- The Paleontological Society
Spinous oniscomorph millipedes are rare faunal components of the upper Palaeozoic (Shear, 1997). Amynilyspes (type species A. wortheni Scudder, 1882; OD) is an Upper Carboniferous spinous oniscomorph (pill millipede) which was first described from the Middle Pennsylvanian (Westphalian D equivalent) Fossil-Lagerstätte of Mazon Creek. Later Fritsch (1899) described two species (A. typicus and A. crescens) from the Wesphalian D Gaskohle of Nýřany in Bohemia. More recently A. typicus was recorded from the Stephanian B of the Saarland (Förster, 1973), then from the Stephanian B of the Blanzy-Montceau-les-Mines Basin (Langiaux and Sotty, 1977; Poplin, 1994). Although myriapods were already known to occur in the Montceau-les-Mines Lagerstätte (Langiaux and Sotty, 1976; Rolfe et al., 1982; Poplin and Heyler, 1994) the presence of Amynilyspes at Montceau-les-Mines was first published in a regional publication (“La Physiophile” Langiaux and Sotty, 1976, 1977), and it has passed almost unnoticed.
Representatives of the genus Amynilyspes are a minor faunal component of Upper Carboniferous faunal assemblages. Hannibal and Feldmann (1981) published a revision of the oniscomorph millipedes from the Carboniferous of North America, including the type specimen of Amynilyspes wortheni Scudder, 1882 and newly collected specimens. Specimens of the genus Amynilyspes subsequently have been illustrated and discussed in various works (Hannibal, 1984, 1997; Shear, 1997). At Mazon Creek Hannibal and Feldmann (1981) listed 10 specimens of A. wortheni, plus an undetermined number of specimens in private collections. The percentages of the whole millipede fauna (excluding arthropleurids) are 0.1 percent in the Braidwood (nonmarine, freshwater) biofacies and 0.014 percent in the Essex (marine) environment (Baird and Anderson, 1997). A survey of fossil millipedes in the collections of the Field Museum of Natural History by one of us (JTH) in 1997 showed that oniscomorphs (mainly Amynilyspes) comprise about 11 percent (24 specimens) of the collection of fossil millipedes, excluding arthropleurids, from Mazon Creek. A single specimen of A. typicus was reported from the Saarland (Germany) by Förster (1973). At Montceau-les-Mines only five specimens of Amynilyspes have been found up to now out of 23,250 sideritic concretions that have yielded animal remains (coprolites excluded). The percentage of the entire millipede faunal component varies between 0.24 percent in the Saint-Louis opencast pit, and 2.33 percent in the Sainte-Hélène opencast pit (Sotty in Chabard and Poplin, 1999). Unfortunately one of the two specimens from the Sainte-Hélène and Blanzy opencast pits briefly described and illustrated by Langiaux and Sotty (1977) has been lost. The five specimens of Amynilyspes presently known from Montceau-les-Mines (as of 04.27.1999, Sotty, personal commun.) represent 3.5 percent of the millipede fauna, excluding arthropleurids.
The geological background and palaeoenvironmental setting of the Montceau-les-Mines Fossil Lagerstätte have been recently discussed (Racheboeuf et al., 2002); it was that of an intramontane basin in which the sideritic fossiliferous concretions appear to have formed in a lacustrine/deltaic complex (streams flowing into lakes). The Stephanian deposits crop out on both sides of the Blanzy-Le Creusot-Bert Stephanian to Permian graben in the northeast part of the Massif Central (central France). Concretion-bearing layers, which yielded the majority of the fossil material available to date, are intercalated between the coal seams of the Blanzy-Montceau Basin which have been extensively exploited since the nineteenth century; they were well exposed in the Saint-Louis, Saint-François and Sainte-Hélène opencast pits. The Saint-Louis and Sainte-Hélène opencast pits yielded respectively three specimens and one specimen of Amynilyspes. The precise age of the concretion-bearing layers within the Stephanian remains uncertain, but a Stephanian B–C age is provisionally retained (Racheboeuf et al., 2002).
At Mazon Creek, Hannibal and Feldmann (1981, p. 732) considered that “oniscomorphs were terrestrial organisms, and their occurrence in the more marine faunal associations [Essex] can be ascribed to fluvial transportation.” Such a conclusion fits with the preliminary conclusions drawn from the assemblage and preservation of the Montceau-les-Mines fauna (Racheboeuf et al., 2002): oniscomorphs were terrestrial organisms.
