[Palaeontology, 2013, pp. 1–20]

NEW ANATOMICAL INFORMATION ON ANOMALOCARIS FROM THE CAMBRIAN EMU BAY SHALE OF SOUTH AUSTRALIA AND A REASSESSMENT OF ITS INFERRED PREDATORY HABITS by ALLISON C. DALEY1,2*, JOHN R. PATERSON3, GREGORY D. EDGECOMBE1, DIEGO C. GARCIA-BELLIDO4 and JAMES B. JAGO5 1Department of Earth Sciences, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK; e-mails: [email protected] [email protected] 2Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol, BS8 1RJ, UK; e-mail: [email protected] 3Division of Earth Sciences, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia; e-mail: [email protected] 4Sprigg Geobiology Centre, School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA 5005, Australia; e-mail: [email protected] 5School of Natural and Built Environments, University of South Australia, Mawson Lakes, SA 5095,Australia; e-mail: [email protected] *Corresponding author.

Typescript received 3 October 2012; accepted in revised form 20 January 2013

Abstract: Two species of Anomalocaris co-occur in the Emu ing of a series of lanceolate blades are similar to those of other Bay Shale (Cambrian Series 2, Stage 4) at Big Gully, Kangaroo anomalocaridids and are found in isolation or associated with Island. Frontal appendages of Anomalocaris briggsi Nedin, body flaps. A single specimen also preserves putative gut diver- 1995, are more common than those of Anomalocaris cf. canad- ticula. The morphology of the appendages, oral cone, gut div- ensis Whiteaves, 1892, at a quarry inland of the wave-cut plat- erticula and compound eyes of Anomalocaris, along with its form site from which these species were originally described. large size, suggests that it was an active predator, and speci- An oral cone has the three large, node-bearing plates recently mens of coprolites containing trilobite fragments and trilobites documented for Anomalocaris canadensis, confirming that with prominent injuries have been cited as evidence of anom- Anomalocaris lacks a tetraradial ‘Peytoia’ oral cone and alocaridid predation on trilobites. Based on frontal appendage strengthening the case for the identity of the Australian speci- morphology, Anomalocaris briggsi is inferred to have been a mens as Anomalocaris. Disarticulated anomalocaridid body predator of soft-bodied animals exclusively and only Anomal- flaps are more numerous in the Emu Bay Shale than in other ocaris cf. canadensis may have been capable of durophagous localities, and they preserve anatomical details not recognized predation on trilobites, although predation (including possible elsewhere. Transverse lines on the anterior part of the flaps, cannibalism) by Redlichia could also explain the coprolites interpreted as strengthening rays or veins in previous descrip- and damage to trilobite exoskeletons found in the Emu Bay tions of anomalocaridids, are associated with internal struc- Shale. tures consisting of a series of well-bounded, striated blocks or bars. Their structure is consistent with a structural function Key words: Radiodonta, Anomalocaris briggsi, coprolites, imparting strength to the body flaps. Setal structures consist- bite marks, predation.

T HE first Australian record of anomalocaridids was based attributed damage to trilobites and the nektaspid Emuc- on a few frontal appendages and a putative oral cone aris (referred to as Naraoia, but see Paterson et al. 2010) attributed to Anomalocaris by McHenry and Yates (1993), and a coprolite containing fragments of the trilobite Re- found in the lower Cambrian (Series 2, Stage 4) Emu Bay dlichia takooensis to predation by Anomalocaris; the copr- Shale on the north coast of Kangaroo Island, South Aus- olite was subsequently re-illustrated and discussed by tralia. Drawing on a sample of 30 frontal appendages, Vannier and Chen (2005). Working on material from Nedin (1995) identified two different Anomalocaris Buck Quarry, Paterson et al. (2011) identified large species from the Emu Bay Shale, one newly named as compound eyes as those of Anomalocaris and illustrated Anomalocaris briggsi and another left under open nomen- associated frontal appendages and the first body flap doc- clature as Anomalocaris sp. Subsequently, Nedin (1999) umented from the Emu Bay Shale.

© The Palaeontological Association doi: 10.1111/pala.12029 1 2 PALAEONTOLOGY

As a result of an ongoing programme of excavation at served material of Anomalocaris cf. canadensis, but frontal Buck Quarry, material that includes additional body parts appendages of both species are also present in the collec- of anomalocaridids is available for study. We evaluate the tions from Buck Quarry. Anomalocaris briggsi is much new collections in the light of the previously documented more common at Buck Quarry, and thus circumstantially, material, emend the descriptions of the two known species it is likely that most of the additional body parts, includ- and strengthen the case for assignment to Anomalocaris ing the large compound eyes (Paterson et al. 2011), (rather than another anomalocaridid genus) by confirming belong to that species. There are no distinct morphs of the identification of the oral cone figured by McHenry and body flaps or setose blades from Buck Quarry, so they Yates (1993). Body flaps and setal blades are described, with have not been attributed to either species. emphasis on structures that have not been recognized pre- viously or that have not received much attention. A single specimen with a partially preserved axial region has puta- SYSTEMATIC PALAEONTOLOGY tive gut diverticula similar to those seen in other anomaloc- aridids and stem lineage arthropods. STEM EUARTHROPODA Order RADIODONTA Collins, 1996

LOCALITY AND MATERIAL Genus ANOMALOCARIS Whiteaves, 1892

The Emu Bay Shale Konservat-Lagerst€atte is restricted to the Big Gully locality (including Buck Quarry), situated Type species. Anomalocaris canadensis Whiteaves, 1892; from the 3 km east of Emu Bay on the north-east coast of Kanga- Stephen Formation (Cambrian Series 3, Stage 5) of British roo Island; for detailed information about the stratigra- Columbia, Canada. phy of the Emu Bay Shale and the overall geology of the area, refer to Gehling et al. (2011). Prior to the excava- tions at Buck Quarry that commenced in September Anomalocaris briggsi Nedin, 1995 2007, all previously documented fossils from the Emu Figures 1, 2 Bay Shale at Big Gully, including those of anomalocarid- ids (McHenry and Yates 1993; Nedin 1995), were sourced 1992 Anomalocaris sp. Nedin, p. 221. from outcrops along the wave-cut platform and adjacent 1993 Anomalocaris sp. McHenry and Yates, pp. 77–81, cliffs to the east of the mouth of Big Gully. New anomal- 84–85, figs 2–7. ocaridid material from Buck Quarry, located approxi- 1995 Anomalocaris briggsi Nedin, pp. 31–35, figs 1, 3A. mately 500 m inland (south) of the original wave-cut 1997 Anomalocaris briggsi Nedin, p. 134. platform site, includes specimens of both Anomalocaris 1999 Anomalocaris briggsi Nedin, p. 989. species recognized by Nedin (1995). Other arthropods 2002 Anomalocaris briggsi Hagadorn, p. 98. described from Buck Quarry thus far are the bivalved taxa 2006 Anomalocaris briggsi Van Roy and Tetlie, pp. 240, Isoxys and Tuzoia (Garcıa-Bellido et al. 2009), nektaspids 244, fig. 1A. (Paterson et al. 2010), the leanchoiliid Oestokerkus (Edge- 2006 Anomalocaris briggsi Paterson and Jago, p. 43. combe et al. 2011), the artiopodans Squamacula and Aus- 2008 Anomalocaris briggsi Hendricks et al., table 1. 2008 Anomalocaris briggsi Paterson et al., p. 320. tralimicola (Paterson et al. 2012) and large compound 2009 Anomalocaris briggsi Garcıa-Bellido et al., p. 1221. eyes of an unidentified taxon (Lee et al. 2011). 2010 Anomalocaris briggsi Daley and Peel, p. 354. Anomalocaridid material from the Emu Bay Shale con- 2011 Anomalocaris briggsi Jago and Cooper, p. 239. sists of isolated appendages, body flaps, setal structures 2011 Anomalocaris briggsi Paterson et al., p. 239, SI fig. 2. = ( ‘gills’ of Whittington and Briggs 1985) and a single 2012 Anomalocaris briggsi Jago et al., p. 252. oral cone, all preserved as part and counterpart in buff- weathering mudstones. These structures show consistent orientation with the plane of each fossil being parallel to Holotype. SAM P40180 (Fig. 1A, B), originally referred to as AUGD 1046-630 (Nedin 1995). bedding. The existence of two species of Anomalocaris in the Emu Bay Shale was demonstrated by two distinct Paratype. SAM P40763, originally referred to as AUGD 1046- morphs of frontal appendages and readily distinguished 335 (Nedin 1995). by the presence (A. briggsi) or absence (Anomalocaris sp.; here referred to Anomalocaris cf. canadensis) of spinules Other material. Fifty-six additional specimens of isolated frontal along the proximal and distal margins of the ventral appendages, of which 26 come from the wave-cut platform and spines (Nedin 1995). The wave-cut platform exposure is adjacent cliff exposure, 27 come from Buck Quarry and the source of the type material of A. briggsi and well-pre- three from an exposure on the road south of Buck Quarry (see DALEY ET AL.: ANOMALOCARIS FROM THE EMU BAY SHALE 3

