INTRODUCTION

With more than 360,000 described species, Coleoptera comprise the most diverse order in the 410 million year history of the Insecta. Their success is usually attributed to one hallmark feature, which is the pair of elytra, or hardened forewings, that cover and protect the folded hind wings that are used in flight. Indeed, Coleoptera were apparently the first Holometabola to have invaded tight spaces like humus, soil, and wood, while retaining the fundamental adaptation of flight. Many of the morphological features defining the Coleoptera, in fact, are related to the “elytrization” of these insects, and collectively serve in working the insect through substrate (Lawrence and Newton, 1982; Grimaldi and Engel, 2005).

The earliest coleopteran relatives are species in the family Tshekardocoleidae from the Early Permian of Obora, Czech Republic, and Tshekarda, Russia (Rohdendorf, 1944; Ponomarenko, 1963; Kukalová, 1969), which are usually placed into the “Protocoleoptera” (Crowson, 1975; Grimaldi and Engel, 2005), an apparently paraphyletic stem group possessing primitive features like extensive venation on long, pointed, tegminous forewings. Some even possessed a sclerotized, external ovipositor, which all Mesozoic and Recent Coleoptera have lost. Roughly contemporaneous with these tshekardocoleids were also some of the earliest representatives of the “Archecoleoptera” (Lubkin and Engel, 2005; Beckemeyer and Engel, 2008), which still possessed wing veins, though reduced, along with the distinctive rows of square areolae on shorter, more typically rounded elytra. These “Archecoleoptera” became more dominant by the Late Permian (e.g., Martynov, 1932, 1937; Rohdendorf, 1944, 1961; Ponomarenko, 1963, 2000, 2003; Kukalová, 1969; Pinto, 1987; Geertsema and van der Heever, 1996). Béthoux (2009) redefined Adiphlebia lacoana Scudder from the Late Carboniferous Mazon Creek Lagerstätten as a stem coleopteran, presumably sister to all other Coleoptera, including the “Protocoleoptera” and “Archecoleoptera.” Under this scenario, Adiphlebioptera represents a stem group to the entire Coleopterida (= “Protocoleoptera,” “Archecoleoptera,” + Coleoptera s. s.), and could not be considered a true beetle without dramatically redefining the order. Recently, Meller et al. (2011) described four new “Protocoleoptera” beetles in the family Permosynidae from the Lunz Formation, Austria (Carnian, Late Triassic), along with the remains of an abdomen putatively belonging to a polyphagan beetle, but without a formal description of the species.

Evidence thus far indicates there was a dramatic change in the coleopteran faunas from the Late Permian to the Triassic. This is attributable to the End Permian Event (EPE) 247 Mya (Erwin, 1993; Bowring et al., 1999), though the stratigraphic sampling is incomplete since fossil insects (including beetles) are essentially lacking from the earliest parts of the Triassic (Induan-Olenekian: 247–241 Mya). Yet the approximately 10 million years after the EPE is evolutionarily a brief interval of time for Coleoptera and many insect groups, since insects in Miocene amber typically reveal very little change from modern ones (Grimaldi and Engel, 2005). Thus, the faunal turnover from the Late Permian to the mid- and Late Triassic probably reflects not sampling bias but a major biotic event (Knoll et al., 1996; Berner, 2002; Huey and Ward, 2005).

