Ichnology of the Devonian (Emsian) Campbellton Formation, New Brunswick, Canada. (2024)

[Traduit par la redaction]

INTRODUCTION

The Devonian (Emsian) Campbellton Formation, exposed along theRestigouche River--Chaleur Bay shoreline in northern New Brunswick,Canada, has been the focus of numerous studies since the late 1800s.Most work has described the flora, which is best preserved toward theeastern exposure of the formation (Kennedy et al. 2012a). Many of thedescribed plant-fossil localities occur higher in the CampbelltonFormation, cropping out from west of Maple Green to east of Point La Nim(Fig. 1A). The formation is known for its rich flora ofzosterophyllophytes, trimerophytes and lycopsids (Gensel and Andrews1984) and was one of the first sources of Devonian plants to bedescribed in the literature (Dawson 1859). More recently an assemblageof terrestrial arthropods, including Eoarthropleura and disarticulatedscorpion cuticle remains (Shear et al. 1996), the millipede Gaspestriagenselorum (Wilson 2006), and the eurypterid cf. Parahughmilleria(Miller et al. 2012), attributed to a near-shore lacustrine environment,have been identified from the eastern end of the formation'sexposure, near Point La Nim.

Fewer plants, including Psilophyton crenulatum (Doran 1980) andSpongiophyton (Gensel et al. 1991), have been described toward thewestern exposure of the Campbellton Formation, near Campbellton andAtholville (Fig. 1A, B), where the base of the formation is inunconformable contact with Val d'Amour Formation rhyolite. Theso-called 'Atholville Beds' (Dineley and Williams 1968),exposed at Campbellton and Atholville, have been examined bypaleontologists since 1881 and have yielded ostracoderms, arthrodires,acanthodians and chondrichthyans (Whiteaves 1881, 1889; Woodward 1889,1892; Traquair 1890, 1893). Later detailed descriptions of the fishfauna are based on numerous fossils: acanthodians (Burrow et al. 2008),cephalaspids (Pageau 1969a; Belles-Isles 1989), chondrichthyans (Milleret al. 2003; Turner and Miller 2008) and placoderms (Young 1983), almostall from the breccia-mudstone at the eastern end of the 'AtholvilleBeds' in Campbellton. In addition to fish, the aquatic assemblageincludes eurypterids (Miller 2007a, 2007b), ostracods (Jones 1889) andgastropods (Whiteaves 1881).

The fauna of the Campbellton Formation was summarized by Kennedy etal. (2012b) but, although noted by these authors, ichnofossils were notdescribed or assigned to an ichnotaxon. The westernmost Atholvilleexposure of the formation, where ichnofossils occur, was likely neverfully examined by workers prior to the 1990s. A low diversityichnofossil assemblage discovered in 1995, represented byMonomorphichnus, ?Taenidium and Helminthoidichnites, was recovered fromsandstone-siltstone beds that lie above the basal vertebrate-bearingbreccia and below the mudstone beds that yielded the numerous eurypteridand fish remains (Fig. 2). The purpose of this paper is twofold: firstto document the only ichnofossils known from the Campbellton Formation;and second to propose that specimens of Monomorphichnus from theCampbellton Formation were produced by the feeding behavior of apterygotid eurypterid.

The ichnofossils Taenidium and Helminthoidichnites are ofteninterpreted as burrows produced by annelids and are typical ofdelta-front paleoenvironments. The presence of Monomorphichnus isintriguing and will be considered in more detail below. Monomorphichnushas typically been interpreted as having been produced by trilobites,some of the earliest interpretations suggesting that they are grazingtraces recording trilobites that made scratch impressions on a channelbed as they were carried along in a current (Crimes 1970; Fillion andPickerill 1990). Ichnospecies of Monomorphichnus described by Fillionand Pickerill (1990) are also suggestive of active sediment disturbance,rather than passive traces left by an animal moved by currents. Wedescribe traces identified as Monomorphichnus below and speculate on thetrace maker and the paleoecological implications. With the exception ofrare tasmanitids (prasinophyte algae) that suggest a marine connection(Blieck and Cloutier 2000), no truly marine fossils have been found inthe Campbellton Formation.

GEOLOGICAL SETTING

The Campbellton Formation was defined as largely fluvial in origin,composed of grey volcanic pebble and boulder conglomerate, grey toreddish arkosic sandstone, and dark grey mudstone with local thin coalbeds (Williams et al. 1985). These lithologies broadly make up the sixmain lithofacies described by Kennedy and Gibling (2011) that constitutethe fill of this subtropical basin: lacustrine with restrictedcirculation, marginal lacustrine, near-shore lacustrine, coastaldeltaic, braided alluvial plain, and proximal alluvium. The CampbelltonFormation is exposed along the banks of the Restigouche River--ChaleurBay, New Brunswick, in two sections (Wilson et al. 2004; Kennedy andGibling 2011): one in the west from Atholville to Campbellton; and theother in the east, from near Maple Green to near Dalhousie (Fig. 1A).Between Atholville and Campbellton (Fig. 1B) a discontinuous section isexposed for about 1.5 km. Forest cover and slumping obscures much of thesection. Along the shore in this section, the Campbellton Formationoverlies rhyolite of the Val d'Amour Formation (Wilson et al.2004). Kennedy and Gibling (2011) measured a total of about 17 m ofsection toward the Atholville end of the exposure (Fig. 2), wheresteeply inclined strata comprise a basal coarse breccia and a successionof interbedded sandstones and mudstones (Fig. 2).

