The Mississippian Tetrapod Footprint Ichnogenus Palaeosauropus: Extramorphological Variation and Ichnotaxonomy

Palaeosauropus primaevus is a tetrapod footprint ichnotaxon first described from the Upper Mississippian (Visean) Mauch Chunk Formation near Pottsville, Pennsylvania, United States. Our relocation of the type locality and stratigraphic horizon of P. primaevus, a long-available but unstudied collection of tetrapod footprints from these strata, and our new collections allow a much fuller characterization of this ichnotaxon and the range of extramorphological variation encompassed by it. P. primaevus is characterized as the footprints of a quadruped with a pentadactyl pes and a tetradactyl manus, in which the pes frequently oversteps the manus and with which tail drags are common. In the manus, all digits are relatively broad and have rounded tips, digit III is longest, and digit IV is more widely separated from digit III than the other digits are from each other. The pes has five digits that are also wide and blunt-tipped, digit IV is longest, and digit V projects nearly laterally. P. primaevus is the track of a relatively large temnospondyl (～400 mm gleno-acetabular length) and documents the Mississippian presence of such large amphibians long before their body fossil record. Palaeosauropus also occurs in Mississippian strata in Indiana and is distinguished from the geologically younger but similar temnospondyl footprint ichnogenus Limnopus by its relatively narrower manus and pes that lack broad and rounded sole impressions.     

Amphibian Body Impressions from the Mississippian of Pennsylvania,USA

Temnocorpichnus isaacleai is a new ichnogenus and ichnospecies of temnospondyl amphibian body impression from the Mississippian (Visean) Mauch Chunk Formation of eastern Pennsylvania, United States. The shovel-shaped head, robust limbs, relatively short trunk and smooth integument diagnose the ichnotaxon and readily distinguish it from Hermundurichnus and Sauropleura, the only other named body impressions of Paleozoic tetrapods. Temnocorpichnus is a compound ichnogenus in which the footprint ichnogenus Batrachichnus is a behaviorally distinct component. The temnospondyl identity of Temnocorpichnus adds to the sparse and earliest records of temnspondyls, which are of Visean age. The smooth integument of the ichnogenus does not support the presence of ventral scales or armor in the earliest temnospondyls, but body proportions of the Mauch Chunk body impressions indicate a relatively terrestrial temnospondyl not matched by any taxon now known from bones. Three closely associated impressions of Temnocorpichnus on a single bedding plane suggest some sort of gregarious behavior in Mississippian temnospondyls and may support speculation that internal fertilization and associated courtship behavior evolved independently in one group of amphibians more than 300 million years ago.     

THE FISH AND AMPHIBIAN SWIMMING TRACES UNDICHNA AND LUNICHNIUM, WITH EXAMPLES FROM THE LOWER PERMIAN OF NEW MEXICO, USA

Abstract: The ichnotaxonomy and stratigraphic, geographic and environmental distribution of fish (Undichna) and amphibian (Lunichnium) swimming traces are reviewed. The ichnospecies of Undichna consist of various combinations of sinusoidal waves of differing complexity. Some of the more complex ichnospecies are made up of elements of the simpler forms, and morphological subset relationships between them are presented. Such subset series represent potential taphoseries relationships (i.e. preservational variants that reflect, for example, undertrails), or series of minor behavioural variations. Such a system can be used to highlight that different ichnospecies occurring at a locality may be taphonomic or minor behavioural variants of each other. Caution should, therefore, be exercised before erecting new ichnospecies on the basis of limited material if its morphology is a subset of an existing ichnospecies. However, the naming of such simpler ichnospecies is valid if they represent a recurrent morphology, and it is valid to erect new ichnospecies whose morphology is not a subset of an existing ichnospecies. Specimens that demonstrate intergradation between ichnotaxa can be used to justify their synonomy. Ichnotaxonomic revisions reduce the number of ichnospecies in Undichna from 14 to nine. U. radnicensis, a highly variable ichnospecies, is synonymized with U. britannica on the basis of material from China that demonstrates they can intergrade. U. prava is a partial U. tricosta, which falls within the minimum diagnosis of U. simplicitas. U. gosiutensis is regarded as a subjective junior synonym of U. quina. U. westerbergensis, originally attributed to a ‘crossopterygian’ fish performing a tetrapod‐like gait, is reassigned as a distinct ichnospecies within Lunichnium because it demonstrates the same morphology, representing similar behaviour, albeit by a different producer. L. anceps and L. gracile are synonymized with L. rotterodium. New specimens of U. bina and L. rotterodium are also described from the Lower Permian Robledo Mountains Formation of southern New Mexico, USA.     

