Acta Geologica Polonica, Vol. 48 (1998), No.4, pp. 377-386 General trends in predation and parasitism upon inoceramids PETER 1. HARRIES & COLIN R. OZANNE Department of Geology, University of South Florida, 4202 E. Fowler Ave., SeA 528, Tampa, FL 33620-5201 USA. E-mail: [email protected] ABSTRACT: HARRIES, P.I. & OZANNE, C.R. 1998. General trends in predation and parasitism upon inoceramids. Acta Geologica Polonica, 48 (4), 377-386. Warszawa. Inoceramid bivalves have a prolific evolutionary history spanning much of the Mesozoic, but they dra­ matically declined 1.5 Myr prior to the Cretaceous-Tertiary boundary. Only the enigmatic genus Tenu­ ipteria survived until the terminal Cretaceous event. A variety of hypotheses have attempted to expla­ in this disappearance. This study investigates the role that predation and parasitism may have played in the inoceramids' demise. Inoceramids show a range of predatory and parasitic features recorded in their shells ranging from extremely rare bore holes to the parasite-induced Hohlkehle. The stratigraphic record of these features suggests that they were virtually absent in inoceramids prior to the Late Turonian and became increasingly abundant through the remainder of the Cretaceous. These results suggest that predation and parasitism may have played a role in the inoceramid extinction, but more rigorous, quantitative data are required to test this hypothesis further. Probably the C011lmonest death for many animals is to be ous-Tertiary boundary (KAUFFMAN 1988). The mar­ eaten by something else. ked demise of such an important group has led to the C. S. Elton (1927) formulation of a wide range of hypotheses to explain this phenomenon. To date, most of these explana­ INTRODUCTION tions have hinged on global change brought on by cooling, alteration of oceanic circulation, or general The inoceramid bivalves arose in the Permian environmental degradation (e.g. KAUFFMAN 1984; and by the Cretaceous were dominant constituents of 1988; KAUFFMAN & al. 1992; MACLEOD 1994; FI­ level-bottom communities in a wide variety of shel­ SCHER & BOTTJER 1995; MACLEOD & HUBER 1996). fal settings. Although they are well-known inhabi­ This overview aims to investigate initial data in sup­ tants of oxygen-depleted, marine facies, they also port of a fUlther hypothesis in this debate: the role of thrived in a wide range of well-oxygenated environ­ predation and parasitism. ments, including shallow-water settings (e.g. KAUFF­ MAN & HARRIES 1996). Hence, the group and even some species appear to have had very broad ecologi­ EVIDENCE OF PREDATION AND cal tolerances that are also minored in their broad PARASITISM IN INOCERAMIDS geographic distribution. Despite their abundance and diversity, all inoceramids, except for species of Te­ Evidence for parasitism on bivalve shells ge­ nuipteria, disappeared 1.5 Myr prior to the Cretace- nerally comprises a variety of pits, scars and addi- 378 PETER J. HARRIES & COLIN R. OZANNE tional calcitic secretions which modify the shell burial compaction, or simply the differential morphology. Predation signatures on molluscs are degradation of the organic matrix that held the typically confined to those predators that either prismatic layer together. Although consistent bore through or bite and crush the shell. Because breakage patterns have been documented in inoceramids are very rarely bored by predators, some predator-prey relationships (e.g. CADEE most evidence for predation intensity derives 1968), this has not been seen from most available from sublethal (rehealed) injuries. The study of inoceramid data. HATTIN (1975) has suggested these features as a proxy for predation intensity is that Ptychodus was an extremely efficient less than ideal (VERMEIl 1982); it is difficult to di­ processor of inoceramids. He hypothesized that rectly relate predatory failure to predatory suc­ their predation and excretion of bivalve material cess. Despite the limitations, it is the best indica­ was responsible for the common inoceramid­ tor available. Common predatory and parasitic fe­ prism-rich calcarenites in mid-Cretaceous atures found on inoceramid valves are described Western Interior sequences. However from the briefly below. numerous specimens investigated from this inter­ val (strata spanning the Cenomanian-Turonian boundary), only a single occurrence of sublethal Boreholes injuries has been documented (see PI. 1, Fig. 1; W ALASZCZYK 1992). Unless these predators were The line of evidence most commonly used to almost 100% efficient, which seems extremely evaluate the role of predation in the fossil record unlikely (see discussion in VERMEIJ 1982), there of invertebrates is the presence of boreholes. In should be evidence of failed prey SUbjugation. most cases they are