The earliest true Coleoptera were diverse by the Anisian (240 Mya), as revealed by 32 “species” or morphotypes, sorted from 584 specimens of primarily elytra in the Grès à Voltzia Formation of the Vosges mountains of northeastern France (Papier et al., 2005). These authors did not propose family classifications for the Grès à Voltzia beetles, stating (as we believe) that “without any visible venation, [it] therefore prevent[s] any systematic study and determination of their affinities” (Papier et al., 2005: 182). The Madygen Formation (Ladinian-Carnian: 236–220 Mya) from the Fergana Valley, straddling Uzbekistan, Kyrgyzstan, and Tajikistan, has yielded the greatest Triassic diversity: some 65 species assigned to nine families (sorted from 3500 specimens) (Ponomarenko, 1969, 1977, 1995). Coleoptera are scattered amid deposits from the Meride limestone in southern Switzerland and northern Italy (Ladinian: 234 Mya); the Keuper Basin (Norian: 222–209 Ma: Brauckmann and Schlüter, 1993); the Argilliti di Riva di Solto Formation near Bergamo, Italy (Rhaetian: 209 Mya: Whalley, 1986; Bechly, 1997), from deposits of similar age in Britain; and throughout central Asia and Asia Minor (i.e., Tolgoy and Protopivskya Formations: Carnian to Rhaetian). In eastern Asia (including Japan), Triassic Coleoptera predominate in deposits from the Ladinian to the Rhaetian (Lin, 1983, 1986, 1992; Lin and Mou, 1989; Fujiyama, 1973). Two very rich southern deposits harbor diverse Coleoptera, which are the Carnian-aged Ipswich series in Queensland, Australia (e.g., Dunstan, 1923; Riek, 1955), and deposits of similar age in the Molteno beds of South Africa (e.g., Riek, 1974, 1976). Scattered Coleoptera are reported in Late Triassic deposits from South America (e.g., Martins-Neto et al., 2006, 2007, 2008), and other than the Cow Branch Formation fauna (herein, and Grimaldi and Fraser, unpubl. data), the North American fauna of Triassic insects has been extremely depauperate.

In this paper we describe the oldest known staphyliniform beetle, specifically belonging to the family Staphylinidae, from the Late Triassic Cow Branch Formation, and discuss its evolutionary implications. Material examined is deposited in the Virginia Museum of Natural History, Martinsville, Virginia (VMNH), and the Yale Peabody Museum of Natural History, Yale University, New Haven, Connecticut (YPM).

GEOLOGICAL SETTING AND PRESERVATION

The deposit is in the Jurassic-Triassic system of rift basins that belong to the Newark Supergroup, which lie along the eastern coast of North America (Olsen, 1986; Olsen et al., 1978, 1991). Insects occur sporadically within Newark supergroup outcrops from Massachusetts to North Carolina (Huber et al., 2003), but only certain outcrops of the Carnian/early Norian-aged Cow Branch Formation consistently yield abundant, diverse, and well-preserved insects and plants (Fraser et al., 1996; Fraser and Grimaldi, 2003). The Cow Branch Formation correlates with the Chinle Formation of the southwestern United States (Olsen et al., 1978; Fraser et al., 1996), and paleomagnetic data as well as the fishes and phytosaurs provide a strong correlation with the Lockatong Formation of Pennsylvania, New Jersey, and New York (Ladinian-Norian: 237–207 Ma) (Olsen and Kent, 1996; Olsen et al., 1996). An abundant, amphibious eosuchian in the Cow Branch, Tanytrachelos Olsen, is closely related to mid-Triassic forms from Europe, such as Tanystropheus Meyer (Olsen et al., 1978; Fraser et al., 1996).

The main insect-bearing outcrops of the Cow Branch Formation are in quarries of the former Solite Corporation near Cascade, Virginia. These outcrops expose over 30 Van Houten cycles, one of which is particularly fossiliferous (Fraser et al., 1996). The insects occur in a one-inch-thick layer of very fine-grained, black, microlaminated lacustrine shale, which lies between thick silt layers. It was from this cycle that Olsen et al. (1978) originally reported insects. Taphonomy of the insects is unique because entire specimens are routinely preserved, not just the dissociated wings that are the primary insect remains for the Triassic. Also, the insects and plants are preserved as silvery films of aluminosilicates, the detail in which for insects includes microtrichia on appendages and wings and facets in eyes. Optimal observation of the insects, though, requires either polarized light filters or an intense, diffuse, nondirectional light source such as a fiber optic ring light. Wetting the specimens with ethanol increases the contrast between the fossilized remains and matrix. Specimens can also be examined using scanning electron microscopy, either in backscatter or secondary electron mode, and obviously uncoated (an environmental SEM is not necessary). Here, we used a Hitachi S-4700 field emission SEM and Zeiss Evo-60 variable pressure SEM at 10 kV, which gave good to reasonable results on just two of the four specimens examined, particularly specimen VMNH 1343. There appears to be little correlation between specimen quality as observed using the visible light spectrum, and quality of the electron signal and image using SEM. For example, specimen YPM 1147 has excellent preservation under the stereomicroscope, and despite repeated attempts to image mouthparts, legs, and antennae, there was virtually no signal using the SEM.