Isaac Lea's Palaeosauropus (= “Sauropus”) primaevus: A Review of His Discovery

In 1849, Isaac Lea named Sauropus primaevus for footprints from Mount Carbon, Pennsylvania, USA, then the oldest fossil vertebrate footprints reported. In 1902, O. P. Hay constructed a new ichnogenus Palaeosauropus for this ichnospecies. Palaeosauropus has been one of the most frequently reported Mississippian footprint ichnogenera in North America and remains a valid ichnotaxon. The holotype of Palaeosauropus (= “Sauropus”) primaevus (referred to as P. primaevus), consisting of a single manus/pes pair, is described and illustrated in Lea (1853) Lea, I. 1853. On the fossil foot-marks in the Red Sandstones of Pottsville, Schuylkill County, Penna. Transactions of the American Philosophical Society, 10(new series): 307–315.  [Google Scholar] and is housed at the Academy of Natural Sciences in Philadelphia, Pennsylvania (ANS9752). Lea's large specimen of P. primaevus (approximately 86 cm by 53 cm), that included a trackway of six manus/pes pairs, described and illustrated in 1853 and 1855, was a combination of ANS9752 and a second specimen represented by a plaster cast housed at the National Museum of Natural History (USNM487148). Historical documents and examination of the Mauch Chunk Formation at Mount Carbon, Pennsylvania, enabled the identification of Lea's tracksite, originally reported to be a few hundred feet (about 75 m) from the former Mount Carbon Hotel. Our forensic evidence indicates the type locality for P. primaevus is approximately 90 m south from the southwest corner of Centre and Main Streets in Mount Carbon, Pennsylvania, with geographical coordinates of N 40° 40' 25.7”, W 76° 11' 14.9”. The type locality is within the middle member of the Mauch Chunk Formation, a fluvial sequence of late Mississippian (Visean) Age.     

The fish swimming trace Undichna unisulca from the Silurian of Sweden: probably the oldest vertebrate locomotion trace fossil

The fish swimming trace Undichna unisulca is reported from a sandstone block collected from the Upper Silurian (Ludlow) Burgsvik Formation of Gotland, Sweden. It represents the oldest record of a vertebrate trace (apart from coprolites), predating previous finds from the Lower Devonian by at least 10 Ma. A thelodont or acanthodian fish may have produced the sinusoidal trails with the aid of their caudal or anal fins while browsing slowly over the sediment whilst searching for food.     

Reinterpretation of crinoid-platyceratid interaction

The well-known association of platyceratid gastropods with crinoids has traditionally been considered an example of coprophagous commensalism. The Occurrence of several crinoid 'stands' ( Platycrinites sp.) from closely spaced bedding surfaces in the upper Mississippian Wymps Gap Limestone member of the Mauch Chunk Formation of southwestern Pennsylvania encourages reinterpretation of this relationship. Crinoid calyces were collected from five separate clusters, two of which contained associated platyceratids. 'Infested' crinoids either died prematurely or were stunted, compared to crinoids in the 'uninfested' clusters. Platyceratid attachment apparently had an adverse effect upon crinoid growth. Serial acetate peels show positioning of the gastropod on the crinoid tegmen over a highly developed anal tube, or chimney. However, the terminus of the anal tube abuts the gastropod's shell and is poorly situated for fecal ingestion by the snail. We suggest that the snail probably pursued another trophic strategy, perhaps taking advantage of aerosol filtration by the crinoid and elevation above the substrate.     