produced by gastropod pre­ Additionally, SAGEMAN (1996) in his study of dators, especially naticids and muricids (SOHL Western Interior calcarenites, suggested that they 1969). Unlike predatory processes that result in formed "through winnowing by storm events fragmentation, where unequivocal causes are dif­ during relative sea-level fall and condensation ficult to determine, boreholes can be readily in­ due to starvation during subseqent rise" (p. 891). terpreted. Because the borer leaves its signature Hence, the primary control appears to be relative in the morphology of the borehole, this predator­ sea-level position and not a function of predatory prey system has the advantage of identifying not efficiency. only the obvious prey, but the predator as well. Inasmuch as predators are rarely completely Typically, completed boreholes are interpreted to efficient and effective attackers of their prey, one represent a successful predatory attack, in which of the ways in which shell attacks can be estima­ the prey was successfully subjugated, killed, and ted is through the relative abundance of repaired consumed. Bored shells also have the advantage shells. Because bivalves precipitate calcium car­ of generally being preserved as reliably as pris­ bonate throughout their lives, earlier ontogenetic tine ones (but see Roy & at. 1994); therefore, events are preserved in their shells. Therefore, population dynamics and estimates of such previous attacks on the shell that produced suble­ aspects as predator efficiency can be reconstruc­ thal injuries have the potential to be recorded, ted. The geologic record is replete with evidence especially those events that resulted in injuries to of boring in a wide variety of groups and by the mantle. Numerous inoceramid specimens a spectrum of predators. To date, only a single show evidence of injury to the mantle and shell horizon in the Lower Maastrichtian is known to (PI. 1, Fig. 4; PI. 2, Fig. 2b). These features have contain inoceramids bored by gastropod preda­ a variety of morphologies, but they generally tors (SCHOPF & HARRIES, in prep.) consist of mantle damage which then is reflected by aberrant growth following the attack. Some of these attacks can be quite localized (PI. 1, Figs Shell breakage and repair 1-2), while in other cases the attack may be more severe and substantially affect the shell morpho­ Unfortunately it is difficult, if not impossible, logy (PI. 1, Figs 3-4 and PI. 2, Fig. 2b). In cer­ to determine whether most fragmentation in ino­ tain instances, the predator may leave a fairly ceramids was due to the action of predators or distinctive bite (e.g. KAUFFMAN 1972), but in the whether it simply reflects shell breakage due to majority of cases it is difficult to precisely deter­ wave and current activity prior to burial, post- mine the predator. GENERAL TRENDS IN PREDATION AND PARASITISM UPON INOCERAMIDS 379 Fecal pellets and regurgitated masses times referred to as "mud blisters" (HOFSTETTER 1965), form when the mantle is irritated and ad­ Another common mode of predation on mari­ ditional nacre is precipitated over the irritant. In ne invertebrates, especially among fish, is to its most extreme form, this results in pearl forma­ swallow bivalves and other benthic organisms. In tion, but in most cases it simply results in the se­ a study of stomach volumes of modern hogfish, cretion of additional nacreous layers. RANDALL & W ARMKE (1967) determined that 42.6% of the stomach contents were bivalves. Clearly, certain fish can playa significant preda­ Parasitic tracks tory role on bivalves, although extrapolating the results of these modern studies directly to the One of the most evident types of paraSItIc fossil record is lenuous. Rays also have the abili­ scars left on modern bivalves is the presence of ty to ingest large quantities of bivalves (GRAY & polydorid worm borings. Polydora produces al. 1997). Unfortunately, stomach contents of a distinctive U-shaped boring, but because the predators are rarely preserved in the fossil boring occurs following shell precipitation, it do­ record. Instead, paleontologists must rely on pre­ es not disrupt the mantle and later shell forma­ served fecal pellets (coprolites) or regurgitation of tion. However, where the parasite resides betwe­ shell masses to reconstruct predation patterns of en the shell and the mantle, dramatic changes in the past. One of the main stumbling blocks to this shell precipitation can occur. Some inoceramid approach is the difficulty in determining which parasites clearly disrupted the mantle's ability to predator produced the various defecated or dis­ precipitate calcium carbonate, while in other ca­ gorged masses present in the fossil record. Shell ses, such as the formation of a Hohlkehle