ISSN 0031-0301, Paleontological Journal, 2009, Vol. 43, No. 5, pp. 527–536. © Pleiades Publishing, Ltd., 2009. Original Russian Text © I.A. Mikhailova, E.Yu. Baraboshkin, 2009, published in Paleontologicheskii Zhurnal, 2009, No. 5, pp. 51–60. The Evolution of the Heteromorph and Monomorph Early Cretaceous Ammonites of the Suborder Ancyloceratina Wiedmann I. A. Mikhailova and E. Yu. Baraboshkin Moscow State University. Moscow, 119899 Russia e-mail: [email protected] Received May 10, 2008 Abstract—The relationship between the appearances of heteromorph and monomorph ammonoids and changes in the abiotic environment was studied. The correlation of these processes was examined for different intervals in the Early Cretaceous. The phylogeny of the superfamily Ancyloceratoidea Gill from the time of appearance of early heteromorphs (due to changes in ecological specialization) and the reversal process of the return to monomorph shells is examined for four superfamilies. The origin of monomorph ammonites of the superfamilies Theodoritoidea Baraboshkin et I. Michailova, superfam. nov., Douvilleiceratoidea Parona et Bonarelli, Parahoplitoidea Spath et Deshayesitoidea Stoyanow from heteromorph ancestral families Criocer- atitidae Gill, Ancyloceratidae Gill, Hemihoplitidae Spath, and Heteroceratidae Spath in the superfamily Ancy- loceratoidea Gill is suggested. DOI: 10.1134/S0031030109050086 Key words: ammonites, Early Cretaceous, phylogeny, Ancyloceratina. PHYLOGENY AND COMPOSITION tive due to the heteromorph superfamily Turrilitoidea OF THE SUPERFAMILY Gill (suborder Turrilitina Gill) and the considerably ANCYLOCERATOIDEA GILL less diverse superfamilies Scaphitoidea Gill and Lyto- In accordance with the system of higher taxa of ceratoidea Neumayr (suborder Lytoceratina Hyatt). Jurassic–Cretaceous ammonoids (Beznosov and Among Ammonitida Zittel, the Late Acanthoceratoidea Mikhailova, 1983, 1985, 1991; Bogoslovskaya et al., Grossouvre (150 genera) are dominant. These are the 1990), the suborder Ancyloceratina Wiedmann descendants of the Jurassic–Cretaceous Haplocera- includes heteromorph ancestors and monomorph toidea Zittel (suborder Haploceratina Zittel). In the first descendants (Fig. 1). half of the Early Cretaceous Perisphinctoidea Stein- mann were sufficiently representative (85 genera), and In the recent American Treatise of Invertebrate together with their descendants Desmoceratoidea Zittel Paleontology (Wright et al., 1996), a revision of Creta- and Hoplitoidea H. Douville constituted the suborder ceous ammonoids included the suborder Ancylocera- Perisphinctina Steinmann. The last suborder Ancylo- tina Wiedmann with three superfamilies: Turrilitoidea ceratina Wiedmann (Superfamily Ancyloceratoidea Gill, Scaphitoidea Gill, and Ancyloceratoidea Gill Gill) is slightly less diverse than Turrilitoidea Gill, (Arkell et al., 1957) Fundamental differences between whereas their monomorph descendants Douvilleicera- these superfamilies have been repeatedly stated in toidea Parona et Bonarelli, Deshayesitoidea Stoyanow, many publications. In addition to the nominal super- and Parahoplitoidea Spath are scarce. family Ancyloceratoidea, the suborder Ancyloceratina includes two superfamilies of monomorph ammonoids: In this paper, the superfamily Ancyloceratoidea is superfamily Douvilleiceratoidea Parona et Bonarelli, divided into eight families: Bochianitidae Spath, Ancy- which at the final stage of its evolution possibly became loceratidae Gill, Heteroceratidae Spath, Hemihopliti- heteromorph again (family Astiericeratidae Breistrof- dae Spath, Hamulinidae Gill, Labeceratidae Spath, Pty- fer) and the superfamily Deshayesitoidea Stoyanow choceratidae Gill, and provisionally Macroscaphitidae with two families: Deshayesitidae Stoyanow and possi- Hyatt. The last two should be considered within the bly Parahoplitidae Spath. Turrilitoidea Gill because of their suture. The generic diversity of the superfamilies of Creta- Our understanding of the relationships between the ceous ammonites is shown in the histogram (Fig. 2). heteromorph and monomorph Ancyloceratina is shown The superfamily Phylloceratoidea Zittel (order Phyllo- in Fig. 3. Recently obtained data, in particular the ceratida Zittel) includes the minimal number of genera. establishment of a new genus Theodorites Baraboshkin The order Lytoceratida Hyatt is relatively representa- et I. Michailova, 2006, allowed updating of the phylo- 527 528 MIKHAILOVA, BARABOSHKIN Triassic Jurassic Cretaceous Period Middle Early Middle Early Early Late Late Late Epoch km cn cp br bt al m st a a n g p a b o b h a d k k v c s i i t t t Age Turrili- tina Turrilitaceae Lytoceratida Scaphitaceae Lytoceratina ? Lytocerataceae Tetragonitaceae Phyllocerataceae Phyllo- ceratida Acanthocerataceae Haploceratina