new anatomical information on anomalocaris from...

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. GARC�IA-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] of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol, BS8 1RJ, UK; e-mail: [email protected] of Earth Sciences, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia; e-mail: [email protected] Geobiology Centre, School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA 5005, Australia; e-mail: [email protected] 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

Bay Shale (Cambrian Series 2, Stage 4) at Big Gully, Kangaroo

Island. Frontal appendages of Anomalocaris briggsi Nedin,

1995, are more common than those of Anomalocaris cf. canad-

ensis Whiteaves, 1892, at a quarry inland of the wave-cut plat-

form site from which these species were originally described.

An oral cone has the three large, node-bearing plates recently

documented for Anomalocaris canadensis, confirming that

Anomalocaris lacks a tetraradial ‘Peytoia’ oral cone and

strengthening the case for the identity of the Australian speci-

mens as Anomalocaris. Disarticulated anomalocaridid body

flaps are more numerous in the Emu Bay Shale than in other

localities, and they preserve anatomical details not recognized

elsewhere. Transverse lines on the anterior part of the flaps,

interpreted as strengthening rays or veins in previous descrip-

tions of anomalocaridids, are associated with internal struc-

tures consisting of a series of well-bounded, striated blocks or

bars. Their structure is consistent with a structural function

imparting strength to the body flaps. Setal structures consist-

ing of a series of lanceolate blades are similar to those of other

anomalocaridids and are found in isolation or associated with

body flaps. A single specimen also preserves putative gut diver-

ticula. The morphology of the appendages, oral cone, gut div-

erticula and compound eyes of Anomalocaris, along with its

large size, suggests that it was an active predator, and speci-

mens of coprolites containing trilobite fragments and trilobites

with prominent injuries have been cited as evidence of anom-

alocaridid predation on trilobites. Based on frontal appendage

morphology, Anomalocaris briggsi is inferred to have been a

predator of soft-bodied animals exclusively and only Anomal-

ocaris cf. canadensis may have been capable of durophagous

predation on trilobites, although predation (including possible

cannibalism) by Redlichia could also explain the coprolites

and damage to trilobite exoskeletons found in the Emu Bay

Shale.

Key words: Radiodonta, Anomalocaris briggsi, coprolites,

bite marks, predation.

THE first Australian record of anomalocaridids was based

on a few frontal appendages and a putative oral cone

attributed to Anomalocaris by McHenry and Yates (1993),

found in the lower Cambrian (Series 2, Stage 4) Emu Bay

Shale on the north coast of Kangaroo Island, South Aus-

tralia. Drawing on a sample of 30 frontal appendages,

Nedin (1995) identified two different Anomalocaris

species from the Emu Bay Shale, one newly named as

Anomalocaris briggsi and another left under open nomen-

clature as Anomalocaris sp. Subsequently, Nedin (1999)

attributed damage to trilobites and the nektaspid Emuc-

aris (referred to as Naraoia, but see Paterson et al. 2010)

and a coprolite containing fragments of the trilobite Re-

dlichia takooensis to predation by Anomalocaris; the copr-

olite was subsequently re-illustrated and discussed by

Vannier and Chen (2005). Working on material from

Buck Quarry, Paterson et al. (2011) identified large

compound eyes as those of Anomalocaris and illustrated

associated frontal appendages and the first body flap doc-

umented from the Emu Bay Shale.

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

[Palaeontology, 2013, pp. 1–20]

As a result of an ongoing programme of excavation at

Buck Quarry, material that includes additional body parts

of anomalocaridids is available for study. We evaluate the

new collections in the light of the previously documented

material, emend the descriptions of the two known species

and strengthen the case for assignment to Anomalocaris

(rather than another anomalocaridid genus) by confirming

the identification of the oral cone figured by McHenry and

Yates (1993). Body flaps and setal blades are described, with

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-

tive gut diverticula similar to those seen in other anomaloc-

aridids and stem lineage arthropods.

LOCALITY AND MATERIAL

The Emu Bay Shale Konservat-Lagerst€atte is restricted to

the Big Gully locality (including Buck Quarry), situated

3 km east of Emu Bay on the north-east coast of Kanga-

roo Island; for detailed information about the stratigra-

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

2007, all previously documented fossils from the Emu

Bay Shale at Big Gully, including those of anomalocarid-

ids (McHenry and Yates 1993; Nedin 1995), were sourced

from outcrops along the wave-cut platform and adjacent

cliffs to the east of the mouth of Big Gully. New anomal-

ocaridid material from Buck Quarry, located approxi-

mately 500 m inland (south) of the original wave-cut

platform site, includes specimens of both Anomalocaris

species recognized by Nedin (1995). Other arthropods

described from Buck Quarry thus far are the bivalved taxa

Isoxys and Tuzoia (Garc�ıa-Bellido et al. 2009), nektaspids

(Paterson et al. 2010), the leanchoiliid Oestokerkus (Edge-

combe et al. 2011), the artiopodans Squamacula and Aus-

tralimicola (Paterson et al. 2012) and large compound

eyes of an unidentified taxon (Lee et al. 2011).

Anomalocaridid material from the Emu Bay Shale con-

sists of isolated appendages, body flaps, setal structures

(= ‘gills’ of Whittington and Briggs 1985) and a single

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

bedding. The existence of two species of Anomalocaris in

the Emu Bay Shale was demonstrated by two distinct

morphs of frontal appendages and readily distinguished

by the presence (A. briggsi) or absence (Anomalocaris sp.;

here referred to Anomalocaris cf. canadensis) of spinules

along the proximal and distal margins of the ventral

spines (Nedin 1995). The wave-cut platform exposure is

the source of the type material of A. briggsi and well-pre-

served material of Anomalocaris cf. canadensis, but frontal

appendages of both species are also present in the collec-

tions from Buck Quarry. Anomalocaris briggsi is much

more common at Buck Quarry, and thus circumstantially,

it is likely that most of the additional body parts, includ-

ing the large compound eyes (Paterson et al. 2011),

belong to that species. There are no distinct morphs of

body flaps or setose blades from Buck Quarry, so they

have not been attributed to either species.

SYSTEMATIC PALAEONTOLOGY

STEM EUARTHROPODA

Order RADIODONTA Collins, 1996

Genus ANOMALOCARIS Whiteaves, 1892

Type species. Anomalocaris canadensis Whiteaves, 1892; from the

Stephen Formation (Cambrian Series 3, Stage 5) of British

Columbia, Canada.

Anomalocaris briggsi Nedin, 1995

Figures 1, 2

1992 Anomalocaris sp. Nedin, p. 221.

1993 Anomalocaris sp. McHenry and Yates, pp. 77–81,

84–85, figs 2–7.

1995 Anomalocaris briggsi Nedin, pp. 31–35, figs 1, 3A.

1997 Anomalocaris briggsi Nedin, p. 134.

1999 Anomalocaris briggsi Nedin, p. 989.

2002 Anomalocaris briggsi Hagadorn, p. 98.

2006 Anomalocaris briggsi Van Roy and Tetlie, pp. 240,

244, fig. 1A.

