Invertebrate Zoology, 2017, 14(1): 27–31 © INVERTEBRATE ZOOLOGY, 2017 Evolution of Palaeozoic ammonoid sutures T.B. Leonova Borissiak Paleontological Institute of the Russian Academy of Sciences. 123, Profsoyuznaya str., Moscow, 117647, Russia. E-mail: [email protected] ABSTRACT. The history of the appearance and evolution of the suture, one of the major structural elements of the shells of ammonoids (a subclass of Cephalopoda), is briefly discussed. Its morphology is considered in the Devonian Anarcestida, the first members of which are very similar to the ancestral Bactritoidea, in the Late Devonian Clymeniida, the Devonian–Permian Tornoceratida, the Carboniferous–Permian Prolecanitida and Goni- atitida, and the Permian Ceratitida. Three major trends in the evolution of the suture are recognized in the order Goniatitida, which were instrumental in the subdivision of this order into suborders. Variations of elements of the sutures allow the recognition of the familial, generic, and specific ranks. How to cite this article: Leonova T.B. 2017. Evolution of Palaeozoic ammonoid sutures // Invert. Zool. Vol.14. No.1. P.27–31. doi: 10.15298/invertzool.14.1.05 KEY WORDS. Ammonoids, Paleozoic, evolution, sutures, systematics. Эволюция лопастных линий у палеозойских аммоноидей Т.Б. Леонова Палеонтологический институт им. А.А.Борисяка РАН, Профсоюзная, 123, Москва, 117647 Россия. E-mail: [email protected] РЕЗЮМЕ: Кратко изложена история становления и развития в палеозое лопастной линии, одного из основных структурных элементов раковины аммоноидей (подклас- са цефалопод). Показаны особенности ее строения у девонских Anarcestida, первые представители которых очень близки к своим предкам Bactritoidea, своеобразных позднедевонских Clymeniida, девонско–пермских Tornoceratida, каменноугольно- пермских Prolecanitida и Goniatitida, пермских Ceratitida. В рамках отряда Goniatitida выделено три главных направления развития лопастной линии, которые находят свое выражение в подразделении отряда на три подотряда. Изменения отдельных элемен- тов лопастной линии позволяют выделять таксоны семейственного, родового и видового ранга. Как цитировать эту статью: Leonova T.B. 2017. Evolution of Palaeozoic ammonoid sutures // Invert. Zool. Vol.14. No.1. P.27–31. doi: 10.15298/invertzool.14.1.05 КЛЮЧЕВЫЕ СЛОВА: Аммоноидеи, палеозой, эволюция, лопастные линии. 28 T.B. Leonova monoids. The general sutural outline is charac- teristic of orders and families, whereas its finer details are characteristic of genera and species. The development of a complexly curved septum and fluted dissected suture is the main trend in the evolution of Ammonoidea. The sutural on- togeny retained in the early whorls allows reli- able reconstructions of the phylogeny of closely related taxa. Fig. 1. A shell of Agathiceras mediterraneum Tou- Material and methods manskaya, 1949, Kungurian, Early Permian, showing a phragmocone (with sutures on its surface) and a Despite the technological advances and the body chamber. A — lateral view; B — apertural view. availability of micro-computed tomography, Рис. 1. Раковина Agathiceras mediterraneum Tou- ammonoid sutures are mainly studied using a manskaya, 1949, кунгур, ранняя пермь. Видны light microscope equipped with a drawing arm фрагмокон (с лопастными линиями на поверхно- (camera lucida) to obtain graphic drawings (the сти) и жилая камера. method used for this study). These drawings A — вид с боковой стороны; B — вид со стороны устья. were then scanned and print–ready copies were produced using graphics software, e.g., Introduction CorelDraw. The sutural outlines produced in this way were scaled, and then analyzed and The ammonoids appeared approximately 400 compared. The elements of the sutures were million years ago, at the end of the Early Devo- designated using the terminology of Ruzhencev nian, and after 335 million years of evolution (1960). The study was based on the collections became extinct at the Mesozoic–Cenozoic of Paleozoic ammonoids housed in the Boris- boundary. For two hundred years they were siak Paleontological Institute, Russian Acade- used by palaeontologists as model objects to my of Sciences, and on some previous literature study morphogenesis and phylogeny. Their com- sources. plexly organized shell retaining all ontogenetic stages allows reconstruction of phylogenies of Results and Discussion groups of various systematic ranks. The body plan of ammonoids includes three The research of several generations of palae- main morphological parameters: a coiled shell, ontologists allows the evolution of the sutures to a complex suture, and the presence of a proto- be traced in all Paleozoic orders. In very general conch. The ammonoid shell was subdivided terms, the results of this research can be summa- into