131Lucas, S.G. and Spielmann, J.A., eds., 2007, The Global Triassic. New Mexico Museum of Natural History and Science Bulletin 41.

THE PROBLEM OF TRIASSIC GONDOLELLID CONODONTSYSTEMATICS (CONODONTOPHORIDA, CONODONTA)

T. KLETS AND A. KOPYLOVA

Novosibirsk State University, Pirogova Street 2, Novosibirsk, Russia, email: fossil@lab.nsu.ru

Abstract—We discuss the problems of systematics of Triassic gondolellid conodontophorids. The basic trends indevelopment of morphological characters are shown.

INTRODUCTION

The taxonomy of gondolellid elements is one of the problems inthe study of conodontophorids. Their morphological similarity origi-nally led researchers to a conclusion about Carboniferous, Permian andTriassic pectiniform elements belonging to a uniform Gondolella Stauffer& Plummer, 1932. N. Bender and D. Stoppel for the first time estab-lished that the Triassic forms refered to Gondolella mombergensis Tatgeactually differ from the Paleozoic species of Gondolella by a more roundedbasal cavity and more extended lanceolate form of platform. Therefore, itis most logical that all Middle and Late Triassic gondolellid elements beconsolidated in the new genus Neogondolella (type species Gondolellamombergensis Tatge), which appeared at the base of the Middle Triassicfrom spathognathodiform elements (Bender and Stoppel, 1965). Then,contrary to the initial value of the genus, all Early Triassic, Permian, andalso unsculptured smooth Carboniferous elements began to be referredto Neogondolella, understanding it in a broad sense (s. l. = sensu lato),and only sculptured Upper Carboniferous conodontophorids were con-sidered as Gondolella (type species Gondolella elegantula Stauffer &Plummer 1932) in a narrow sense (s. str. = sensu strictiore) (Ziegler,1973). Further research indicates morphological distinctions andphylomorphogenetic connections between genera of gondolellidconodontophorids (Mosher, 1968b; Hayashi, 1968; Budurov, 1976;Buriy, 1989; Kozur, 1989; Orchard, 1991; Buryi, 1996). However, theconventional systematics does not exist now. H. Kozur, considering thetaxonomy of Permian and Triassic gondolelloid conodontophorids indetail, considered that Neogondolella Bender & Stoppel had evolvedfrom platform-less Neospathodus Mosher through the transitional formsof Chiosella Kozur from the end of the Olenekian Stage to the beginningof the Anisian Stage and that Neogondolella is the basic group of theMiddle to the beginning of the Late Triassic (Kozur, 1989). It is neces-sary to note that the author made these conclusions based on research onof the Tethyan region.

Recently, the geography of locations of the Triassicconodontophorids has been considerably expanded due to new finds inareas of the Russian Arctic (Dagys, 1984; Konstantinov etc., 1997; Klets,2000; Klets and Yadrenkin, 2001; Klets and Kopylova, 2006). The loca-tions of the Olenekian forms in the up-stream of the Lena River, onKotelny island (Novosibirsk islands), and in the basin of the DzhugadzhakRiver (Omolon massif) has been established. It was documented bymany specimens that have allowed specification of the stratigraphicdistribution of Neogondolella. Research has shown that in northernlalitudes in the Early Olelnekian endemic Neogondolella buurensis, N.composita, N. jakutensis, N. taimyrensis, N. sibirica, having characteris-tics of Neogondolella in the form of the basal cavity and in platformmicrostructure (honey comb structure) were widely distributed (Dagys,1984, tab. I, figs. 8-12; tab. II, figs. 1-16; tab. III, figs. 1-2; tab. V, figs. 4;tab. XI, figs. 1-4; tab. XII, figs. 1-2; tab. IV, figs. 1-8; Fig. 1). Therefore,specimens of Neogondolella buurensis from A. A. Dagys’ collection hadbeen referred by Kozur (1989, pl. 15, fig. 6-7) to Paragondolella sweeti,perhaps, wrongly. Records of Early Olenekian neogondolells(Neogondolella elongata Sweet) are known also in British Columbia,

Western Pakistan, India and Svalbard (Sweet, 1970; Mosher, 1973; Goel,1977; Dagys and Korchinskaya, 1989). Therefore, most probably, thegenus Neogondolella had evolved from Neospathodus already by thebeginning of the Early Olenekian and was widely distributed in southernand northern lalitudes (Fig. 1).

The study of conodontophorids in the north of Middle Siberia,the Northeast and the Far East of Russia, and also the analysis of numer-ous references shows that gondolellids are a rather conservative group, inspite of high enough rates of transformations of platform and blade-likeelements. This feature of the group extremely complicates establishmentof genera. It also originally formed the basis for their reference to onegenus, Gondolella Stauffeã & Plummer 1932. There are some trendsestablished during research on the evolution of the Triassic forms whereboth irreversible and reversible morphological changes are recognized. Asthe research shows, a character on the upper or lower side of an elementtaken separately is a poor indicator of closely related genera. In connec-tion with the reversibility of many morphological characters in evolu-tionary trends, according to separately taken characters, for example thestructure of a platform, Early Triassic Neogondolella are similar to MiddleTriassic Paragondolella and Late Triassic Norigondolella (Fig. 1). Thestructure of the basal cavity of platform-less Early Triassic Neospathodusis rather like the structure of the basal cavity of Anisian Nicoraella andRhaetian Misikella. Therefore, for diagnoses of genera it is necessary totake into consideration the structure of both sides. For more correct andreliable evolutionary constructions, all morphological changes are trackedon adult ontogenetic stages. In establishing genera, we use as a basis themorphological terminology developed by I. Barskov with colleagues(Barskov et al., 1975; Barskov, 1985).