2006 Anomalocaris briggsi Paterson and Jago, p. 43.

2008 Anomalocaris briggsi Hendricks et al., table 1.

2008 Anomalocaris briggsi Paterson et al., p. 320.

2009 Anomalocaris briggsi Garc�ıa-Bellido et al., p. 1221.

2010 Anomalocaris briggsi Daley and Peel, p. 354.

2011 Anomalocaris briggsi Jago and Cooper, p. 239.

2011 Anomalocaris briggsi Paterson et al., p. 239, SI fig. 2.

2012 Anomalocaris briggsi Jago et al., p. 252.

Holotype. SAM P40180 (Fig. 1A, B), originally referred to as

AUGD 1046-630 (Nedin 1995).

Paratype. SAM P40763, originally referred to as AUGD 1046-

335 (Nedin 1995).

Other material. Fifty-six additional specimens of isolated frontal

appendages, of which 26 come from the wave-cut platform and

adjacent cliff exposure, 27 come from Buck Quarry and

three from an exposure on the road south of Buck Quarry (see

2 PALAEONTOLOGY

Supplementary Information for catalogue numbers). Three spec-

imens with multiple appendages come from the wave-cut plat-

form and adjacent cliffs (see Supplementary Information). All

material is housed in the palaeontological collections at the

South Australian Museum (prefix SAM P), Adelaide, Australia.

Emended diagnosis. Anomalocaris with long, distally taper-

ing frontal appendages consisting of 14 podomeres sepa-

rated by triangular regions of flexible cuticle; podomeres

2–12 bearing a pair of proximally curving ventral spines

that are longer than the height of the associated podo-

mere and originate from the distal margin of the ventral

surface of the podomere; proximal base and entire distal

length of the ventral spines with prominent spinules; ven-

tral spines terminate in a point with a pair of short spines

flanking it; podomeres 1 and 13 with pair of short, spike-

like ventral spines; podomere 14 with forked terminal

end; elongated dorsal spines projecting forward medially

from the distal margins of podomeres 12–14.

Description. Complete frontal appendages 87–175 mm long

(mean = 119 mm, SD = 30 mm, n = 7), as measured along the

outwardly convex dorsal margin. Podomeres are tall and narrow

in the proximal region, but shorter and more elongated towards

the distal end. Boundaries between podomeres are often pre-

served as simple lines (Fig. 1C–D), but occasionally, the bound-

aries are preserved as elongated triangular regions that extend

from half to almost the full height of the podomeres (Fig. 1A–B). The triangular regions are interpreted as more flexible cuti-

cle, based on their pockmarked and mottled preservation

(Fig. 1A; McHenry and Yates 1993, figs 6–7). The most proximal

podomere appears to be as long as at least four or five of the

immediately succeeding podomeres (Fig. 1C–D), is much taller

(Fig. 1A–B) and has an irregular attachment margin that may be

concave in outline (Fig. 1).

A pair of spines extends from the distal margin of the ventral

surface of podomeres 1–13 (vs in Figs 1B, D, 2). SAM P46984/5

(Paterson et al. 2011, SI fig. 2c), P46925, P15000 and P47020

(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

height of the associated podomere), have several spines along the

distal margin and terminate in a trident of spines (Figs 1B, D, 2).

Podomere 13 bears simple, nonspinose ventral spines no longer

than the height of the podomere, tapering to a point (Fig. 1B).

Podomeres 2–12 have proximally curved ventral spines up to two

or three times as long as the height of the associated podomere.

Proximal ventral spines are longest on podomeres 6 and 7. The

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 1–2 mm in length (as in Figs 1B, D,

2). The proximal bases of ventral spines 2–13 and the proximal ven-

tral margin of their associated podomeres bear five or more narrow,

closely spaced basal spines, 1.5–3 mm long (bs in Figs 1B, D, 2).

The basal spines are vertically orientated in proximal podomeres,

and angled proximally in more distal podomeres. Ventral spines on

podomeres 2–12 show as many as twelve spinules, 1–2 mm long,

evenly spaced along the entire length of their distal margins (sp in

Figs 1B, D, 2). Some specimens (SAM P40180, P40761/40178,

P31953, P15000) show similar spinules extending along the proxi-

mal margins, matching those on the distal margin in location and

size (Fig. 2; ventral spines on podomeres 10 and 12 in Fig. 1B;

podomeres IV and VI in McHenry and Yates 1993, fig. 3).

The distal end of the appendage is narrow and elongated,

with a pronounced ventral curvature (Fig. 1A–B). SAM P43724,

P14681 and P40180 (ts in Fig. 1B) show that podomere 14

tapers to a pair of simple spines, giving the terminal end of the

appendage a forked appearance (Fig. 2). Single dorsal spines (ds

in Figs 1B, 2) extend from the medial distal region of the dorsal

margin on podomeres 12 and 13 at an oblique angle to the

appendage. SAM P43724 shows that the dorsal spine on podo-

mere 12 is only 3–4 mm long, but that on podomere 13 is much

longer and arches over nearly the full length of the terminal

podomere (ds in Fig. 2). Podomere 14 has a relatively long dor-

sal spine that protrudes from just above the forked terminal end

of the appendage (Fig. 2).

Remarks. The original description of Anomalocaris briggsi

(Nedin 1995, p. 33) is largely confirmed. We amended

the diagnosis to include mention of the origination of the

ventral spines from the distal region of the ventral surface

of the podomere, as this is a unique characteristic of

A. briggsi that readily allows identification of incomplete

specimens. Nedin (1995) described spinules on the ventral

spines of podomere 13 and a bifurcation of the dorsal

spine on podomere 14; however, these features were not

evident in the more complete, newly collected specimens.

The other difference from Nedin’s (1995) reconstruction

is the presence in some specimens of spinules along the

proximal margin of the ventral spines (Fig. 2). Whilst

four specimens show this feature clearly, many more

specimens with well-preserved proximal margins to their

ventral spines show no evidence of the presence of spin-

ules. Owing to its inconsistency, these proximal spinules

were not included in the diagnosis.

Anomalocaris cf. canadensis Whiteaves, 1892

Figure 3

1995 Anomalocaris sp. Nedin, pp. 31, 33–36, figs 2, 3B.



2006 Anomalocaris sp. Paterson and Jago, p. 43.

2011 Anomalocaris sp. nov. Paterson et al., p. 239.

Material. Eleven specimens, with six from Buck Quarry (SAM

P14985, P15374, P43616, P45749, 48158, 48164) adding to the

two previously described specimens (SAM P40807, originally

referred to as AUGD 1046-600, and P40822, originally referred

to as AUGD 1046-346; Nedin 1995) and an additional three

specimens (P44851, P42037 and possibly P44859) from the

wave-cut platform (see Supplementary Information).

DALEY ET AL . : ANOMALOCARIS FROM THE EMU BAY SHALE 3

A

B

C

D

4 PALAEONTOLOGY

Description. Anomalocaris frontal appendages with 14 podo-

meres, ranging from 70 to 183 mm long (mean = 136 mm,

SD = 47 mm, n = 4) measured along the dorsal margin. Podo-

meres appear roughly rectangular in compacted lateral view with

dorsal margins wider than ventral margins, imparting a convex

profile along the dorsal length of the appendage with the distal

end being curled under (Fig. 3A–B, G–H). The size of the podo-

meres decreases distally. Podomere boundaries are preserved as

straight or slightly curved lines, with no evidence of arthrodial

membrane or flexible cuticle between them, likely due to the

tightly coiled nature of the specimens.

