The new aeshnopteran family Enigmaeshnidae is proposed for Enigmaeshna deprei gen. et sp. nov., the first fossil insect collected as imprint in the Earliest Cenomanian clay of the Puy-Puy quarry at Tonnay-Charente (Charente-Maritime, SW France). The bed bearing E. deprei was previously known for its highly diversified fossil plant assemblage. Although this taxon belongs to the much derived clade Aeshnodea, it is characterized by several unique hind wing venation characters, never found in other Aeshnoptera, viz. part of MAb distal of the trigonal planate very long, and presence of five posterior branches of AA directed towards posterior wing margin.

Introduction

Although Aeshnoptera are rather frequent in the Jurassic and Cretaceous fossil record, they almost all belong to the most inclusive clades of this group (Nel et al. 1994; Bechly et al. 2001). Mesozoic representatives of the Recent clade Neoaeshnida Bechly, 1996 are almost exclusively represented by the Gomphaeschnidae Tillyard and Fraser, 1940, sister group of the Aeshnodea Bechly, 1996. The few Mesozoic fossils of the latter clade belong to the family Allopetaliidae Cockerell, 1913 (genus Baissaeshna Pritykina, 1977). Little is known on the aeshnopteran history during the Late Cretaceous because of the lack of significant fossils. Thus, the present discovery of an Aeshnodea in the lowermost Cenomanian of France is of great interest in the knowledge of its diversity and morphological disparity during this crucial period of its evolution. The new fossil is characterized by several unique characters, allowing us to include it within a new family.

The fossil dragonfly comes from the Puy-Puy quarry, at Tonnay-Charente (Charente-Maritime, SW France), about 20 km from the Charente river estuary (Fig. 1). In this quarry, the uppermost Albian-lowermost Cenomanian deposits are transgressive and erosive on the Kimmeridgian substratum. These deposits are mainly composed of fluvial and paralic sand, but contain several clay intercalations with local concentrations of plant compressions or lignite and amber (Néraudeau et al. 2005). Stratigraphically (Fig. 2), the clay level containing fossil arthropod imprints is located about seven metres under the first facies clearly dated as Early Cenomanian, a marine shelly sand (lithological sub-unit B1) containing dense accumulation of the large benthic foraminifera Orbitolina conica (Vullo et al. 2003). The clay level bearing the fossil Aeshnodea corresponds to the base of the sand and clay alternations (lithological sub-unit A2), underlying the shelly sand. Just a few decimeters underneath the fossiliferous clay there is 2–3 m thick fluvial azoic sand arranged in large cross beddings (top of the sub-unit A1). The clay bearing arthropods and plants is devoid of sporomorphs and cannot be palaeontologically dated in this quarry (Peyrot et al. 2005). However, stratigraphical correlations with well-dated sections of other quarries from the same region (Néraudeau et al. 2002, in press), suggest an earliest Cenomanian age for the lithological sub-unit A2 from Puy-Puy.

The clay containing the fossil Aeshnodea corresponds to the basal part of the two main levels rich in plant compressions (P1, P2), as previously described by Gomez et al. (2004) and Néraudeau et al. (2005). Apart from numerous fossil ferns, conifers and angiosperms, the level P1 delivered a few imprints of undetermined Blattodea and decapod crustaceans. The Aeshnodea imprint was fossilized at a clay surface at a few centimeters of an 80-cm-13ong Dammarophyllum leaf (Coniferale: Araucariaceae or Podocarpaceae).

Systematic palaeontology

In the description below we follow the wing venation nomenclature of Riek and Kukalová-Peck (1984), amended by Kukalová-Peck (1991), Nel et al. (1993), and Bechly (1996). The higher classification of fossil and extant Odonatoptera, as well as familial and generic characters followed in the present work, are based on the phylogenetic system proposed by Bechly (1996) and Bechly et al. (2001) for the Mesozoic Aeshnoptera.

Fig. 1.

Map of the Tonnay-Charente area (SW France) with location of the Puy-Puy quarry with Early Cenomanian deposits (A) and geological section (B) with the position of the studied sample with fossil Odonata (arrow). A1, fluvial sand with large cross beddings; A2, estuarine alternation of sand and clay, with three main fossiliferous levels (Pl, plant compressions and arthropod imprints; P2, plant compressions only; GB, arthropods tracks); B1, marine shelly sand.

Fig. 2.

Anisopteran Enigmaeshna deprei gen. et sp. nov. from Early Cenomanian of the Puy-Puy quarry (Tonnay-Charente, SW France). Holotype MNHN-LP-R 63889, photomicrograph (A) and explanatory drawing (B). Abbreviations: a.l., anal loop; A×1, A×2, primary antenodal cross-veins; CuAa, distal branch of cubitus anterior; CuP, cubitus posterior; IR2, intercalary radial vein; MA, median anterior; MP, median posterior; N, nodus; Pt, pterostigma; RP2, RP3/4, radius posterior; t.p., trigonal planate.

Palaeoenvironmental discussion

Sedimentological and palaeontological characteristics of the fossiliferous clay of Puy-Puy indicate a coastal depositional environment with significant continental inputs (Néraudeau et al. 2005). First, sand and clay alternations of the sub-unit A2 (Fig. 2) are characteristic of an estuarine environment. The ripple marks and the arthropod tracks observed in the sandstones (GB in Fig. 1) overlying the insect-bearing clay are characteristic of a sandy tidal beach. The “azoic” sand with large cross beddings (sub-unit A1) preceding the clay with plants and arthropods is typical of a fluviatil series (Néraudeau et al. 2005). Moreover, a rich floristic assemblage is associated to the fossil arthropod imprints. Ferns, conifers, and angiosperms are highly diversified (more than thirty forms), and usually represent distinct taxa compared to other Late Albian and Early Cenomanian beds bearing plant compressions of the same region (Coiffard et al. 2004; Gomez et al. 2004; Le Diourion 2005; BG unpublished data). The particular high diversity and plant association of the P1/P2 beds at Puy-Puy quarry may correspond to freshwater marsh or pond in floodplain or mouth estuary. Fossil wood is relatively uncommon, with two identified taxa (Agathoxylon and Podocarpoxylon) (Perrichot 2005), but fossil leaf imprints are very abundant, with the outstanding abundance and diversity of angiosperms (e.g., Myrtophyllum cf. angustum), the presence of Araucariaceae or Podocarpaceae (e.g., Dammarophyllum), Cupressaceae-Taxodiaceae (e.g., Glenrosa sp.), other coniferales (e.g., Geinitzia reichenbachii), pteridophytes (e.g., cf. Osmunda cretacea), ginkgoales (e.g., Nehvizdya andegavense) (Le Diouron 2005; Néraudeau et al. 2005). Thus the life environment of Enigmaeshna deprei was probably an estuarine forest context combining a mosaic pattern of marine and fluvial influences.

Compared to the insect assemblages previously discovered in the Late Albian/Early Cenomanian ambers from the same region (Charente-Maritime, SW France) (Néraudeau et al. 2002, 2003; Perrichot 2005), the outcrop of Puy-Puy appears original and exciting because it is the first that contains clay with insect imprints. Moreover, contrasting with the about 1000 specimens of arthropods found regionally in amber, it is the first time that an Odonata is recorded in the mid Cretaceous deposits from Charentes. It can be assumed that further analyses of the fossiliferous clay of Puy-Puy will enrich the knowledge of the Albian—Cenomanian insects from France.