New evidence of nearshore Mid-Triassic <Emphasis Type="Italic">Zoophycos</Emphasis>: morphological and paleoenvironmental characterization

Zoophycos is a well-known trace fossil common throughout the Phanerozoic. Paleozoic forms show important differences in morphology and habitat distribution with respect to the Jurassic, Cretaceous, and Cenozoic ones. Therefore, Early–Middle Triassic is considered a crucial time-span for the understanding of the evolution of this trace fossil. So far, Early Triassic Zoophycos is unknown and Middle Triassic forms were recorded only in deposits from Thuringia. The morphology and paleoenvironment of Zoophycos from the middle–upper Muschelkalk of the Iberian Range is herein described. The best-preserved trace fossils occur in a dolomicritic bed Ladinian in age, and are represented by small forms with a subcircular, slightly lobed outline and very little penetration depth. They were deposited in a very shallow, quiet-water environment with transition to supratidal/emerged areas. The low diversity of both trace fossils and skeletal remains point to stressful conditions related to strong salinity variations and/or poor water circulation. A comparison was made with Zoophycos from Anisian deposits of the Muschelkalk in Germany. This showed that both forms are quite simple and penetrate only the shallowest tiers, although they are different in whorl outline and lobe shape. This confirms that, notwithstanding the morphological variability of this group, Zoophycos still maintained a quite simple structure in the Triassic. A shallow-water environment was deduced for both localities, confirming that at least until the Early Jurassic Zoophycos had not definitively migrated toward deep-water areas.     

Evolutionary trend of Zoophycos morphotypes from the Upper Cretaceous–Lower Miocene in the type pelagic sections of Gubbio,Italy

About 200 Zoophycos specimens, including 90 specimens studied in detail, have been analysed in the continuous Upper Cretaceous–Lower Miocene pelagic sedimentary type sections of the Gubbio area (the Contessa Highway, Contessa Quarry and Bottaccione sections, Northern Apennines). The sediments are reddish to grey limestones and marls of the Scaglia Group and marls with volcaniclastic deposits of the Bisciaro Formation. The aim was to examine the evolutionary trend of what is probably the most debated trace fossil of all time, from the Upper Cretaceous to Lower Miocene. Despite having been found in beds ranging from the Cambrian to the present, no consensus has been reached regarding mode of construction, tracemaker or ethological explanation for Zoophycos. Four Zoophycos morphotypes are recognized at Gubbio showing variations of major and minor lamellae, apex, lobes and whorls: the Cretaceous–Eocene cone‐shaped type 1, the Upper Eocene–Middle Oligocene helicoidal type 2, the Oligocene lobate type 3 and the Upper Oligocene–Lower Miocene flat type 4. The very high ichnodensity in some beds (hundreds of specimens in discrete levels of the Bisciaro Formation, now destroyed by quarrying) seems to find explanation in abnormal concentrations of phytodetritus and organic matter on the seafloor in some periods. This very high abundance in discrete levels reflects a change in sedimentation and seafloor conditions at pre‐flysch deposition. Due to such high ichnodensity, many adjacent specimens display deformed outer margins. Taphonomic analysis shows a variation of whorls, laminae and U‐shaped lobes, reflecting ontogenetic development of the tracemaker(s) (?sipunculid worms).     

Cambrian stem-group annelids and a metameric origin of the annelid head

The oldest fossil annelids come from the Early Cambrian Sirius Passet and Guanshan biotas and Middle Cambrian Burgess Shale. While these are among the best preserved polychaete fossils, their relationship to living taxa is contentious, having been interpreted either as members of extant clades or as a grade outside the crown group. New morphological observations from five Cambrian species include the oldest polychaete with head appendages, a new specimen of Pygocirrus from Sirius Passet, and an undescribed form from the Burgess Shale. We propose that the palps of Canadia are on an anterior segment bearing neuropodia and that the head of Phragmochaeta is formed of a segment bearing biramous parapodia and chaetae. The unusual anatomy of these taxa suggests that the head is not differentiated into a prostomium and peristomium, that palps are derived from a modified parapodium and that the annelid head was originally a parapodium-bearing segment. Canadia, Phragmochaeta and the Marble Canyon annelid share the presence of protective notochaetae, interpreted as a primitive character state subsequently lost in Pygocirrus and Burgessochaeta, in which the head is clearly differentiated from the trunk.     

