PHYLOGENY AND SYSTEMATICS OF PERISPHINCTIDS AS INTERPRE'I D FROM SUTURE ONTOGENIES TAMAZ LOMINADZE & MEVLUD SHARIKADZE Georgian Technical University, Department of Geology and Paleontology, Tbilisi, Georgia. ILYIA KVANTALIANI Geological Instute of Academy of Sciences of Georgia, Tbilisi, Georgia. LOMINADZt~ T., SHARIKADZt~ M. & KVANTALIANI I. 1993. Phylogeny and systematics of Perisphinctids as interpreted from suture ontogenies. [Phylog~nie et syst~matique des P~risphinctid~s interpr~t~es ~ partir de l'On- tog~n~e'des sutures]. GEOBIOS, M.S. n" 15 : 275-286. ABSTRACT Mode of early differentiation of the inner part of the suture line is most important for taxonomy of Perisphinctids. Six types of suture lines can be distinguished, each characteristic of corresponding superfamily : a) the perisphinc- toidal type is characterized by asymmetric division of the internilateral lobe (IlI2), in adult specimens the two branches are non-isolated and aslant ; b) the stephanoceratoidal type is characterized by the formation of a new lobe near the peak of the saddle I/D, on the inner slope of the lobe I and by the following sinking ; c) the olcostephanoidal type is defined by symmetric (IlI1) or asymmetric (I211) division of the lobe I ; d) the desmocera- toidal type by symmetric division of the internilateral lobe (1111) and the formation of sagging suture lobe ; e) the hoplitoidal type by early symmetric division of the lobe I, and by the formation of a generally linear sutural lobe ; and 0 the cardioceratoidal type by the formation of an independent lobe in the saddle I/D. KEYS-WORDS : PERISPHINCTINA, EVOLUTION, SUTURE LINE, PHYLOGENESIS. R~SUM~ Le mode de diff4renciation pr4coce de la partie interne de la ligne de suture s'est r6v~14 d'une importance capitale pour la taxinomie des Perisphinctides. Ainsi, on peut distinguer six types de lignes de suture, chacun ~tant carac- t~ristique d'une superfamille : a) le type p~risphincto~de montre une division asym~trique du lobe lat~ro-interne (IlI2), les deux branches obliques n'~tant pas isol~es sur les exemplaires adultes ; b) le type st4phanocerato~de est caract4ris~ par la formation d'un nouveau lobe pros du sommet de la selle I/D, sur la pente interne du lobe Iet sur les pentes suivantes ; c) le type olcost~phano~de est d~fini par la division sym~trique (Ili1) ou asym~trique (I211) du lobe I ; d) le type desmoceratoide montre la division sym~trique du lobe lateral interne (Ili1) et la formation d'un lobe arqu~ ; e) le type hoplitoide se singularise par une division sym~trique pr~coce du lobe Iet par la formation d'un lobe sutural g~n~ralement lin~aire ; enfin 0 le type cardioc~rato~de pr@sente la formation d'un lobe ind~pendant darts la selle I/D. MOTS-CLI~S : PERISPHINCTINA, I~VOLUTION, LIGNE DE SUTURE, PHYLOGEN~SE. INTRODUCTION We have thoroughly investigated the ontogeny of hundreds of suture lines in Perisphinctina. The Perisphinctina represent one of the most signifi- data attained enable us to establish various cant and widespread group of ammonites. They trends in their evolution. are of great importance for the Jurassic and Cre- When considering the problems of suture line taceous biostratigraphy as well as for the solu- evolution in onto-phylogeny, the mode of for- tion of many questions of ammonites biology. mation of new elements, [indexation of suture 276 (1989) ~o a certain degree differs from the termi- i nology suggested in this paper], their location ,:,,,Vl and pattern as well as the discrimination of ho- I mologous and analogous lobes deserve special at- r tention. The processes of formation and evolution of new elements of suture lines were discussed in historical aspect. Besidesour own observations, data of other au- thors have been analyzed (Westermann 1956 ; Schindewolf 1963, 1965, 1966 ; Mikhailova 1983 ; Kullmann & Wiedmann 1970 ; Wiedmann & \ ~W2.2 Kullmann 1981 ; Thierry 1975, 1978 ; Shevirev 1960 ; Beznosov 1960 ; Alekseev 1982 ; Shulgina L u ,(D 1985, and others). Comparison of some ammonoid suture-symbol terminologies is given below (Table 1). ~W0,25 Wedekind- Ruzhentsev Terminology Schindewolf accepted by us E, external lobe V, ventral lobe V, ventral lobe I, internal lobe D, dorsal lobe D, dorsal lobe L, lateral lobe U, umbilical lobe L, lateral lobe U1, first umbilical I, internilateral I, internilateral lobe lobe lobe U2, second umbilical Ui,first umbilical U, umbilical J lobe lobe lobe Figure 1 - Ontogenetic development of suture line in Macro- vephalites sp. juv. ; sample N301/1, Northern Caucasus, r. Table I Ardon, Lower Callovian. 1,2 - first and second lines ; Wl,W2...