TAPHONOMY, PALEOENVIRONMENT, AND PALEOECOLOGY

At least a couple of the specimens are very likely to be molts. Pseudoglyphea cf. P. spinosa and Clytiopsis argentoratensis (Figure 2.1) have their cephalothoraxes and abdomina misaligned, and the abdomen is facing upward while the cephalothorax is upside down. This is interpreted as an indication of a molt. Furthermore, one specimen of C. argentoratensis (Figure 2.5) has its cephalothorax split along the median line. This is a way some lobsters molt (Glaessner 1969, R431). One other specimen, Oosterinkia neerlandica, has its abdomen misaligned with the cepahalothorax as well, typically known as the Salter's position (Schäfer 1951) or Open Molt Position (Bishop 1986). This is likely to happen typically in the case of a molt (see Bishop 1986; Feldmann and Tshudy 1987). Moreover, Glaessner (1969, R431) mentioned that some lobsters molt by opening up between the transition from cephalothorax to the first abdominal somite and split along the median line, thereby leaving the cephalothorax and abdomen behind separately. The configuration of the remains of Oosterinkia neerlandica also resembles figure 29 in Mertin (1941). The author described molts of Oncopareia Bosquet 1854 with an open carapace split and misalignment of the cephalothorax and abdomen. However, the split is not observed in this specimen. The other specimens from this study could be either a molt or a fossilized part of a dead lobster.

The majority of the lobsters exhibits no cuticle implying that the exoskeleton has been dissolved due to diagenesis. Bivalve shells are also preserved without the actual shell. As a result, the preservation is moldic since the lobsters are preserved with relief.

None of the specimens is complete. If nearly complete, the cephalothorax and abdomen are separated. The specimens, therefore, could not have been buried alive or very fast after their death by high sedimentation rates. Lobsters buried under these circumstances should be complete and articulated for the most part. The specimens, thus, have been lying on the bottom for a while after death or were disintegrated molts. If some of the remains are actual corpses, then they must have been exposed for an extended period of time, and, hence, experienced considerable decomposition that allowed the disarticulation of the lobster. Disarticulation took mainly place between the cephalothorax and the abdominal region as none of those region are still connected (Figure 2, Figure 4, and Figure 5).

Allison (1986) demonstrated that a freshly killed lobster of Nephrops Leach 1841 and the shrimp Palaemon Weber 1795 were hardly affected by strong rotation in a barrel (125 rpm for 5 hrs), while the same animals were severely damaged after they had decomposed for two weeks before being subjected to the same experiment. Other indications of a low-intermediate sedimentation rate are the presence of epi- and infaunal organisms, the horizontal orientation of most of the fossils found in the quarry, and the thin layers of sediment surrounding the lobsters.

Plotnick (1986) studied the taphonomy of modern shrimp and suggested that scavengers and infaunal organisms could be important in the destruction of buried arthropod remains. The number of epifaunal scavengers in the Muschelkalk sea was probably limited given the very limited crustacean fauna in terms of total specimens (<10) and number of species (5). On the other hand, burrows are found (e.g., Rhyzocorallium) in the Winterswijk quarry complex. Bioturbation might, thus, have limited the preservation potential of lobsters.

Decomposition due to microbial activity has a profound effect on the preservation potential of the lobsters as well. Chan (1970) observed highest densities of chitinoclastic bacteria on molted arthropod skeletons in intertidal and fresh-water sediments, which could suggest enhanced decomposition. Plotnick (1986) observed that fresh remains of modern shrimp were resistant to rough handling; when decomposition proceeded, the remains disarticulated by moderate disturbance. The lobsters from this study were, thus, probably not buried quickly but the corpses or molts were able to disintegrate at least by decomposition. The low-intermediate sedimentation rate enhanced microbial decay in this case.

Not a single specimen is complete and some show possible signs of wear exemplified by the absence of most rostra (Figure 2, Figure 5) and the incompleteness of the cephalothorax and abdomen (Figure 5). Most of the specimens are, however, not severely damaged suggesting limited transport. The presence of a number of nearly complete fish (see Oosterink and Poppe 1979) also indicates a limited energy level. On the other hand, the vast number of loose bones of vertebrates (see Oosterink et al. 2003) suggests that it was not completely still water. The bones might have been displaced by various scavengers or hunters that were active on the carcasses of the reptiles. Lankamp (2002) documented bite marks on a nothosaur bone, possibly caused by a Nothosaurus. Reptile bones might, thus, be more susceptible to transport than other smaller animals of the Anisian time period of Winterswijk due to scavengers and predators that move part of the carcass. In addition, the bones are more susceptible to transport when the bones themselves are not connected anymore by organic tissue after predation, scavenging, and decomposition. The hypothesis of limited transport is further strengthened by the completeness of the vast majority of the bivalves. Also, sometimes the valves are still connected.