Supplementary Information for catalogue numbers). Three spec- evenly spaced along the entire length of their distal margins (sp in imens with multiple appendages come from the wave-cut plat- Figs 1B, D, 2). Some specimens (SAM P40180, P40761/40178, form and adjacent cliffs (see Supplementary Information). All P31953, P15000) show similar spinules extending along the proxi- material is housed in the palaeontological collections at the mal margins, matching those on the distal margin in location and South Australian Museum (prefix SAM P), Adelaide, Australia. size (Fig. 2; ventral spines on podomeres 10 and 12 in Fig. 1B; podomeres IV and VI in McHenry and Yates 1993, fig. 3). Emended diagnosis. Anomalocaris with long, distally taper- The distal end of the appendage is narrow and elongated, ing frontal appendages consisting of 14 podomeres sepa- with a pronounced ventral curvature (Fig. 1A–B). SAM P43724, rated by triangular regions of flexible cuticle; podomeres P14681 and P40180 (ts in Fig. 1B) show that podomere 14 2–12 bearing a pair of proximally curving ventral spines tapers to a pair of simple spines, giving the terminal end of the appendage a forked appearance (Fig. 2). Single dorsal spines (ds that are longer than the height of the associated podo- in Figs 1B, 2) extend from the medial distal region of the dorsal mere and originate from the distal margin of the ventral margin on podomeres 12 and 13 at an oblique angle to the surface of the podomere; proximal base and entire distal appendage. SAM P43724 shows that the dorsal spine on podo- length of the ventral spines with prominent spinules; ven- mere 12 is only 3–4 mm long, but that on podomere 13 is much tral spines terminate in a point with a pair of short spines longer and arches over nearly the full length of the terminal flanking it; podomeres 1 and 13 with pair of short, spike- podomere (ds in Fig. 2). Podomere 14 has a relatively long dor- like ventral spines; podomere 14 with forked terminal sal spine that protrudes from just above the forked terminal end end; elongated dorsal spines projecting forward medially of the appendage (Fig. 2). from the distal margins of podomeres 12–14. Remarks. The original description of Anomalocaris briggsi (Nedin 1995, p. 33) is largely confirmed. We amended Description. Complete frontal appendages 87–175 mm long the diagnosis to include mention of the origination of the (mean = 119 mm, SD = 30 mm, n = 7), as measured along the outwardly convex dorsal margin. Podomeres are tall and narrow ventral spines from the distal region of the ventral surface in the proximal region, but shorter and more elongated towards of the podomere, as this is a unique characteristic of the distal end. Boundaries between podomeres are often pre- A. briggsi that readily allows identification of incomplete served as simple lines (Fig. 1C–D), but occasionally, the bound- specimens. Nedin (1995) described spinules on the ventral aries are preserved as elongated triangular regions that extend spines of podomere 13 and a bifurcation of the dorsal from half to almost the full height of the podomeres (Fig. 1A– spine on podomere 14; however, these features were not B). The triangular regions are interpreted as more flexible cuti- evident in the more complete, newly collected specimens. cle, based on their pockmarked and mottled preservation The other difference from Nedin’s (1995) reconstruction – (Fig. 1A; McHenry and Yates 1993, figs 6 7). The most proximal is the presence in some specimens of spinules along the podomere appears to be as long as at least four or five of the proximal margin of the ventral spines (Fig. 2). Whilst immediately succeeding podomeres (Fig. 1C–D), is much taller four specimens show this feature clearly, many more (Fig. 1A–B) and has an irregular attachment margin that may be concave in outline (Fig. 1). specimens with well-preserved proximal margins to their A pair of spines extends from the distal margin of the ventral ventral spines show no evidence of the presence of spin- surface of podomeres 1–13 (vs in Figs 1B, D, 2). SAM P46984/5 ules. Owing to its inconsistency, these proximal spinules (Paterson et al. 2011, SI fig. 2c), P46925, P15000 and P47020 were not included in the diagnosis. (Fig. 1C, D) show that the ventral spine pairs attached very clo- sely together medially on the sagittal axis. The ventral spines of podomere 1 are relatively short (length no more than half the Anomalocaris cf. canadensis Whiteaves, 1892 height of the associated podomere), have several spines along the Figure 3 distal margin and terminate in a trident of spines (Figs 1B, D, 2). Podomere 13 bears simple, nonspinose ventral spines no longer 1995 Anomalocaris sp. Nedin, pp. 31, 33–36, figs 2, 3B. than the height of the podomere, tapering to a point (Fig. 1B). 1997 Anomalocaris sp. Nedin, p. 134. Podomeres 2–12 have proximally curved ventral spines up to two 1999 Anomalocaris sp. Nedin, p. 989. or three times as long as the height of the associated podomere. 2006 Anomalocaris sp. Paterson and Jago, p. 43. Proximal ventral spines are longest on podomeres 6 and 7. The 2011 Anomalocaris sp. nov. Paterson et al., p. 239. ventral spines of podomeres 2–12 have an even width along most of their length before tapering abruptly to a terminal spine, flanked by two auxiliary spines 1–2mminlength(asinFigs1B,D, Material. Eleven specimens, with six from Buck Quarry (SAM 2). The proximal bases of ventral spines 2–13 and the proximal ven- P14985, P15374, P43616, P45749, 48158, 48164) adding to the tral margin of their associated podomeres bear five or more narrow, two previously described specimens (SAM P40807, originally closely spaced basal spines, 1.5–3 mm long (bs in Figs 1B, D, 2). referred to as AUGD 1046-600, and P40822, originally referred The basal spines are vertically orientated in proximal podomeres, to as AUGD 1046-346; Nedin 1995) and an additional three and angled proximally in more distal podomeres. Ventral spines on specimens (P44851, P42037 and possibly P44859) from the podomeres 2–12 show as many as twelve spinules, 1–2mmlong, wave-cut platform (see Supplementary Information). 4 PALAEONTOLOGY

A

B

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D DALEY ET AL.: ANOMALOCARIS FROM THE EMU BAY SHALE 5

FIG. 2. Reconstruction of Anomalocaris briggsi frontal appendage in lateral view. Podomeres had a pair of ventral spines but, for clar- ity, only one ventral spine is shown per podomere. Abbreviations as in Figure 1.