Podomeres 1 to at least 11 each show paired ventral spines

protruding from the centre of their ventral margins (vs in

Fig. 3B, H). Podomeres 12 and 13 lack complete ventral margins

in all specimens, so the presence of ventral spines is unknown.

Podomere 14 does not show ventral spines (po14 of left append-

age in Fig. 3B). The ventral spine of podomere 1 is preserved

only in SAM P15374, where it is nearly as long as the height of

the associated podomere and tapers to a point flanked by two

thin auxiliary spines less than 1 mm long. Podomeres 2 to at

least 11 have ventral spines that alternate in length, with those

on the even-numbered podomeres being longest. The ventral

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

distal end of the appendage no more than one-fourth the height

of the associated podomere. Most of these ventral spines termi-

nate in a point flanked by two auxiliary spines protruding at an

oblique angle and 1–3 mm long (as in Fig. 3B, H). However, in

SAM P40807, the right appendage shows a ventral spine with

two pairs of auxiliary spines on podomere 4 (1–4 in Fig. 3D).

These spines seem to be clearly attached to the ventral spine

with no articulations or boundaries at their bases. The left

appendage of SAM P40807 shows at least three, and possibly

four, auxiliary spines (1–4? in Fig. 3C) on the ventral spine of

podomere 2/4 (podomeres cannot be counted to the proximal

portion of the appendage). In this case, a clear boundary sepa-

rates auxiliary spine 2 from the ventral spine, so it could be an

overlap of one of the auxiliary spines from the other ventral

spine of the pair from that podomere. In SAM P15374, the sec-

ond ventral spine from the proximal end shows two pairs of

auxiliary spines, and possible one more on the right side from a

third pair (1–5? in Fig. 3E). A similar morphology is evident in

SAM P42037, where the ventral spine on podomere 2 shows

three auxiliary spines on the left side and two on the right (1–5in Fig. 3F).

The most proximal podomere is not completely preserved in

any specimen, but SAM P40822 shows it to be elongated to a

length equivalent to the following three podomeres with a

rounded, outwardly convex proximal margin. The most distal

margin of podomere 14 is preserved in only one specimen

(po14 of the left appendage in Fig. 3B) where it appears

rounded with a small terminal spine (ts in Fig. 3B). Simple,

elongated dorsal spines on podomeres 10–14 are located medi-

ally on the sagittal axis of the most distal region of the dorsal

margin of the podomere and arch forward over the full length

of the podomere distal to it (ds in Fig. 3B, H).

Remarks. Nedin (1995) described some of this material as

Anomalocaris sp. and not Anomalocaris canadensis because

the Emu Bay Shale material was interpreted as having the

longest ventral spines on the odd-numbered podomeres,

but A. canadensis has the longest ventral spines on the

even-numbered podomeres (Whiteaves 1892; Briggs 1979;

Whittington and Briggs 1985). This was based largely on

SAM P40807 (Nedin 1995, fig. 2A, B) and SAM P40822.

SAM P40822 has an incomplete distal end, and the proxi-

mal region does not preserve podomere boundaries, so it

F IG . 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.

F IG . 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.


A

C

G H

D E F

B

6 PALAEONTOLOGY

cannot be determined whether the longest ventral spines

are on the even or odd podomeres. In SAM P40807, the

situation is clearer. We consider the number of podo-

meres in SAM P40807 to be one more than originally

counted; a line of articulation is visible between podo-

meres 1 and 2 (right appendage in Fig. 3A–B), but this

boundary was not included in a previous camera lucida

drawing of this specimen (Nedin 1995, fig. 2B). With that

boundary identified, the longest ventral spines of these

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

appendages and those of A. canadensis is a newly

described feature, the presence of extra pairs of auxiliary

spines on some of the ventral spines. The left and right

frontal appendages of SAM P40807 each show a ventral

spine with two pairs of auxiliary spines (Fig. 3B–D)instead of the one pair observed in A. canadensis (Whit-

eaves 1892; Briggs 1979; Whittington and Briggs 1985).

The presence of two pairs of auxiliary spines is also seen

in the appendages of A. saron (Hou et al. 1995, figs 2B–F,3). Other A. cf. canadensis appendages show single ventral

spines with three pairs of auxiliary spines (SAM P15374,

P42037), which bears some resemblance to the shorter

ventral spines of A. briggsi (e.g. the ventral spine of po12

in fig. 1B). Owing to this inconsistent ventral spine mor-

phology, we have left these Emu Bay Shale specimens

under open nomenclature.

Nedin (1995) also compared this material to specimens

from the Chinese Chengjiang biota that were formerly

attributed to Anomalocaris canadensis by Hou and Bergs-

tr€om (1991). The Chengjiang specimens were, however,

subsequently reassigned by Hou et al. (1995) to A. saron

(frontal appendages in Hou and Bergstr€om 1991, pl. 2,

fig. 2; Chen et al. 1994, figs 1–2) and Anomalocaris sp.

(frontal appendages in Hou and Bergstr€om 1991, pl. 2,

fig. 3).

ANATOMICAL DESCRIPTION OFISOLATED ANOMALOCARIS ELEMENTS

Oral cone

A single specimen of an Anomalocaris oral cone from the

Emu Bay Shale (SAM P31956) is derived from the wave-

cut platform and was figured as a ‘possible mouth of

Anomalocaris’ by McHenry and Yates (1993, p. 82). Rest-

udy of the specimen (Fig. 4) after removal of a calcite

crust by acid dissolution shows that it conforms to the

morphology of the oral cone of A. canadensis described

by Daley and Bergstr€om (2012, especially fig. 2a–dtherein) in all respects. The specimen exhibits triradial

symmetry with three large plates (L in Fig. 4B) arranged

with the largest separated from the other two by about

125 degrees and the two slightly smaller plates separated

F IG . 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.

A B

F IG . 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.


A

C D

E

F

G

H I

B

8 PALAEONTOLOGY

by about 110 degrees (compared with angles of 130–140and 90–100 degrees in Daley and Bergstr€om 2012). In

between the three large plates are small and medium

plates with an irregular number and arrangement (11 on

left side, 7 on right side, 4 posteriorly). Scale-like nodes

are preserved on the large and medium plates, some with

an asymmetrical profile and most with the peaks broken

off. Daley and Bergstr€om (2012) described subdivisions at

the outer margins of the large and medium plates as con-

sisting of up to five folds extending no more than one-

fourth the total length of the plate. In the Emu Bay Shale

specimen, two individual plates show one and two subdi-

visions that extend to about half the length of the plate

(left side of Fig. 4B). In the series of four plates just to

the left of the anterior large plate, three shorter plates

appear to be subdivisions of an adjacent longer plate that

extends all the way into the central region, despite the

presence of clear divisions and boundaries.

The outline of the oral cone is irregular, but is roughly

rounded rather than diamond-shaped or rectangular, a

distinction that was formerly thought to separate the

Anomalocaris oral cone from that of Peytoia (Collins

1996). Daley and Bergstr€om (2012) showed that the Bur-

gess Shale Anomalocaris oral cone is round. The central

region of the Emu Bay Shale oral cone does not consist

of an opening, but instead, the three large plates extend

into it, similar to the small and irregular central gap

described for A. canadensis. One of the large plates has

four rounded teeth-like projections (t in Fig. 4B). Daley

and Bergstr€om (2012, fig. 2f) also reported four teeth on

one of the larger plates in A. canadensis (ROM 61669).

