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A Revised Chitinozoan Classification

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A Revised Chitinozoan Classification J. Paleont., 73(4), 1999, pp. 549-570 Copyright ? 1999, The Paleontological Society 0022-3360/99/0073-0549$03.00 A REVISEDCHITINOZOAN CLASSIFICATION FLORENTIN PARIS, YNGVE GRAHN, VIIU NESTOR, AND ISKRA LAKOVA Laboratoirede Paleontologie,UPR 4661 du CNRS, Universit6de RennesI, 35042 Rennes-cedex,France <[email protected]>, Universidadede Estatodo Rio de Janeiro-UERJ,Faculdade de Geologia,20559-900 Rio de Janeiro,Brazil <[email protected]>, TallinnTechnical University, Institute of Geology, 7 EstoniaAvenue, 10143 Tallinn,Estonia <[email protected]>, and GeologicalInstitute, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria<[email protected]> ABSTRACT-The successful definitionof chitinozoangenera dependsprimarily on the precisionof the criteriaused. A standardized morphologicalterminology based upon detailsfrom scanningelectron microscope observations of the most representativetaxa bearing these charactersis thereforeproposed. The 143 genera,or subgenera,described so far in the literatureare reviewedin orderto exclude invalidtaxa and obviousjunior synonyms.Particular attention is paid to preventingthe overlapof genericdefinitions of the 56 genera ultimatelyretained. A brief accountof the diagnosticfeatures and stratigraphicrange of selectedgenera is given, andbasic information concerningthe type materialof these genera is listed. Finally, a supragenericclassification of the whole Chitinozoagroup based on diagnosticfeatures whose hierarchyis establishedon statisticaland evolutionarygrounds, is given. One new subfamily,Pogonochitin- inae, three new genera,Baltochitina, Hyalochitina, and Saharochitina,and a new species Baltochitinanolvaki, are defined.The sub- species Fungochitinafungiformis spinifera is elevatedto a specificrank. INTRODUCTION of all 143 genera described and, after excluding those genera we a HITINOZOANSCONSTITUTE a groupof organic-walledmicro- regarded as invalid by ICZN (third version), propose syn- C list based on the criteria we consider to be essential. fossils, well represented in Early Ordovician (late Trema- onymy the are not suffi- doc) to latest Devonian (latest Famennian) marine sediments Because many of existing generic diagnoses we the definition of selected from nearly all Paleozoic oceans. They are found isolated or in ciently definite, supplement original with their features. we chainlike structures in most sedimentary or low grade metamor- genera respective diagnostic By doing so, to of the definitions, which phic rocks, where their abundance usually ranges from a small hope prevent overlapping generic has to be one of the and most constant number of specimens to several hundred (exceptionally up to proven greatest problems in chitinozoan several thousand) specimens per gram of rock. The length of a taxonomy. chitinozoan vesicle (basic isolated element) ranges from ca. 50 to 2,000 Jim (with an average size of around 150-250 Jim). CHITINOZOAN MORPHOLOGY They constitute an enigmatic group of fossils whose biologic General terminology.-A chitinozoan individual may be de- affinities and significance are still interpreted in a variety of fined as a small organic-walled vesicle with an opening. Well- ways (see review in Miller, 1996), more than 60 years after their preserved chitinozoans (i.e., in full relief and not eroded or dis- first description by Eisenack (1931). Personally, we favor the torted) share three major characteristics (Fig. 1): 1) they are hypothesis of eggs of soft-bodied metazoans (Paris, 1981, p. 84; made up of an organic membrane delimiting a cavity; 2) they Paris and Nolvak, in press) referred as chitinozoophorans by have an aperture sealed with a plug; and 3) they normally dis- Grahn (1981). They have proven to be very efficient stratigraph- play a radial symmetry. The actual chemical composition of the ic tools, and they are extremely useful for paleogeographic re- chitinozoan vesicle remains unknown. Therefore, this definition constructions. However, a unanimously accepted taxonomy is is so broad that various organisms, or part of organisms may be now strongly needed in order to make application of chitinozoan included. Size limits (<2,000 Ijm and >50 jim) or stratigraphic genera for paleogeographic and paleoenvironmental investiga- range restriction (exclusively of Paleozoic age, unless reworked) tions more reliable. restrict this definition and allow various present day cysts, co- There have been many attempts to classify chitinozoans. They coons, or eggs of invertebrates (insects, annelids, molluscs, etc.) were carried out through individual initiatives (Eisenack, 1931, to be excluded from the chitinozoans. When present, the external 1968, 1972; Van Oyen and Calandra, 1963; Jansonius, 