At Campbellton, the unconformable upper contact with the overlyingCarboniferous Bonaventure Formation lies beneath the Restigouche River(Dineley and Williams 1968; Wilson et al. 2004). Some authors (Pageau1968, 1969a, b) have considered the Campbellton Formation outcrops to bepart of either the Battery Point Formation or the LaGarde and PirateCove formations (Wilson et al. 2004; Bourque et al. 2005), which arefound north of Chaleurs Bay in Gaspe, Quebec. Based on recentpalynological data, the Campbellton Formation is of Emsian age (Blieckand Cloutier 2000). The miospores belong to the Emphanisporitesannulatus--Camarozonotriletes sextantii Assemblage Zone (Richardson andMcGregor 1986), which corresponds approximately to the Polygnathusdehiscens to Polygnathus serotinus conodont zones of early Emsian toearly late Emsian age (Blieck and Cloutier 2000). McGregor (1973, 1977)considered the outcrops along the Restigouche River to be within thePragian 'caperatus-emsiensis' and early to late Emsian'sextantii-Grandispora' to 'annulatus-lindlarensis'spore zones. This places the age of these strata between thePragian-Emsian boundary at 407 [+ or -] 2.8 Ma and the end of Emsian at397.5 [+ or -] 2.7 Ma (Ogg 2004). Wilson et al. (2004) have provided analternative age for the Campbellton Formation, suggesting that itstraddles the Emsian-Eifelian boundary. Their interpretation is based ona radiometric date of 407.4 [+ or -] 0.8 Ma in the Val d'AmourFormation (Wilson et al. 2004). They recognized an angular unconformityseparating the Val d'Amour and Campbellton formations and suggestedan age difference of about 10 million years.

Kennedy and Gibling (2011) were the first authors to place theCampbellton Formation into a detailed sedimentological,paleoenvironmental and paleoecological context. Historically, thedepositional environment of the Campbellton Formation has beenconsidered fluvial (Dineley and Williams 1968; Williams et al. 1985) ordescribed as a coarsening-upward alluvial-lacustrine sequence (Rust etal. 1989; Gamba 1990; Wilson et al. 2004). Kennedy and Gibling (2011)described strata at the Atholville locality as reflecting amouthbar-delta front-prodelta setting (Fig. 1C). The horizon containingichnofossils can be placed within Kennedy and Gibling's'Section 1, Facies Association 4 Sandy Coastal-deltaic'setting (9 m above the base of the measured section; Fig. 2; Kennedy etal. 2012b; fig.4), which consists predominately of horizontally beddedsandstone and ripple cross-laminated sandstone, interbedded with lessermassive to laminated siltstone to fine sandstone, massive sandstone, andtrough-cross-bedded sandstone. Kennedy and Gibling (2011) and Kennedy etal. (2012b) interpreted the association as a sandy deltaic-proximalmouthbar environment with shifting channels and moderate to high energycurrent flow. Transported terrestrial plant debris is common throughout,with rare articulated and disarticulated aquatic fossils. Ichnofossilsoccur within a siltstone in a delta-front setting (Fig. 1C, 2).

BIOSTRATIGRAPHY

Within the mouthbar-delta-front-prodelta setting (Kennedy andGibling 2011; Kennedy et al. 2012b) three ichnotaxa,Helminthoidichnites, ?Taenidium and Monomorphichnus, have beenidentified from a single horizon in the delta front sediments. Above theichnofossil bed is a 2-m-thick mudstone (Fig. 2) attributed to aprodelta setting (Kennedy and Gibling 2011). This unit grades from adark-grey to black mudstone near its base to a brown mudstone at thetop. Near the base of the section plants, ostracods and eurypterids(Miller 1996; Miller 2007a), as well as fish (Kennedy et al. 2012b), arecommonly preserved. The upper brown mudstone is devoid of ostracods andhas few plant fossils, but has yielded a partially articulated shark(Miller et al. 2003), disarticulated cephalaspids, placoderms andacanthodians, and both articulated and disarticulated eurypterids(Miller 2007a).

The ichnofossil bed lies near the top of 10 m of interbeddedsiltstone and sandstone (Kennedy and Gibling 2011; Kennedy et al. 2012b)deposited in alternating mouthbar and delta-front environments (Fig. 2).These rocks have yielded abundant plant detritus, but only rare fish andpterygotid remains (Bourque et al. 2005). Ichnotaxa described here wererecovered by one of us (RFM) from a siltstone horizon within thissedimentary package (Fig. 1C). These specimens were collected at anundetermined distance above the unconformity with the rhyolites of theVal d'Amour Formation, which have been dated as 407.4 [+ or -] 0.8Ma (Kennedy and Gibling 2011).

METHODOLOGY AND MATERIALS

Specimens were collected in 1995 and 2012. All specimens wereexamined in the laboratory, coated in ammonium chloride, andphotographed with low raking light to accentuate the vertical relief andmorphology of the specimens' surface. Detailed measurements of thetraces were taken with a digital caliper for sub-millimeter precision ofthe width, length and spacing of the scratch traces. Specimens arereposited in the paleontology collection of the New Brunswick Museum,NBMG 20585-20588.

SYSTEMATIC ICHNOLOGY

Ichnogenus Helminthoidichnites Fitch 1850

Helminthoidichnites tenuis Fitch 1850

(Fig. 3A, 5C)

MATERIAL: NBMG 20585, 20587.

HORIZON AND LOCALITY: Campbellton Formation, Devonian (Emsian),Atholville, New Brunswick (47[degrees]59.792'N /66[degrees]42.730'W).

DIAGNOSIS: Unbranched narrow burrows that are straight to acutelycurved, in which individual traces do not cross or intersect. Theseburrows have a uniform width that can range up to a maximum of 3 mm.(From Hoffman and Mountjoy 2010.)

DESCRIPTION: Sample NBMG 20587 preserves three burrows; and sampleNBMG 20585 preserves two burrows that are sub parallel to each other anddo not overlap. Both sets of burrows are preserved in light-greysiltstone, vertically flattened to 1.14 mm high, and infilled with abuff to light-grey, very fine-grained sandstone. Length varies from28.37 mm to 59.55 mm, whereas widths vary only slightly around anaverage of 3.15 mm.

REMARKS: Helminthoidichnites is a tubular trace that can occur atthe surface or in the shallow subsurface. The ichnogenus is monospecificand is distinguished from Gordia in that an individual trace does notcross or loop itself. Helminthoidichnites is distinguished fromHelminthopsis in that it does not meander.

Ichnogenus ? Taenidium Heer 1877

? Taenidium isp. (Fig. 3B, C)

MATERIAL: NBMG 20588.

HORIZON AND LOCALITY: Campbellton Formation, Devonian (Emsian),Atholville, New Brunswick (47[degrees]59.792'N /66[degrees]42.730'W).

DIAGNOSIS: Straight to meandering burrows that are unbranched,unwalled, and backfilled in segments of tightly packed sediment thatvary considerably in width. The burrows have sharp boundaries that formnon-compart-mentalized or thin annulated segments perpendicular to thelength of the burrow. The burrows lack a defining lining (Keighley andPickerill 1994).