This oral cone confirms the identity of the anomaloca-

ridid appendages from the Emu Bay Shale as being from

Anomalocaris. The specimen comes from the wave-cut

platform, as do both species of Anomalocaris, so it is not

possible to determine its specific assignment.

Body flaps

Emu Bay Shale Anomalocaris body flaps (Figs 5–6) have

been found almost exclusively at Buck Quarry. Fifty-five

specimens consisting of single flaps and 15 assemblages

consisting of two or more flaps, or flaps with setal struc-

tures, have been sourced from Buck Quarry, whereas only

four specimens of single flaps have been collected from

the wave-cut platform and adjacent cliffs (see Supplemen-

tary Information for catalogue numbers). Flaps range in

size up to 73 mm in width (SAM P48153), as measured

from the tip of the flap directly across to the attachment

area. Body flaps from the Emu Bay Shale are found iso-

lated or closely associated with two or three flaps of simi-

lar size and preservation (Fig. 6F). SAM P47203, SAM

P46354 and P45441 consist of single flaps with closely

associated setal structures (Fig. 5C, E), and SAM P44236

shows setal blades (Fig. 5I) and a partially preserved axial

region (Fig. 5H) in close association with the flap

(described below).

Flaps are subtriangular in outline, with a longer,

broadly convex margin towards the anterior (based on

comparison with full-body specimens of Anomalocaris)

and a shorter margin, usually straight (Figs 5D–E, H, 6A,

C) or broadly concave (Figs 5A–C, 6F), directed towards

the posterior. The margin of attachment is straight

(Figs 5A, 6A–C) in specimens where it is not obscured by

or continuous with irregular organic material, presumably

parts of the rest of the body (Figs 5B–C, E, H, 6F). The

most conspicuous structures on the surface of the flaps

are evenly spaced, subparallel lines oriented transversely

on the anterior half of the flaps (Figs 5A, D, 6C). There

are up to twelve of these transverse lines, which originate

at the anterior margin of the flap and extend about half-

way into the flap at an angle of 35–45˚. The lines end

along a straight line in the centre of the flap, but no solid

feature defines this boundary (Fig. 5A–D), nor is there

any evidence of a boundary line along the margin of the

flap. The transverse lines typically run parallel to one

another, but SAM P15133 shows them branching and

pinching off (arrows in Fig. 5B). In addition to the trans-

verse lines, one specimen (SAM P43656) preserves fine,

faint striations in the posterior region of the flap (black

arrow in Fig. 5D).

Emu Bay Shale flaps preserve internal microstructures

of the transverse lines (Fig. 6). In most specimens, the

external, surficial morphology of the transverse lines is as

simple, slightly curved lines preserved as thin impressions

or raised ridges on the flap (Fig. 5A–C, E, H). A few

specimens show that below these simple external lines,

the internal structure consists of distinct boundary lines

delimiting a series of tiny raised blocks or bars between

them (Fig. 6C–D, F–H). The boundary lines are simple

and slightly curved upward and outward in the anterior

F IG . 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.


A

B

F H

G

E

D

C

10 PALAEONTOLOGY

region of the flap, with the distance between them

decreasing gradually towards the outer margin of the flap

(Fig. 6D, G). Between the boundary lines is a series of

thin raised bars, often perpendicular to the boundary

lines (Fig. 6D), but sometimes in an imbricated arrange-

ment (Fig. 6G). The raised bars are spaced about as far

apart as they are wide (Fig. 6D) or are very closely spaced

(Fig. 6H). In one specimen, each bar shows striations

(Fig. 6G). In fainter, possibly more decomposed or

decayed specimens, the boundary lines are not visible,

and the inner structure appears as a series of small bars

and/or indentations with indistinct margins (Fig. 6E).

The raised bars are regarded as being internal because

some specimens show them together with the simple lines

of the external surface of the flap, as a series of raised

swellings beneath or near them (white arrows in Fig. 5D).

In SAM P47153, simple external lines are visible on the

dorsal surface at the distal end of the flap (bottom half of

Fig. 6B), and the convex swellings of the upper surface of

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

concave depressions into the underlying impression of the

ventral surface of the flap on the sediment, representing

the lower surface of the internal bars (right side of

Fig. 6A) and demonstrating the internal nature of the

structures. Less well-preserved specimens show partial

decay preferentially located along the transverse lines

(black arrows in Fig. 6E). Two specimens also show regu-

larly spaced raised bars running between the transverse

lines, perpendicular to and bounded by them (black

arrows in Fig. 5F and white arrows in Fig. 6E).

Setal blades (‘gills’)

Material collected from Buck Quarry includes 36 speci-

mens interpreted as possible isolated setal structures

belonging to Anomalocaris, the ‘gills’ of Whittington and

Briggs (1985). The most well-preserved, isolated setal

structures are small (blades less than 1 cm long) and con-

sist of a series of lanceolate blades attached at one end

and free-hanging at the other (Fig. 5G). Isolated specimen

SAM P45525 (Fig. 5G) preserves a curved line to which

the lanceolate blades are attached. Some specimens, such

as SAM P45599, show several larger setal structures that

overlap and setae that are preserved as a series of parallel-

sided blades.

Setal blades are found in association with both frontal

appendages and body flaps. The slab with the holotype of

Anomalocaris briggsi (SAM P40180) preserves a mass of

fibrous, thin filaments, which may be setal blades, about

2 cm from the dorsal margin of the appendage. Four

specimens of anomalocaridid body flaps are preserved

with nearby setal structures. In SAM P47203, these consist

of a mass of roughly parallel blades (thin lines) that are

situated anterior and central to the preserved flap, near

its base (black arrow in Fig. 5C). SAM P44236 preserves

a small setal structure that consists of a central ramus

with eight small blades branching from it (Fig. 5I). In

SAM P45441, the setal structure consists of a mass of

highly textured, tangled threads or thin blades (Fig. 5E).

SAM P46354 shows a faint impression of a lamellar struc-

ture near its flap.

Possible axial region

Although flaps are common in the collections from Buck

Quarry, they are nearly all detached from the rest of the

body, apart from the association with detached setal

blades noted above. A single specimen, SAM P44236

(Fig. 5H), preserves a fragment of the axial region of the

Anomalocaris body. It consists of a body flap attached to

a large fragment of distorted cuticle that extends the full

length of the flap. Near the attachment of the body flap

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-

ior to the pairs, in line with those on the left side (white

arrows in Fig. 5H). These swellings are approximately 4–5 mm in diameter and have gradual margins that are

continuous with the cuticle surrounding it, as though the

body cuticle is draped over internal high-relief structures.

Preparation of one of the swellings yielded an internal

structure consisting of densely packed spheres. This speci-

men is also associated with the clear setal structure

(Fig. 5I) described in the previous section (white box in

Fig. 5H). The rest of the cuticular material is indistinct

with no recognizable features.

F IG . 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.