Description. Anomalocaris frontal appendages with 14 podo- podomere 2/4 (podomeres cannot be counted to the proximal meres, ranging from 70 to 183 mm long (mean = 136 mm, portion of the appendage). In this case, a clear boundary sepa- SD = 47 mm, n = 4) measured along the dorsal margin. Podo- rates auxiliary spine 2 from the ventral spine, so it could be an meres appear roughly rectangular in compacted lateral view with overlap of one of the auxiliary spines from the other ventral dorsal margins wider than ventral margins, imparting a convex spine of the pair from that podomere. In SAM P15374, the sec- profile along the dorsal length of the appendage with the distal ond ventral spine from the proximal end shows two pairs of end being curled under (Fig. 3A–B, G–H). The size of the podo- auxiliary spines, and possible one more on the right side from a meres decreases distally. Podomere boundaries are preserved as third pair (1–5? in Fig. 3E). A similar morphology is evident in straight or slightly curved lines, with no evidence of arthrodial SAM P42037, where the ventral spine on podomere 2 shows membrane or flexible cuticle between them, likely due to the three auxiliary spines on the left side and two on the right (1–5 tightly coiled nature of the specimens. in Fig. 3F). Podomeres 1 to at least 11 each show paired ventral spines The most proximal podomere is not completely preserved in protruding from the centre of their ventral margins (vs in any specimen, but SAM P40822 shows it to be elongated to a Fig. 3B, H). Podomeres 12 and 13 lack complete ventral margins length equivalent to the following three podomeres with a in all specimens, so the presence of ventral spines is unknown. rounded, outwardly convex proximal margin. The most distal Podomere 14 does not show ventral spines (po14 of left append- margin of podomere 14 is preserved in only one specimen age in Fig. 3B). The ventral spine of podomere 1 is preserved (po14 of the left appendage in Fig. 3B) where it appears only in SAM P15374, where it is nearly as long as the height of rounded with a small terminal spine (ts in Fig. 3B). Simple, the associated podomere and tapers to a point flanked by two elongated dorsal spines on podomeres 10–14 are located medi- thin auxiliary spines less than 1 mm long. Podomeres 2 to at ally on the sagittal axis of the most distal region of the dorsal least 11 have ventral spines that alternate in length, with those margin of the podomere and arch forward over the full length on the even-numbered podomeres being longest. The ventral of the podomere distal to it (ds in Fig. 3B, H). spines on podomere 2 are as long as the podomere is high. The rest of the ventral spines decrease in size distally, those near the Remarks. Nedin (1995) described some of this material as distal end of the appendage no more than one-fourth the height Anomalocaris sp. and not Anomalocaris canadensis because of the associated podomere. Most of these ventral spines termi- the Emu Bay Shale material was interpreted as having the nate in a point flanked by two auxiliary spines protruding at an longest ventral spines on the odd-numbered podomeres, oblique angle and 1–3 mm long (as in Fig. 3B, H). However, in but A. canadensis has the longest ventral spines on the SAM P40807, the right appendage shows a ventral spine with two pairs of auxiliary spines on podomere 4 (1–4 in Fig. 3D). even-numbered podomeres (Whiteaves 1892; Briggs 1979; These spines seem to be clearly attached to the ventral spine Whittington and Briggs 1985). This was based largely on with no articulations or boundaries at their bases. The left SAM P40807 (Nedin 1995, fig. 2A, B) and SAM P40822. appendage of SAM P40807 shows at least three, and possibly SAM P40822 has an incomplete distal end, and the proxi- four, auxiliary spines (1–4? in Fig. 3C) on the ventral spine of mal region does not preserve podomere boundaries, so it

FIG. 1. Anomalocaris briggsi Nedin, 1995. Frontal appendages in lateral aspect. A–B, holotype, SAM P40180, previously illustrated by Nedin (1995, fig. 1A). C–D, SAM P47020a, previously illustrated by Paterson et al. (2011, SI fig. 2a, b). Abbreviations: as, auxiliary spine; bs, basal spines; ds, dorsal spine; fc, flexible cuticle (arthrodial membrane); po, podomere; sp, spinules; ts, terminal spine; vs, ventral spine. Scale bars represent 1 cm. 6 PALAEONTOLOGY

A B

C D E F

GH DALEY ET AL.: ANOMALOCARIS FROM THE EMU BAY SHALE 7

AB

FIG. 4. Anomalocaris oral cone. A–B, SAM P31956, ventral view; previously illustrated by McHenry and Yates (1993, fig. 8). Abbrevi- ations: L, large plates; t, teeth on inner margin of a large plate. Scale bars represent 5 mm. cannot be determined whether the longest ventral spines Nedin (1995) also compared this material to specimens are on the even or odd podomeres. In SAM P40807, the from the Chinese Chengjiang biota that were formerly situation is clearer. We consider the number of podo- attributed to Anomalocaris canadensis by Hou and Bergs- meres in SAM P40807 to be one more than originally trom€ (1991). The Chengjiang specimens were, however, counted; a line of articulation is visible between podo- subsequently reassigned by Hou et al. (1995) to A. saron meres 1 and 2 (right appendage in Fig. 3A–B), but this (frontal appendages in Hou and Bergstrom€ 1991, pl. 2, boundary was not included in a previous camera lucida fig. 2; Chen et al. 1994, figs 1–2) and Anomalocaris sp. drawing of this specimen (Nedin 1995, fig. 2B). With that (frontal appendages in Hou and Bergstrom€ 1991, pl. 2, boundary identified, the longest ventral spines of these fig. 3). appendages are on the even-numbered podomeres, mak- ing it indistinguishable from A. canadensis in this respect. The sole difference between the Emu Bay Shale frontal ANATOMICAL DESCRIPTION OF appendages and those of A. canadensis is a newly ISOLATED ANOMALOCARIS ELEMENTS described feature, the presence of extra pairs of auxiliary spines on some of the ventral spines. The left and right Oral cone frontal appendages of SAM P40807 each show a ventral spine with two pairs of auxiliary spines (Fig. 3B–D) A single specimen of an Anomalocaris oral cone from the instead of the one pair observed in A. canadensis (Whit- Emu Bay Shale (SAM P31956) is derived from the wave- eaves 1892; Briggs 1979; Whittington and Briggs 1985). cut platform and was figured as a ‘possible mouth of The presence of two pairs of auxiliary spines is also seen Anomalocaris’ by McHenry and Yates (1993, p. 82). Rest- in the appendages of A. saron (Hou et al. 1995, figs 2B–F, udy of the specimen (Fig. 4) after removal of a calcite 3). Other A. cf. canadensis appendages show single ventral crust by acid dissolution shows that it conforms to the spines with three pairs of auxiliary spines (SAM P15374, morphology of the oral cone of A. canadensis described P42037), which bears some resemblance to the shorter by Daley and Bergstrom€ (2012, especially fig. 2a–d ventral spines of A. briggsi (e.g. the ventral spine of po12 therein) in all respects. The specimen exhibits triradial in fig. 1B). Owing to this inconsistent ventral spine mor- symmetry with three large plates (L in Fig. 4B) arranged phology, we have left these Emu Bay Shale specimens with the largest separated from the other two by about under open nomenclature. 125 degrees and the two slightly smaller plates separated

FIG. 3. Anomalocaris cf. canadensis Whiteaves, 1892. Frontal appendages in lateral aspect. A–D, SAM P40807, pair of frontal append- ages, previously illustrated by Nedin (1995, fig. 2A). C, auxiliary spines on ventral spine of podomere 2 or 4 of specimen to left in A– B. D, auxiliary spines on ventral spine of podomere 4 of specimen to right in A–B. E, SAM P15374, auxiliary spines on ventral spine of podomere 2. F–H, SAM P 42037; F, auxiliary spines on ventral spine of podomere 2; G–H, lateral view. Abbreviations as in Fig- ure 1. Numbers in C–F indicate auxiliary spines. Scale bars represent 5 mm in A–B, G–H and 2 mm in C–F. 8 PALAEONTOLOGY