DESCRIPTION: Sample NBMG 20588 preserves a simple unbranchingcylindrical burrow preserved in convex hyporelief, with a length of106.9 mm and width, varying with vertical relief of surface exposure,from 19.4 mm to 23.9 mm. The burrow is unwalled and exhibits annulatedrib-like characteristic features on the surface. This surface texturetrends perpendicular to the direction of the burrow. Rib diameter rangesfrom 2.4 mm to 2.8 mm, with a spacing that varies between 1.2 mm and 1.4mm, and is continuous along the exposed burrow margin.

REMARKS: The taxonomic assignment of this specimen is unclear sincethe distinguishing feature of menisci-backfill within the burrows is notpreserved despite the clear annulations on the outer margin of thetrace. According to Keighley and Pickerill (1994), Taenidium isdistinguished from Beaconites and Ancorichnus in comprising burrows thatare unlined and lack definition around the margin, likely due to activebackfilling. The menisci may simply not be preserved internally due tothe uniform lithology that infills the burrow and are only preserved asannulations along the burrow's outer margin. Alternatively, theburrow may be uniformly filled, and the regular annulations are afeature of the excavation of the burrow along its margin rather than theresult of backfilling. if the latter is the case, it does not conform tothe generic concept for Taenidium or any other known ichnotaxon. Wequestionably assign the trace to Taenidium, as ?Taenidium as it mostclosely resembles this ichnogenus. Because we have only a singleexample, the preservation of the infill is poor, and the menisci islacking, we cannot attribute it to a species.

Ichnogenus Monomorphichnus Crimes 1970

Monomorphichnus multilineatus Alpert 1976 (Figs. 3A,D, 4A-E, 5A,B,D-I)

MATERIAL: NBMG 20584-20588.

HORIZON AND LOCALITY: Campbellton Formation, Devonian (Emsian),Atholville, New Brunswick (47[degrees]59.792'N /66[degrees]42.730'W).

DIAGNOSIS: A series of straight to sigmoidal ridges with paralleldig traces, the central traces being deeper than the outer traces (afterAlpert 1976).

DESCRIPTION: Five specimens with multiple examples ofMonomorphichnus multilineatus preserved as convex hyporelief ridges,with the trace ranging from weakly to strongly convex. The traces arecomposed of a series of straight to sigmoidal ridges. They have anoverall elliptical to lensoidal shape, and contain sets of parallel tosubparallel ridges interpreted as scratch traces. The individual traceshave a minimum length of 15 mm and a maximum length of 41.9 mm, andwidths vary from 13.4 mm to 32.1 mm. The length to width ratio variesslightly, from 1:1 to 1.4, such that overall the trace is only slightlylonger than wide. Ridges are spaced 1.6 mm to 2.2 mm apart with somevariability. in rare cases, traces are bilobate with a slightly concavedepression between the two sets of ridges. Each set of ridges isgenerally 8.6 mm wide and tapers at its termination on both sides(medially and proximally). The ichnofossils vary in depth, and thebedding surfaces on which Monomorphichnus is preserved do not representthe sediment-water interface but rather shallow underprints. Noassociated traces of legs or body impressions were observed.

REMARKS: First described by Crimes (1970) for traces preserved inthe Ffestiniog Stage of the Upper Cambrian from northern Wales,Monomorphichnus has now been described from sedimentary rocks spanningthe Cambrian (Crimes 1970; Narbonne and Hofmann 1987) to the Triassic(Shone 1979). Previously Monomorphichnus has been attributed to thetrilobite being dragged along the sediment-water interface by currents.Crimes (1970) also suggested that trilobites were grazing as they weredragged along, leaving behind linear drag impressions. Examples ofMonomorphichnus were described by Shone (1979), who attributed them toindeterminate arthopods with similar morphological traits to trilobites.

A comprehensive account of the ichnotaxonomy of Monomorphichnus wasprovided by Fillion and pickerill (1990). They reviewed the ichnogenusand considered its synonymy with other ichnogenera (Ctenichnites,Eoichnites, Taonichnites and Medusichnites), however they decided toretain Monomorphichnus due to ambiguity as to the whereabouts and statusof type specimens of these ichnogenera and given they are widely usedichnotaxon in literature they did not want to introduce confusion andthreaten nomenclatural stability. The taxonomic status ofMonomorphichnus is clearly in need of review, but this is beyond thescope of the current manuscript. Fillion and Pickerill (1990) emendedMonomorphichnus and included several new ichnospecies; but they stillspecified that it was made predominantly by trilobites being draggedacross the sediment by a current.

DISCUSSION

Helminthoidichnites, ?Taenidium and Monomorphichnus are preservedwithin delta-front sediments (Kennedy and Gibling 2011; Kennedy et al.2012b). Few other faunal remains have been recovered within thedelta-front--proximal-mouthbar setting of the Campbellton Formationdespite over more than 20 years of field visits to the beds yieldingichnofossils. A single chelicera of the eurypterid Pterygotus anglicus(NBMG 10237; Miller 2007a) has been found, as well as partial fin spinestentatively attributed to the shark Doliodusproblematicus (NBMG 10237,12074; see Miller et al. 2003 for a description). A fin spine identifiedas belonging to the acanthodian Ankylacanthus incurvus (NBMG 11976) (seeBurrow et al. 2008 for a description), and partial headshields ofCephalaspis sp. (NBMG 11971, 11972, 11973) have been previouslydocumented from this locality (Kennedy et al. 2012b). While rare in thedelta-front-proximal-mouthbar setting, all of these fossils arerelatively abundant several metres up-section in the prodelta setting(Burrow et al. 2008; Miller 1996; Miller 2007a; Miller et al. 2003),suggesting that eurypterids, cephalaspids, chondrichthyans andacathodians may have migrated across paleoenvironments. The tracesTaenidium and Helminthoidichnites are usually thought to have been madeby annelid worms. Although Monomorphichnus is most often attributed to atrilobite tracemaker, and are frequently preserved in deeper marineenvironments, the trace has also been described from shallow marine,fluvial and estuarine environments (Fillion and Pickerill 1990). Thisichnogenus has been preserved in rocks as young as Permian (Lucas et al.2005) and Triassic (shone 1979), where the authors suggested it couldhave been made by arthropods in non-marine settings, given thattrilobites do not extend into non-marine environments or beyond thePermian period. Extensive research has shown that the CampbelltonFormation was deposited in a non-marine environment, although distalconnections to normal marine environments may have been present (Blieckand Cloutier 2000). The lack of trilobites found in the formation,despite extensive collecting since the 1880s, is consistent with thepaleoenvironmental interpretations of a non-marine setting, andtherefore trilobites are not considered a plausible trace maker for theMonomorphichnus described here.