Taxonomic papers on other arthropods from this deposit include ones on the oldest araneoid spiders (Selden et al., 1999), the earliest definitive thrips (order Thysanoptera) (Grimaldi et al., 2004), the first Western Hemisphere record of the Mesozoic mecopteridan family Pseudopolycentropodidae (Grimaldi et al., 2005), a cockroach (order Blattaria) (Vršanský, 2003), and a diverse fauna of early Diptera (Blagoderov et al., 2007). Other orders in the Cow Branch Formation besides these and the Coleoptera are Hemiptera, Orthoptera, and Plecoptera (Fraser et al., 1996; Grimaldi, unpubl. data). Autochthonous taxa in the deposit are primarily the waterbugs (Belostomatidae and other Nepomorpha [Hemiptera]), making this one of the earliest aquatic insect faunas (Sinitshenkova, 2002; Grimaldi and Engel, 2005). All the other insects, though, and probably all of the plants are allochthonous. Plants include bennettitaleans, cycads, ferns, ginkophytes, and most commonly, conifers. Most insects preserved in the Cow Branch Formation were probably living amid the vegetation that bordered an ancient lake.

SYSTEMATIC PLACEMENT

PLACEMENT WITHIN COLEOPTERA

A distinctive feature of the family Staphylinidae is the truncated elytra, which occur sporadically in other families but which are distinguishable by the proportions of the elytra and abdomen, and overall body shape. Other families with truncated elytra include the Nitidulidae (especially carpophilines), Histeridae, Silphidae, and Melyridae, but these have truncated elytra with only three to four abdominal segments exposed (Staphylinidae typically have six abdominal segments exposed) and the bodies tend to be much broader, flatter, and not at all fusiform. Another key synapomorphy of Staphylinidae (contiguous procoxae) is not visible in the Solite specimens, since none of the specimens have the ventral body surface exposed (all are just dorsal or lateral in preservation).

FIGURE 1.

Dorsal habitus (without legs) of exemplar Staphylinidae, with labels for structures referred to in the text. A. Phloeocharinae. B. Pseudopsinae. C. Trichophyinae. D. Tachyporinae. E. Trigonurinae. All to the same scale. Original. Abbreviations: lat sclrt. tIX, lateral tergal sclerites of abdominal segment IX.

SYSTEMATIC PALEONTOLOGY

FIGURE 2.

Photomicrographs of holotype (VMNH of Leehermania prorova, gen. et sp. n., showing dorsal surface. A. Part (VMNH 734a). B. Counterpart (VMNH 734b).

FIGURE 3.

Photomicrographs of paratype (VMNH 1233) of Leehermania prorova, gen. et sp. n., showing dorsal surface. A. Part (VMNH 1233a). B. Partial counterpart of posterior half (VMNH 1233b).

FIGURE 4.

Photomicrographs of paratypes of Leehermania prorova, gen. et sp. n., both showing dorsal surfaces. A. VMNH 1446. B. VMNH FN 442, its left elytron is slightly extended away from body.

FIGURE 5.

Photomicrograph of paratype (VMNH 1343) of Leehermania prorova, gen. et sp. n., showing dorsal surface. The specimen is broader than others because of taphonomic distortion. This specimen was imaged also using secondary electron SEM (fig. 7). Part VMNH 1343a.

FIGURE 6.

Photomicrograph of paratype of Leehermania prorova, gen. et sp. n., counterpart of VMNH 1343b.

FIGURE 7.

Scanning electron micrographs (secondary electron images) of VMNH 1343a. A. Anterior portion of body (original magnification 20×). B. Detail of head, showing some antennal segmentation and setation (original magnification 200×). C. Detail of posterior end, showing lateral tergal sclerites of abdominal segment IX (lat sclrt. tIX) and scattered stiff setae (original magnification 70×).

FIGURE 8.

Photomicrographs of paratype (YPM 1147) of Leehermania prorova, gen. et sp. n., lying in lateral view. A. Part, YPM 1147a. B. Counterpart, YPM 1147b.

FIGURE 9.

A. Photomicrograph of paratype, YPM 36447, exposed in a ventrolateral position; its right elytron is slightly lifted away from the body. B. Reconstruction of Leehermania prorova, gen. et sp. n., based largely on the holotype (VMNH 734) and paratype VMNH 1343.

FIGURE 10.