The Fish Trail Undichna quadrisulcata isp. nov. from the Eocene of Spitsbergen

Abstract

Undichna quadrisulcata isp. nov. is described from the Eocene of Spitsbergen, where it occurs together with xiphosuran (horseshoe crabs) traces in upper shoreface to foreshore deltaic sandstone. This is the first record of a marine (deltaic) Undichna from the Eocene. The trail consists of two or three pairs of paralleling sinusoidal grooves (in epirelief) or ridges (in hyporelief). Previous records of this trace fossil from the Carboniferous and Permian were assigned to U. insolentia Anderson, 1976 Anderson, A. M. 1976. Fish trails from the early Permian of South Africa. Palaeontology 19(2): 397–409. [Google Scholar], which, however, comprises a more complex pattern. The repeated occurrence of U. quadrisulcata isp. nov. in the Carboniferous, Permian, Triassic and Eocene, independent from U. insolentia, justifies its own ichnospecies name and suggests a different kind of producer. U. quadrisulcata isp. nov. is interpreted as a fish trail, probably produced by a representative of Amiiformes (actinopterygian, ray-finned fish) or coelacanth fish.     

Middle Pennsylvanian Ichnofauna from Eastern Oklahoma,USA

The Keota site, in the Middle Pennsylvanian (Desmoinesian) Keota Sandstone Member, McAlester Formation (Krebs Group) of Haskell County, Oklahoma, yields an extensive ichnofossil assemblage of arthropod trackways, insect resting traces, arthropod feeding and grazing traces, fish swimming traces, and tetrapod footprints. This ichnofossil assemblage occurs in a 0.8 to 1.5-m-thick unit of thinly laminated and ripple-laminated sandstone at the base of the Keota Sandstone Member that is interpreted as a tidal flat sandstone. The arthropod traces are assigned to the ichnotaxa Diplichnites gouldi Gevers types A and B, Diplopodichnus biformis Brady, Paleohelcura tridactyla Gilmore, Tonganoxichnus buildexensis Mángano, Buatois, Maples and Lanier, Gordia marina Emmons, cf. Cochlichnus sp. and Treptichnus bifurcus Miller. The fish swimming traces are assigned to Undichna britannica Higgs, and the tetrapod tracks to Notalacerta ichnosp. and Pseudobradypus ichnosp. The Keota ichnofossil assemblage thus documents the first North American Pennsylvanian record of Paleohelcura tridactyla and the first record of Pseudobradypus from the western United States. This ichnofossil assemblage also provides compelling evidence of a freshwater habitat in a tidal flat setting during deposition of the fossil-bearing sandstone at the Keota site. Indeed, the Keota ichnofossil assemblage is characteristic of a Carboniferous-Permian Tonganoxichnus assemblage that identifies nonmarine tidal flat settings.     

Thinopus and a Critical Review of Devonian Tetrapod Footprints

Devonian tetrapod tracks and trackways can be recognized by three criteria: morphology of the manus and pes impressions that matches known Devonian tetrapod skeletal morphology, manus smaller than pes, and the alternating trackway pattern that results from lateral sequence walking in quadrupedal tetrapod locomotion. The first reported Devonian tetrapod track, named Thinopus antiquus, from Pennsylvania, is not a tetrapod track and is likely an impression of a fish coprolite(s). A critical review of the published Devonian track record indicates only three can be verified as produced by a tetrapod trackmaker—Genoa River, Australia; Easter Ross, Scotland; and Valentia Island, Ireland. The supposed tetrapod tracks from the Middle Devonian of the Zache?mie quarry, Poland, fail the criteria for identification as Devonian tetrapod tracks. Indeed, no convincing case has been made that the Zache?mie structures are tetrapod tracks. Instead, they are reinterpreted as fish nests/feeding traces (ichnogenus Piscichnus). The oldest Devonian tetrapod trackway is Givetian and this is the oldest record of a tetrapod, but the sparse record of Devonian tetrapod tracks is of no other biostratigraphic and little paleobiogeographic significance. Bona fide Devonian tetrapod tracks are from nonmarine facies, so they do not support a marginal marine origin of tetrapods. They indicate lateral sequence walking and pelvic-limb-propelled, fully terrestrial (subaerial) locomotion in freshwater environments by at least some Devonian tetrapods.     