Jones (2011) described examples of superficially similar tracesfrom the Devonian Catskill Formation of Pennsylvania. These traces wereassigned to a new ichnospecies Undichna multilobata; Undichna representsfish-fin trails. These traces resemble those described here from theCampbellton Formation. They differ in being composed of 3-5 horizontalpaired sets of 'scratch marks' arranged into two linear paths.They were interpreted as the result of placoderm fish dragging orpushing off the sediment. The traces described herein are too irregularin their arrangement to be comparable to those described by Jones(2011).

Vertebrate origins for Monomorphichnus have been considered. Theplethora of disarticulated and articulated fish remains (Kennedy et al.2012b) from the Campbellton site has yielded fin spines with denticles(Burrow et al. 2008; Kennedy et al. 2012b), but these denticles, whichcould presumably produce parallel scratch impressions, are too small tobe a plausible candidate for the Monomorphichnus specimens. Largerspines previously identified as Climatius latispinosus are nowattributed the shark Doliodus problematicus (Miller et al. 2003) and notarranged in a way that could be responsible for Monomorphichnus. Thewell-documented paleoenvironment and inferred salinities of theCampbellton Formation exclude marine animals, and thus trilobites, aspossible trace producers, as mentioned above. Although one to onecomparisons are rarely possible between ichnofauna and biotaxa, and thepossibility of a hitherto unknown trace maker not represented amongknown body fossils in the Campbellton Formation cannot be fullyexcluded, we suggest that Monomorphichnus multilineatus as describedhere is attributed to pterygotid eurypterids. These are currently theonly known arthropods, except for ostracods, known from thevertebrate-bearing beds of Campbellton Formation and have morphologicalfeatures that closely fit the Monomorphichnus traces described here.

In the 'Atholville Beds' of the Campbellton Formationonly a single eurypterid species, Pterygotus anglicus, has beenidentified. This species is among the largest known arthropods, with abody length of two metres or more (Kjellesvig-Waering 1964; Chlupac1994). Chelicerae of different sizes have been identified in theAtholville exposure, indicating animals ranging in length from about 65to 170 cm (Miller 2007a). Based on our interpretation of traceformation, measurements of Monomorphichnus multilineatus suggest thatthe animal that made the traces was considerably smaller than themaximum size known for these eurypterids in the Campbellton Formation.

Kjellesvig-Waering (1964) concluded that there was no doubt thatmost pterygotids were marine, but also lived in nearshore areas such asbays, estuaries and lagoons. He compared them to present-day Xiphosura,which make incursions into brackish waters and up rivers into freshwaterenvironments. Trewin and Davidson (1996) considered that Pterygotusanglicus found in Early Devonian rocks of the Midland Valley of Scotlandspent their whole life in fresh water. The Early Devonian fish beds ofthe Midland Valley are considered lacustrine (Trewin and Davidson 1996;Braddy 2000, 2001), with Pterygotus anglicus at sites such asTillywhandland sharing 'Lake Forfar' with acanthodians(Mesacanthus, Ischnacanthus and Euthacanthus) and ostracoderms(Cephalaspis pagei). Trewin and Davidson (1996) suggested that since thefull size range of Pterygotus anglicus individuals is found in the lakebeds, it may have spent its full life cycle in fresh water. A'mass-moult-mate' hypothesis (Braddy 2001; Vrazo and Braddy2011) suggested that eurypterids migrated en masse into nearshore andmarginal environments such as lagoons to mate and then moult, as theyprobably required a quiet current-free place. As suggested by theseauthors, the brackish shoreline environments may have provided asuitable site for moulting, and perhaps account for a range of sizes ofindividuals from one small locality in the Campbellton Formation (Miller1996, 2007a). The single Pterygotus anglicus specimen recovered from thedelta-front setting supports the idea that the animals also migratedup-river.

Little evidence exists for the diet and feeding strategy ofpterygotid eurypterids. However, based on body morphology some areconsidered to have been active swimmers and top predators, probablyfeeding on fish (Elliott and Petriello 2011; McCoy et al. 2015; Miller2007a; Selden 1984). Selden (1984) considered the possible function ofpterygotid chelicera, concluding that the animals could rapidly extendthese organs during hunting and that the curved tip and multipledenticles of the chelicerae were effective in cutting up prey. Andersonet al. (2014) examined visual acuity in the pterygotid Acutiramuscummingsi and suggested that with its poor vision and cheliceralmorphology (see Laub et al. 2010) Acutiramus probably trapped, graspedand sliced weak soft-bodied prey rather than pursuing actively swimmingarmored prey. Anderson et al. (2014) concluded the ecological role ofAcutiramus may have been predation on thin-shelled and soft-bodied prey.McCoy et al. (2015) examined vision in other pterygotids from a smalldataset including Jaekelopterus and Pterygotus, the latter includingspecimen of Pterygotus anglicus (NBMG 10000) from the CampbelltonFormation. They concluded that these forms had more robust chelicera andbetter visual acuity than Acutiramus, and were thus active, visuallycapable predators. McCoy et al. (2015) also noted that Jaekelopterusvision was less acute in smaller specimens, suggesting vision improvedas the animals grew to adults. This might indicate that even ifPterygotus anglicus was an active high-level predator, as a juvenile itsvision may have been not as good. Pterygotids as a group probably haddiverse feeding strategies. Poschmann et al. (2016) reiterated this ideaand, based on visual capability and other body characteristics,considered the stylonurid Rhenopterus diensti as being adapted tocrawling on the substrate, feeding on slowmoving soft prey such asworm-like animals, as evidenced by trace fossils found in the samedeposits. Poschmann et al. (2016) concluded that the agile pterygotidJaekelopterus rhenaniae more likely chased active prey.