A B

C D

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H I DALEY ET AL.: ANOMALOCARIS FROM THE EMU BAY SHALE 9 by about 110 degrees (compared with angles of 130–140 the wave-cut platform and adjacent cliffs (see Supplemen- and 90–100 degrees in Daley and Bergstrom€ 2012). In tary Information for catalogue numbers). Flaps range in between the three large plates are small and medium size up to 73 mm in width (SAM P48153), as measured plates with an irregular number and arrangement (11 on from the tip of the flap directly across to the attachment left side, 7 on right side, 4 posteriorly). Scale-like nodes area. Body flaps from the Emu Bay Shale are found iso- are preserved on the large and medium plates, some with lated or closely associated with two or three flaps of simi- an asymmetrical profile and most with the peaks broken lar size and preservation (Fig. 6F). SAM P47203, SAM off. Daley and Bergstrom€ (2012) described subdivisions at P46354 and P45441 consist of single flaps with closely the outer margins of the large and medium plates as con- associated setal structures (Fig. 5C, E), and SAM P44236 sisting of up to five folds extending no more than one- shows setal blades (Fig. 5I) and a partially preserved axial fourth the total length of the plate. In the Emu Bay Shale region (Fig. 5H) in close association with the flap specimen, two individual plates show one and two subdi- (described below). visions that extend to about half the length of the plate Flaps are subtriangular in outline, with a longer, (left side of Fig. 4B). In the series of four plates just to broadly convex margin towards the anterior (based on the left of the anterior large plate, three shorter plates comparison with full-body specimens of Anomalocaris) appear to be subdivisions of an adjacent longer plate that and a shorter margin, usually straight (Figs 5D–E, H, 6A, extends all the way into the central region, despite the C) or broadly concave (Figs 5A–C, 6F), directed towards presence of clear divisions and boundaries. the posterior. The margin of attachment is straight The outline of the oral cone is irregular, but is roughly (Figs 5A, 6A–C) in specimens where it is not obscured by rounded rather than diamond-shaped or rectangular, a or continuous with irregular organic material, presumably distinction that was formerly thought to separate the parts of the rest of the body (Figs 5B–C, E, H, 6F). The Anomalocaris oral cone from that of Peytoia (Collins most conspicuous structures on the surface of the flaps 1996). Daley and Bergstrom€ (2012) showed that the Bur- are evenly spaced, subparallel lines oriented transversely gess Shale Anomalocaris oral cone is round. The central on the anterior half of the flaps (Figs 5A, D, 6C). There region of the Emu Bay Shale oral cone does not consist are up to twelve of these transverse lines, which originate of an opening, but instead, the three large plates extend at the anterior margin of the flap and extend about half- into it, similar to the small and irregular central gap way into the flap at an angle of 35–45˚. The lines end described for A. canadensis. One of the large plates has along a straight line in the centre of the flap, but no solid four rounded teeth-like projections (t in Fig. 4B). Daley feature defines this boundary (Fig. 5A–D), nor is there and Bergstrom€ (2012, fig. 2f) also reported four teeth on any evidence of a boundary line along the margin of the one of the larger plates in A. canadensis (ROM 61669). flap. The transverse lines typically run parallel to one This oral cone confirms the identity of the anomaloca- another, but SAM P15133 shows them branching and ridid appendages from the Emu Bay Shale as being from pinching off (arrows in Fig. 5B). In addition to the trans- Anomalocaris. The specimen comes from the wave-cut verse lines, one specimen (SAM P43656) preserves fine, platform, as do both species of Anomalocaris,soitisnot faint striations in the posterior region of the flap (black possible to determine its specific assignment. arrow in Fig. 5D). Emu Bay Shale flaps preserve internal microstructures of the transverse lines (Fig. 6). In most specimens, the Body flaps external, surficial morphology of the transverse lines is as simple, slightly curved lines preserved as thin impressions Emu Bay Shale Anomalocaris body flaps (Figs 5–6) have or raised ridges on the flap (Fig. 5A–C, E, H). A few been found almost exclusively at Buck Quarry. Fifty-five specimens show that below these simple external lines, specimens consisting of single flaps and 15 assemblages the internal structure consists of distinct boundary lines consisting of two or more flaps, or flaps with setal struc- delimiting a series of tiny raised blocks or bars between tures, have been sourced from Buck Quarry, whereas only them (Fig. 6C–D, F–H). The boundary lines are simple four specimens of single flaps have been collected from and slightly curved upward and outward in the anterior

FIG. 5. Anomalocaris body flaps and setal blades. A, SAM P45343a, nearly complete flap. B, SAM P15133a, flap with arrows indicat- ing bifurcations of transverse lines. C, SAM P47203, flap with arrow indicating setal blades. D, SAM P43656, flap with serrated blocks making up the transverse lines (white arrows) and striations on posterior part of flap (black arrow). E–F, SAM P45441; E, flap with associated setal blades at base; F, detail of E, showing vertical bars between two transverse lines on anterior part of flap (arrows). G, SAM P45525a, isolated setal structure showing individual lanceolate blades. H–I, SAM P44236a; H, flap with associated setal structure and paired swellings, indicated by arrows; I, enlargement of boxed area in H, showing setal blades attached to a ramus. Scale bars rep- resent 5 mm in A–E, H and 2 mm in F–G, I. 10 PALAEONTOLOGY

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E

G

F H DALEY ET AL.: ANOMALOCARIS FROM THE EMU BAY SHALE 11 region of the flap, with the distance between them as SAM P45599, show several larger setal structures that decreasing gradually towards the outer margin of the flap overlap and setae that are preserved as a series of parallel- (Fig. 6D, G). Between the boundary lines is a series of sided blades. thin raised bars, often perpendicular to the boundary Setal blades are found in association with both frontal lines (Fig. 6D), but sometimes in an imbricated arrange- appendages and body flaps. The slab with the holotype of ment (Fig. 6G). The raised bars are spaced about as far Anomalocaris briggsi (SAM P40180) preserves a mass of apart as they are wide (Fig. 6D) or are very closely spaced fibrous, thin filaments, which may be setal blades, about (Fig. 6H). In one specimen, each bar shows striations 2 cm from the dorsal margin of the appendage. Four (Fig. 6G). In fainter, possibly more decomposed or specimens of anomalocaridid body flaps are preserved decayed specimens, the boundary lines are not visible, with nearby setal structures. In SAM P47203, these consist and the inner structure appears as a series of small bars of a mass of roughly parallel blades (thin lines) that are and/or indentations with indistinct margins (Fig. 6E). situated anterior and central to the preserved flap, near The raised bars are regarded as being internal because its base (black arrow in Fig. 5C). SAM P44236 preserves some specimens show them together with the simple lines a small setal structure that consists of a central ramus of the external surface of the flap, as a series of raised with eight small blades branching from it (Fig. 5I). In swellings beneath or near them (white arrows in Fig. 5D). SAM P45441, the setal structure consists of a mass of In SAM P47153, simple external lines are visible on the highly textured, tangled threads or thin blades (Fig. 5E). dorsal surface at the distal end of the flap (bottom half of SAM P46354 shows a faint impression of a lamellar struc- Fig. 6B), and the convex swellings of the upper surface of ture near its flap. the internal bars are visible beneath the external lines fur- ther towards the medial region of the flap (top of Fig. 6B). The more proximal region of the flap preserves Possible axial region concave depressions into the underlying impression of the ventral surface of the flap on the sediment, representing Although flaps are common in the collections from Buck the lower surface of the internal bars (right side of Quarry, they are nearly all detached from the rest of the Fig. 6A) and demonstrating the internal nature of the body, apart from the association with detached setal structures. Less well-preserved specimens show partial blades noted above. A single specimen, SAM P44236 decay preferentially located along the transverse lines (Fig. 5H), preserves a fragment of the axial region of the (black arrows in Fig. 6E). Two specimens also show regu- Anomalocaris body. It consists of a body flap attached to larly spaced raised bars running between the transverse a large fragment of distorted cuticle that extends the full lines, perpendicular to and bounded by them (black length of the flap. Near the attachment of the body flap arrows in Fig. 5F and white arrows in Fig. 6E). to this cuticle are four, high-relief oval swellings in a paired arrangement, lined up approximately 2 mm apart, and a further two swellings situated anterior and poster- Setal blades (‘gills’) ior to the pairs, in line with those on the left side (white arrows in Fig. 5H). These swellings are approximately 4– Material collected from Buck Quarry includes 36 speci- 5 mm in diameter and have gradual margins that are mens interpreted as possible isolated setal structures continuous with the cuticle surrounding it, as though the belonging to Anomalocaris, the ‘gills’ of Whittington and body cuticle is draped over internal high-relief structures. Briggs (1985). The most well-preserved, isolated setal Preparation of one of the swellings yielded an internal structures are small (blades less than 1 cm long) and con- structure consisting of densely packed spheres. This speci- sist of a series of lanceolate blades attached at one end men is also associated with the clear setal structure and free-hanging at the other (Fig. 5G). Isolated specimen (Fig. 5I) described in the previous section (white box in SAM P45525 (Fig. 5G) preserves a curved line to which Fig. 5H). The rest of the cuticular material is indistinct the lanceolate blades are attached. Some specimens, such with no recognizable features.

