ISSN 08695938, Stratigraphy and Geological Correlation, 2010, Vol. 18, No. 4, pp. 376–391. © Pleiades Publishing, Ltd., 2010. Original Russian Text © O.A. Lutikov, I.E. Temkin, B.N. Shurygin, 2010, published in Stratigrafiya. Geologicheskaya Korrelyatsiya, 2010, Vol. 18, No. 4, pp. 28–44. Phylogeny and Evolution of Ontogeny of the Family Oxytomidae Ichikawa, 1958 (Mollusca: Bivalvia) O. A. Lutikova, I. E. Temkinb, and B. N. Shuryginc aScientific Research Institute of Paleontology, Stratigraphy and Sedimentology, St. Petersbyrg, Russia email: [email protected] bDivision of Invertebrate Zoology, American Museum of Natural History, New York and Smithsonian Institution, PO Box 37012, MRC 163, Washington, DC 200137012, USA email: [email protected] cInstitute of Petroleum Geology and Geophysics, Siberian Branch, Russian Academy of Sciences pr. Akad. Koptyuga 3, Novosobirsk90, 630090 Russia email: [email protected] Received August 02, 2009; in final form, November 17, 2009 Abstract—We described ontogenies and reconstructed morphogeneses of hinges in some supraspecific taxa of the bivalve family Oxytomidae Ichikawa, 1958 from the Mesozoic of Russia. The phylogeny of the family is reconstructed using evolutionary and cladistic methods. The appearance of the endemic genus Arctotis Bodylevsky, 1960 in the epicontinental seas of Siberia can be explained in terms of gradual transformations of the ligament and byssal apparatus in the Northern Siberian members of Praemeleagrinella Lutikov et Shury gin, 2009 and Praearctotis Lutikov et Shurygin, 2009. Key words: bivalves, Oxytomidae, taxonomy, ontogeny, phylogeny, Mesozoic. DOI: 10.1134/S0869593810040027 INTRODUCTION according to the increase of the coefficients of similar ity in unweighted characters and that a phylogram is Bivalves of the family Oxytomidae Ichikawa, 1958 based on the principle of parsimony, without consider (superfamily Pectinoidea Rafinesque, 1815) are wide ing chronoclines (Krassilov, 1977; Eldredge, Cracraft, spread in the Jurassic and Cretaceous of Russia, North 1980; , 1988). The evolutionary America, Europe, Asia, Australia, and New Zealand Sovremennaya… approach, despite being rather subjective, considers an and are commonly used in biostratigraphy. Longterm assembly of morphological criteria, divergence rates studies of the Mesozoic members of this group from and qualitative differences among taxa. In the evolu Russia and the analysis of numerous publications tionary approach, the ranks of taxa are based on the show that there is a general agreement between most perceived degree of divergence from the common authors in the interpretation of the speciesgroup taxa, ancestor, often ascribing differing ranks to sister while the taxonomies of the genusgroup taxa differ. groups (Calow, 1986). In this paper an attempt is made There is no agreement about generic and subgeneric to use both methods and compare the results. assignment of many species, primarily because of insufficient knowledge of the morphology and func tion of hinge structures. MATERIAL AND METHODS This study is aimed at (1) reconstructing the phy This paper is based on the material from the origi logeny of the genusgroup taxa in the family Oxytomi nal and museum collections of Oxytomidae (Appen dae, mainly based on the characters of the hinge and dix 1). We considered only those taxa that possess the byssal complexes of the north Siberian Jurassic–Cre diagnostic set of characters of the family Oxitomidae taceous members of the family and (2) evaluation of as defined by the current classification (Cox and Newell, characteristics allowing separation and systematiza 1969). To reconstruct the evolution of the family we tion of the genusgroup taxa. examined eight supraspecific taxonomic groups. To The systematization of taxa in paleontology is often avoid confusion due to nomenclatural ranks, these based on phylogenetic reconstructions and to a large groups were considered as equivalent supraspecific extent depends on the methodological approach to taxa without a rank (Appendix 2). Originally, the these reconstructions (Sovremennaya…, 1988). The assignment of the species to supraspecific groups was cladistic method suggests that taxa are grouped made by taking into account all previously known and 376 PHYLOGENY AND EVOLUTION OF ONTOGENY 377 two new supraspecific taxa (Lutikov and Shurygin, taxa was created using the program NDE v.0.5.0 2009). We used exemplars of type species or species (Page, 2001). Of these, six characters were binary, from the type regions to define a set of supraspecific whereas four had three states, and one character had characters. When it was not possible to examine the four states. The coding at the species level was mainly types, we used published original descriptions