DISCUSSION

Anomalocaridid material from the Emu Bay Shale

includes a diverse collection of specimens showing iso-

lated body parts. Although whole bodies have yet to be

found, the disarticulated material is informative owing to

the novel preservation at the Emu Bay Shale locality. This

locality not only has yielded a species of Anomalocaris

unique to this site, but also brings to light structures in

the body flaps that are not evident in anomalocaridids

from Chengjiang, the Burgess Shale or Fezouata. This

parallels the preservation of ommatidial lenses on the sur-

face of the eyes of Emu Bay Shale Anomalocaris (Paterson

et al. 2011), the corresponding surface being smooth and

devoid of structure in anomalocaridid eyes from Chengji-

ang and the Burgess Shale. The unique taphonomic path-

way of the Emu Bay Shale ensures preservation of

detailed microstructures not preserved in other Cambrian

fossil Lagerst€atten, but the overall morphology and size of

the specimens are similar enough to other Cambro–Ordo-vician anomalocaridids that their identity is assured, despite

their disarticulated nature and novel preservation. The

Emu Bay Shale is also the main locality yielding alleged

evidence for the inferred predatory lifestyle of Anomaloc-

aris, particularly in regards to trilobites (Conway Morris

and Jenkins 1985; Nedin 1999; Vannier and Chen 2005).

Morphology of anomalocaridid body flaps

The identity of the structures described herein as Anomal-

ocaris body flaps was established by comparison with the

most morphologically similar articulated specimens, those

of Anomalocaris saron and Amplectobelua symbrachiata

from the Chengjiang biota in China, a comparison

enhanced by similarities in style of preservation. The

spacing and orientation of the transverse lines are similar

in Emu Bay Shale and Chengjiang body flaps, with Ano-

malocaris saron specimens showing as many as 18 trans-

verse lines on a single flap (Hou et al. 1995, figs 4–5).The transverse lines of both Amplectobelua and Anomaloc-

aris from Chengjiang show bifurcations and anastomoses

similar to those seen in some Emu Bay Shale specimens

(Chen et al. 1994, figs 3B, 4D; Hou et al. 1995, figs 4–6),and one specimen is described as showing a series of

faint, fine striations along the posterior margin (Chen

et al. 1994, fig. 3B). Associated setal blades are also

observed near the attachment area of the flaps in the

Chengjiang anomalocaridids (Chen et al. 1994, figs 1B, 2–3; Hou et al. 1995, figs 4–6), as are present in the Emu

Bay Shale material. However, unlike the Emu Bay Shale

specimens, Amplectobelua and Anomalocaris saron have a

pronounced boundary line that cuts through the middle

of the flap, dividing an anterior region with transverse

lines from a posterior region without lines (Chen et al.

1994, figs 1D, 2, 3A; Hou et al. 1995, figs 4A, 5). Chengji-

ang specimens of Amplectobelua also preserve a structure

of the same nature as the transverse lines running along

the margin of the flap (Chen et al. 1994, fig. 4B), which

has not been observed in the Emu Bay Shale material.

Despite these differences, the similarities between the

Emu Bay Shale specimens and Anomalocaris saron and

Amplectobelua symbrachiata are strong enough to confirm

the identity of these specimens as anomalocaridid body

flaps.

The Burgess Shale has the greatest anomalocaridid

diversity of any Cambrian Konservat-Lagerst€atte (Whit-

tington and Briggs 1985; Daley et al. 2009; Daley and

Budd 2010), and many whole-body specimens have well-

preserved body flaps. However, transverse lines are typi-

cally poorly preserved and are only present in about half

of the whole-body specimens of Peytoia (USNM 274143/

47, USNM 274164, USNM 274144/48, USNM 247145/62

and USNM 274146) and three of the ten Hurdia speci-

mens (ROM 59320, ROM 60010, ROM 60029) with visi-

ble flaps. The transverse lines are most obvious in Peytoia

nathorsti (Whittington and Briggs 1985, figs 20, 28, 30, 42

–43, 50–51, 59), where they are described as evenly spaced

and highly reflective, with negligible relief such that they

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

91, 94; Daley et al. 2013, fig. 14F) and an unidentified

anomalocaridid USNM 274154 (and counterparts 274156

and 274161) (Whittington and Briggs 1985, figs 81–88,100; Daley et al. 2013, fig. 14D). The transverse lines of

the flaps of these Burgess Shale taxa typically extend from

the anterior margin to at least halfway into the flap

(Whittington and Briggs 1985, figs 20, 59, 91, 94), but

sometimes extending the full length (Whittington and

Briggs 1985, figs 28, 30, 42–43, 51–52, 81–88, 100). Hur-dia victoria has diminutive flaps, but some specimens

show clear transverse lines that also cover almost the

entire surface of the flap (Daley et al. 2013, figs 18A–B,20D–F, 21A–B). A feature unique to Burgess Shale taxa is

that specimens of Peytoia (Whittington and Briggs 1985,

fig. 30), Hurdia (Daley et al. 2013, fig. 20D–F) and the

unidentified anomalocaridid USNM 274154 (Whittington

and Briggs 1985, figs 82–88) show partially decomposed

body flaps with the transverse lines extending outward

beyond the margin of the flap, suggesting that the trans-

verse lines were more decay resistant than the flap itself.

The only anomalocaridid from the Burgess Shale that

does not preserve clear transverse lines is Anomalocaris

canadensis. ROM 51212 (Collins 1996, fig. 4.2) may pre-

serve faint transverse lines on its body flaps, but both

ROM 51212 and ROM 51211 (Collins 1996, fig. 4.1) pre-

serve very fine striations along through the anterior half

12 PALAEONTOLOGY

of their body flaps, bounded by a clear line that bisects

the flap. These striations are similar to what is evident on

the posterior margin of the Emu Bay Shale specimen

SAM P43656 (black arrow in fig. 5D) and in Chengjiang

material (Chen et al. 1994, fig. 3B).

Anomalocaridid body flaps are also preserved in the

lower and middle Cambrian of Nevada and Utah and

the Lower Ordovician Fezouata Formation of Morocco.

A specimen interpreted to be the posterior body region

of Peytoia nathorsti from the middle Cambrian Marjum

Formation of Utah shows a series of parallel lines pass-

ing through the anterior region of most of the body

flaps, beginning along the anterior margin and extending

into the body flap at an angle of approximately

45 degrees (Briggs and Robison 1984). These are similar

in orientation, spacing and location to the transverse

lines of anomalocaridids from the Emu Bay Shale, Chen-

gjiang and Burgess Shale. Cambrian specimens from the

Pioche Formation of Nevada consist of three partial

putative bodies with flaps and a single isolated flap (Lie-

berman 2003). The three body specimens do not have

transverse lines visible on their flaps, but the single iso-

lated flap (with length of only 15 mm) is described as

having five transverse lines that extend through the

whole flap in a wide arc from the proximal anterior

margin to the distal posterior margin (Lieberman 2003,

pp. 683–684, fig. 6.5). A much larger partial body of an

anomalocaridid described from the Spence Shale Mem-

ber in Utah consists of several body flaps bearing trans-

verse lines that parallel the anterior margin of the flap

and extend for most of its length (Briggs et al. 2008, fig.

1). The putative transverse lines in both these specimens

are orthogonal to the transverse lines in other anomaloc-

aridid material from the Emu Bay Shale, Chengjiang and

Burgess Shale, which run from the distal anterior margin

towards the centre of the flap, rarely reaching the pos-

terior margin. Ordovician material includes two incom-

plete anomalocaridid bodies. In one specimen (YPM

226437, called YPM 226637 in the Supplementary Infor-

mation of Van Roy and Briggs 2011), two flaps preserve

transverse lines (Van Roy and Briggs 2011, figs 1a, c,

S2a, b) that are subparallel and present only in the ante-

rior region of the flap (for the more posterior flap) or

along the more proximal region of the second, partially

preserved flap. The transverse lines have little to no

relief and are visible as black lines that are either highly

reflective or dark stained (Van Roy and Briggs 2011, fig.