The morphology of Pterygotus anglicus (Fig. 6A-D) suggests that ifthe parallel scratch morphology of Monomorphichnus was made by thatanimal, it most likely resulted from sediment disturbance by either thepostcheliceral appendages, the gnathobases (Fig. 6C-D) and coxa (Fig.6C), or the denticles (Fig. 6A-B) on the fixed and free rami of thechelicera (Huxley and Salter 1859; Clarke and Ruedemann 1912; Miller2007a). Based on the size and number of striations preserved, we ruleout the postcheliceral appendages, which in Pterygotus anglicus aresimple and non-spiniferous. Seldon (1986) indicated that the anteriorwalking leg (limb II) of pterygotid eurypterids was not a slenderwalking leg, but a small palp, as illustrated by Huxley and Salter(1859). As the first postcheliceral appendage of Pterygotus anglicus isa palp, its purpose being sensation, locomotion, and feeding it couldpotentially create a trace in the sediment; however the Monomorphichnustraces always occur as a set of multiple, parallel scratches. Thegnathobases on the legs of Pterygotus anglicus (Huxley and Salter 1859;Miller 2007a) have 11 to 12 teeth and are located on the proximal end ofthe appendage (Fig. 6C-D). They are used for carrying or masticatingfood but, given their position on the body, may not have been used as ascoop to dig in the sediment.

The third possibility is that the chelicerae were used to dig orrake the sediment. Each chelicera has one curved terminal denticle, oneprimary denticle, and intermediate and smaller denticles in between, fora total of approximately 25 denticles. Raking or sieving the sedimentusing the chelicerae (Fig. 6A) might be responsible for theMonomorphichnus scratch morphology (Figs. 4, 5). Some arthropods, forexample crabs, use a raking or sieving feeding method (Hadlock 1980;Bauchau and PasselecqGerin 1988), including the hermit crab (Pagurusrubricatus) that uses its cheliped to excavate a shallow trench, anduses the chelicerae to transfer sediment and food to the mouth (Schembri1982). Tshudy and Sorhannus (2000) proposed a raking-and-sievingfood-gathering method for fossil decapods that possess cheliceraesimilar to those of pterygotids. Crayfish exhibit an array of feedingstrategies that have been described as opportunistic or generalist, andactively feed on fish similar to the methods used by eurypterids.Crayfish use multiple feeding strategies in addition to active predationincluding: foraging for benthic invertebrates, and scavenging ondeceased vertebrates and invertebrates, or as omnivores feeding onorganic plant matter (see Longshaw and Stebbing 2016 and referencestherein).

These strategies also vary with the seasons and different stages inlife cycles. We hypothesize that pterygotid eurypterids may have had amore diverse diet and feeding strategy than only the lie-and-waitpredation or active hunting of fish. We speculate that Pterygotusanglicus may have raked the sediment using chelicerae to dislodgeannelids responsible for ?Taenidium and Helminthoidichnites. This was aforaging strategy used by another eurypterid, Hibbertopterus, whichevolved specialized sweep-feeding appendages to rake soft sediment tocapture small invertebrates (Jeram and Selden 1993; Selden et al. 2005).Specimens of Monomorphichnus and Helminthoidichnites typically occurtogether on the same bedding surfaces (Fig. 3A and Fig. 5) and theformer may cross-cut the latter (Fig. 3A). We conclude that ifMonomorphichus multilineatus described from the Campbellton Formationwas produced by Pterygotus anglicus and is found directly associatedwith ?Taenidium and Helminthoidichnites, Pterygotus anglicus may havehad alternate feeding strategies during its life cycle, preying onsoft-bodi

doi:10.4138/atlgeol.2017.001

ACKNOWLEDGEMENTS

The authors thank J. McGovern and K. Kennedy for assistance anddiscussion in the field. We thank P. Getty, V. McCoy and an anonymousreviewer for their careful reviews of this manuscript and R. Fensome forhis thorough review and edits to the manuscript. We thank S. Lucas, N.Minter and L. Dafoe for useful taxonomic discussions.

REFERENCES

Alpert, S.P. 1976. Trilobite and star-like trace fossils from theWhite-Inyo Mountains, California. Journal of Paleontology, 50, pp.226-239.

Anderson, R.P., McCoy, V.E., McNamara, M.E., and Briggs, D.E. 2014.What big eyes you have: the ecological role of giant pterygotideurypterids. Biology letters, 10. https://doi.org/10.1098/rsbl.2014.0412

Bauchau, A.G. and Passelecq-Gerin, E. 1988. Adaptive structures tofilter-feeding in the sand crab Scopimera gordonae Serene and Moosa,1981 (Crustacea Decapoda Brachyura Ocypodidae). Indo-Malayan Zoology, 5,pp. 23-29.

Belles-Isles, M. 1989. Yvonaspis, nouveau genre d'Osteostraci(Vertebrata, Agnatha) du Devonien (Emsien--Eifelien) des Gres de Gaspe(Quebec, Canada). Canadian Journal of Earth Sciences 26, pp. 2396-2401.https:// doi.org/10.1139/e89-204

Blieck, A. and Cloutier, R. 2000. Biostratigraphical correlationsof Early Devonian vertebrate assemblages of the Old Red SandstoneContinent. In Palaeozoic vertebrate biochronology and globalmarine/non-marine correlation. Final Report of IGCP 328 (1991-1996).Edited by A. Blieck and S. Turner. Courier ForschungsinstitutSenckenberg, 223, pp. 223-269

Bourque, P.-A., Desbiens, S., and Gensel, P.G. 2005.Silurian-Devonian biota and paleoenvironments of Gaspe Peninsula andnorthern New Brunswick. North American Paleontology Conference 2005,Field Guide, NAPC 2005, Halifax, Nova Scotia, 143 p.

Braddy, S.J. 2000. Eurypterids from the Early Devonian of theMidland Valley of Scotland. Scottish Journal of Geology, 36, pp.115-122.

Braddy, S.J. 2001. Eurypterid palaeoecology: palaeobiological,ichnological and comparative evidence for a 'mass-moult-mate'hypothesis.