Zoophycos composite ichnofabrics and tiers from the Permian neritic facies in South China and south‐eastern Australia

Gong, Y.‐M., Shi, G.R., Zhang, L.‐J. & Weldon, E.A. 2009: Zoophycos composite ichnofabrics and tiers from the Permian neritic facies in South China and south‐eastern Australia. Lethaia, Vol. 43, pp. 182–196. Zoophycos composite ichnofabrics (ZCI) comprising two or more suites of the same form of Zoophycos are widespread and densely distributed in Early and Middle Permian (Cisuralian–Guadalupian) neritic limestones (Qixia and Maokou Formations) of palaeotropical origin in the Laibin area, Guangxi, South China. Similar ZCI also occur in neritic greywackes of glaciomarine origin from the Middle Permian (Guadalupian) Westley Park Sandstone Member (Broughton Formation) in the southern Sydney Basin, south‐eastern Australia. Zoophycos from both regions consists of planar spreite with major and minor lamellae and a cylindrical tunnel interpreted as a marginal tube and/or axial shaft. The cylindrical tunnel is herein considered to be an essential component of Zoophycos, and thus can be used to define and characterize the morphological variability of Zoophycos. It is suggested that the variation of spreite and major and minor lamellae originated from the different morphologies and migration manners of the cylindrical tunnel. The shallowest, shallow, middle and deepest Zoophycos tiers have been distinguished in ZCI on the basis of cross‐cutting relationships, the soft‐sediment deformation and the contrast in colour between Zoophycos and its host rock. The multiple tiers may represent the substrate consistency spectrum from a softground through a stiffground to a firmground. The different Zoophycos tiers may have been constructed by tracemakers of either different or the same taxonomic affinities in response to the gradual accretion and lithification of sediment layers on the seafloor. The tracemakers appeared to be very sensitive to neither climate nor lithology. The width of the planar spreiten of Zoophycos decreases slightly with the depth of tiering in ZCI. □Composite ichnofabric, Permian, South China, south‐eastern Australia, tier, Zoophycos.     

Stable deep-sea macrobenthic trace maker associations in disturbed environments from the Eocene Lefkara Formation,Cyprus

Ichnological analysis of Eocene deep-pelagic whitish chalky calcilutites interstratified with high-energy calcarenite beds in the lower part of the Petra Tou Romiou section (southern Cyprus) was conducted to interpret the development and evolution of the trace maker associations during calcilutite deposition after high-energy episodes. The trace fossil assemblage from the chalky calcilutites consists of Chondrites isp. (Chondrites intricatus and Chondrites targionii), Planolites isp., Taenidium isp., Thalassinoides isp., and Zoophycos isp., typical of the Zoophycos ichnofacies. A composite chalky ichnofabric reveals a multi-tiered association of burrowing animals: the uppermost tier determines a mottled background, the upper tier shows the highest trace fossil abundance and diversity (Planolites, Taenidium and Thalassinoides), the middle tier features Zoophycos and large Chondrites, and the deepest tier consists mainly/exclusively of small Chondrites. This ichnofabric has an autocomposite character, associated with bioturbation by a single ichnocoenosis and gradual upward migration of the tiered macrobenthic community as the pelagic calcilutite sedimentation slowly progresses. There are no changes in the trace fossil assemblage between or within calcilutite intervals, regardless of the associated calcarenite beds. This supports a stable, mature, background calcilutite trace maker association, which recovers shortly after the deposition of high-energy calcarenites. In turn, there would have been a rapid re-establishment of paleoenvironmental conditions during pelagic calcilutite accumulation after episodic deposition of any calcarenitic material.     

Complex behavioural patterns and ethological analysis of the trace fossil Zoophycos: evidence from the Lower Devonian of South China

The trace fossil Zoophycos is abundant in the shallow‐marine deposits (tempestites) of the Lower Devonian (Emsian) Yangmaba Formation in Ganxi of Sichuan, South China. It often occurs as part of complex trace fossils that comprise different integrated elements: scratch traces, simple to complex spreiten structures with marginal tubes (Zoophycos) and vertical tunnels. The complex Zoophycos burrows consist of spreiten with a marginal tube, preserved as convex hyporeliefs on the sole of an erosion surface. The exquisite, complex spreiten are interpreted to have been formed by deposit‐feeding behaviour, where the animal constructed the trace upwards without leaving faeces in the spreiten. The width of the marginal tube in different whorls is almost constant. The scratches are observed on the wall of the marginal tubes. The Zoophycos intergrades with Spongeliomorpha and Chondrites and was later cut by vertical shafts. All these features together indicate that the Zoophycos‐maker might have been a vermiform polychaete instead of a predator such as a decapod crustacean (Spongeliomorpha producer). Based on stratigraphical and ichnological features, the complex trace fossils resulted from the complex activity of different opportunistic organisms (r‐strategist) that quickly occupied and thrived within the quiet, nutrient‐rich environment after storm events.     