1c). YPM 26639 also has a preserved flap, with pro-

nounced transverse lines (Van Roy and Briggs 2011, fig.

S3a, b) that are preserved as robust structures with

relief. The structure is a relatively thick line with a rim

along either side (as seen in Emu Bay Shale specimens),

but the inner region does not have the raised ridges or

bars evident in the Australian material.

Interpretation of the transverse lines. The transverse lines

on the anterior part of the body flaps have been described

under two alternative nomenclatures that imply different

functions – they are variously described as veins (Chen

et al. 1994; Hou et al. 1995) or as strengthening rays

(Whittington and Briggs 1985). In Chengjiang anomaloc-

aridids, Chen et al. (1994) referred to these lines as

‘canals’ and ‘veins’ and drew support for this interpreta-

tion from the ‘wrinkled, three-dimensionally preserved

structure in one specimen’ of Amplectobelua (Chen et al.

1994, p. 1306). They also called these structures ‘canal

systems’ (p. 1305) for Anomalocaris, based on comparison

with Amplectobelua. Unlike species of Anomalocaris and

Amplectobelua from Chengjiang, a well-defined central

‘vein’ along the middle of the flap is lacking in Emu Bay

Shale Anomalocaris. The indistinct nature of a marginal

line (‘vein’) in the Emu Bay Shale material, if it were

originally present (as is the case in Chengjiang Amplecto-

belua), could be attributed to comparatively poor preser-

vation of the anterior margin of the flaps in most

specimens, whereas the absence of a central line/vein is

harder to attribute to it not being preserved. The appar-

ently blind termination of the lines at their posterior ends

is inconsistent with a network of veins, but is not incon-

sistent with a mechanical role for these structures. It is

also difficult to reconcile the apparently rigid internal

structures associated with the transverse lines in Emu Bay

Shale Anomalocaris with an originally tubular structure as

would be expected for veins or canals.

Whittington and Briggs (1985) discussed the swimming

motion of anomalocaridids and interpreted the transverse

lines as likely being strengthening rays that would also

have assisted with movements in a function similar to fin

rays in fishes. They quote Webb (1975, p. 47), who said

that ‘individual segments are capable of fairly extensive

independent movement because muscular forces are

transmitted to stiff fin rays supporting a thin, highly flexi-

ble finweb’. The former also suggested that the strength-

ening rays would have been most prominent in the

anterolateral region of the flap because they would have

assisted in maintaining the most hydrodynamic shape to

the lobe during the downward stroke of the swimming

motion (Whittington and Briggs 1985, fig. 103b). This

position of the transverse lines is well documented in

anomalocaridids from the Emu Bay Shale, Chengjiang

and the Burgess Shale. Several Burgess Shale specimens

also show the transverse lines protruding from the ragged

margins of partially decayed Peytoia and Hurdia body

flaps, providing further evidence of the robust nature of

the transverse lines and their function as structural ele-

ments.

The structure of the transverse lines in the anomaloc-

aridids essentially consists of a pair of distinct bound-

ary lines sandwiching an area of raised blocks or bars.


Functionally analogous microstructures are also seen in

the stiffening rods of fin-like structures that a variety of

other animals use to propel themselves through fluid, be

it water or air. For example, the fin rays of the median

and paired fins of many Actinopterygii (ray-finned fishes)

consist of two semilunate half rays (hemitrichs) that are

joined together by thin fibres of collagen and elastin

(Lanzing 1976; Geerlink and Videler 1987; Lauder et al.

2006). Differential movement of the two hemitrichs

imparts flexibility to the fin, allowing it a small degree of

bending whilst still retaining a stiff and strong overall

structure that can withstand the forces generated along

the distal margin of the fin during forward propulsion. In

several batoid (stingrays and skates) families (Dasyatidae,

Potamotrygonidae, Rajidae, Urotrygonidae), fin rays of

the pectoral wings consist of a pair of catenated calcified

chains, which imparts flexibility and strength to the wing,

and oscillatory swimmers also exhibit cross-bracing con-

sisting of cartilaginous extensions that join adjacent fin

rays (Schaefer and Summers 2005), similar to the branch-

ing seen in the transverse lines of Anomalocaris body flaps

from Emu Bay Shale. Even the wing veins of some

insects, like dragonflies, consist of two layers of chitin

with a mass of protein and muscle fibrils in between,

albeit arranged into the tubular form of the vein (Wang

et al. 2008). A general morphology of two boundary

structures enclosing an inner region of densely packed

fibres imparts flexibility and strength to the propulsive

fins and flaps of a variety of animals and may be compa-

rable in function to the microstructure of the transverse

lines of body flaps in specimens of Anomalocaris from the

Emu Bay Shale.

Setal structures and possible axial region structures in

anomalocaridids

The setal structures described for Anomalocaris from the

Emu Bay Shale have a morphology comparable to those

seen in the Burgess Shale taxa Hurdia (Daley et al. 2009,

figs 2E, S2C, H), Peytoia (Daley et al. 2009, fig. S2A–B, D–F, I) and Opabinia (Bergstr€om 1986, fig. 1F; Budd 1996,

fig. 1A–B; Budd and Daley 2012, fig. 4C–D), but are gen-

erally much smaller in size. Hurdia has large setal struc-

tures on the body, but in the anterior region just behind

the head, there are three or four pairs of smaller setal

structures comparable in size to the isolated structures

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

Hurdia setal structures (Daley et al. 2009, fig. 2E; Daley

et al. 2013, fig. 15), which have been compared with the

‘transverse rods’ of Peytoia (Whittington and Briggs

1985), suggesting that these mineralized, nodular rods are

the attachment points for the setal blades (Bergstr€om

1987; Daley et al. 2009). Setal structures are poorly pre-

served in other anomalocaridids, but are described as

lamellar structures in Anomalocaris canadensis (Whitting-

ton and Briggs 1985, p. 579, fig. 3; Collins 1996), Ano-

malocaris saron (Chen et al. 1994, p. 1305, fig. 2; Hou

et al. 1995, pp. 165, 167, figs 4–6) and Amplectobelua

symbrachiata (Chen et al. 1994, fig. 3a).

The only known specimen from the Emu Bay Shale

with a putative axial region of the body has paired high-

relief structures that are arranged serially amidst a large

area of indistinct body cuticle (Fig. 5H). The closely allied

taxon Opabinia from the Burgess Shale has three-dimen-

sional diverticula preserved in a paired arrangement on

either side of the gut in the axial region of the body, with

an elliptical shape and a smooth or laminated surface

(Budd and Daley 2012, p. 90, fig. 7A–F). Other Cambrian

taxa such as the armoured lobopodians Kerygmachela

(Budd 1999) and Pambdelurion (Budd 1998) and the

euarthropod Leanchoilia (Butterfield 2002) have gut div-

erticula with a similar shape and position, and these are

either phosphatized or preserved in darker material than

the rest of the specimen. Based on similarities in struc-

ture, position and preservation, the swellings observed in

the Emu Bay Shale Anomalocaris specimen may also

represent diverticula of the gut, which are recognized as

well in the co-occurring bivalved arthropod Isoxys

(Garc�ıa-Bellido et al. 2009), the leanchoiliid Oestokerkus

(Edgecombe et al. 2011) and the artiopodans Squamacula

and Australimicola (Paterson et al. 2012). Paired patches

of nodular mineralization are also associated with the gut

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;personal observation of unpublished material) from the

Burgess Shale, and in Peytoia nathorsti from the Marjum

Formation (Briggs and Robison 1984, p. 5, figs 3, 4).