FIG. 6. Anomalocaris body flaps, showing detail of the transverse lines. A–B, SAM P47153; A, flap showing both the external and internal morphology of the transverse lines; B, enlargement of boxed area in A, showing external morphology of simple transverse lines (lower half) and the seriated blocks as internal structure underneath them. C–D, SAM P14822a, previously illustrated by Paterson et al. (2011, SI fig. 1f); C, flap with seriated blocks for transverse lines; D, enlargement of boxed area in C. E, SAM P46963a, flaps showing vertical bars between seriated transverse lines (white arrows) and preferential decay occurring along transverse lines (black arrows). F– G, SAM P47142; F, pair of body flaps with seriated transverse lines; G, enlargement of boxed area in F, showing striations on the seri- ated blocks of the transverse lines. H, SAM P45672, flap with highly striated transverse lines. Scale bars represent 5 mm in A, C, E–F, H and 3 mm in B, D, G. 12 PALAEONTOLOGY

DISCUSSION lines from a posterior region without lines (Chen et al. 1994, figs 1D, 2, 3A; Hou et al. 1995, figs 4A, 5). Chengji- Anomalocaridid material from the Emu Bay Shale ang specimens of Amplectobelua also preserve a structure includes a diverse collection of specimens showing iso- of the same nature as the transverse lines running along lated body parts. Although whole bodies have yet to be the margin of the flap (Chen et al. 1994, fig. 4B), which found, the disarticulated material is informative owing to has not been observed in the Emu Bay Shale material. the novel preservation at the Emu Bay Shale locality. This Despite these differences, the similarities between the locality not only has yielded a species of Anomalocaris Emu Bay Shale specimens and Anomalocaris saron and unique to this site, but also brings to light structures in Amplectobelua symbrachiata are strong enough to confirm the body flaps that are not evident in anomalocaridids the identity of these specimens as anomalocaridid body from Chengjiang, the Burgess Shale or Fezouata. This flaps. parallels the preservation of ommatidial lenses on the sur- The Burgess Shale has the greatest anomalocaridid face of the eyes of Emu Bay Shale Anomalocaris (Paterson diversity of any Cambrian Konservat-Lagerst€atte (Whit- et al. 2011), the corresponding surface being smooth and tington and Briggs 1985; Daley et al. 2009; Daley and devoid of structure in anomalocaridid eyes from Chengji- Budd 2010), and many whole-body specimens have well- ang and the Burgess Shale. The unique taphonomic path- preserved body flaps. However, transverse lines are typi- way of the Emu Bay Shale ensures preservation of cally poorly preserved and are only present in about half detailed microstructures not preserved in other Cambrian of the whole-body specimens of Peytoia (USNM 274143/ fossil Lagerst€atten, but the overall morphology and size of 47, USNM 274164, USNM 274144/48, USNM 247145/62 the specimens are similar enough to other Cambro–Ordo- and USNM 274146) and three of the ten Hurdia speci- vician anomalocaridids that their identity is assured, despite mens (ROM 59320, ROM 60010, ROM 60029) with visi- their disarticulated nature and novel preservation. The ble flaps. The transverse lines are most obvious in Peytoia Emu Bay Shale is also the main locality yielding alleged nathorsti (Whittington and Briggs 1985, figs 20, 28, 30, 42 evidence for the inferred predatory lifestyle of Anomaloc- –43, 50–51, 59), where they are described as evenly spaced aris, particularly in regards to trilobites (Conway Morris and highly reflective, with negligible relief such that they and Jenkins 1985; Nedin 1999; Vannier and Chen 2005). are barely visible in low-angle lighting (Whittington and Briggs 1985, p. 584). They are preserved in a similar fash- ion in Amiella ornata (Whittington and Briggs 1985, figs Morphology of anomalocaridid body flaps 91, 94; Daley et al. 2013, fig. 14F) and an unidentified anomalocaridid USNM 274154 (and counterparts 274156 The identity of the structures described herein as Anomal- and 274161) (Whittington and Briggs 1985, figs 81–88, ocaris body flaps was established by comparison with the 100; Daley et al. 2013, fig. 14D). The transverse lines of most morphologically similar articulated specimens, those the flaps of these Burgess Shale taxa typically extend from of Anomalocaris saron and Amplectobelua symbrachiata the anterior margin to at least halfway into the flap from the Chengjiang biota in China, a comparison (Whittington and Briggs 1985, figs 20, 59, 91, 94), but enhanced by similarities in style of preservation. The sometimes extending the full length (Whittington and spacing and orientation of the transverse lines are similar Briggs 1985, figs 28, 30, 42–43, 51–52, 81–88, 100). Hur- in Emu Bay Shale and Chengjiang body flaps, with Ano- dia victoria has diminutive flaps, but some specimens malocaris saron specimens showing as many as 18 trans- show clear transverse lines that also cover almost the verse lines on a single flap (Hou et al. 1995, figs 4–5). entire surface of the flap (Daley et al. 2013, figs 18A–B, The transverse lines of both Amplectobelua and Anomaloc- 20D–F, 21A–B). A feature unique to Burgess Shale taxa is aris from Chengjiang show bifurcations and anastomoses that specimens of Peytoia (Whittington and Briggs 1985, similar to those seen in some Emu Bay Shale specimens fig. 30), Hurdia (Daley et al. 2013, fig. 20D–F) and the (Chen et al. 1994, figs 3B, 4D; Hou et al. 1995, figs 4–6), unidentified anomalocaridid USNM 274154 (Whittington and one specimen is described as showing a series of and Briggs 1985, figs 82–88) show partially decomposed faint, fine striations along the posterior margin (Chen body flaps with the transverse lines extending outward et al. 1994, fig. 3B). Associated setal blades are also beyond the margin of the flap, suggesting that the trans- observed near the attachment area of the flaps in the verse lines were more decay resistant than the flap itself. Chengjiang anomalocaridids (Chen et al. 1994, figs 1B, 2– The only anomalocaridid from the Burgess Shale that 3; Hou et al. 1995, figs 4–6), as are present in the Emu does not preserve clear transverse lines is Anomalocaris Bay Shale material. However, unlike the Emu Bay Shale canadensis. ROM 51212 (Collins 1996, fig. 