The occurrence of representatives of the genus Amynilyspes in the Montceau-les-Mines fauna supports the tropical distribution of pill millipedes during the Upper Carboniferous (Hannibal and Feldmann, 1981; Hannibal, 1984). In North America, A. wortheni occurs in the Westphalian D equivalent Mazon Creek fauna of Illinois. In Europe, A. typicus and A. crescens occur in the Wesphalian D Gaskohle of Nýřany in Bohemia, Czech Republic (Fritsch, 1899). Amynilyspes typicus also occurs in the Stephanian B of the Saarland, Germany (Förster, 1973). We have also been able to confirm the occurrence of Amynilyspes in the Westphalian B of the West Midlands, England (Table 1). The species has also been noted as occurring in the Westphalian D of Ohio (Hook and Baird, 1993) and, questionably, in the Carboniferous of Nova Scotia (Scudder, 1895). We have not confirmed the identity of the Ohio or Nova Scotia material. According to the Late Carboniferous (Westphalian) reconstruction by Scotese and McKerrow (1990, fig. 19, p. 15), all these occurrences—including Montceau-les-Mines—were tropical, within about 10 degrees north and south of the equator (Fig. 1). The distribution of fossil oniscomorphs is not surprising as modern diplopods are common in tropical environments characterized by high rainfall (Coleman and Crossley, 1996, p. 88).
Class Diplopoda Blainville inGervais, 1844
Superorder Oniscomorpha Pocock, 1887
Small to large-sized millipedes with 11 to 14 terga. Collum small; second tergum (shield) laterally expanded; pygidium rounded. Pleura free.
This superorder encompasses short millipedes, all of which have the ability to roll into a ball. Three orders are included in this superorder: Glomerida, Sphaerotheriida, and Amynilyspedida. Only the Amynilyspedida are known with certainty from the Carboniferous.
Order AmynilyspedidaHoffman, 1969
Moderate to large-sized oniscomorph millipedes with 14 arched terga. Terminal tergum relatively small. Dorsal surface of terga may be flattened.
The number of terga is the main character used to distinguish the Amynilyspedida (with 14 terga) from the Sphaerotheriida (with 13 terga) and the Glomerida (with 11 to 12 terga). The terminal segment of the Amynilyspedida is also smaller than that of the other two orders, and especially so compared to that of the Sphaerotheriida. Indeed, the size of the terminal segment of at least some of the Amynilyspedida approaches that of the Glomeridesmida. The Amynilyspedida include the genera Amynilyspes Scudder, 1882; Glomeropsis Fritsch, 1899; Archiscudderia Fritsch, 1899; and Palaeosphaeridium Peach, 1914. It may also include the form described by Hannibal and Feldmann (1981) as ?Sphaerotheriida.
Fritsch (1899) frequently misinterpreted the segmentation of the millipedes he named from Nýřany. Examination of his type material of fossil Oniscomorpha in the Narodny Muzeum, Prague, shows that most oniscomorph specimens he described and illustrated actually have 14 segments.
Modern oniscomorphs have a reduced number of terga (11–13) compared to those of the Carboniferous. The Amynilyspedida resemble the Sphaerotheriida more than the Glomerida in their segment number and in their tropical to subtropical distribution.
Family AmynilyspedidaeHoffman, 1969
(=Acroglomeridae Fritsch, 1899)
Moderate-sized oniscomorph diplopods with 14 terga and prominent, simple spines. Up to 30 mm long. Eyes large. No ozopores.
We agree with Hoffman's suggestion (1969, p. R585–586), seconded by Müller (1989, p. 170), that Amynilyspes should be in a family separate from Glomeropsis and Achiscudderia. Glomeropsis and Achiscudderia differ from Amynilyspes in the following ways: species of these two genera lack spines, have dorsal ornamentation composed mostly of very fine pustules and/or pits, and have pleurites with less rounded interior margins than those of Amynilyspes. While Glomeropsis and Archiscudderia should be excluded from the Amynilyspedidae, they probably should be referred to a single new family of the Amynilyspedida, not two separate families as has been suggested by Hoffman and Müller, who based their suggestions on the drawings of Fritsch (1899), which are in some ways inaccurate. Palaeosphaeridium may also belong to the same family as Glomeropsis and Archiscudderia. The new family may also include “Paraglomeris carbonaria” Schlechtendal, 1912 and the indeterminate arthropod described by Pruvost (1930, p. 217, pl. 7, fig. 6). However, the identity of those two specimens is in need of confirmation.