Palaeogeography, Palaeoecology, Palaeoclimatology, 172, pp.115-132. https://doi.org/10.1016/S0031 0182(01)00274-7

Burrow, C.J., Turner, S., Desbiens, S., and Miller, R.F. 2008.Early Devonian putative gyracanthid acanthodians from eastern Canada.Canadian Journal of Earth Sciences, 45, pp. 897-908.https://doi.org/10.1139/E08-033

Chlupac, I. 1994. Pterygotid eurypterids (Arthropoda, Chelicerata)in the Silurian and Devonian of Bohemia. Journal of the Czech GeologicalSociety, 39, pp. 147-162.

Clarke, J.M. and Ruedemann, R. 1912. The Eurypterida of New York.Memoirs of the New York State Museum, 14, Vol. 1 and 2, 628 p.https://doi.org/10.5962/bhl. title.66889

Crimes, T.P 1970. Trilobite tracks and other trace fossils from theUpper Cambrian of North Wales. Geological Journal, 7, pp. 47-68.https://doi.org/10.1002/ gj.3350070104

Dawson, J.W 1859. On fossil plants from the Devonian rocks ofCanada. Quarterly Journal of the Geological Society, London, 15, pp.477-488. https://doi.org/10.1144/GSL. JGS.1859.015.01-02.57

Dineley, D.L. and Williams, B.P J. 1968. The Devonian continentalrocks of the Lower Restigouche River, Quebec. Canadian Journal of EarthSciences, 5, pp. 945-953. https://doi.org/10.1139/e68-091

Doran, J.B. 1980. A new species of Psilophyton from the LowerDevonian of northern New Brunswick. Canadian Journal of Botany, 58, pp.2241-2262. https:// doi.org/10.1139/b80-259

Elliott, D.K. and Petriello, M.A. 2011. New poraspids (Agnatha,Heterostraci) from the Early Devonian of the western United States.Journal of Vertebrate Paleontology, 31, pp. 518-530.https://doi.org/10.1080 /02724634.2011.557113

Fillion, D. and Pickerill, R.K. 1990. Ichnology of the LowerOrdovician Bell Island and Wabana groups of Newfoundland.Palaeontographica Canadiana, 7, pp. 1-119.

Fitch, A. 1850. A historical, topographical and agricultural surveyof the County of Washington. Part 2-5. Transactions of the New YorkAgricultural Society, 9, pp. 753-944.

Gamba, C.A. 1990. Sedimentological and tectonic implications of thePoint la Nim and Campbellton formations, western Chaleur Bay, MaritimeCanada. Unpublished M.Sc. thesis, University of Ottawa, Ottawa, Ontario,249 p.

Gensel, P.G. and Andrews, H.N. 1984. Plant life in the Devonian.Praeger, New York, 380 p.

Gensel, P.G., Chaloner, W.G., and Forbes, WH. 1991. Spongiophytonfrom the late Lower Devonian of New Brunswick and Quebec, Canada.Palaeontology, 34, pp. 149-168.

Hadlock, R.P 1980. Alarm response of the intertidal snail Littorinalittorea (L.) to predation by the crab Carcinus maenas (L.). TheBiological Bulletin, 159, pp. 269-279. https://doi.org/10.2307/1541092

Heer, O. 1877. Flora fossilis helvetiae. Die vorweltliche Flora derSchweiz. Verlag J. Wurster & Co., Zurich, parts 3-4 (1877) pp.91-182.

Hofmann, H.J. and Mountjoy, E.W 2010. Ediacaran body fossils andtrace fossils in Miette Group (Windermere Supergroup) near SalientMountain, British Columbia, Canada. Canadian Journal of Earth Sciences,47, pp. 1305-1325.

Huxley, T.H. and Salter, J.W 1859. On the anatomy and affinities ofthe genus Pterygotus and description of new species of Pterygotus.Memoirs of the Geological Survey of the United Kingdom, Monograph 1, 105p.

Jeram A.J. and Selden PA. 1993. Eurypterids from the Visean of EastKirkton, West Lothian, Scotland. Transactions of the Royal Society ofEdinburgh: Earth Sciences, 84, pp. 301-308.https://doi.org/10.1017/S0263593300006118

Jones, T.R. 1889. Notes of the Palaeozoic bivalved Entomostraca No.XXVII. On some North American (Canadian) species. Annals and Magazine ofNatural History, 6, pp. 373-387.https://doi.org/10.1080/00222938909460354

Jones, WT. 2011. Ichnotaxonomy and paleoenvironmental analysis oftrace fossils in the Late Devonian Catskill Formation, north-centralPennsylvania, USA. Unpublished Ph.D. thesis, University of Kansas,Lawrence, Kansas, 237 p.

Keighley, D.G. and Pickerill, R.K. 1994. The ichnogenus Beaconitesand its distinction from Ancorichnus and Taenidium. Palaeontology, 37,pp. 305-338.

Kennedy, K. and Gibling, M.R. 2011. The Campbellton Formation, NewBrunswick, Canada: paleoenvironments in an Early Devonian terrestriallocality. Canadian Journal of Earth Sciences, 48, pp. 1561-1580.https://doi.org/10.1139/e11-055

Kennedy, K., Gensel, P.G., and Gibling, M.R., 2012a.Paleoenvironmental inferences from the classic Lower Devonianplant-bearing locality of the Campbellton Formation, New Brunswick,Canada. Palaios, 27, pp. 424-438.https://doi.org/10.2110/palo.2012.p12-004r

Kennedy, K., Miller, R.F., and Gibling, M.R., 2012b.Paleoenvironments of Early Devonian fish and other aquatic fauna of theCampbellton Formation, New Brunswick, Canada. Paleogeography,Paleoclimatology, Paleoecology, 361-362, pp. 61-72. https://doi.org/10.1016/j.palaeo.2012.08.002

Kjellesvig-Waering, E.N. 1964. A synopsis of the familyPterygotidae Clarke and Ruedemann, 1912 (Eurypterida). Journal ofPaleontology, 38, pp. 331-361.

Laub, R. S., V. P Tollerton Jr., and R. S. Berko f. 2010. Thecheliceral claw of Acutiramus (Arthropoda: Eurypterida): functionalanalysis based on morphology and engineering principles. Bulletin of theBuffalo Society of Natural Sciences, 39, pp. 29-42.