BASIC TRENDS IN DEVELOPMENT OFMORPHOLOGICAL CHARACTERS

Platform

During certain times, the platform of gondolellids was evolvingfrom platform-less conodonts, for example: Neospatho-dus Pseudogondolella Paragondolella, Neospathodus Chiosella,Neospathodus Neogondolella. Also, the platform could disappearcompletely: Clarkina Neospathodus, Mockina Parvigondolella,Neogondolella Celsigondolella. There was no similar trend in theoccurrence and (or) disappearance of the platform in the evolutionaryline Neospathodus Nicoraella Mosherella Misikella.

Sculpture of Platform

The sculpture consists of nodes, grooves and ribs developed onlyon the platform of gondolellids. Sculptured conodontophorids such asScythogondolella and Icriospathodus appeared for the first time in theTriassic during the Olenekian Stage. Strongly- sculptured gondolellidsarose in the Ladinian (Budurovignathus and Pseudofurnishius) and be-came very widely distributed in the Late Carnian-Norian(Metapolygnathus Epigondolella Mockina).

132

FIGURE 1. Scheme of phylomorphogenesis of Triassic conodontophorids.

133Carina

The main similarity of gondolellid conodontophorids is in thecarina, but in some cases, being combined with other characters, itsdevelopment can be used to establish genera. In spite of variety of carinamorphology even within a species, it is possible to identify three basictypes:

1. Anterior denticles are the highest. Denticles in the posteriorpart of a carina are also high. Denticles in the middle part of an elementare the lowest and frequently merged. This type of carina is most typicalof Neogondolella and Norigondolella.

2. All denticles are high and equal or nearly equal in height. Thistype is especially shown in elements with a reduced or completelymissing platform—Chiosella, Parvigondolella—but can be characteris-tic of platform-bearing Scythogondolella and some Neogondolella.

3. Denticles in the anterior part of a carina are very high, mergedalmost along all of the height and are also compressed from the sides.Denticles are gradually reduced in the direction of the posterior edge andbecome more rounded. This type is well shown in Paragondolella andits descendants Metapolygnathus Epigondolella Mockina. It is alsocharacteristic of some species of Budurovignathus.

Free Blade

A free blade is well advanced only in conodonts in which theplatform occupies one-half of the length of the element. It is well shownin Clarkina (Induan- the beginning of the Olenekian), then again it isobserved in Budurovignathus (Ladinian–bottom of Carnian) andParagondolella Metapolygnathus Epigondolella Mockina (top ofCarnian-Norian to bottom of Rhaetian). Neogondolella, Pseudogondolellaand some species of Paragondolella, as well as Norigondolella, are tear-shaped and extended in length, but different on width and have a plat-form with missing or advancing, very poorly free blade (all till 1-2/10 ofthe length of the conodonts).

Keel

An important morphological character is the keel—a longitudinalaxial eminence on the upper surface of conodonts. Trends in the changeof its morphological features are connected to trends in the developmentof a platform and presence of a free blade. The structure of the lowersurface changes in platform-less elements in the lines Neospatho-dus Chiosella and Neospathodus Nicoraella Mosherella Misikella.In an anterior direction, the basal cavity of all genera is narrowed (differ-ent genera have various degrees of narrowing) and the deepening alwayshas a V-shaped form.

The form of the keel of platform-bearing conodonts not having afree blade (or in which the blade is poorly advanced) is a convertiblecharacter. In the line Pseudogondolella Paragondolella NorigondolellaInduan conodonts with a poorly advanced platform have a V-shapedkeel, younger Paragondolella has a straight lower surface, and NorianNorigondolella has a V-shaped keel again. The similar trends (transitionfrom V-shaped keel to straight) are traced in the lines Neospatho-dus Neogondolella Budurovignathus, Neospathodus Neogondol-ella Pseudofurnishius, and Pseudogondolella Paragondolella Gladi-gondolella.

In the Late Triassic conodonts Metapolygnathus Epigondol-ella Mockina Parvigondolella with a well advanced free blade, theform of keel varies in the opposite direction from almost straight up to V-shaped.

Thus, for the establishment of genera of gondolellids it is impor-tant to use all characters, as during evolution morphological features havechanged in parallel and were not independent from each other. Probably,some changes could be connected functional morphologically.

ACKNOWLEDGMENTS

The work was financially supported by IGCP-Project 467; grant07-05-00204 from the Russian Foundation for the Basic Research.

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