Modern oniscomorphs do not bear prominent spines, but may have transverse ornamentation (Hoffman, 1982, p. 691; Golovatch, 1976). Glomerids may have tuberculate cuticular projections and Corsikomeris remyi Verhoeff, 1943 is an example of a very tuberculate form (see illustrations in Mauriès, 1969). The tuberculation of some of the extant forms may consist of hardened exudates (Blower, 1985, p. 62–63). Extant sphaerotheriids may bear very small spines. There is a transverse row of very fine spines, for instance, on the posterior of the head capsule of Arthrosphaera brandti Humbert, 1865.
Genus AmynilyspesScudder, 1882
Amynilyspes wortheni Scudder, 1882 (OD).
As for the family.
Three species have previously been assigned to the genus Amynilyspes: Amynilyspes wortheni Scudder, 1882, A. typicus Fritsch, 1899, and A. crescens Fritsch, 1899. Amynilyspes wortheni has been recently revised and its morphology well described (Hannibal and Feldmann, 1981; see also Hannibal, 1984). The other two named species have not been revised, however.
Amynilyspes typicus certainly has 14 segments although Fritsch's drawing of a fairly complete specimen (1899, Taf. 147, fig. 1) is erroneous showing more segments than are present. Examination of Fritsch's figured material in the Narodny Muzeum, Prague, verifies that the terga are distinctly granulated. The granulations are most pronounced on the posterior of the terga (a feature seen on Fritsch's drawings), except for those on the shield which are more pronounced medially. In general the tuberculation is similar to that seen in well-preserved specimens (e.g., Field Museum of Natural History PE 12802, see Hannibal, 1984, p. 14) attributed to A. wortheni. Indeed, A. typicus is either closely related to, or might even be conspecific with A. wortheni. Undescribed fossil oniscomorphs (A. sp. in Table 1) from Great Britain are also tuberculate, and may be conspecific with specimens that have been referred to as A. typicus. A. fatimae is only very finely granulose on lateral parts of shield and terga.
Fritsch (1899) distinguished A. crescens by the crescentic growth lines (“Anwachslinien”) on the terga below the spines. Fritsch's description and illustrations also show that the millipede has tubercles on the lateral sides of the terga. According to Fritsch, the only specimen of that species was deposited in the Naturhistoriches Museum Wien, but as reported by Forster (1973, p. 69), the specimen is missing (Summesberger, personal commun., 2001).
Amynilyspes cf. typicus. Poplin, 1994, p. 294.
Species of Amynilyspes with terga 3–12 dorsally flattened in anterior half and weakly to markedly rounded in posterior half, without transverse sulcus delineating the two parts; two rows of dorsolateral spines; dorsomedial row of short spines sometimes developed; shield without spines; tergum 13 markedly convex in longitudinal section, without flattened anterior half, and with two strong dorsolateral tubercles connected by transverse, elevated ridge; pygidium very reduced, short, and rounded; shield and terga with very finely spaced granulation on lateral parts only.
Fourteen arched terga with flattened dorsal surface. Total length of terga 2–14 measured along dorsum c. 26.8 mm. Maximum width between 5.0 mm and 6.0 mm for largest specimen (MNHN SOT 2134), with last terga (12–13) tapering slightly in width.
Head partly but poorly preserved in specimens MNHN SOT 2134 and 14983. Suboval, rounded in outline. Width c. 2.2 mm. The best preserved antenna (MNHN SOT 2134, Fig. 4.1) shows seven segments, 0.6 mm to 0.4 mm long proximally to distally, about 0.2 mm wide; their sides are weakly concave.
Collum (tergum 1) barely visible. Appears only in cross section on external mould of specimen MNHN SOT 2134 as short (0.5 mm long), thin and flattened plate.
Shield (tergum 2) entirely smooth, devoid of spines and nodes, weakly concave dorsally and laterally, almost saddlelike, and rounded at its posterior dorsal margin. Not enlarged laterally; bordered anteriorly by a rim with a series of closely spaced, fine transverse ridges (Figs. 3.1, 3.3, 4.5–7, 5.1). Free lateral margins regularly rounded. Length about 2.9 mm (MNHN SOT 2134). Anterior margin thickened (c. 0.3 mm), subvertical, and weakly convex anteriorly (Figs. 3.3, 4.5, 4.6).