Longshaw, M. and Stebbing, P. 2016. Biology and ecology ofcrayfish. Taylor and Francis, Boca Raton, Florida, 325 p.https://doi.org/10.1201/b20073

Lucas, S.G., Minter, N.J., Spielmann, J.A., Hunt, A.P., and Braddy,S.J. 2005. Early Permian ichnofossil assemblage from the Fra CristobalMountains, southern New Mexico. The Permian of central New Mexico. NewMexico Museum of Natural History and Science Bulletin, 31, pp. 140-150.

McCoy, V.E., Lamsdell, J.C., Poschmann, M., Anderson, R.P., andBriggs, D.E. 2015. All the better to see you with: eyes and claws revealthe evolution of divergent ecological roles in giant pterygotideurypterids. Biology Letters, 11, 20150564.https://doi.org/10.1098/rsbl.2015.0564

McGregor, D.C. 1973. Lower and Middle Devonian spores of easternGaspe, Canada. I. Systematics. Palaeontographica Abteilung B, 142, pp.1-77.

McGregor, D.C. 1977. Lower and Middle Devonian spores of easternGaspe, Canada. II. Biostratigraphic significance. PalaeontographicaAbteilung B, 163, pp. 111-142.

Miller, R.F. 1996. Note on Pterygotus anglicus Agassiz(Eurypterida: Devonian) from the Campbellton Formation, New Brunswick.Atlantic Geology, 32, pp. 95-100. https://doi.org/10.4138/2080

Miller, R.F. 2007a. Pterygotus anglicus Agassiz (Chelicerata:Eurypterida) from Atholville, Lower Devonian Campbellton Formation, NewBrunswick, Canada. Palaeontology, 50, pp. 981-999.https://doi.org/10.1111/ j.1475-4983.2007.00683.x

Miller, R.F. 2007b. Nineteenth century collections of Pterygotusanglicus Agassiz (Chelicerata; Eurypterida) from the CampbelltonFormation, New Brunswick, Canada. Atlantic Geology, 43, pp. 197-209.https://doi. org/10.4138/5649

Miller, R.F., Cloutier, R., and Turner, S. 2003. The oldestchondrichthyan from the Early Devonian period. Nature, 425, pp. 501-504.https://doi.org/10.1038/nature02001

Miller, R.F., Kennedy, K., and Gibling, M.R. 2012. A eurypteridfrom the lacustrine facies of the Early Devonian Campbellton Formation,New Brunswick, Canada. Atlantic Geology, 48, pp. 14-19. https://doi.org/10.4138/atlgeol.2012.002

Narbonne, G.M. and Hofmann, H.J. 1987. Ediacaran biota of theWernecke Mountains, Yukon, Canada. Palaeontology, 30, pp. 647-676.

Ogg, J.G. 2004. Status of divisions of the International GeologicTime Scale. Lethaia, 37, pp. 183-199. https://doi.org/10.1080/00241160410006492

Pageau, Y. 1968. Nouvelle faune ichthyologique du Devonien moyendans les Gres de Gaspe (Quebec). I. Geologie et ecologie. NaturalisteCanadien, 95, pp. 1459-1497.

Pageau, Y. 1969a. Nouvelle faune ichthyologique du Devonien moyendans les Gres de Gaspe (Quebec). II. Morphologie et systematique.Premiere section: A. Eurypterides, B. Ostracodermes, C. Acanthodiens etSelaciens. Naturaliste Canadien, 96, pp. 399-478.

Pageau, Y. 1969b. Nouvelle faune ichthyologique du Devonien moyendans les gres de Gaspe (Quebec). II. Morphologie et systematique.Deuxieme section: Arthrodires: Dolicothoraci. Naturaliste Canadien, 96,pp. 805-889.

Poschmann, M., Schoenemann, B., and McCoy, V.E. 2016. Telltaleeyes: the lateral visual systems of Rhenish Lower Devonian eurypterids(Arthropoda, Chelicerata) and their palaeobiological implications.Palaeontology, 59, pp. 295-304. https://doi.org/10.1111/pala.12228

Richardson, J.B. and McGregor, D.C. 1986. Silurian and Devonianspore zones of the Old Red Sandstone continent and adjacent regions.Geological Survey of Canada, Bulletin, 364, 79 p. https://doi.org/10.4095/120614

Rust, B. R., Lawrence, D.A., and Zaitlin, B.A. 1989. Thesedimentology and tectonic significance of Devonian and Carboniferousterrestrial successions in Gaspe, Quebec. Atlantic Geology, 25, pp.1-13. https://doi. org/10.4138/1666

Schembri, PJ. 1982. Functional morphology of the mouthparts andassociated structures of Pagurus rubricatus (Crustacea: Decapoda:Anomura) with special reference to feeding and grooming. Zoomorphology,101, pp. 17-38. https://doi.org/10.1007/BF003 12028

Selden, P.A. 1984. Autecology of Silurian eurypterids, pp. 39-54.In Autecology of Silurian organisms (Vol. 32). Edited by M.G. Bassettand J.D. Lawson, J. D. Special Papers in Palaeontology, 32,Palaeontological Association, London, 295 p.

Seldon, P.A. 1986. A new identity for the Silurian arthropodNecrogammarus. Palaeontology, 29, pp. 629-631.

Selden, P.A., Corronca, J.A., and Hunicken, M.A. 2005. The trueidentity of the supposed giant fossil spider Megarachne. BiologyLetters, 1, pp. 44-48.

Shear, W, Gensel, P., and Jeram, A. 1996. Fossils of largeterrestrial arthropods from the Lower Devonian of Canada. Nature, 384,pp. 555-557. https://doi. org/10.1038/384555a0

Shone, R.W 1979. Giant Cruziana from the Beaufort Group. GeologicalSociety of South Africa Transactions, 82, pp. 371-375.

Traquair, R.H. 1890. Notes on the Devonian fishes of Scaumenac Bayand Campbelltown in Canada. Geological Magazine, 7, pp. 15-22.https://doi. org/10.1017/S0016756800146126

Traquair, R.H. 1893. Notes on the Devonian fishes of Campbelltownand Scaumenac Bay in Canada-No. 2. Geological Magazine, 10, pp. 145-149.https://doi. org/10.1017/S0016756800170232

Trewin, N.H. and Davidson, R.G. 1996. An Early Devonian lake andits associated biota in the Midland Valley of Scotland. Transactions ofthe Royal Society of Edinburgh: Earth Sciences, 86, pp. 233-246.https:// doi.org/10.1017/S0263593300007641

Tshudy, D. and Sorhannus, U. 2000. Pectinate claws in decapodcrustaceans: convergence in four lineages. Journal of Paleontology, 74,pp. 474-486. https://doi. org/10.1017/s0022336000031735

Turner, S. and Miller, R.F. 2008. Protodus jexi Woodward, 1892(Chondrichthyes), from the Lower Devonian Campbellton Formation, NewBrunswick, Canada. Acta Geologica Polonica, 58, pp. 133-145.