Late Mississippian vertebrate palaeoecology and taphonomy,Buffalo Wallow Formation,western Kentucky,USA

Aquatic vertebrates are reported from several facies of the Late Mississippian (Chesterian/Elviran/Serpukhovian) Buffalo Wallow Formation in western Kentucky, USA. Rhizodont bones and the partially articulated skeleton of a large anthracosaur (proterogyrinid) were found in rocks interpreted as a fluvial‐estuarine palaeochannel. Smaller, disarticulated tetrapod remains (anthracosaurs, whatcheeriids) were found in a weathered siltstone in an apparent channel margin‐sand flat facies. A putative oxbow‐abandoned channel facies contains skeletal elements of rhizodonts (cf. Rhizodus), colosteiids, Gyracanthus, Ageleodus, Cynopodius, xenacanthoids and palaeonisiciforms. Near the top of the channel fill, lungfish (cf. Tranodis) are found in carbonate‐rich nodules, which appear to be aestivation burrows. A presumed lacustrine facies contained a near‐complete colosteid. Thinning section, palaeosols, pedogenically‐altered carbonates and missing strata suggest tectonic and climatic overprints upon these depositional sequences. Multiple, incised channels in a low‐accommodation setting are interpreted to have provided local faunal traps for aquatic vertebrates. Late Mississippian palaeoclimate changes may have caused water table fluctuations, which might have aided in trapping and preserving aquatic vertebrates.     

Sublethal injuries in non-marine microconchid tubeworms from the Lower Carboniferous of West Virginia,USA

More than 10,000 non-marine microconchid tubeworms (order Tentaculita) from the Lower Carboniferous (Mauch Chunk Group) of West Virginian, USA, have been inspected with respect to the occurrence of specimens having repaired injuries. The inspection showed that only nine specimens bear distinct regenerations of their tubes which constitute only 0.08% of the total specimens. This value, although much lower than that obtained from other encrusting tentaculitoid tubeworms, is very similar to that calculated before for the thousands of Early Devonian planktonic tentaculitids. This clearly indicates that sample size (specimen number) is critical for obtaining the reliable data about the proportion of regenerated vs. unaffected specimens. The sublethal injuries present in these few individuals probably resulted from failed predation, most probably by grazing fishes. However, the repaired injuries only indicate that some individuals survived but do not provide any information about the predation intensity on the group in the given paleoenvironment. Microconchids encrusted a given substrate in large quantities, so grazing fishes may have easily removed the majority of individuals, leaving no trace of predation activity in the Early Carboniferous, non-marine paleoenvironments of what is now West Virginia.     

A tetrapod footprint assemblage with possible swim traces from the Jurassic–Cretaceous boundary,Anning Formation,Konglongshan, Yunnan,China

A small tetrapod footprint assemblage from the Anning Formation (Upper Jurassic–Lower Cretaceous) at Konglongshan Town, Yunnan Province, China, contains possible swim traces attributable to theropod dinosaurs based on their tridactyl and mesaxonic pes morphology. Morphotypes are tentatively assigned to the ichnogenera Characichnos and Wintonopus, a third one is similar to Hatcherichnus. Due to the inherent variability observed in tetrapod swim tracks, the names are used here informally describing footprints that reflect a distinct trackmaker behavior rather than anatomically accurate images of the pes anatomy. Variation of the imprint shape is obviously due to extramorphological effects and does not indicate taxonomic diversity of trackmakers. Elongate, slender impressions associated with these tracks are discussed here as possible tail traces. Trackmakers were possibly buoyant and active swimming individuals touching and scratching the bottom of deeper waterbodies with the distal ends of their digits. The orientation of the traces perpendicular to preserved ripples suggest cross-current movement and activities.     