Phylogenetic schema of Staphylinidae s.l. after Newton (2011), with placement of Leehermania indicated and Mesozoic ranges of subfamilies highlighted based on records summarized in table 1 and personal observations of Pselaphinae and Aleocharinae in Burmese amber, Phloecarinae in New Jersey amber, and Paederinae in the Crato Formation of Brazil.

DISCUSSION

Based on the morphological characters provided above, L. prorova can be placed confidently within Staphylinidae (contra Yue et al., 2010), although it remains unclear whether Leehermania is representative of a stem group to the tachyporine lineage or should be placed within one of the existing subfamilies. Regardless, L. prorova is the oldest species of the family Staphylinidae, itself numbering more than 57,000 described species today (Herman, 2001b; A.F Newton, unpubl. database). Given this Recent diversity, the existence of only one species of Staphylinidae in the Cow Branch Formation contrasts dramatically with that of the order Diptera preserved in this same deposit (Blagoderov et al., 2007).

The Mesozoic record of Staphylinidae is in need of considerable revision, particularly the types of taxa such as Mesostaphylinus, Laostaphylinus, and Tikhomirova's and Ryvkin's material (observations by one of us [D.A.G.] of Tikhomirova's type material revealed a significant number of inaccuracies in the descriptions). Nonetheless, the available material does shed some light onto the historical diversity of the family. By the Late Jurassic several species of recognizable subfamilies, such as Scaphidiinae, Omaliinae, Tachyporinae, Olisthaerinae, Oxytelinae, and Piestinae, were present in the fauna and, given the phylogenetic placement of these groups, it suggests that a great deal of the higher diversification of Staphylinidae had already taken place (fig. 10). Certainly, the Jurassic staphylinid fauna remains to be better explored and revised (e.g., Cai and Huang, 2010), but the insights currently available support an early diversification of the family into the major “Group” lineages by the Late Triassic. Clarke and Chatzimanolis (2009) argued that the Staphylinine group of subfamilies were established by the Early Cretaceous, and few if any of the subfamilies of Staphylinidae are younger than the Early Cretaceous, although Trichophyinae and Habrocerinae might be of Late Cretaceous, perhaps Early Tertiary, age. Fortunately, attributions of at least six of the families in the Cretaceous are definitive, since they are preserved with fidelity in amber. Regardless, the major radiations of the family, at least at the higher level, seem to predate the rifting of Gondwana. It is therefore not surprising that austral disjunct distributions are not reflected at the subfamily level, although there are certainly much younger tribes or generic clades of Staphylinidae that correlate with such a vicariant pattern (e.g., Newton, 1985; and the Omaliinae genus Metacorneolabium Steel: Thayer, 1985).

Implications of a staphylinid of Norian-Carnian age are significant, specifically for timing the radiation of the coleopteran suborder Polyphaga, which comprises at least 85% of all living species and the great bulk of families. As discussed above, the basal suborder of beetles, the Archostemata, has a long, diverse fossil record, with stem-group fossils occurring as early as the Permian. The suborder Adephaga likewise has an excellent fossil record, including definitive Caraboidea (Trachypachidae and Carabidae) in the Triassic, including from the Solite quarries (Ponomarenko, 2002; Grimaldi and Engel, 2005; unpubl.). Definitive Polyphaga from the Triassic, however, have been both elusive and ambiguous. Meller et al. (2011) attributed an isolated abdomen to this suborder, and Papier et al. (2005) reported a possible staphylinid in the Grès-à-Voltzia Formation from France (the unique specimen of which, unfortunately, has the middle portion of the body damaged and obscured). Ponomarenko (2002), in his summary of the fossil record of beetles, mentioned Hydrophilidae, Artematopodidae, Elateridae, and Curculionoidea (Obrieniidae) in the Late Triassic. However, the fossils on which these attributions are based either do not belong to these families, or are at best ambiguous. For example, the putative weevil family Obrieniidae was later classified as an archostematan (Gratshev and Zherikhin, 2003; Grimaldi and Engel, 2005). Thus, Leehermania appears to be the oldest definitive polyphagan, and this underscores a dimension to the exceptional diversity of modern Coleoptera, which is the accrual of taxa through expansive periods of time.

Table 1.

Mesozoic Staphylinidae (C = compression; A = amber inclusion).

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