Anomalocaris saron from Chengjiang also has paired, seri-

ally repeated structures in close association with the gut

(Chen et al. 1994, p. 1305, figs 1–2) that appear nodular

and are preserved in darker material than the rest of the

body and have been interpreted as digestive glands

(Vannier and Chen 2005, fig. 11A; Vannier 2009, fig. 5E).

Similar structures have also been observed in Amplectobe-

lua symbrachiata (Chen et al. 1994, 2x to 4x in fig. 3A)

and have been equated to the paired nodular patches in

Peytoia nathorsti from the Burgess Shale.

Reassessing the evidence for predatory habits of

Anomalocaris

Emu Bay Shale fossils have played a key role in establish-

ing the idea that Anomalocaris was a top visual predator

14 PALAEONTOLOGY

in Cambrian ecosystems. Cited evidence includes damage

to trilobites and allegedly to nektaspids (Conway Morris

and Jenkins 1985; Nedin 1999), large coprolites contain-

ing trilobite fragments (Nedin 1999; Vannier and Chen

2005) and the discovery of large, high-resolution com-

pound eyes attributed to Anomalocaris (Paterson et al.

2011). However, durophagy in anomalocaridids, particu-

larly feeding on trilobites, has been recently brought into

question (Hagadorn 2009a; Hagadorn et al. 2010; Daley

and Bergstr€om 2012), and the functional inability for the

oral cone to produce certain injuries to trilobite exoskel-

etons has been noted previously (e.g. Whittington and

Briggs 1985; Hou et al. 1995).

Nedin (1999) documented an elongate (43 9 28 mm)

coprolite from the Emu Bay Shale containing identifiable

fragments of the trilobite Redlichia takooensis, including a

genal spine, thoracic pleurae and parts of the cephalon

with distinctive terrace line ornamentation (Nedin 1999,

fig. 4; Vannier and Chen 2005, fig. 9). Nedin attributed

this coprolite to Anomalocaris based not only on its size,

but also his proposed model on how Anomalocaris could

fracture trilobite cuticle by repeated flexure of the exo-

skeleton using its frontal appendages (Nedin 1999, fig. 3).

A number of other trilobite-dominated aggregates have

been sourced from Buck Quarry (Fig. 7A–H) and appear

to represent bone fide coprolites (sensu Hagadorn 2009b),

as opposed to ecological or environmental (e.g. current)

accumulations (sensu Vannier and Chen 2005). These iso-

lated aggregates are mainly elongate, contain fragmented

sclerites of the trilobites Redlichia takooensis and/or

Estaingia bilobata and are commonly enveloped by a coat-

ing of iron oxide. SAM P45413 (Fig. 7A–B) is elongate

(preserved length and width: 31 and 12 mm, respec-

tively), tapers at one end and contains sclerites of Redli-

chia, including a relatively complete right thoracic pleura

from an individual that would have been around 50 mm

long; this estimate is supported by the fact that thoracic

pleurae in Redlichia have a fairly consistent width (tr.)

along most of the trunk. Elongated specimens such as

SAM P45413 (Fig. 7A–B) and SAM P47144 (Fig. 7H)

may represent coprolites excreted whilst the animal was

in motion, whereas rounded specimens such as SAM

P47146 (Fig. 7C–D) and P15255 were possibly deposited

when the animal was stationary. In SAM P45413, the iron

oxide coating is largely restricted to the sclerite aggregate

(Fig. 7A–B) and could represent the solid component of

the faeces, whereas many other specimens (e.g. P47146,

sclerite-bearing portion 25 mm long, 14 mm wide) show

aggregates fringed by more extensive iron oxide haloes

(Fig. 7C–D), which has been interpreted to represent dif-

fusion of the fluidized component into the surrounding

sediment (cf. Nedin 1999; Vannier and Chen 2005). Some

coprolites contain concentrated Estaingia fragments, for

example, SAM P15470a, b (length 23 mm, width 7 mm)

and SAM P47144a, b (incomplete length 28 mm long,

width 8 mm; Fig. 7H), whereas P45433 (length 50 mm,

width 20 mm; Fig. 7E–G) contains Estaingia sclerites,

including a librigena (Fig. 7F) and a complete thoracic

segment with its long axis oriented parallel to the long

axis of the coprolite (Fig. 7G), together with fragments of

Redlichia. Currently twelve coprolites are known from the

Emu Bay Shale Konservat-Lagerst€atte; eight contain frag-

ments of Redlichia takooensis, three contain fragments of

Estaingia bilobata and one contains fragments of both

species. Estaingia is much more abundant in the Lag-

erst€atte than Redlichia, so the higher number of coprolites

containing fragments of Redlichia suggests that Anomaloc-

aris preferentially preyed on this less common taxon.

Unequivocal evidence of predation damage to trilobite

exoskeletons is relatively rare in the Emu Bay Shale. Pre-

viously documented specimens of Redlichia show injuries

to both sides of the thorax (Conway Morris and Jenkins

1985, figs 1, 2; Nedin 1999, fig. 2B; Daley and Paterson

2012, p. 19), with individuals ranging from 50 to

210 mm in estimated length. However, the injury

reported by Nedin (1999, fig. 2A) to the right lateral pos-

terior shield of the nektaspid Emucaris (referred to as

Naraoia) continues well into the surrounding sediment,

indicating that this is not an injury but rather represents

the uneven edge where a fragment has broken off of the

rock sample (Paterson et al. 2010, pl. 2, fig. 2). Some

injuries to Emu Bay Shale trilobites appear to have been

fatal (contra Conway Morris and Jenkins 1985) because

there is no evidence of healing or repair around the

affected areas, as has been seen in other injured trilobites

from the middle Cambrian of the Northern Territory,

Australia (Jago and Haines 2002) and British Columbia,

Canada (Rudkin 1979). A large specimen (P48149) from

the coast with a scattering of Redlichia fragments is prob-

ably not a coprolite, but may represent the remains of an

attack that shattered this relatively large Redlichia speci-

men (Fig. 7I). Anomalocaridids are often suspected to

have inflicted such injuries on Cambrian trilobites (Rud-

kin 1979, 2009; Briggs and Mount 1982; Babcock and

Robison 1989; Pratt 1998; Babcock 1993, 2003; Nedin

1999; Jago and Haines 2002; Babcock and Peel 2007), but

recent arguments (Hagadorn 2009a; Hagadorn et al.