Occurrence ofByronia Matthew andSphenothallus Hall in the Lower Cambrian of China

Rare phosphatic tubular fossils from the Lower-Middle Cambrian Kaili Formation of Guizhou Province, southern China were originally identified as non-calcified algae or ‘worms’ (ScoleciellusLiu). Re-examination of these fossils indicates that specimens identified as non-calcified algae areSphenothallus taijiangensis n. sp., while specimens identified asScoleciellus belong toByronia natus (Liu).Sphenothallus taijiangensis andByronia natus from Lower Cambrian strata in the Kaili Formation are the oldest known representatives of their genera. In addition,B. natus (Liu) is the only known species ofByronia with the exception ofB. annulata Matthew (Middle Cambrian, British Columbia). CambrovitusMao et al., a tubular fossil from Middle Cambrian strata in the Kaili Formation, originally was classified as a hyolithid. However, the discovery of a nearly complete specimen possessing an apical attachment disk shows thatCambrovitus, likeByronia andSphenothallus, probably was a thecate cnidarian polyp.     

Zoophycos in storm-affected environments: a case study from lower Maastrichtian deposits of the Mateur-Beja area (Northern Tunisia)

Abstract

The lower Maastrichtian deposits of the Mateur-Beja area in northern Tunisia are mainly composed of fine-grained marl and limestone alternations occasionally interbedded by coarse-grained calcarenites and gravel deposits. In the coarse-grained intervals sedimentary structures are indicative of storm-induced high-energy currents in an outer ramp to slope setting and of local reworking by bottom currents in the basin. In deeper environments, fine-grained sediments accumulated mainly while settling from storm-induced suspensions. The lower Maastrichtian deposits contain abundant Zoophycos exhibiting two main morphotypes, skirt-shaped Zoophycos in deposits around storm-wave base and tongue-shaped Zoophycos in somewhat deeper sediments. The types differ in burrow architecture, morphology of lobes, and size of structural elements. These differences are attributed to different behavioral programs modulated by the availability of benthic food that decreased seaward. Storm-affected environments seem to be a prerequisite for these Zoophycos-producers to choose their habitat.     

Ethological analysis of the trace fossil Zoophycos: hints from the Arctic Ocean

Löwemark, L. 2011: Ethological analysis of the trace fossil Zoophycos: Hints from the Arctic Ocean. Lethaia, Vol. 45, pp. 290–298. The distribution of the trace fossil Zoophycos in Quaternary marine sediments from the Arctic Ocean was studied in twelve piston and gravity cores retrieved during the Swedish icebreaker expeditions YMER80, Arctic Ocean‐96 and LOMROG I & II. The sampled cores span an area from the Makarov Basin to the Fram Strait. Zoophycos was only found in two cores taken at more than 2 km water depth on the slope of the Lomonosov Ridge, but was absent in cores obtained at shallower depth, confirming earlier observations of the trace maker’s bathymetric preferences. The two cores containing Zoophycos are characterized by quiet sedimentation and slightly enhanced food flux compared with the general Arctic. The occurrence of Zoophycos in these cores in a setting that is characterized by extreme seasonal variations in food flux due to the total ice coverage during winters and high primary productivity during the long summer days, is interpreted to be a cache‐behaviour response to pulsed flux of food to the benthic realm. □Arctic Ocean, ethology, Quaternary, spreiten, trace fossils, Zoophycos.     

