PALAIOS, 2007, v. 22, p. 691–694 Research Note DOI: 10.2110/palo.2006.p06-117r
EVIDENCE OF PRIAPULID SCAVENGING FROM THE EARLY CAMBRIAN CHENGJIANG DEPOSITS, SOUTHERN CHINA JIAN HAN,* ZHIFEI ZHANG, JIANNI LIU, and DEGAN SHU Department of Geology and State Key Laboratory of Continental Dynamics, Northwest University, Xi’an 710069, China e-mail:
[email protected]
ABSTRACT A Laojieella specimen of the Lower Cambrian Chengjiang Lagersta¨tte in Yunnan Province, southern China, contains a tubular organism inside its digestive tract. The gut content appears to resemble Archotuba conoidalis, a sessile animal generally regarded as being closely related to cnidarians. This example demonstrates that Laojieella might be a scavenger. Reasons for the extreme paucity of recognizable remains in gut contents are discussed. Such fossils offer new insights into the reconstruction of the complex food web of the benthic community of the Chengjiang fauna. INTRODUCTION The Priapulida, characterized by a retractable proboscis bearing quincunxially or diagonally aligned pharyngeal spines (Land, 1970; Adrianov and Malakhov, 1996), are a small group of marine infaunal worms represented by 18 extant species. They are generally observed living in marginal marine biotopes as predators and, occasionally, as prey (Lang, 1948; Land, 1970). The role of priapulids is usually negligible in modern marine environments except under some special circumstances (Shirley, 1990). Fossil priapulids are distributed widely from the Early Cambrian to Late Carboniferous (Schram, 1973; Conway Morris, 1997) and are well documented as a major component of Cambrian benthic communities (Conway Morris, 1977; Sun and Hou, 1987; Hou and Bergstro¨m, 1994; Hou et al., 1999, 2004; Zhao et al., 1999, 2001; Han et al., 2004, 2006a, 2006b; Huang et al., 2004a, 2004b; Hu, 2005; Ivantsov et al., 2005; Zhang and Hua, 2005). Priapulids are especially abundant in some sections of the Lower Cambrian Chengjiang deposits, southern China (Steiner et al., 2005; Dornbos and Chen, 2006; Han et al., 2006a). Fossil priapulids lived in diverse settings: open shelf (e.g., Chengjiang; Hu, 2005) or deep marine (e.g., Burgess Shale) environments, fine-grained (e.g., Chengjiang, Burgess Shale, Sinsk biota) or coarse-grained siliciclastic sediments (e.g., Kaili biota; see Zhao et al., 1999, 2001; and Shipai biota; see Zhang and Hua, 2005), carbonate or phosphate sediments (Mu¨ller and Hinz-Schallreuter, 1993; Zhang and Pratt, 1996), and in well-oxygenated or dyserobic environments (Ivantsov et al., 2005). Predator-prey interactions are among the most significant of all organism-organism interactions. Predation, a fundamental ecological process with profound effects on the morphology, distribution, abundance, and evolution of metazoans, has its earliest fossil evidence at the Neoproterozoic-Cambrian transition (Babcock, 2003). A combination of methods, analyses, and observations involving, for example, functional morphology, phylogeny, ichnology, theoretical and actual analyses of soft-bodied fossils, coprolites, bite marks, borings, and gut contents and faunal associations have been developed to infer predator-prey interactions from the fossil record (Bruton, 1981; Jensen, 1990; Conway Morris and Bengtson, 1994; Butterfield, 2001; Babcock, 2003). It is difficult to distinguish scavenging behavior from hunting in the
fossil record because of the dearth of evidence in the fossil record and because of the flexibility of metazoan feeding strategies; for instance, many carnivorous arthropods capable of hunting are also opportunistic scavengers (Babcock, 2003). Nevertheless, several features can be used to determine if scavenging has occurred once predator and prey have been morphologically or taxonomically identified: (1) The activity of predator and prey can be estimated using functional morphological analysis. Some prey organisms actually seem more vigorous and active than predators when functional morphological analysis is applied (e.g., the priapulid Ottoia and arthropod Sidneyia; see Bruton, 1981, 2001). (2) One can determine whether prey organisms were dead (e.g., by presence of body fragments or molted carapaces) before being ingested by predators. (3) One can determine whether predators have access to living prey. For instance, the Cambrian lobopod Microdictyon has been interpreted previously with a habit of climbing on the medusiformed Eldonia with its legs, based on somewhat consistent co-occurrence (Chen et al., 1995). Alternatively, this has been interpreted as a selective case of scavenging because Eldonia is generally considered to have been a free-floating form (Budd, 2001), and this presumption can be partly supported by our unpublished observation that Chengjiang lobopods more frequently cooccurred with priapulids