Terga 3–12 similar in size. In specimen MNHN SOT 14983 length of terga 7–11 varies between 1.7 mm and 1.9 mm, and width is about 5 mm; tergum 12 shorter (1.3 mm) and narrower (4.5 mm). In lateral view, height varies from 3.0 mm to 2.8 mm backwards. Lateral side of terga weakly convex, almost vertical. In cross section, terga moderately convex dorsally. Longitudinally, anterior half of each tergum almost flat, while the posterior half, between the two spines, markedly convex, without sulcus separating two parts. Anterior margin of each tergum bending ventrally, forming a flat, subvertical wall. Posterior half of each tergum bearing two robust, smooth, subcylindrical spines (Fig. 3.1, 3.2, 3.5, 3.6). On terga 3–10, spines are 4.0 mm to 3.8 mm apart backwards, 3.5 mm apart on tergum 11, and 2.8 mm apart on tergum 12. In lateral view spines regularly inserted at c. 2 mm from the lateroventral free margin of the terga (MNHN SOT 14983). Spines inserted at about 45 degrees, posterolaterally oriented, and weakly curved posteriorly. Maximum length observed on preserved spines is about 2 mm for a diameter of 0.5 mm (MNHN SOT 2134). Specimen MNHN SOT 2129, although laterally compressed, exhibits dorsomedial row of well-differentiated, smaller spines (Fig. 3.9). Specimens MNHN SOT 2134 and 14983 exhibit no dorsomedial node nor tubercle or spine. Ozopores absent.
Tergum 13 shorter and narrower than other terga (length = 1.0 mm; width = 3.5 mm) without developed spines, but with two strong tubercles united at their base by well-differentiated, elevated rounded ridge (Fig. 3.4–3.6). Summits of two tubercles 1.5 mm apart (MNHN SOT 14983).
Pygidium small, short (length = 0.9 mm), sub-semicircular in posterior view (height = 1.9 mm; width 3 mm), with weakly rounded posterior margin. Ventral margin rounded (MNHN SOT 14983) (Fig. 3.4, 3.5).
Pleura are preserved on ventral side, still articulated with inner side of lateral part of terga, in three of the available specimens. Most of them are pressed dorsad against the terga, a postmortem attitude. Eleven pairs of pleura on the best preserved specimen, corresponding to post shield tergites 3 to 13. Tergo-pleural articulation is located very close to tergal ventral free margin (Figs. 2.4, 4.3). On ventral side of pleura it consists of an anterior tubercle followed by a relatively deep and narrow longitudinal furrow (Figs. 2.6, 4.3, 4.4). Pleura small (length c. 1.5 mm; width c. 1.2 mm), almost flat, weakly concave ventrally, spatulalike or leaflike in outline, their maximum width located at midlength. Their inner margin regularly rounded in anterior pleura, becoming somewhat truncated backwards. Anterior and posterior margins are bounded by a well-differentiated, rounded rim, getting narrower at their free rounded extremity (Figs. 2.6, 4.4).
Ventral, external side of coxae partly preserved on specimen MNHN SOT 2134, with legs still articulated, but poorly preserved (Fig. 4.1, 4.2). Sterna not observed.
Some legs partly preserved on specimens MNHN SOT 2134 and 14983. Extended legs suggest that their total length was at least about 2 mm. Posterior right legs of specimen 2134 markedly antero-posteriorly flattened (Fig. 4.2).
Exoskeleton with very finely spaced granulation on lateral parts of shield and terga 3 to 12 only.
To honor Mrs Fatima Amllal.
Holotype, left side and ventral external mould of an almost complete specimen (MNHN SOT 2134); paratypes, external mold of an almost complete specimen (MNHN SOT 2129A and B), and left side and ventral external mold of a slightly distorted specimen (MNHN SOT 14983A and B).
Although the Montceau-les-Mines specimens of Amynilyspes fatimae appear to be better preserved three-dimensionally than specimens from Mazon Creek, measurements of individual terga remain uncertain owing to telescoping or stretching apart of the terga (Hannibal and Feldmann, 1981). However, the length of the collum is about 0.5 mm; that of the shield is 2.9 mm; that of terga 3–10 can be estimated to 1.8 mm to 1.9 mm; tergum 11 is 1.7 mm long; tergum 12 about 1.3 mm long; tergum 13 is 1.0 mm long, and the pygidium is 0.9 mm long. Hence the total length of the animal was probably between 22 mm and 26.8 mm (measurements drawn from specimens MNHN SOT 2134 and 14983). In this way, A. fatimae appears to have been somewhat smaller than A. wortheni (up to 28.5 mm; see Hannibal and Feldmann, 1981), but larger than A. typicus (see Fritsch, 1899, pl. 145, figs. 1, 2, and pl. 147, fig. 1).