In summary, a low-intermediate sedimentation rate caused the decay of the lobsters epifaunally, while bioturbation might have caused further decay infaunally. Limited hydrological activity, on the other hand, enhanced the preservation. Although other paleoenvironmental factors also had a major negative impact on the diversity and number of individuals of lobsters (see discussion below), the low number of finds over decades of collecting is also likely to be in part caused by the low preservation potential.

Fossils of the Anisian strata of Winterswijk are dominated by marine fossils such as ammonites, fishes, bivalves, gastropods, brachiopods, and stromatolites (Oosterink 1986). Amphibians and famous aquatic reptiles from this site such as Nothosaurus, Cymatosaurus, and Anarosaurus are also associated with marine strata from other localities (Oosterink et al. 2003). In one case (MAB k2859) a bivalve is found in association with a lobster (Pseudoglyphea cf. P. spinosa). The presence of numerous fossil footprints (Demathieu and Oosterink 1983) together with fossil mudcracks, and wave ripples (Oosterink et al. 2003) imply a very shallow sea and periods of exposure. Thus, sea level was not constant. The oldest layers of the quarry (Röt and lowermost Muschelkalk) in particular were terrestrially influenced (Diedrich 2001). The arid climate permitted no huge influx of freshwater and caused high levels of evaporation followed by higher salinities (Oosterink et al. 2003). The presence of the crustacean Halycine cf. agnota and the minerals dolomite and celestine also indicate a higher salinity (Oosterink 1981). In addition, absence of corals, echinoids, and crinoids, and the presence of only few brachiopods indicates an unstable environment, possibly with changing salinities. The rare presence of the mineral gypsum (Oosterink and Winkelhorst 2003) might also indicate higher salinities, although the authors stated that it might have been derived from alteration of pyrite. The common occurrence of pyrite crystals suggests oxygen depletion.

The described lobsters were also inhabitants of this shallow marine realm. They are, however, small (cephalothorax lengths without rostrum vary from 11 to 17 mm for Clytiopsis spp. and about 25 mm for Pseudoglyphea cf. P. spinosa). This is comparable to lengths given in Förster (1967) for the two taxa (7.6–15.5 and 35 mm, respectively). Förster (1967) mentioned Clytiopsis thuringica to have a length of 13.2 mm. Interestingly, species of the presumed predecessor and descendent of Clytiopsis, the Upper Permian Protoclytiopsis antiqua Birshtein 1958 and the Carnian Paraclytiopsis hungaricus Oravecz 1962 (see Förster 1967), are notably larger than Clytiopsis spp. (62 and 23 mm, respectively). The reduced length of Clytiopsis spp. may also be due to the ecological stress of high salinities. A common bivalve from the Anisian strata from Winterswijk , Myophoria vulgaris, was also considered small (Faber 1959) and Oosterink (1981) mentioned that ammonites, lobsters, fishes, and reptiles were relatively small. Gall (1971) noted that the early Anisian fauna found in the French Vosges Mountains also consisted of small specimens, even compared to the French Muschelkalk fauna. Finally, Urlichs (2001) mentioned a dwarfed fauna in Anisian strata of the German localities Rübersdorf and Borgholzhausen, and from upper Ladinian strata of St. Kassian, Italy. Gall (1971) explained that negative ecological stress caused by high salinities might be a reason for the dwarfed fauna. Oosterink et al. (2003) provided additional causes such as food scarcity, high temperatures, and toxic levels because of, for example, pyrite formation. The first two causes are related to a high salinity. Thus, the small lobsters support earlier suggestions of ecological stress caused by high salinities.

The environment during the deposition of the Muschelkalk differs from the preceding Grès à Voltzia deposits (early Anisian) found in France in which most of the specimens of Clytiopsis have been found. In addition, the diversity of crustaceans was higher in the French occurrence: 15 genera versus four from Winterswijk (see Gall and Grauvogel-Stamm 2005). The shale lenses of the Grès à Voltzia were deposited in a deltaic environment, where terrestrial, freshwater/brackish, and marine fossils were found that have suffered from changes in salinity, temperature, and oxygen content (Gall and Grauvogel-Stamm 2005). The crustaceans would have lived in a freshwater to brackish environment (Gall 1985; Gall and Grauvogel-Stamm 2005). Clytiopsis, thus, must have been able to live in different environments and under a stressed regime.

Having a combination of very weak chelae, a relatively thin and smooth cephalothorax, and strong abdomen, Clytiopsis probably did not burrow, but, most likely, had a mixed crawling-swimming mode of life. Indeed, no definite infilling of a burrow was found surrounding or in the close proximity of the lobsters.

The predators of the lobsters must have been either fishes, like today, or the various aquatic reptiles that inhabited the Winterswijk area at that time. Diedrich and Schulz (2003) mentioned reptiles that would have preyed upon the lobsters in leftover, small water bodies. The lobsters might have fed on the various bivalves and gastropods and/or stromatolites found in the Winterswijk quarry complex.