rather than Eldonia. Such Cambrian Burgess Shale–type faunas as the Early Cambrian Chengjiang and Middle Cambrian Burgess Shale faunas provide unparalleled anatomical and ecological information on the initiation of Phanerozoic life. To date, more than 180 species have been recovered from various deposits of the Lower Cambrian Chengjiang Lagersta¨tte (Steiner et al., 2005); the number of organisms new to science is still growing (Chen, 2004; Liu et al., 2004; Chen et al., 2005; Hou et al., 2005; Hu, 2005; Shu, 2005; Han et al., 2006b; Lu et al., 2006; Shu et al., 2006). Potential predators or scavengers among the Chengjiang fauna are quite diverse, including anomalocaridids (Nedin, 1999), ctenophores, chaetognaths, eldoniids, lobopods (Budd, 2001; Babcock, 2003), and a majority of large arthropods that account for more than three-quarters of the animal species (Hu, 2005). Predator-prey relationships of the Chengjiang fauna are being tentatively reconstructed, although many coprolites with discernible and identifiable inclusions have been reported (Chen et al., 2002; Hu, 2005; Vannier and Chen 2005). Direct fossil evidence that ties an organism into the food chain, including scavenging, however, has not been reported previously from the Chengjiang deposits. This paper describes evidence of priapulid scavenging from the Lower Cambrian Chengjiang deposits in southern China by describing a fossil priapulid, Laojieella sp., that contains a tubular animal in its alimentary canal. Fossils such as this offer new insights into the reconstruction of the complex food web of the benthic community of the Chengjiang fauna. FOSSIL MATERIAL AND PRESERVATION
* Corresponding author. Current address: Department of Geology, Northwest University, Xi’an 710069, China.
All specimens from the Chengjiang Lagersta¨tte were excavated from the Jianshan section, Haikou Town, Kunming, Yunnan Province, and are deposited at the Early Life Institute (ELI), Northwest University, Xi’an, China. An incomplete and almost flattened specimen of Laojieella sp.
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FIGURE 1—Laojieella sp., ELI-0001500 from the Lower Cambrian Chengjiang deposits. Scale bar ⫽ 1 mm. A) Outline of the animal. B) Line drawing of the animal. C) Close-up of the introvert of Laojieella sp. D) Close-up of prey. E) Complete specimen of Paraselkirkia sinica, ELI-0001405, showing proboscis, gut, partly protruded trunk, outer tube, and the terminal cover and the tube end. F–H) Specimens of Archotuba conoidalis, ELI-0001600–ELI-0001602, showing the slightly curved tube and the transverse septa within the tube.
(ELI-0001500) preserves gut remains. The anterior part of the Laojieella specimen is better preserved compared to the other parts, and the margin of the animal is exposed only partially (Figs. 1A–B). The tissue in the posterior part has been replaced almost completely by pseudomorphs of coarse pyrite or aluminosilicates, which produced an area much larger than the original diameter of the animal. Three well-preserved specimens (Figs. 1F–H) of Archotuba conoidalis Hou et al., 1999 (ELI-0001600– ELI-0001602) and one specimen (Fig. 1E) of Paraselkirkia sinica (⫽ Paraselkirkia jinningensis Hou et al., 1999; ⫽ Selkirkia sinica Luo and Hu, 1999) (ELI-0001405) are presented here for comparison. Archotuba has been previously interpreted to be a cnidarian (Huang et al., 2004b) and is presumed to possess a set of tentacles around the aperture (Chen and Zhou, 1997), which is comparable to the Burgess Shale Cambrorhytium (Conway Morris and Robison, 1986); however, the tentacles have never been confirmed. Little is known of the internal anatomy except for a set of separated transverse septa and a black-colored strand thought to represent the gut.
spines arranged in a quincunx (Fig. 1C). The area succeeding the spinose proboscis is smooth surfaced, followed by an area with at least 20 spines, also arranged diagonally. The rest of the trunk, although not preserved completely, was presumably devoid of ornamentation. The gut is preserved rather faintly, but it can be traced along in the sagittal position. All these features are highly reminiscent of an Early Cambrian Chengjiang priapulid-like worm Laojieella thecata Han et al., 2006b, that also bears a thecalike structure and a possible caudal appendage on the posterior trunk, as well as having a few club-shaped, discrete mud infillings in the gut. The specimen ELI-0001500 is assigned tentatively to Laojieella sp. because none of these diagnostic features are seen in it. The proboscis of this Laojieella specimen is completely everted compared with the invaginated proboscis of L. thecata in the holotype (Han et al., 2006b, figs. 2–3), indicating that the proboscis of Laojieella sp. is capable of eversion and retractability.