Bioturbational disturbance of the Cretaceous-Palaeogene (K-Pg) boundary layer: Implications for the interpretation of the K-Pg boundary impact event

Detailed field observations across and along the Cretaceous-Palaeogene (K-Pg) boundary interval in the Caravaca section, SE Spain, together with laboratory analyses reveal a well-developed lowermost Danian dark-colored trace fossil assemblage. The trace fossils range continuously from the bioturbated horizons in the dark boundary layer (lowermost Danian), to the uppermost Maastrichtian sediments. The rusty boundary layer at the base of the dark boundary layer, usually related to the K-Pg boundary impact, is traditionally considered as undisturbed. However, ichnological analysis at the Caravaca section shows that this rusty boundary layer is cross-cut vertically by Zoophycos and Chondrites, but also penetrated laterally by Chondrites, revealing an important colonization of the substrate. Stereomicroscope analysis shows sharp burrow margins of dark-colored Chondrites directly against the surrounding red sediment of the rusty layer. Colonization of unfavorable substrates by Zoophycos and Chondrites tracemakers, as that represented by the rusty boundary layer, was possible because of constructing of open, probably of actively ventilated burrows that facilitate colonization of sediments poor in oxygen and food. Significant bioturbational disturbance of the rusty layer can cause vertical and horizontal redistribution of the components related to the K-Pg boundary impact and, in consequence, to induce erroneous interpretations. A detailed ichnological analysis of the K-Pg boundary interval, with special attention to the rusty layer, reveals an essential tool to avoid misinterpretations.     

A crown‐group demosponge from the early Cambrian Sirius Passet Biota,North Greenland

Calibration of the divergence times of sponge lineages and understanding of their phylogenetic history are hampered by the difficulty in recognizing crown versus stem groups in the fossil record. A new specimen from the lower Cambrian (Series 2, Stage 3; approximately 515 Ma) Sirius Passet Biota of North Greenland has yielded a diagnostic spicule assemblage of the extant demosponge lineages Haploscleromorpha and/or Heteroscleromorpha. The specimen has disarticulated approximately in situ, but represents an individual sponge that possessed monaxon spicules combined with a range of slightly smaller sigma, toxa and unique spiral morphologies. The combination of spicule forms, together with their relatively large size, suggests that the sponge represents the stem lineage of Haploscleromorpha + Heteroscleromorpha. This is the first crown‐group demosponge described from the early Cambrian and provides the most reliable calibration point currently available for phylogenetic studies.     

Recent Priapulidae and their Early Cambrian ancestors: comparisons and evolutionary significance

Although priapulid worms form a relatively small phylum in present-day marine environments, they were important animals in Cambrian endobenthic communities. Two Early Cambrian priapulids, namely Xiaoheiqingella peculiaris and Yunnanpriapulus halteroformis nov. gen., nov. sp. from the Maotianshan Shale Lagerstätte of SW China are revised and described. Several key-features of the body plan of Recent Priapulidae are recognized in these two forms: 1) the four-fold body division (introvert, neck, trunk, and caudal appendage); 2) the well-developed introvert armed with ca. 25 longitudinal rows of scalids; 3) the caudal appendage; 4) the pharyngeal teeth arranged in a pentagonal disposition (Xiaoheiqingella); 5) the ventral nerve cord present in Yunnanpriapulus. This morphology indicates close evolutionary relationships with modern priapulids. Xiaoheiqingella and Yunnanpriapulus nov. gen. are tentatively placed within the recent family Priapulidae. The Priapulidae lineage may therefore have a remote origin (Early Cambrian) much older than was previously assumed (Priapulites; Late Carboniferous). The functional morphology of Xiaoheiqingella and Yunnanpriapulus nov. gen. suggests that these two worms were chiefly carnivorous with possible occasional mud-eating habits.     

Zoophycos and umbellula (Pennatulacea): Their synthesis and identity

The trace fossil Zoophycos has the shape of a low-angled helicoidal sheet constructed of numerous spirally radiating and adjacent dwelling burrows, each lined with retextured sediment derived from the adjacent or underlying beds. Such spiral sheets are here considered the products of a sea pen or closely allied organism with its trunk at the sea floor and its tubular stem suspended in, and voluting laterally through, the underlying soft sediments. Peristaltic movements of the stem fluidise the sediment in the annular space around the stem and allow both the lateral voluting motion of the stem and the pumping of nutrient-rich mud up to the sea floor. The organic content of the mud is delivered to the feeding filters of polyps of the animal which lie along the length of the stem and through these it passes into circulatory canals. Nutrient particles are then distributed by water currents through the length of the organism.The above proposed mechanism of feeding fits the probable ecology and structure of the Umbellulidae and explains the form, structure and occurrence of Zoophycos and related fossils.     