- first, second and etc. whorls. In most Perisphinctina the primary suture and initial lobe lines consist of five lobes. These are : ventral lobe (V), lateral lobe (L), umbilical lobe tion of the secondary saddle may be considered as (U), internilateral (I) and dorsal lobe (D). The a result of their location on the umbilical seam, ventral lobe is always bifid, while the other lobes where new elements usually are formed and on are undivided. It is noteworthy that in Macro- the other hand of the whorl narrowing in the cephalites the primary suture is sixlobate (Fig. 1). area of primary constriction. The existence of a The sixth element occurs as a result of division of sixlobate primary suture in the above mentioned the umbilical lobe. At the base of the latter a ammonites may also be the result of relatively small secon- dary saddle becomes reduced and high chamber pressure at this early stage of evo- the suture line becomes fivelobate. It should be lution - compared with the period of reduction of noted that a similar pattern is observed in Tetra- the secondary saddle. gonitidae (Schindewolf 1968 ; Mikhailova 1977, 1979 ; Krivoshapkina 1978 ; Sharikadze 1984). In It must be noted, that in Desmoceratoidea and Tetragonitidae, the secondary saddle, which was Hoplitoidea the formation of new lobes is well ac- also formed at the base of umbilical lobe, beco- celereted, and new elements appear in more and mes reduced at the end of the first whorl and the more earlier stages of evolution. For example, the line becomes fivelobate too (Schindewolf & Kri- division of the lobe I in the Early Aptian Pseudo- voshapkina negated this reduction in Tetragoniti- haploceras takes place at the beginning of the se- dae). There is no doubt, that these data cannot cond whorl, in the Late Aptian Pseudosilesites - be considered as evidence for direct genetic rela- in the middle of the first whorl, in the middle tions between Tetragonitidae and Macrocephaliti- Albian Parasilesites (MIKHAILOVA, 1983, fig.79) - dae. Firstly, the bifidity of the umbilical lobe is on the third line, and in the Early Turonian not always well pronounced in these two groups, Beschtubeites beschtubensis ILYIN (Hoplitoidea, and secondly, the secondary saddle vanishes wi- Placenticeratidae) - as soon as in the primary su- thout any trace. It has no influence upon sube- ture (Mikhailova 1983, fig. 106). Thus, also in quent evolution of the lobe. The early formation some Placenticeratidae the primary suture is six- of the umbilical lobe and the subsequent reduc- lobate, but in difference from the above cases the 277 u't VlfVl ^N"b L U | 1) V v ~#6 W3,7 vl 'qq' r.., ~ \ k/ " '' U ~W3.5 \ ./-V~ w 3 W18s IF'~,L ~J2 hF~ 'r V! L U I2I I D J.. "%2 % ,,./ V Tv L/W! x..!~,~.[~.~.j. Wo,2 ~ Wo,65 J Figure 3 - Dorsoplanites gr~cilis SPATH ; sample N2145/26, Figure 2 - Ontogenetic development of suture line in Eplvi~ Eastern slope of nearpolar Ural, r. Jatria, Volgian. gatites nikitini MICHAILOV ; sample Nll/4n Russian Platform, r. Volga, v. Kadhpir, Middle Volgian. The general outline of the ventral lobe remains secondary saddle is not reduced. It should be no- almost invariable in ontogeny and phylogeny. ted, that in all cases under discussion, the exist- Only a limited complication by secondary ele- ence of a six-lobate primary suture has no taxo- ments can be observed. The lateral lobe is almost nomic significance. always asymmetrically trifid with exception of some hoplitidae ; in adult Late Cretaceous Pla- It is worth mentioning that in some Macrocepha- centiceratidae in particular, this lobe is asymme- lites and Cadoceras the primary suture someti- trically bifid (Mikhailova 1983). The umbilical mes "sits astride" of the prosuture. At the same lobe which occurs last in Mezozoic ammonites is time the primary suture looks rudimentary - it is usually the smallest of all initial lobes, it occurs weakly divided. It consists of four lobes that always of the primary suture in a strictly definite strictly differ in size and configuration from each site, i.e. on the lobe and divides it into two equal other as well as from other initial suture lines. It parts. In the area of initial squeeze, as a result of must be noted that the ventral lobe remains un- narrowing of the whorl, the lobe is reduced and divided. looks often like a small hollow. Later on the um- bilical lobe gradually shifts to the margin of the There is a regular size variation of elements of shell. In most cases lobe U becomes trifid and the initial suture lines in ontogeny and in phylo- asymmetrical, though in some Olcostephanoidea geny. In particular, older elements are greater it is asymmetrically bifid (Figs. 2,3). (protolobes : V,L,D) in comparison with younger ones (metalobes : I and U). Lateral and inner No essential changes are observed in the evolu- saddles dominate over the saddles of the primary tion of the dorsal lobe ; the process of complica- suture. Equality between separate elements of tion of the dorsal lobe follows the common sche- suture line is preserved to a considerable extent me of various groups.