THE HOST PRIAPULID
There is nothing left within the gut but a rigid, conical, slender tube with a smooth surface preserved in a whitish color, approximately 3.5 mm long and 0.5 mm at maximum width. The apertural end is oriented toward the posterior of the Laojieella specimen. There is a mass of what appears to be gut contents adjacent to the aperture relief above the bed-
The single specimen of Laojieella sp. (ELI-0001500) is elongate and more than 8 cm long (Fig. 1A). The anterior part of the body tapers forward ending in a spinose lanciform proboscis bearing two sets of
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ding plane. The tube is flattened and slightly concave in a sagittal position, and the posterior part near the apical end is slightly curved. Four or five transverse ridges within the tube possibly represent septa (Fig. 1D). DISCUSSION The possibility that the present tubulous organism is a hyolith like Linevitus, Burithes, or Ambrolinevitus (Hou et al., 1999, 2004) or the priapulid worm Paraselkirkia is unlikely because of the different body proportions (Fig. 1E) and the lack of a lidlike operculum and a slightly curved end. It is quite consistent, however, with the features of Archotuba, which shows a length-to-breadth ratio of approximately one-sixth and a slightly curved slender tube with several transverse septa (Figs. 1F–H). Nevertheless, Archotuba in the Chengjiang deposits is found frequently attached to the outer surface of brachiopods, hyoliths, and trilobites (see Hou et al., 2004, fig. 12.6), suggesting a sessile epifaunal life habit. The Archotuba specimen here, considering its orientation in the gut, may have been seized preferentially from the apertural end by the everted pharyngeal teeth of the Laojieella specimen. Archotuba could have been swallowed whole as the invagination of the pharynx of Laojieella. It seems that Laojieella was not powerful enough to break the tube of Archotuba, based on its completeness. It is difficult to envision that Laojieella was able to lift its proboscis above the seafloor to eat Archotuba from the apertural end unless Archotuba was already lying dead on the sea bottom. This is because the hydrostatic skeleton of the body cavity provided form and support of Laojieella; it also had no appendages like those of lobopods and arthropods with which to seize objects. This specimen of Laojieella thus most likely scavenged Archotuba, even though the pharyngeal teeth of Laojieella indicate a predatory habit. This case is reminiscent of hyoliths found in the gut of Ottoia (Conway Morris, 1977, 1998), a taxon that has been interpreted both as a predator (Conway Morris, 1977) and a scavenger (Bruton, 2001; Hu, 2005). CONCLUSION There are no explanations for the near lack of recognizable remains in the gut of organisms in the Chengjiang Lagersta¨tte. The case presented here is itself an event of low frequency, and several factors are proposed for the lack of this phenomenon: 1. Nonbiomineralized species, which make up a large proportion of the currently known 180 species of the Chengjiang fauna, are probably never preserved in the gut of predators. Trilobite exoskeletons, the outer tube of tubular priapulid worm selkirkiids, bivalve shells of arthropods, outer shells of hyoliths and some brachiopods, and tubular Archotuba, as well as the dorsal sclerites of lobopods from the Chengjiang fauna— representing a total of about 20 species—have a high potential to be preserved as gut contents. Poriferans and chancelloriids have never been found as gut contents; they were rarely swallowed, probably due to the presence of their sharp spicules, but their lack of identification may also be due to their millimeter-scale size. 2. Some Cambrian predators developed powerful apparatuses to destroy hard parts and digest soft tissues of their quarry. There is convincing evidence of broken, disarticulated sclerites from Cambrian fossil deposits other than the Chengjiang (Babcock, 2003). Fragments of a eodiscoid trilobite have been found in a Fuxianhuia-like arthropod from the Middle Cambrian Kaili fauna (Zhu et al., 2004), suggesting that arthropods by this time had used gnathobases and large appendages to break down the exoskeleton of some prey. These apparatuses are seen widely in Chengjiang arthropods and some large lobopods (Hou et al., 1989, 1999; Chen et al., 2002; Babcock, 2003; Maas et al., 2004; Zhang et al., 2004; Liu et al., 2006). This, taken together with the degradation function of the digestive glands within the alimentary tract of these animals (Hou et al., 1999, 2004; Butterfield, 2002; Chen et al., 2002, plate 15, fig. 2; Vannier