2010; Daley and Bergstr€om 2012) suggest that the oral

cone of Anomalocaris – which is prone to wrinkling, fold-

ing and tearing – would have been too soft and pliable to

break the mineralized exoskeleton of a trilobite. The oral

cone of anomalocaridids could not occlude (Whittington

and Briggs 1985; Hagadorn 2009a; Hagadorn et al. 2010)

and the irregular shape and small size of the central

opening in Anomalocaris made it unsuitable for strong

biting motions (Daley and Bergstr€om 2012), but the oral

cone may have been capable of breaking weakly mineral-

ized trilobites (Hagadorn 2009a). This supports the


suggestion of Conway Morris and Jenkins (1985) that

healed injuries in Redlichia resulted from attacks that

occurred during the unmineralized stage immediately fol-

lowing moulting. Some modern aquatic predators

(including cannibals) that feed on freshly moulted arthro-

pods are able to detect specific moulting hormones (e.g.

ecdysone) released by their prey (Marshall et al. 2005;

Jackrel and Reinert 2011). It is possible that some ano-

malocaridids could use chemoreception to detect freshly

moulted trilobites and other arthropods, which would

complement their visual acuity (Plotnick et al. 2010; Pat-

erson et al. 2011). Nevertheless, the scenario of Anomaloc-

aris feeding upon postecdysial, ‘soft-shelled’ trilobites,

whilst plausible, cannot account for the mineralized trilo-

bite fragments present in coprolites, unless Nedin’s

(1999) model is warranted. This model, which involves

A B

F G

I

D C

E

H

F IG . 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.

16 PALAEONTOLOGY

Anomalocaris lodging a trilobite in its oral cone and using

its appendages to break the trilobite exoskeleton by repeated

flexure, would undoubtedly cause damage to the oral cone

and appendages in the form of broken spines or scarring;

however, no damage of this type has been observed.

The considerable diversity of anomalocaridid frontal

appendages and oral cones (Whittington and Briggs 1985;

Chen et al. 1994; Hou et al. 1995; Nedin 1995; Collins

1996; Lieberman 2003; Briggs et al. 2008; Daley et al. 2009;

Caron et al. 2010; Daley and Budd 2010; Daley and Peel

2010; Daley and Bergstr€om 2012) indicates that these stem-

group arthropods had a varied diet and range of feeding

strategies. The functional morphology of the frontal

appendages suggests that some anomalocaridid taxa may

have been durophagous predators, whilst others fed exclu-

sively on soft-bodied organisms (Briggs 1979; Whittington

and Briggs 1985; Collins 1996; Nedin 1999; Daley and Budd

2010), which represent up to 98 per cent of individuals in

some Cambrian deposits (Caron and Rudkin 2009). Whilst

the presence of more than one anomalocaridid taxon in a

single Cambrian Konservat-Lagerst€atte is not unique (Da-

ley and Budd 2010), the co-occurrence of two similar-sized

Anomalocaris species from the Emu Bay Shale implies that

different feeding mechanisms might have been employed to

exploit disparate prey resources and alleviate interspecific

competition. Anomalocaris cf. canadensis, with its short,

stout ventral spines, was likely a durophagous predator or

scavenger, whereas the frontal appendages of A. briggsi were

too fragile for such a feeding mode (Nedin 1999). Anomal-

ocaris briggsi likely fed in a way comparable to that

described for Hurdia and Peytoia (= Laggania) (Whitting-

ton and Briggs 1985; Nedin 1995; Daley and Budd 2010),

with the appendages functioning like a net apparatus to trap

small prey items in their long spinose ventral spines as they

moved through the water column or through the substrate.

If anomalocaridids were not strictly durophagous pre-

dators, few other organisms in the Emu Bay Shale can be

identified as candidates for inflicting damage to trilobites

and producing large coprolites. Given the size of copro-

lites, prey fragments within some coprolites (individuals

of Redlichia >40 mm) and injured Redlichia (up to

210 mm in length), at least some of the predators may

have had a body size greater than 20 cm in length. A very

large, as yet unnamed species of Tuzoia (Garc�ıa-Bellido

et al. 2009) may have approached this length, but the

known appendages in another species of this genus (see

Caron et al. 2010, fig. DR4A–C) seem ill equipped to

handle trilobites, especially as Tuzoia is interpreted to be

free-swimming (Vannier et al. 2007). The only other

arthropod taxon of that size from the Emu Bay Shale

(other than the anomalocaridids) is Redlichia takooensis,

with a length of up to 25 cm (Paterson and Jago 2006).

Conway Morris and Jenkins (1985) suggested that the

injuries in Redlichia from the Emu Bay Shale may be the

result of cannibalism. In modern arthropod populations,

cannibalism is common, especially when other food

resources are limited (for reviews, see Fox 1975; Richard-

son et al. 2010). It is morphologically feasible that Redli-

chia was capable of durophagy, as redlichiids are known

to possess gnathobasic appendages (Shu et al. 1995;

Ramsk€old and Edgecombe 1996; Fortey and Owens 1999;

Hou et al. 2009). In some modern arthropods such as

Limulus, the nonmineralized (chitinous) gnathobases are

capable of crushing clam shells (Botton 1984; Shuster

et al. 2003), and Sidneyia from the Burgess Shale, which

has unmineralized gnathobasic limbs, has been found

with trilobite fragments in its alimentary tract (Bruton

1981), as have Utahcaris from the Spence Shale and an

undescribed fuxianhuiid from the Kaili biota, but the

trunk appendages of these latter two taxa are poorly

known (Conway Morris and Robison 1988; Zhu et al.

2004; Vannier and Chen 2005). The width of the alimen-

tary tract in Eoredlichia (Hou et al. 2009) and other

Cambrian trilobites (Chatterton et al. 1994; Lin 2007;

Lerosey-Aubril et al. 2012) is relatively consistent and

occupies approximately one-quarter of the axis, indicating

an alimentary tract up to 12 mm wide in the largest

known specimens of Redlichia. This would allow excretion

of solid faeces of the sizes represented by the sclerite-

dense portion of the coprolites from the Emu Bay Shale.

Regardless of durophagous tendencies, Anomalocaris

was undoubtedly a highly mobile visual predator, given

its large body size, spinose frontal appendages, triradial

mouth with a dentate inner margin, high-resolution com-

pound eyes and streamlined body with flexible body flaps

and a large tripartite tail fan. Whilst A. cf. canadensis

from the Emu Bay Shale cannot be completely ruled out

as a durophagous predator, it is likely that A. briggsi at

least was restricted to unmineralized prey items.

Acknowledgements. This research was made possible by funding

from Australian Research Council grants (LP0774959,

DP120104251) and a National Geographic Society Research &

Exploration grant (#8991-11), as well as financial assistance

from Beach Energy Ltd. and the South Australian Museum.

Logistical support was provided by SeaLink. ACD was supported

by grants from the Swedish Research Council (Veterskapsr�adet)

and the Palaeontological Association; DGB’s visits to Australia

were supported by grants from the Spanish Research Council

(CSIC, PA 1001105) and the Spanish Ministry of Science

(RYC2007-00090, CGL 2006-12254BTE and CGL 2009-07073).

We sincerely thank the Buck family for continued access to the

field site and acknowledge R. Atkinson, M. Binnie, G. Brock, A.

Camens, M. Gemmell, K. Kenny, P. Kruse, J. Laurie, B.

McHenry, N. Schroeder and E. Thomson for assistance in the

field and laboratory. This project benefitted from discussion and

support from our Emu Bay Shale research collaborators, M. Lee

and J. Gehling. Comments from D. Briggs, M. Wills and an

anonymous referee greatly improved the manuscript.


Editor. Philip Donoghue

SUPPORTING INFORMATION

Additional Supporting Information may be found in the online

version of this article:

Table S1. Anomalocaridid material from the Emu Bay Shale,

South Australian Museum collections.

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