Haplocerataceae Oppeliiaceae Sonniniiaceae Hildocerataceae Ammonitina Perisphinctina Ancyloceratina Eoderocerataceae Ammonitida Psilocerataceae Stephanocerataceae Hoplitaceae Desmocerataceae Perisphinctaceae Deshayesitaceae Ancylocerataceae Parahoplitaceae Douvilleicerataceae Fig. 1. Phylogeny of the Jurassic-Cretaceous ammonoids (Beznosov and Mikhailova, 1983). genetic relationships of taxa of family and suprafamil- However, the umbilical perforation may not decrease ial rank. and the transition from monomorphs to heteromorphs The origin of the superfamilies Ancyloceratoidea will be then incomplete. and Perisphinctoidea is not contested. The original Umbilical perforation is found in several genera in family Bochianitidae was apparently ancestral to sev- eral families. Figure 3 shows four families, which were the suborder Ancyloceratina: Leptoceras Uhlig (Thieu- certainly ancestral to monomorph Douvilleiceratoidea, loy, 1966), Paraspiticeras Kilian (Wiedmann, 1966; Parahoplitoidea, Deshayesitoidea, and Theodoritoidea Doguzhaeva and Mikhailova, 1982), Turkmeniceras Baraboshkin et I. Michailova, superfam. nov. Tovbina (Bogdanova, 1971), Theodorites Baraboshkin et I. Michailova (Baraboshkin and Mikhailova, 2006), It was found that the evolutionary transformation of Luppovia Bogdanova, Kakabadze et I. Michailova the shell of potential ancestral monomorphic ammonoids resulted in the development of an umbilical (Kakabadse et al., 1978), Caspianites Casey perforation. This perforation did not affect the embry- (Bogdanova and Mikhailova, 1975), Hemihoplites onic shell. The first whorl always comes into contact Spath (Sharikadze et al., 1989), Audouliceras Thomel with the protoconch. The second whorl, after the initial (Mikhailova and Baraboshkin, 2007), and Leptocera- constriction, is a straight shaft, then becomes a flat arc, toides Thompson. The above genera in some cases are making a circle (Fig. 3, insert). The third whorl begins assigned to the superfamily Ancyloceratoidea Gill, after the second perforated whorl with the first whorl. while others are assigned to their possible descendants. PALEONTOLOGICAL JOURNAL Vol. 43 No. 5 2009 THE EVOLUTION OF THE HETEROMORPH 529 The first whorl with a protoconch is rarely observed, Number of genera but the presence of the umbilical perforation is certain 160 in Koeneniceras I. Michailova et Baraboshkin (Bara- 140 boshkin and Mikhailova, 2002). However, a decrease of the umbilical perforation and completion of the whorl 120 may not be present and the stage of monomorph shells 100 is not reached. 80 The superfamily Ancyloceratoidea is generally less 60 diverse than Turrilitoidea, although the planispiral loosely coiled shell became dominant (family Criocer- 40 atitidae Gill and Ancyloceratidae Gill). While the 20 ammonitid features remained unchanged (trifid umbili- 0 cal lobe (U))—the suture of adult ammonites can be very complicated although restricted to four basic ele- ments: VUID. The transition from the family Heteroceratidae Hoplitoidea Turrilitoidea Spath to the superfamily Deshayesitoidea Stoyanow Scaphitoidea Lytoceratoidea Parahoplitoidea Tetragonitoidea Haploceratoidea Deshayesitoidea Superfamilies Perisphinctoidea Phylloceratoidea (genera Heteroceras, Colchidites Djanelidze, Turkmen- Desmoceratoidea Ancyloceratoidea Acanthoceratoidea iceras) is the most thoroughly studied; the latter is Douvilleiceratoidea included in the superfamily Deshayesitoidea based on the presence of a small perforation. The heteromorph Fig. 2. A histogram showing the number of genera in super- origin of the monomorph Deshayesitoidea is supported families of Cretaceous ammonoids (after Wright et al., 1996, modified). by the reduction of the first umbilical lobe (U1) and a return to a four-lobed suture. The explanation of this fact became possible after such a sutural change was tral to Paraspiticeras, shows a tendency to secondary described in Caspianites wassiliewskyi Renngarten coiling. (Bogdanova and Mikhailova, 1975). The morphogenesis of the suture in the superfamily A crescent-like cross-section of the first whorl is Douvilleiceratoidea proceeds by the appearance of new replaced in C. wassiliewskyi and similar forms by a elements by separating the umbilical (U) and inner lat- rounded cross-section. Therefore, this five-lobed pri- eral1 (I) lobes to form the lobes U , U , I , and I . mary suture, inherited from Perisphinctoidea, became 1 2 1 2 reduced and shifted to the initial stages, being pre- Schindewolf (1966) studied sutural morphogenesis in served in the second- or third-line suture (Fig. 4). This the ancestral genus Paraspiticeras (in P. schindewolfi type of primary suture—unstable five-lobed suture—is Wiedmann). The separation of two umbilical lobes probably typical for most ancyloceratids.