1964, ornamentation of a chitinozoan vesicle is fairly distinctive com- 1967, 1970; Tappan, 1966; Taugourdeau,1966, 1981; Paris, pared to the ornament of almost all other organic-walled micro- 1981; Achab et al., 1993) or under the authorityof the chiti- fossils of similar age (i.e., acritarchs, spores, and foraminiferal nozoan Subcommission of the "Commission Internationale de linings). Microfloredu Paleozoique"(CIMP) (Taugourdeau et al., 1967). A detailed morphological terminology was first introduced by In the last 25 years, major improvementsin the knowledge of Combaz and Poumot (1962) and then subsequently completed chitinozoanmorphology have been achieved, primarilydue to by Combaz et al. (1967) under the direction of the Chitinozoa the routineuse of the ScanningElectron Microscope (SEM). In Subcommission of CIMP. Most recent papers dealing with chi- addition,numerous new occurrenceshave greatly increasedthe tinozoan systematics have used either the English adaptation chitinozoanrecord, so that it now includes more than 1,000 taxa proposed by Laufeld (1974) or the French terminology adopted describedfrom almost all continents.We are convincedthat suf- by Paris (1981). These terminologies are still valid and well ficient data exist to propose a standard terminology and a general adapted for the description of the chitinozoans. Only a few mod- classificationof chitinozoansthat integratesthe taxa described ifications or additions are necessary in order to integrate the since the last extensive revision (Taugourdeauet al., 1967; Com- most recent morphological details revealed by SEM observa- baz et al., 1967). Our aim is to integrateall originalmorpholo- tions. One of our aims is to promote a standard morphological gies recorded during the last 30 years into a general classification nomenclature that would be unanimously accepted and used. of the group. Particularattention is paid to the definitionof the The main parts of a chitinozoan vesicle are illustrated, show- morphologiccharacters, and to the establishmentof a hierarchy ing the three principal morphological types of chitinozoans (Fig. among these morphologic elements. A critical review is made 1). The basic element is the vesicle, with a bulging part called 549 This content downloaded on Thu, 7 Mar 2013 06:52:12 AM All use subject to JSTOR Terms and Conditions 550 JOURNAL OF PALEONTOLOGY,V. 73, NO. 4, 1999 Apertural pole Apertural pole Apertural pole 0 (1 z shoulder I- - E flanks 0 margin process I apex (=appendix) apex Antiapertural pole Antiapertural pole FIGURE 1-Main morphological features of the three principal types of chitinozoans (modified from Paris, 1981, fig. 56). the chamber. The aperture is either situated directly on the cham- that were not accurate enough or were already used with a dif- ber or at the distal end of a tubelike neck. In order to clarify ferent meaning. It also introduces the morphologic terms we use discussion and descriptions, an arbitrary orientation of the ves- for the discrimination of the chitinozoan genera we have select- icle has been adopted. The apertural pole is regarded as repre- ed. In addition, references are made to recently published SEM senting the top of the vesicle. This means that, in a chainlike images which illustrate almost all of these terms. structure, the upper (or last) vesicle has a free aperture. However, 1) antiapertural pole: lower part of the vesicle, opposite the no biological nor physiological significance has to be given to aperture. this orientation, which is exclusively conventional. A collarette, 2) aperture: large opening at the top of the vesicle, delimited frequently corresponding to a thinning of the wall, may be pres- either by the lips of the neck or collarette, or if these two other ent around the aperture. The plug sealing this aperture is either elements are absent, by the border of the chamber (Fig. 1). This term is instead of called an operculum or a prosome depending on its internal or preferred "mouth", which has physiological external position and on its role in inter-vesicle linking (see def- significance. 3) apertural plug: general term designating the simple or initions below). The base, which corresponds to the antiapertural complex plug sealing the aperture, represented either by the end of the vesicle, may display various linkage structures around operculum or by the prosome (see definitions below). the apex. This base is from the flanks the separated by margin. 4) apertural pole: arbitrarily designated as the upper part of This zone proves to be of prime importance for chitinozoan tax- the vesicle. as it onomy, frequently bears peculiar ornamentation (e.g., pro- 5) apex: point of emergence of the axis of symmetry on the cesses or The flanks carina). themselves may be separated from base of the chamber (Fig. 1). the neck by the flexure
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