Other material examined
Internal mold of the dorsal side of an almost complete, outstretched, specimen preserved in siltstone. Unumbered specimen, coll. Langiaux.
Material and occurrence
Three more or less complete, three-dimensionally preserved, decalcified specimens preserved in sideritic concretions: MNHN SOT 2129, 2134, and 14983. Montceau-les-Mines Fossil Lagerstätte, Saint-Louis opencast pit, Stephanian B. The specimen MNHN SOT 2134 is from bed ‘0’ of the Saint-Louis opencast pit (see Pacaud and Sotty, 1994); more detailed locality information is lacking for the other two specimens. They are part of the D. Sotty collection belonging to the Muséum National d'Histoire Naturelle of Paris (MNHN SOT), and deposited in the Museum d'Histoire Naturelle, 14 rue Saint-Antoine, F-71400 Autun (Chabard and Poplin, 1999). The fourth specimen, the internal mold of an almost complete specimen preserved in siltstone, comes from the Sainte-Hélène opencast pit and is a part of the Langiaux collection housed in the Musée des Fossiles de “La Physiophile” at Montceau-les-Mines.
Amynilyspes fatimae n. sp. can be easily distinguished from the three other species of the genus (A. wortheni, A. typicus, A. crescens) by the total lack of ornamentation on the exoskeleton, except for the very reduced, fine and spaced granulation on lateral parts of shield and terga 3 to 12; otherwise, the exoskeleton of A. fatimae is entirely smooth. Coarse granulation, as it appears on latex molds of Figure 3.4 and 3.8, is an artefact resulting from acid preparation of specimens. Other characteristics of the new species A. fatimae include: the pronounced saddlelike longitudinal profile of the shield which is devoid of spines and nodes; the lack of a transverse sulcus on the terga, and the reduced pygidium. However the most important feature is undoubtedly the dorsal morphology of the tergum 13 with its two dorso-lateral tubercles connected by a transverse, elevated, rounded ridge. In A. wortheni tergum 13 is devoid of spines or any relief.
The cooccurrence of two morphologies, with or without a dorsal median row of tubercles, is interpreted herein as an intraspecific variation (see Fig. 6), like that postulated for A. wortheni. Indeed, a second occurrence of the same two morphotypes at two geographically and temporally distinct localities makes it more likely that species of Amynilyspes were indeed dimorphic. Dimorphism of the terga is known for extant oniscomorphs. The pygidium of males of extant sphaerotheriids may differ from that of females (Attems, 1928, p. 206).
Because of postmortem crushing, interpretation of the head capsule is difficult. Large, subrounded to subrectangular features seen on the latex molds probably represent the mandibular cardines and/or stipites. Additional mouth parts and other head parts may also be present. Eleven pair of pleura can be seen on the best preserved specimen of A. fatimae (MNHN SOT 2134). As in extant sphaerotheriids, these pleura correspond with individual, postshield terga. It is likely, but unproven, that Amynilyspes had 12 pair of pleura, two less than the total number of segments. The pleura of Amynilyspes fatimae are generally similar to those of modern oniscomorphs, but they differ in some respects. The overall shape of the pleura of extant oniscomorphs is quadrangular, while the pleura of A. fatimae are more rounded (compare Fig. 2.6, 2.7; Fritsch, 1899, fig. 353; Manton, 1954, text-fig. 4; Manton, 1977, fig. 8.6; Manton, 1979, fig. 7). The anterior rim of the pleuron of A. fatimae, with its prominent anterior node, is more or less like that in modern sphaerotheriids (Fig. 2.7; Fritsch, 1899, fig. 353), which have an expanded, nodose proximal termination of the anterior ridge. The remainder of the side of the pleuron of A. fatimae that articulates with the tergum appears to be less complex than that of modern forms, but that portion of the pleura may simply not be seen in the fossil. The posterior ridge seen on the fossil pleura are more prominent than those on the modern forms, but it is possible that dorsal features of the fossil have been compressed onto the ventral side.
