, Okensis Zone, Originalis Subzone (refigured from Hryniewicz et al. 2015, Fig. 9D); d, f, g Marievka, Upper Volgian: d MSU 121/41, Catenulatum Zone, catenulatum horizon, bed M15, f MSU 121/35, Fulgens Zone, involutum horizon, bed M14, g MSU 121/42, Fulgens Zone, tenuicostatum horizon (?), beds 10–12; e MSU 121/12, Kashpur, Upper Volgian, Fulgens Zone, bed 23, subfulgens horizon: h MSU 121/43, Nordvik, Middle–Upper Volgian boundary beds: i MSU 121/44, Sorkappland, Lower Kimmeridgian, Cymodoce Zone, cymodoce horizon, section 4, bed 5; j, k Kuhn Island, Middle Volgian, Groenlandicus Zone, lambecki horizon, j CASP K16185, k CASP K16154; l MSU 121/20, Veselovskaya 5 well. Middle–Upper Volgian boundary beds: m SGM 1355/89, in situ record within the body chamber of Dorsoplanites sp., Vasstak Elva, Middle Volgian; n specimen in private collection of A. Stupachenko, in situ record within the body chamber of Dichotomoceras sp., Mikhalenino, Upper Oxfordian, Serratum Zone; q MSU 121/27, Glebovo, Middle Volgian, Nikitini Zone; s SGM 1355/57, in situ record withion the body chamber of Laugeites lambecki (Ilov.), Festningen, Middle Volgian, Groenlandicus Zone, lambecki horizon, bed 131; t MSU 121/19, Kelevudagh Mt, Lower Hauterivian, bed 177; u SGM VH17/39, Gorodischi, Upper Kimmeridgian, Autissiodorensis Zone, Subborealis Subzone, subborealis horizon, bed 9/24; o, p Laevilamellaptychus sp., Rybaki, Upper Oxfordian, Serratum Zone, o MSU 121/1, imprint of the inner surface, p MSU 121/2; r imprint of the inner surface of Laevaptychus sp., MSU2549, Hvadukassy, Upper Kimmeridgian, Mutabilis Zone