4.2) may pre- specimens, Amplectobelua and Anomalocaris saron have a serve faint transverse lines on its body flaps, but both pronounced boundary line that cuts through the middle ROM 51212 and ROM 51211 (Collins 1996, fig. 4.1) pre- of the flap, dividing an anterior region with transverse serve very fine striations along through the anterior half DALEY ET AL.: ANOMALOCARIS FROM THE EMU BAY SHALE 13 of their body flaps, bounded by a clear line that bisects Interpretation of the transverse lines. The transverse lines the flap. These striations are similar to what is evident on on the anterior part of the body flaps have been described the posterior margin of the Emu Bay Shale specimen under two alternative nomenclatures that imply different SAM P43656 (black arrow in fig. 5D) and in Chengjiang functions – they are variously described as veins (Chen material (Chen et al. 1994, fig. 3B). et al. 1994; Hou et al. 1995) or as strengthening rays Anomalocaridid body flaps are also preserved in the (Whittington and Briggs 1985). In Chengjiang anomaloc- lower and middle Cambrian of Nevada and Utah and aridids, Chen et al. (1994) referred to these lines as the Lower Ordovician Fezouata Formation of Morocco. ‘canals’ and ‘veins’ and drew support for this interpreta- A specimen interpreted to be the posterior body region tion from the ‘wrinkled, three-dimensionally preserved of Peytoia nathorsti from the middle Cambrian Marjum structure in one specimen’ of Amplectobelua (Chen et al. Formation of Utah shows a series of parallel lines pass- 1994, p. 1306). They also called these structures ‘canal ing through the anterior region of most of the body systems’ (p. 1305) for Anomalocaris, based on comparison flaps, beginning along the anterior margin and extending with Amplectobelua. Unlike species of Anomalocaris and into the body flap at an angle of approximately Amplectobelua from Chengjiang, a well-defined central 45 degrees (Briggs and Robison 1984). These are similar ‘vein’ along the middle of the flap is lacking in Emu Bay in orientation, spacing and location to the transverse Shale Anomalocaris. The indistinct nature of a marginal lines of anomalocaridids from the Emu Bay Shale, Chen- line (‘vein’) in the Emu Bay Shale material, if it were gjiang and Burgess Shale. Cambrian specimens from the originally present (as is the case in Chengjiang Amplecto- Pioche Formation of Nevada consist of three partial belua), could be attributed to comparatively poor preser- putative bodies with flaps and a single isolated flap (Lie- vation of the anterior margin of the flaps in most berman 2003). The three body specimens do not have specimens, whereas the absence of a central line/vein is transverse lines visible on their flaps, but the single iso- harder to attribute to it not being preserved. The appar- lated flap (with length of only 15 mm) is described as ently blind termination of the lines at their posterior ends having five transverse lines that extend through the is inconsistent with a network of veins, but is not incon- whole flap in a wide arc from the proximal anterior sistent with a mechanical role for these structures. It is margin to the distal posterior margin (Lieberman 2003, also difficult to reconcile the apparently rigid internal pp. 683–684, fig. 6.5). A much larger partial body of an structures associated with the transverse lines in Emu Bay anomalocaridid described from the Spence Shale Mem- Shale Anomalocaris with an originally tubular structure as ber in Utah consists of several body flaps bearing trans- would be expected for veins or canals. verse lines that parallel the anterior margin of the flap Whittington and Briggs (1985) discussed the swimming and extend for most of its length (Briggs et al. 2008, fig. motion of anomalocaridids and interpreted the transverse 1). The putative transverse lines in both these specimens lines as likely being strengthening rays that would also are orthogonal to the transverse lines in other anomaloc- have assisted with movements in a function similar to fin aridid material from the Emu Bay Shale, Chengjiang and rays in fishes. They quote Webb (1975, p. 47), who said Burgess Shale, which run from the distal anterior margin that ‘individual segments are capable of fairly extensive towards the centre of the flap, rarely reaching the pos- independent movement because muscular forces are terior margin. Ordovician material includes two incom- transmitted to stiff fin rays supporting a thin, highly flexi- plete anomalocaridid bodies. In one specimen (YPM ble finweb’. The former also suggested that the strength- 226437, called YPM 226637 in the Supplementary Infor- ening rays would have been most prominent in the mation of Van Roy and Briggs 2011), two flaps preserve anterolateral region of the flap because they would have transverse lines (Van Roy and Briggs 2011, figs 1a, c, assisted in maintaining the most hydrodynamic shape to S2a, b) that are subparallel and present only in the ante- the lobe during the downward stroke of the swimming rior region of the flap (for the more posterior flap) or motion (Whittington and Briggs 1985, fig. 103b). This along the more proximal region of the second, partially position of the transverse lines is well documented in preserved flap. The transverse lines have little to no anomalocaridids from the Emu Bay Shale, Chengjiang relief and are visible as black lines that are either highly and the Burgess Shale. Several Burgess Shale specimens reflective or dark stained (Van Roy and Briggs 2011, fig. also show the transverse lines protruding from the ragged 1c). YPM 26639 also has a preserved flap, with pro- margins of partially decayed Peytoia and Hurdia body nounced transverse lines (Van Roy and Briggs 2011, fig. flaps, providing further evidence of the robust nature of S3a, b) that are preserved as robust structures with the transverse lines and their function as structural ele- relief. The structure is a relatively thick line with a rim ments. along either side (as seen in Emu Bay Shale specimens), The structure of the transverse lines in the anomaloc- but the inner region does not have the raised ridges or aridids essentially consists of a pair of distinct bound- bars evident in the Australian material. ary lines sandwiching an area of raised blocks or bars. 14 PALAEONTOLOGY