and Chen, 2005; Liu et al., 2006), was probably responsible for the rare occurrence of recognizable gut contents. Many fossil coprolites consisting of hyolith outer shells and arthropod bivalve shells, however, have been reported from the Chengjiang fauna (Chen et al., 1996; Chen and Zhou, 1997; Hou et al., 1999, 2004; Vannier and Chen, 2002, 2005). The vast majority of these types of gut contents are intact but devoid of soft tissues, suggesting that phosphatic or calcitic biomineralized exoskeletons in the Early Cambrian were too strong to be broken by apparatuses or degraded by the digesting systems of their contemporaneous predators. This further implies that swallowing quarry whole seems to be one of the important feeding strategies of Cambrian predators and scavengers. ACKNOWLEDGMENTS We thank Dr. S. Turner (Queensland Museum, Brisbane, Australia) for reviewing an early draft and two anonymous reviewers for constructive comments that greatly improved this paper. Thanks also to Zhai Juanping and Cheng Meirong (ELI) for photography and to Guo Hongxiang and Ji Yanbing (ELI) for fossil collections. This work was supported by the National Natural Science Foundation of China (grants 40332016, 32070207, and 04062003), the National ‘‘973’’ Project (grant 2006CB806401), and the Program for Chengjiang Scholars and Innovative Research Team in University (PCSIRT) of the Educational Ministry of China. REFERENCES ADRIANOV, A.V., and MALAKHOV, V.V., 1996, Priapulida: Structure, Development, Phylogeny, and Classification: KMK Scientific Press, Moscow, 268 p. BABCOCK, L.E., 2003, Trilobites in Paleozoic predation-prey systems, and their role in reorganization of early Paleozoic ecosystems, in Kelley, P.H., Kowalewski M., and Hansen, T.A., eds., Predator-Prey Interactions in the Fossil Record: Plenum, New York, p. 55–93. BRUTON, D.L., 1981, The arthropod Sidneyia inexpectans, Middle Cambrian, Burgess Shale, British Columbia: Philosophical Transactions of the Royal Society of London, ser. B, vol. 295, p. 619–656. BRUTON, D.L., 2001, A death assemblage of priapulid worms from the Middle Cambrian Burgess Shale: Lethaia, v. 34, p. 163–167. BUDD, G.E., 2001, Ecology of Nontrilobite Arthropods and Lobopods in the Cambrian, in Zhuravlev, A.Y., and Riding, R., eds., The Ecology of the Cambrian Radiation: Columbia University Press, New York, p. 404–427. BUTTERFIELD, N.J., 2001, Cambrian food webs, in Briggs, D.E.G., and Crowther, P.R., eds., Palaeobiology II: Blackwell Science, London, p. 40–43. BUTTERFIELD, N.J., 2002, Leanchoilia guts and the interpretation of three-dimensional structures in Burgess Shale–type fossils: Paleobiology, v. 28, p. 155–171. CHEN, J.-Y., 2004, The Dawn of the Animal World: Jiangsu Publishing House of Science and Technology, Nanjing, China, 366 p. In Chinese. CHEN, J.-Y., HUANG, D.-Y., and BOTTJER, D.J., 2005, An early Cambrian problematic fossil: Vetustovermis and its possible affinities: Proceedings of the Royal Society, v. 272, p. 2003–2007. CHEN, J.-Y., and ZHOU, G.-Q., 1997, Biology of the Chengjiang fauna: Bulletin of the National Museum of Natural Science, Taichung (Taiwan), v. 10, p. 11–106. CHEN, J.-Y., ZHOU, G.-Q., and RAMSKO¨LD, L., 1995, The Cambrian lobopodian Microdictyon sinicum and its broader significance: Bulletin of the National Museum of Natural Science, Taichung (Taiwan), v. 5, p. 1–93. CHEN, J.-Y., ZHOU, G.-Q., ZHU, M.-Y., and YEH, K.Y., 1996, The Chengjiang Biota— A Unique Window of the Cambrian Explosion: National Museum of Natural Science, Taichung (Taiwan), 222 p. In Chinese with English abstract. CHEN, L.-Z., LUO, H.-L, HU, S.-X., YIN, J.-Y., JIANG Z.-W., WU, Z.-L., LI, F., and CHEN, A.-L., 2002, Early Cambrian Chengjiang Fauna in Eastern Yunnan, China: Yunnan Science and Technology Press, Kunming, 199 p. In Chinese with English summary. CONWAY MORRIS, S., 1977, Fossil priapulid worms: Special Papers in Palaeontology, no. 20, p. 1–95. CONWAY MORRIS, S., 1997, The cuticle structure of 495 myr-old type species of the fossil worm Palaeoscolex, P. piscatorum (?Priapulida): Zoological Journal of the Linnean Society, v. 119, p. 69–82. CONWAY MORRIS S., 1998, The Crucible of Creation: The Burgess Shale and the Rise of Animals: Oxford University Press, Oxford, 242 p. CONWAY MORRIS, S., and BENGTSON, S., 1994, Cambrian predators—Possible evidence from boreholes: Journal of Paleontology, v. 68, no. 1, p. 1–23. CONWAY MORRIS, S., and ROBISON, R.A., 1986, Middle Cambrian Priapulids and other
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