Mode of life
As for A. wortheni, the development of the dorsolateral erect spines of A. fatimae most probably precluded burrowing, and aerial, possibly arboreal, climbing activity appears likely (Hannibal and Feldmann, 1981). Such a mode of life fits with the assumed swampy forested palaeoenvironment of the Montceau-les-Mines Fossil-Lagerstätte (Fig. 6; Poplin, 1994). The excellent 3D preservation with antennae and legs still articulated are indicative of a rapid burial, probably in a sudden mudflow, as suggested for the limulid Alanops magnificus (Racheboeuf et al., 2002). The body of the three available specimens of A. fatimae are markedly longitudinally arched dorsoventrally, with only weak lateral bending. This dorsoventral bending strongly suggests that A. fatimae was capable of enrollment, like that reconstructed for A. wortheni (Hannibal and Feldmann, 1981, fig. 5b), but its coiling may have been somewhat different. The emarginated anterolateral margins of the terga should probably be shorter, narrower in A. fatimae, but this is probably partly compensated by the narrower, subtriangular, flanks of the terga which possibly allowed coiling with a less important lateral re-covering on the terga. The progressive narrowing of terga 11 to 13, and pygidium, also support the ability of A. fatimae to coil. However, the most important and typical feature of the new species lies in the dorsal morphology of the tergum 13 as well as in the very small-sized pygidium. In A. wortheni tergum 13 lacks laterodorsal spines and a transverse sulcus, in A. fatimae tergum 13 exhibits two well-developed laterodorsal tubercles connected dorsally by a transverse elevated, rounded ridge. The pygidium is almost vertical in lateral view, opposite to its weakly oblique profile in A. wortheni (Hannibal and Feldmann, 1981). An attempt was made to reconstruct the enrollment by fitting together the terga of A. fatimae along the emarginations, like that reconstructed for A. wortheni (Hannibal and Feldmann, 1981, text-fig. 5). It shows that a complete enrollment is possible only if there is a re-covering of the anterior half of each tergum by the posterior half of the preceding tergum. The collum is reduced and the anterior margin of the shield is thickened, almost vertical and weakly concave. The ventral, rounded margin of the pygidium most probably fits with the anterior margin of the shield when the enrollment was achieved. Amynilyspes and Archiscudderia have a series of closely spaced transverse ridges on the anterior rim of the shield. These probably functioned as part of the enrollment mechanism and/or mechanisms to lock the head and collum in position. In this way, when coiled, A. fatimae appears like a spinous sphere (Fig. 2.5), the pygidium concealing the head, as in modern oniscomorphs (sphaerotheriids, glomerids; Ruppert and Barnes, 1994, p. 816). The development of the transverse, nodose dorsal ridge of the tergum 13 represents an evolutionary tendency for better protection.
No ozopores can be seen on specimens of A. fatimae, nor have any been detected on A. wortheni (Hannibal and Feldmann, 1981, p. 743). The lack of ozopores is significant. All extant spinous millipedes (polydesmidans in the genera Desmoxytes, Tridontomus, and Pandirodesmus; see, for example, Golovatch and Enghoff, 1994) have ozopores. So do at least most of the spinous Carboniferous Euphoberiidae. Among extant oniscomorphs (none of which are spinous), ozopores are only found on glomerids; sphaerotheriids lack ozopores. Thus Amynilyspes appears to lack chemical defensive mechanisms needed by most other spinous millipedes, and must have relied on physical methods such as coiling and spines for defense.
We thank C. Poplin (MNHN, Paris) who invited us to study the newly processed concretions and unpublished material, and D. Sotty and D. Chabard (Musée d'Histoire naturelle, Autun) for the loan of specimens in their care. J. Langiaux and J.-J. Bonnot (Musée des Fossiles de ‘La Physiophile,’ Montceau-les-Mines) are greatly acknowledged for the loan of the specimen under their care. G. C. Baird (State University of New York College at Fredonia) and the two anonymous reviewers are greatly acknowledged for their critical comments which helped us to improve the manuscript. For providing information or other aid we thank J. Clatworthy (Lapworth Museum of Geology, University of Birmingham), A. Ross (The Natural History Museum, London), and other members of the Geological Curators Group, V. Turek and R. Prokop (Narodny Muzeum, Prague), G. Buckley and S. Lidgard (Field Museum of Natural History, Chicago), and H. Summesberger (Naturhistorisches Museum, Wien). Photographs were taken by N. Podevigne (UMR 5125, Villeurbanne). This paper is a contribution to the Research Program of UMR 5125-PEPS (CNRS, Université Claude-Bernard–Lyon 1) on the Structure and Functioning of Aquatic Palaeoecosystems.
- Accepted 21 April 2003.