Vrazo, M.B. and Braddy, S.J. 2011. Testing the'mass-moult-mate' hypothesis of eurypterid palaeoecology.Palaeogeography, Palaeoclimatology, Palaeoecology, 311, pp. 63-73.https://doi.org/10.1016/j.palaeo.2011.07.031

Whiteaves, J.F. 1881. On some fossil fishes, Crustacea and Molluscafrom the Devonian rocks at Campbellton, N.B., with description of fivenew species. Canadian Naturalist and Quarterly Journal of Science, 10,pp. 93-101.

Whiteaves, J.F. 1889. Illustrations of the fossil fishes of theDevonian rocks of Canada, part II. Transactions of the Royal Society ofCanada, 6, pp. 77-96.

Williams, G.L., Fyffe, L.R., Wardle, R.J., Colman-Sadd, S.P, andBoehner, R.C. 1985. Lexicon of Canadian stratigraphy, Volume VI,Atlantic region. Canadian Society of Petroleum Geologists, Calgary, 572p.

Wilson, H.M. 2006. Juliformian millipedes from the Lower Devonianof Euramerica: implications for the timing of millipede cladogenesis inthe Paleozoic. Journal of Paleontology, 80, pp. 638-649. https://doi.org/10.1666/0022-3360(2006)80[638:JMFTLD]2.0. CO;2

Wilson, R.A., Burden, E.T., Bertrand, R., Asselin, E., andMcCracken, A.D. 2004. Stratigraphy and tectono-sedimentary evolution ofthe Late Ordovician to Middle Devonian Gaspe Belt in northern NewBrunswick: evidence from the Restigouche area. Canadian Journal of EarthSciences, 41, pp. 527-551. https://doi.org/10.1139/e04-011

Woodward, A.S. 1889. Acanthodian fishes from the Devonian ofCanada. Annals and Magazine of Natural History, 4, pp. 183-184.https://doi. org/10.1080/00222938909460500

Woodward, A.S. 1892. On the Lower Devonian fish-fauna ofCampbellton, New Brunswick. Geological Magazine, 9, pp. 1-6.https://doi.org/10.1017/S0016756800188533

Young, V.T. 1983. Taxonomy of the arthrodire Phlyctaenius from theLower or Middle Devonian of Campbellton, New Brunswick, Canada. Bulletinof the British Museum of Natural History 371, pp. 1-35.

Olivia a. King (1-2), Randall F. Miller (1) * and Matthew R.Stimson (1)

(1.) Steinhammer Palaeontology Laboratory, Natural ScienceDepartment, New Brunswick Museum, Saint John, New Brunswick E2K 1E5,Canada

(2.) Department of Earth Sciences, Dalhousie University, Halifax,Nova Scotia B3H 4R2, Canada

* Corresponding author <[emailprotected]>

Date received: 20 July 2016 f Date accepted: 29 November 2016

Editorial responsibility: Robert A. Fensome

Caption: Figure 1. (A) Location map of the Campbellton Formationalong the Restigouche River--Chaleur Bay shoreline, New Brunswick.Exposures to the east near Dalhousie Junction contain abundant plantsand terrestrial land animals. (B) Exposures to the west, nearCampbellton-Atholville, contain fish, pterygotid eurypterids andichnofossils. (C) Photograph of trace-fossil locality. (Modified afterKennedy et al. 2012b.)

Caption: Figure 2. Stratigraphic log of trace-fossil locality, partof the Campbellton Formation. (Modified after Kennedy et al. 2012b.)

Caption: Figure 3. (A) NBMG 20587, ichnofossil from the Devonian(Emsian) Campbellton Formation, with accompanying close up ofMonomorphichnus multilineatus (white arrows), and Helminthoidichitestenuis (black arrows). (B) NBMG 20588, ichnofossil from the Devonian(Emsian) Campbellton Formation featuring ?Taenidium. (C) Close-up of?Taenidium. (D) NBMG 20586, ichnofossil from the Devonian (Emsian)Campbellton Formation preserving Monomorphichnus multilineatus.

Caption: Figure 4. (A) NBMG 20584, ichnofossils from the Devonian(Emsian) Campbellton Formation. (B-E) close-ups of Monomorphichnusmultilineatus (white arrows).

Caption: Figure 5. (A) NBMG 20585, iehnofossil from the Devonian(Emsian) Campbellton Formation, (B) Interpretive sketch of NBMG 20585,with Monomorphichnus multilineatus and Helminthoidichnites tenuis, (C)Close-up of Helminthoidichnites tenuis on NBMG 20585, (D-I) Close-ups ofMonomorphichnus multilineatus on NBMG 20585.

Caption: Figure 6. (A) NBMG 10237, a single chelicera of theeurypterid Pterygotus anglicus from delta-front sediments (Kennedy etal. 2012b) of the Campbellton Formation (modified after Miller 2007b;figs, 1, 5). (B) NBMG 15170b a single chelicera of the eurypteridPterygotus anglicus from prodelta sediments (Kennedy et al. 2012b) ofthe Campbellton Formation. (C) NBMG 10132, a single gnathobase of coxaof the eurypterid Pterygotus anglicus from the Campbellton Formation,showing 12 denticles (Miller 2007b; fig.11). (D) Interpretive sketch ofgnathobase on coxa and walking legs of the eurypterid Pterygotusanglicus (Huxley and Salter 1859; plate XII). (E) Schematicreconstruction of a pterygotid eurypterid, illustrating identifiablestructures--chelicera, gnathobase and postcheliceralappendages--possibly responsible for Monomorphichnus (modified afterMiller 2007b; fig. 3). The morphology of the postcheliceral appendages'walking legs' of Pterygotus anglicus is not well-known fromthe Campbellton Formation specimens, the anterior limb (limb II) hereillustrated as a palp after Selden (1986).