Trusheimichnus New Ichnogenus From the Middle Triassic of the Germanic Basin,Southern Germany

The study of Jurassic Zoophycos from south‐eastern France has led us to some original results concerning its morphological organization and paleoenvironmental significance. Zoophycos represents a spreite constituted by a coiling lamina, constructed upwards in sediments, with only one opening at the sediment‐water interface. Zoophycos, produced by a deep sediment feeder, is emplaced late in an almost coherent substrate, intermediate between soft and firm ground. This suggests periods of very low or no sedimentation during which time the trace was constructed.

The Zoophycos studied developed on slope areas, characterized by a particular style of sedimentation: periods of nutrient supplies coming from proximal areas, alternating with periods of sedimentary breaks. Other paleoecologic and paleoethologic characteristics of the Zoophycos‐producer are discussed here: working activity, competition behavior, substrate modification, growing pattern and burrow oxygenation are the most interesting.     

Lapworthellids and other skeletonised microfossils from the Cambrian Stage 3 of the northern Montagne Noire,southern France

The Montagne Noire (southern France) possesses one of the most complete Cambrian successions in the western peri-Gondwana margin and might provide a good stratigraphic reference for both regional charts and international correlations. However, to date, the lower Cambrian succession of the northern Montagne Noire has been supposed to be devoid of biostratigraphically significant fossils. The complex tectonostratigraphic framework of the area (a range divided into Axial Zone, northern and southern Montagne Noire) exacerbated problems related to regional correlations and palaeogeographic reconstructions. As a result, the chronostratigraphic context of the lower Cambrian of northern Montagne Noire is still uncertain and stratigraphic reports have broadly relied on putative lithostratigraphic correlations with the southern Montagne Noire. The purpose of this study is to characterise, for the first time, the fossil record of carbonate beds and lenses of the northern Montagne Noire occurring at the top of the siliciclastic-dominated Marcory Formation, in order to provide regional bio- and chronostratigraphic constraints on lower Cambrian strata. Moreover, this study is aimed at improving international chronostratigraphic correlation. Carbonate beds and lenses cropping out along the Orque Cliff, in the Mélagues thrust slice, were investigated. They yielded a faunal assemblage constituted of molluscs (Igorella cf. ungulata and Igorella moncereti n. sp.), hyoliths (Conotheca brevica), chancelloriids (Archiasterella cf. pentactina and Allonnia sp.) and tommotiids (Lapworthella rete). L. rete is recorded in upper Meishucunian (Cambrian Stage 3) strata of the Yangtze Platform (South China) where it is used as index fossil of the Cambrian Stage 3 Sinosachites flabelliformis–Tannuolina zhangwentangi Assemblage Zone. Therefore, the presence of this tommotiid provides evidence that the studied carbonate beds and lenses are Cambrian Age 3 (Atdabanian according to the Siberian chart). The upper part of the Marcory Formation in the Mélagues slice, dated as Cambrian Stage 3, might represent a lateral equivalent of the mixed (carbonate-siliciclastic) Pardailhan Formation defined in the southern Montagne Noire.     

Internal soft-tissue anatomy of cambrian 'orsten' arthropods as revealed by synchrotron x-ray tomographic microscopy

The world-famous ‘Orsten’ Konservat-Lagerstätte has yielded detailed information about Cambrian arthropods and their morphology. Internal organs or soft tissues have, however, rarely been reported, an obvious palaeobiological drawback. In this study, we employed synchrotron radiation X-ray tomographic microscopy (SRXTM) to study microscopic ‘Orsten’ arthropods from the Cambrian of Sweden: Skara minuta and two phosphatocopine species, Hesslandona sp. and Hesslandona trituberculata. This exceptionally high-resolution technique reveals internal organs or soft tissues that allow detailed comparison with equivalent structures in extant crustaceans and functional inferences to be made. The S. minuta specimen shows the digestive system and muscles that extend to the extremities. The slanting anterior portion of the head and anterior position of the mouth with a straight oesophagus suggest a primarily brushing and scraping way of feeding. The prominent head appendage muscles indicate muscle strength and good capacity for food manipulation. In the phosphatocopines the bulbous labrum is one of the most prominent morphological structures of the body. All specimens analysed reveal pairs of muscle bundles within the labrum. Based on comparisons with extant crustacean relatives, these muscles would fulfil the function of moving the labrum up and down in order to open the buccal cavity. The results of this pilot study demonstrate that there is still much to be learned about the ‘Orsten’ taxa.     

Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians

Burgess Shale-type deposits are renowned for their exquisite preservation of soft-bodied organisms, representing a range of animal body plans that evolved during the Cambrian ‘explosion’. However, the rarity of these fossil deposits makes it difficult to reconstruct the broader-scale distributions of their constituent organisms. By contrast, microscopic skeletal elements represent an extensive chronicle of early animal evolution—but are difficult to interpret in the absence of corresponding whole-body fossils. Here, we provide new observations on the dorsal spines of the Cambrian lobopodian (panarthropod) worm Hallucigenia sparsa from the Burgess Shale (Cambrian Series 3, Stage 5). These exhibit a distinctive scaly microstructure and layered (cone-in-cone) construction that together identify a hitherto enigmatic suite of carbonaceous and phosphatic Cambrian microfossils—including material attributed to Mongolitubulus, Rushtonites and Rhombocorniculum—as spines of Hallucigenia-type lobopodians. Hallucigeniids are thus revealed as an important and widespread component of disparate Cambrian communities from late in the Terreneuvian (Cambrian Stage 2) through the ‘middle’ Cambrian (Series 3); their apparent decline in the latest Cambrian may be partly taphonomic. The cone-in-cone construction of hallucigeniid sclerites is shared with the sclerotized cuticular structures (jaws and claws) in modern onychophorans. More generally, our results emphasize the reciprocal importance and complementary roles of Burgess Shale-type fossils and isolated microfossils in documenting early animal evolution.     

Image processing techniques to improve characterization of composite ichnofabrics

Abstract

Image processing techniques, including the Analyze Particles tool offered by Fiji software and the Intensity Profile by ICY (IP-ICY), were applied in core and outcrop examples to improve characterization of autocomposite ichnofabrics. Analyze Particles gives information about particle shape and size in the studied image. This tool was applied to Chondrites assemblages in composite ichnofabrics in view of selected images of modern marine hemipelagic cores from Site U1385 of IODP Expedition 339. Differences in size, relative abundance, density and distribution of Chondrites were interpreted as related to variations within the population of Chondrites tracemakers. Intensity Profile quantifies pixel values of the infilling material of traces, proving helpful to discriminate between specimens, evaluate the horizon of colonization, and approach the penetration depth. Its application to the analysis of Zoophycos improves characterization of composite ichnofabrics from deep-sea pelagic calcilutites of the Petra Tou Romiou section (Eocene Lefkara Formation; southern Cyprus). Some suites of Zoophycos were interpreted as associated with different phases of colonization from several horizons. Moreover, it was possible to discriminate structures pertaining to different specimens, as opposed to those from the same specimen.     

Biomechanical analyses of Cambrian euarthropod limbs reveal their effectiveness in mastication and durophagy

Durophagy arose in the Cambrian and greatly influenced the diversification of biomineralized defensive structures throughout the Phanerozoic. Spinose gnathobases on protopodites of Cambrian euarthropod limbs are considered key innovations for shell-crushing, yet few studies have demonstrated their effectiveness with biomechanical models. Here we present finite-element analysis models of two Cambrian trilobites with prominent gnathobases—Redlichia rex and Olenoides serratus—and compare these to the protopodites of the Cambrian euarthropod Sidneyia inexpectans and the modern American horseshoe crab, Limulus polyphemus. Results show that L. polyphemus, S. inexpectans and R. rex have broadly similar microstrain patterns, reflecting effective durophagous abilities. Conversely, low microstrain values across the O. serratus protopodite suggest that the elongate gnathobasic spines transferred minimal strain, implying that this species was less well-adapted to masticate hard prey. These results confirm that Cambrian euarthropods with transversely elongate protopodites bearing short, robust gnathobasic spines were likely durophages. Comparatively, taxa with shorter protopodites armed with long spines, such as O. serratus, were more likely restricted to a soft food diet. The prevalence of Cambrian gnathobase-bearing euarthropods and their various feeding specializations may have accelerated the development of complex trophic relationships within early animal ecosystems, especially the ‘arms race'' between predators and biomineralized prey.