Functionally analogous microstructures are also seen in the attachment points for the setal blades (Bergstrom€ the stiffening rods of fin-like structures that a variety of 1987; Daley et al. 2009). Setal structures are poorly pre- other animals use to propel themselves through fluid, be served in other anomalocaridids, but are described as it water or air. For example, the fin rays of the median lamellar structures in Anomalocaris canadensis (Whitting- and paired fins of many Actinopterygii (ray-finned fishes) ton and Briggs 1985, p. 579, fig. 3; Collins 1996), Ano- consist of two semilunate half rays (hemitrichs) that are malocaris saron (Chen et al. 1994, p. 1305, fig. 2; Hou joined together by thin fibres of collagen and elastin et al. 1995, pp. 165, 167, figs 4–6) and Amplectobelua (Lanzing 1976; Geerlink and Videler 1987; Lauder et al. symbrachiata (Chen et al. 1994, fig. 3a). 2006). Differential movement of the two hemitrichs The only known specimen from the Emu Bay Shale imparts flexibility to the fin, allowing it a small degree of with a putative axial region of the body has paired high- bending whilst still retaining a stiff and strong overall relief structures that are arranged serially amidst a large structure that can withstand the forces generated along area of indistinct body cuticle (Fig. 5H). The closely allied the distal margin of the fin during forward propulsion. In taxon Opabinia from the Burgess Shale has three-dimen- several batoid (stingrays and skates) families (Dasyatidae, sional diverticula preserved in a paired arrangement on Potamotrygonidae, Rajidae, Urotrygonidae), fin rays of either side of the gut in the axial region of the body, with the pectoral wings consist of a pair of catenated calcified an elliptical shape and a smooth or laminated surface chains, which imparts flexibility and strength to the wing, (Budd and Daley 2012, p. 90, fig. 7A–F). Other Cambrian and oscillatory swimmers also exhibit cross-bracing con- taxa such as the armoured lobopodians Kerygmachela sisting of cartilaginous extensions that join adjacent fin (Budd 1999) and Pambdelurion (Budd 1998) and the rays (Schaefer and Summers 2005), similar to the branch- euarthropod Leanchoilia (Butterfield 2002) have gut div- ing seen in the transverse lines of Anomalocaris body flaps erticula with a similar shape and position, and these are from Emu Bay Shale. Even the wing veins of some either phosphatized or preserved in darker material than insects, like dragonflies, consist of two layers of chitin the rest of the specimen. Based on similarities in struc- with a mass of protein and muscle fibrils in between, ture, position and preservation, the swellings observed in albeit arranged into the tubular form of the vein (Wang the Emu Bay Shale Anomalocaris specimen may also et al. 2008). A general morphology of two boundary represent diverticula of the gut, which are recognized as structures enclosing an inner region of densely packed well in the co-occurring bivalved arthropod Isoxys fibres imparts flexibility and strength to the propulsive (Garcıa-Bellido et al. 2009), the leanchoiliid Oestokerkus fins and flaps of a variety of animals and may be compa- (Edgecombe et al. 2011) and the artiopodans Squamacula rable in function to the microstructure of the transverse and Australimicola (Paterson et al. 2012). Paired patches lines of body flaps in specimens of Anomalocaris from the of nodular mineralization are also associated with the gut Emu Bay Shale. in the anomalocaridids Peytoia nathorsti (Whittington and Briggs 1985, p. 584, figs 20, 30, 50) and Anomalocaris canadensis (Whittington and Briggs 1985, p. 579, figs 3–6; Setal structures and possible axial region structures in personal observation of unpublished material) from the anomalocaridids Burgess Shale, and in Peytoia nathorsti from the Marjum Formation (Briggs and Robison 1984, p. 5, figs 3, 4). The setal structures described for Anomalocaris from the Anomalocaris saron from Chengjiang also has paired, seri- Emu Bay Shale have a morphology comparable to those ally repeated structures in close association with the gut seen in the Burgess Shale taxa Hurdia (Daley et al. 2009, (Chen et al. 1994, p. 1305, figs 1–2) that appear nodular figs 2E, S2C, H), Peytoia (Daley et al. 2009, fig. S2A–B, D and are preserved in darker material than the rest of the –F, I) and Opabinia (Bergstrom€ 1986, fig. 1F; Budd 1996, body and have been interpreted as digestive glands fig. 1A–B; Budd and Daley 2012, fig. 4C–D), but are gen- (Vannier and Chen 2005, fig. 11A; Vannier 2009, fig. 5E). erally much smaller in size. Hurdia has large setal struc- Similar structures have also been observed in Amplectobe- tures on the body, but in the anterior region just behind lua symbrachiata (Chen et al. 1994, 2x to 4x in fig. 3A) the head, there are three or four pairs of smaller setal and have been equated to the paired nodular patches in structures comparable in size to the isolated structures Peytoia nathorsti from the Burgess Shale. from the Emu Bay Shale (Fig. 5G, I). The isolated setal structure of SAM P45525, with its scalloped margin of attachment (Fig. 5G) is particularly similar to isolated Reassessing the evidence for predatory habits of Hurdia setal structures (Daley et al. 2009, fig. 2E; Daley Anomalocaris et al. 2013, fig. 15), which have been compared with the ‘transverse rods’ of Peytoia (Whittington and Briggs Emu Bay Shale fossils have played a key role in establish- 1985), suggesting that these mineralized, nodular rods are ing the idea that Anomalocaris was a top visual predator DALEY ET AL.: ANOMALOCARIS FROM THE EMU BAY SHALE 15 in Cambrian ecosystems. Cited evidence includes damage and SAM P47144a, b (incomplete length 28 mm long, to trilobites and allegedly to nektaspids (Conway Morris width 8 mm; Fig. 7H), whereas P45433 (length 50 mm, and Jenkins 1985; Nedin 1999), large coprolites contain- width 20 mm; Fig. 7E–G) contains Estaingia sclerites, ing trilobite fragments (Nedin 1999; Vannier and Chen including a librigena (Fig. 7F) and a complete thoracic 2005) and the discovery of large, high-resolution com- segment with its long axis oriented parallel to the long pound eyes attributed to Anomalocaris (Paterson et al. axis of the coprolite (Fig. 7G), together with fragments of 2011). However, durophagy in anomalocaridids, particu- Redlichia. Currently twelve coprolites are known from the larly feeding on trilobites, has been recently brought into Emu Bay Shale Konservat-Lagerst€atte; eight contain frag- question (Hagadorn 2009a; Hagadorn et al. 2010; Daley ments of Redlichia takooensis, three contain fragments of and Bergstrom€ 2012), and the functional inability for the Estaingia bilobata and one contains fragments of both oral cone to produce certain injuries to trilobite exoskel- species. Estaingia is much more abundant in the Lag- etons has been noted previously (e.g. Whittington and erst€atte than Redlichia, so the higher number of coprolites Briggs 1985; Hou et al. 1995). containing fragments of Redlichia suggests that Anomaloc- Nedin (1999) documented an elongate (43 9 28 mm) aris preferentially preyed on this less common taxon. coprolite from the Emu Bay Shale containing identifiable Unequivocal evidence of predation damage to trilobite fragments of the trilobite Redlichia takooensis, including a exoskeletons is relatively rare in the Emu Bay Shale. Pre- genal spine, thoracic pleurae and parts of the cephalon viously documented specimens of Redlichia show injuries with distinctive terrace line ornamentation (Nedin 1999, to both sides of the thorax (Conway Morris and Jenkins fig. 4; Vannier and Chen 2005, fig. 9). Nedin attributed 1985, figs 1, 2; Nedin 1999, fig. 2B; Daley and Paterson this coprolite to Anomalocaris based not only on its size, 2012, p. 19), with individuals ranging from 50 to but also his proposed model on how Anomalocaris could 210 mm in estimated length. However, the injury fracture trilobite cuticle by repeated flexure of the exo- reported by Nedin (1999, fig. 2A) to the right lateral pos- skeleton using its frontal appendages (Nedin 1999, fig. 3). terior shield of the nektaspid Emucaris (referred to as A number of other trilobite-dominated aggregates have Naraoia) continues well into the surrounding sediment, been sourced from Buck Quarry (Fig. 7A–H) and appear indicating that this is not an injury but rather represents to represent bone fide coprolites (sensu Hagadorn 2009b), the uneven edge where a fragment has broken off of the as opposed to ecological or environmental (e.g. current) rock sample (Paterson et al. 2010, pl. 2, fig. 2). Some accumulations (sensu Vannier and Chen 2005). These iso- injuries to Emu Bay Shale trilobites appear to have been lated aggregates are mainly elongate, contain fragmented fatal (contra Conway Morris and Jenkins 1985) because sclerites of the trilobites Redlichia takooensis and/or there is no evidence of healing or repair around the Estaingia bilobata and are commonly enveloped by a coat- affected areas, as has been seen in other injured trilobites ing of iron oxide. SAM P45413 (Fig. 7A–B) is elongate from the middle Cambrian of the Northern Territory, (preserved length and width: 31 and 12 mm, respec- Australia (Jago and Haines 2002) and British Columbia, tively), tapers at one end and contains sclerites of Redli- Canada (Rudkin 1979). A large specimen (P48149) from chia, including a relatively complete right thoracic pleura the coast with a scattering of Redlichia fragments is prob- from an individual that would have been around 50 mm ably not a coprolite, but may represent the remains of an long; this estimate is supported by the fact that thoracic attack that shattered this relatively large Redlichia speci- pleurae in Redlichia have a fairly consistent width (tr.) men (Fig. 7I). Anomalocaridids are often suspected to along most of the trunk. Elongated specimens such as have inflicted such injuries on Cambrian trilobites (Rud- SAM P45413 (Fig. 7A–B) and SAM P47144 (Fig. 7H) kin 1979, 2009; Briggs and Mount 1982; Babcock and may represent coprolites excreted whilst the animal was Robison 1989; Pratt 1998; Babcock 1993, 2003; Nedin in motion, whereas rounded specimens such as SAM 1999; Jago and Haines 2002; Babcock and Peel 2007), but P47146 (Fig. 7C–D) and P15255 were possibly deposited recent arguments (Hagadorn 2009a; Hagadorn et al. when the animal was stationary. In SAM P45413, the iron 2010; Daley and Bergstrom€ 2012) suggest that the oral oxide coating is largely restricted to the sclerite aggregate cone of Anomalocaris – which is prone to wrinkling, fold- (Fig. 7A–B) and could represent the solid component of ing and tearing – would have been too soft and pliable to the faeces, whereas many other specimens (e.g. P47146, break the mineralized exoskeleton of a trilobite. The oral sclerite-bearing portion 25 mm long, 14 mm wide) show cone of anomalocaridids could not occlude (Whittington aggregates fringed by more extensive iron oxide haloes and Briggs 1985; Hagadorn 2009a; Hagadorn et al. 2010) (Fig. 7C–D), which has been interpreted to represent dif- and the irregular shape and small size of the central fusion of the fluidized component into the surrounding opening in Anomalocaris made it unsuitable for strong sediment (cf. Nedin 1999; Vannier and Chen 2005). Some biting motions (Daley and Bergstrom€ 2012), but the oral coprolites contain concentrated Estaingia fragments, for cone may have been capable of breaking weakly mineral- example, SAM P15470a, b (length 23 mm, width 7 mm) ized trilobites (Hagadorn 2009a). This supports the 16 PALAEONTOLOGY