a body chamber (from 0.5 to 1.5 whorls) rized as follows. In the Emsian, at the end of the and a phragmocone working as a buoyancy Early Devonian, representatives of the subclass device. Paleontologists usually study ammonoid Ammonoidea had a two-lobed suture inherited sutures formed on the shell surface as an expres- from bactritoids (designated by the formula sion of the intersection of septa (Fig. 1). The VO, i.e., ventral and omnilateral lobes (cover- sutures include lobes (expressions of curved ing the entire flank); these are the earliest am- surfaces directed adorally) separated by orally monoid genera Anetoceras, Erbenoceras, Te- directed saddles. The lobes can be simple, ser- icherticeras, etc. (order Anarcestida, family rated, festooned, etc., whereas the saddles are Anetoceratidae) (Fig. 2). The next stage is the most frequently simply rounded. The sutural appearance of a dorsal lobe (formula VO:D), outlines are taxon-specific, and are used as the which occurred at the end of the Emsian (genera main diagnostic character for Paleozoic am- Mimosphinctes, Talenticeras family Mimo- Evolution of Palaeozoic ammonoid sutures 29 Fig. 2. Evolution of the Paleozoic ammonoid sutures. Рис. 2. Эволюция лопастных линий аммоноидей в палеозое. sphinctidae, etc.). At the very end of the Emsian, the hatchling and by the morphology of several in the order Anarcestina (family Anarcestidae, subsequent septa, in which the number and genera Anarcestes, Cabrieroceras, Archocer- arrangement of lobes is considered to be funda- as, etc.), the omnilateral lobe was replaced by mental for the definition of the body plan of the the umbilical (U), the formula of the suture is mollusk. VU:D (Fig. 2). In the Middle Devonian (Give- Almost the entire diversity of the septal tian), representatives of suborder Gephurocera- margins (sutures) can be found among Anarces- tina (genus Tamarites, etc.) acquire the inner tida (Early Devonian, Emsian — end of the lateral lobe (I); such sutures are described by the Devonian) known to exist in Paleozoic am- formula VU:ID. The external lateral lobe (L) monoids, with the exception of the complexly appeared in the Middle Devonian, when the subdivided sutures of the “Mesozoic type” that four-lobed (VLU:D) order Tornoceratida (ge- appeared at the end of the Paleozoic. For exam- nus Tornoceras, etc.) appeared. In the Late ple, a broad, tripartite ventral lobe appeared in Devonian (Famennian) five-lobed (VLU:ID) the Early Devonian in the suborder Auguritina. Sporadoceratidae (Sporadoceras, etc.) appeared Later, in the Late Devonian, this character reap- (Fig. 2). All subsequent sutural modifications peared in the members of the suborder Ge- appeared on the basis of these five main lobes, phuroceratina. In some Gephuroceratina, the which define the current system of the subclass suture was very complex due to the appearance Ammonoidea. of additional ventral or umbilical lobe (up to 54 The suture type is defined by the morpholo- lobes around a whorl). In members of the subor- gy of primary suture formed by a rear mantle of der Timanoceratina, the ventral lobe was bipar- 30 T.B. Leonova tite. In general, most members of the oldest ognized based on the fundamental differences ammonoid order have the suture described by in the development of the primary lateral lobe the sutural formula VU:D (Bogoslovsky, 1969). (L) and umbilical (U) lobe: Goniatitina, Adrian- Members of the order Clymeniida, which itina, and Cyclolobina. In representatives of the existed only for a very short time (the very end suborder Goniatitina, the total number of lobes of the Devonian (Famennian)) were strikingly in the suture remained eight almost throughout different from all other ammonoids. Instead of their history (genera Glaphyrites, Paragastrio- the ventral lobe they had a ventral saddle result- ceras, etc), with the exception of some Schisto- ing from the dorsal, rather than the ventral, (as ceratoidea (Carboniferous), with a suture in in most ammonoids) siphuncle (genus Clyme- which the umbilical lobe U was further subdi- nia, etc). Following the “archaic diversity” of vided. In the majority of Goniatitina, the sutural the sutures of Devonian ammonoids assigned to complexity increased by altering the width and the order Anarcestida with five suborders and depth of main lobes, less commonly by develop- Clymeniida with two suborders (Shevyrev, ment of teeth and projections on the main lobes, 2006), four large groups were formed by the without forming new elements. The margins of beginning of the Carboniferous, each character- the lobes and saddle usually remained entire. ized by a particular evolutionary trend and re- The two youngest families Metalegoceratidae ceiving an ordinal rank. (Early Permian) and Spirolegoceratidae (Mid- The