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Nonmarine Cretaceous Protovirgularia: Possible Dragonfly Larva Tracemaker

umented from recent aquatic nonmarine environments (Chamberlain, 1975; Ratcliffe and Fagerstrom, 1980; Tevesz and McCall, 1982; Metz, 1987). This communication adds to the database by discussing trails produced by dragonfly larvae (Order Odonata, Erythrodiplax) in an abandoned clay and sand pit in central New Jersey. Trails (Fig. 1) were formed on the surface of silty clays deposited in puddles, ponds, and streams. Due to the degree of saturation of the clay, the larvae sank slightly below the sediment surface prior to moving. As a result an elevated, median, ridge-like shape as well as alternate lateral chevrons produced by the legs during locomotion, commonly were formed. The alternate arrangement of the chevrons occurred due to a lack of placing left and right legs simultaneously. Rarely, due to oversaturation of the sediment, the median ridge collapsed soon after the dragonfly larvae had passed. Overall, the appearance of the recent crawling trail compares very favorably with the trace fossil examples of Protovirgularia cited by Kim et al. (2000). With the exception of this latter work, however, all trace fossil specimens of Protovirgularia have been recorded from a variety of marine paleoenvironments. Recently, the author was sent a reprint of a paper entitled “Trace Fossil Protovirgularia, McCoy, 1850, from the Nonmarine Cretaceous Jinju Formation of the Sacheon area, Korea” (Kim et al., 2000). The Jinju Formation consists of sandstone, mudstone, and shale deposited in a lacustrine environment (Kim et al., 2000). Specimens of Protovirgularia were found preserved in convex epirelief on the surface of a finegrained sandstone. Description of the trace fossil included width of traces 5–20 mm, width of median ridge 0.7–0.9 mm, distance between lateral appendages 1–2 mm, variable length of lateral appendages, and alternate lateral appendage arrangement. Interestingly, the recent dragonfly larva-produced crawling trails noted by this author included an example (Fig. 1) averaging 15 mm in width, a median ridge of 1–3 mm, alternate arrangement and variable length of, as well as comparable distances between lateral appendages to that of the Protovirgularia trace fossil form. In addition, narrower median ridges were observed being formed by immature larvae. Furthermore, the recent crawling trail bears a striking similarity to the type specimens of Protovirgularia McCoy 1850 (see Han and Pickerill, 1994). Although rejecting the premise, Kim et al. (2000) did note the potential confusion of the material with that of a plant origin. This rejection was based on the lack of carbonized material, positive relief preservation of the specimens, a style incompatible with that of a plant origin, and evidence of bioturbation of the bedding plane by Planolites, which is also found preserved in positive relief. Thus, they felt confident that the structures could be assigned to Protovirgularia. Tracemakers proposed have included crabs (Gümbel, 1879), arthropods or annelids (Richter, 1941; Volk, 1961; Claus, 1965; Greiner, 1972), and bivalves (Han and Pickerill, 1994). Recently, Seilacher and Seilacher (1994), Mángano et al. (1998), Ekdale and Bromley (2001), and Mángano et al. (in press) have provided convincing evidence of a bivalve origin. Interestingly, however, chevrons produced by these cleft-foot bivalves are always paired and symmetrical (e.g., Seilacher and Seilacher, 1994). In contrast, the Cretaceous lacustrine documentation of Protovirgularia by Kim et al. (2000) is the first such reported from nonmarine strata. Fossil evidence indicates that the earliest true Odonata (dragonflies) evolved by the Triassic (Gillott, 1995). Thus, this author proposes that dragonfly larvae may have played an important role in the production of Protovirgularia-like traces, particularly since the Triassic, in aquatic nonmarine environments. Furthermore, they may have been at least partially responsible for the fossil ichnotaxon detailed by Kim et al. (2000).