A B

DC

F G

E

H I

FIG. 7. Trilobite-dominated aggregates from the Emu Bay Shale interpreted as coprolites (A–H) and remnants of an attack (I). A–B, SAM P45413; A, part, coprolite with Redlichia fragments; B, counterpart. C–D, SAM P47146; C, aggregate fringed with extensive iron oxide halo; D, enlargement of sclerite-bearing central portion of aggregate. E–G, SAM P45433; E, part of aggregate containing both Estaingia and Redlichia fragments; F, enlargement of boxed area in E, showing librigena of Estaingia bilobata; G, enlargement from the counterpart of Estaingia thoracic segment indicated on part by arrow in E. H, SAM P47144a, aggregate containing concentrated Estain- gia fragments. I, SAM P48149, loose aggregate of Redlichia fragments possibly representing the remnants of an attack. Scale bars repre- sent 5 mm in A–E, H, 2 mm in F, G and 10 mm in I. suggestion of Conway Morris and Jenkins (1985) that malocaridids could use chemoreception to detect freshly healed injuries in Redlichia resulted from attacks that moulted trilobites and other arthropods, which would occurred during the unmineralized stage immediately fol- complement their visual acuity (Plotnick et al. 2010; Pat- lowing moulting. Some modern aquatic predators erson et al. 2011). Nevertheless, the scenario of Anomaloc- (including cannibals) that feed on freshly moulted arthro- aris feeding upon postecdysial, ‘soft-shelled’ trilobites, pods are able to detect specific moulting hormones (e.g. whilst plausible, cannot account for the mineralized trilo- ecdysone) released by their prey (Marshall et al. 2005; bite fragments present in coprolites, unless Nedin’s Jackrel and Reinert 2011). It is possible that some ano- (1999) model is warranted. This model, which involves DALEY ET AL.: ANOMALOCARIS FROM THE EMU BAY SHALE 17

Anomalocaris lodging a trilobite in its oral cone and using result of cannibalism. In modern arthropod populations, its appendages to break the trilobite exoskeleton by repeated cannibalism is common, especially when other food flexure, would undoubtedly cause damage to the oral cone resources are limited (for reviews, see Fox 1975; Richard- and appendages in the form of broken spines or scarring; son et al. 2010). It is morphologically feasible that Redli- however, no damage of this type has been observed. chia was capable of durophagy, as redlichiids are known The considerable diversity of anomalocaridid frontal to possess gnathobasic appendages (Shu et al. 1995; appendages and oral cones (Whittington and Briggs 1985; Ramskold€ and Edgecombe 1996; Fortey and Owens 1999; Chen et al. 1994; Hou et al. 1995; Nedin 1995; Collins Hou et al. 2009). In some modern arthropods such as 1996; Lieberman 2003; Briggs et al. 2008; Daley et al. 2009; Limulus, the nonmineralized (chitinous) gnathobases are Caron et al. 2010; Daley and Budd 2010; Daley and Peel capable of crushing clam shells (Botton 1984; Shuster 2010; Daley and Bergstrom€ 2012) indicates that these stem- et al. 2003), and Sidneyia from the Burgess Shale, which group arthropods had a varied diet and range of feeding has unmineralized gnathobasic limbs, has been found strategies. The functional morphology of the frontal with trilobite fragments in its alimentary tract (Bruton appendages suggests that some anomalocaridid taxa may 1981), as have Utahcaris from the Spence Shale and an have been durophagous predators, whilst others fed exclu- undescribed fuxianhuiid from the Kaili biota, but the sively on soft-bodied organisms (Briggs 1979; Whittington trunk appendages of these latter two taxa are poorly and Briggs 1985; Collins 1996; Nedin 1999; Daley and Budd known (Conway Morris and Robison 1988; Zhu et al. 2010), which represent up to 98 per cent of individuals in 2004; Vannier and Chen 2005). The width of the alimen- some Cambrian deposits (Caron and Rudkin 2009). Whilst tary tract in Eoredlichia (Hou et al. 2009) and other the presence of more than one anomalocaridid taxon in a Cambrian trilobites (Chatterton et al. 1994; Lin 2007; single Cambrian Konservat-Lagerst€atte is not unique (Da- Lerosey-Aubril et al. 2012) is relatively consistent and ley and Budd 2010), the co-occurrence of two similar-sized occupies approximately one-quarter of the axis, indicating Anomalocaris species from the Emu Bay Shale implies that an alimentary tract up to 12 mm wide in the largest different feeding mechanisms might have been employed to known specimens of Redlichia. This would allow excretion exploit disparate prey resources and alleviate interspecific of solid faeces of the sizes represented by the sclerite- competition. Anomalocaris cf. canadensis, with its short, dense portion of the coprolites from the Emu Bay Shale. stout ventral spines, was likely a durophagous predator or Regardless of durophagous tendencies, Anomalocaris scavenger, whereas the frontal appendages of A. briggsi were was undoubtedly a highly mobile visual predator, given too fragile for such a feeding mode (Nedin 1999). Anomal- its large body size, spinose frontal appendages, triradial ocaris briggsi likely fed in a way comparable to that mouth with a dentate inner margin, high-resolution com- described for Hurdia and Peytoia (= Laggania) (Whitting- pound eyes and streamlined body with flexible body flaps ton and Briggs 1985; Nedin 1995; Daley and Budd 2010), and a large tripartite tail fan. Whilst A. cf. canadensis with the appendages functioning like a net apparatus to trap from the Emu Bay Shale cannot be completely ruled out small prey items in their long spinose ventral spines as they as a durophagous predator, it is likely that A. briggsi at moved through the water column or through the substrate. least was restricted to unmineralized prey items. If anomalocaridids were not strictly durophagous pre- dators, few other organisms in the Emu Bay Shale can be Acknowledgements. This research was made possible by funding identified as candidates for inflicting damage to trilobites from Australian Research Council grants (LP0774959, and producing large coprolites. Given the size of copro- DP120104251) and a National Geographic Society Research & lites, prey fragments within some coprolites (individuals Exploration grant (#8991-11), as well as financial assistance of Redlichia >40 mm) and injured Redlichia (up to from Beach Energy Ltd. and the South Australian Museum. 210 mm in length), at least some of the predators may Logistical support was provided by SeaLink. ACD was supported have had a body size greater than 20 cm in length. A very by grants from the Swedish Research Council (Veterskapsradet) large, as yet unnamed species of Tuzoia (Garcıa-Bellido and the Palaeontological Association; DGB’s visits to Australia et al. 2009) may have approached this length, but the were supported by grants from the Spanish Research Council known appendages in another species of this genus (see (CSIC, PA 1001105) and the Spanish Ministry of Science Caron et al. 2010, fig. DR4A–C) seem ill equipped to (RYC2007-00090, CGL 2006-12254BTE and CGL 2009-07073). We sincerely thank the Buck family for continued access to the handle trilobites, especially as Tuzoia is interpreted to be field site and acknowledge R. Atkinson, M. Binnie, G. Brock, A. free-swimming (Vannier et al. 2007). The only other Camens, M. Gemmell, K. Kenny, P. Kruse, J. Laurie, B. arthropod taxon of that size from the Emu Bay Shale McHenry, N. Schroeder and E. Thomson for assistance in the (other than the anomalocaridids) is Redlichia takooensis, field and laboratory. This project benefitted from discussion and with a length of up to 25 cm (Paterson and Jago 2006). support from our Emu Bay Shale research collaborators, M. Lee Conway Morris and Jenkins (1985) suggested that the and J. Gehling. Comments from D. Briggs, M. Wills and an injuries in Redlichia from the Emu Bay Shale may be the anonymous referee greatly improved the manuscript. 18 PALAEONTOLOGY

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