of type based on the type species. To estimate the taxonomic species. Individual variability was assessed in samples weight of the morphological characters within the from fossil populations. family Oxytomidae, for the 11 chosen characters, we recognized subgroups corresponding to individual states of characters for the cladistic analysis (see Methodology of Studies of Morphogenesis below). We recognized 27 subgroups of oxytomids Because there is no agreement about the choice of (Fig. 1a). After the initial calculation of coefficients of characters determining the hinge mechanisms of oxy similarity (Fig. 1b) in eight supraspecific groups, seven tomids, we partly used the terminology used for buchi were accepted as valid. Groups chosen with identical ids, as the best developed for bivalves with a pterioid characters were considered synonymous. For the cla hinge (Zakharov, 1981). The terminology of oxytomid distic study, morphological trends of the chosen char morphology is discussed in detail in our previous paper acters were examined within major phyletic lineages. (Lutikov and Shurgin, 2009), in which we recognized For the evolutionary method, the phylogenetic recon several types and subtypes of ontogenetic changes of struction was made after the analysis of the chrono the ligament pit (resilifer). The morphogenesis of the clines and recognition of trends. Taking into account hinge structures was studied using the comparison of the trend toward quantitative changes of some charac homologous components in all oxytomids examined. ters in chronological lineages (chronoclines), genus We used Remane’s homology criteria (Severtsov, groups taxa were recognized. For this, the taxonomic 1987). The studies of the hinge were twostaged. At the weight of some characters (e.g., the resilifer obliquity, first stage, we recognized an archetype, a set of non the angle of the ligamental plate, the presence or specialized ancestral (plesiomorphic) characters, for absence of the denticle) was reduced for parallel phy the supposed initial form at the level of the genus logenetic lineages. group taxa. We accepted the morphology of the species Eumorphotis (Asoella) confertoradiata Tokuyama, 1959 (Aviculopectinidae Meek et Hayden, 1864) from the METHODS Lower Norian of Japan as a hypothetical ancestral form. We considered characters with relative symme Phylogenetic Analysis try as nonspecialized a priori. The umbo of the arche type occupied a central position; the wideangled The phylogenetic analysis was performed using two resilifer was delineated by the ligament grooves diverg methods. For the evolutionary method, the phyloge ing from the axis of symmetry; transligament fields netic reconstructions and the presumed taxonomic were of approximately the same size. Further special ranks were based on the morphological analysis. The ization within the family proceeded towards the dis nodes of divergence were determined from a relative tortion of symmetry. At the second stage, the compo taxonomic value of characters based on their stability nents of the hypothetical archetype were compared in the supraspecific groups included in the analysis. with the corresponding homologous components of The order of character transformations was assumed the oxytomid shells. Growth variability was assessed to follow the succession of the historical development primarily in adult specimens by the analysis of growth of the taxon. The extrapolation of phylogenetic con lines. In some cases the interpretation of the changes clusions was done in two stages: (1) from characters to in the ligament and byssal character complexes were a historical succession of ontogenies and (2) from a obtained from the examination of specimens of differ morphological trend in a historical succession of ent sizes from the same sample of borehole core or ontogenies to a taxon of a corresponding rank. samples from the same bed. For the cladistic analysis, the morphological char acter matrix was analyzed under the parsimony as an Recognition of Characters and Morphological Trends optimality criterion using Winnona, (version 2.0; Based on the studies of the Pectinoidea, Shurygin Goloboff, 1999), without preliminary character and Lutikov (1991), we chose 11 characters of the weighting or ordering. The stratigraphically earliest outer and inner shell surfaces for the supraspecific genus Oxytoma was used as an outgroup. The character classification (Appendix 2). The characters were eval data matrices were managed using WINCLADA uated according to the previously developed grada v.1.00.08 (Nixon, 1999–2002). The phylogeny at the tional system (Lutikov and Shurygin, 2009). Based on level of the supraspecific groups considered was recon the characters recognized, a matrix of 11 characters