A fish and tetrapod fauna from Romer's Gap preserved in Scottish Tournaisian floodplain deposits

The end‐Devonian mass extinction has been framed as a turning point in vertebrate evolution, enabling the radiation of tetrapods, chondrichthyans and actinopterygians. Until very recently ‘Romer's Gap’ rendered the Early Carboniferous a black box standing between the Devonian and the later Carboniferous, but now new Tournaisian localities are filling this interval. Recent work has recovered unexpected tetrapod and lungfish diversity. However, the composition of Tournaisian faunas remains poorly understood. Here we report on a Tournaisian vertebrate fauna from a well‐characterized, narrow stratigraphic interval from the Ballagan Formation exposed at Burnmouth, Scotland. Microfossils suggest brackish conditions and the sedimentology indicates a low‐energy debris flow on a vegetated floodplain. A range of vertebrate bone sizes are preserved. Rhizodonts are represented by the most material, which can be assigned to two taxa. Lungfish are represented by several species, almost all of which are currently endemic to the Ballagan Formation. There are two named tetrapods, Aytonerpeton and Diploradus, with at least two others also represented. Gyracanths, holocephalans, and actinopterygian fishes are represented by rarer fossils. This material compares well with vertebrate fossils from other Ballagan deposits. Faunal similarity analysis using an updated dataset of Devonian–Carboniferous (Givetian–Serpukhovian) sites corroborates a persistent Devonian/Carboniferous split. Separation of the data into marine and non‐marine partitions indicates more Devonian–Carboniferous faunal continuity in non‐marine settings compared to marine settings. These results agree with the latest fossil discoveries and suggest that the Devonian–Carboniferous transition proceeded differently in different environments and among different taxonomic groups.     

The First Stem Tetrapod from the Lower Carboniferous of Gondwana

The first stem tetrapod from Gondwana, Ossinodus pueri gen. et sp. nov, is described from fragmentary material that includes a skull table and many important parts from the postcranial skeleton. It was recovered together with a typically non-marine to marginal (near) marine fish fauna from the Lower Carboniferous (mid Viséan) Ducabrook Formation, Queensland, Australia. Phylogenetic analysis hypothesises that Ossinodus belonged to a clade that includes Whatcheeria and Pederpes , positioned on the stem of the crown tetrapods, one step crownward of Tulerpeton . Hind limb morphology suggests that small specimens of Ossinodus were primarily aquatic but that larger ones were less so.     

Crocodile swim tracks from the latest Cretaceous of Europe

Recently discovered evidence of tracks in the continental beds of the Late Cretaceous Tremp Formation in the southern Pyrenees (NE Iberian Peninsula) has been identified as scratch marks made by buoyant crocodiles. The tracks are preserved in two distinct environments and substrates (marly limestones originating in a littoral mud flat and fine‐grained sandstones deposited in fluvial settings). Most of the crocodylian traces are ascribed to ichnogenus Characichnos, whereas a single plantigrade pes track is assigned to ichnogenus cf. Crocodylopodus. The crocodylian swim traces (Characichnos ichnofacies) found in the early and late Maastrichtian co‐occur with Brontopodus ichnofacies attributable to terrestrial tetrapods (titanosaur sauropods, cf. Brontopodus ichnogenus; and hadrosaurid ornithopods, Hadrosauropodus ichnogenus). Analysis of the tracks allows the interpretation of palaeoenvironmental settings and track production. Thus, in lagoonal environments, swim tracks of crocodylians were produced during the rise of the water level in successive tide cycles; in fluvial settings, the swim traces of crocodylians were produced within the channel at the low‐water stage. To date, there are no reports of Late Cretaceous crocodylian tracks in Europe, and the studied evidence represents the first and youngest track record of the group in the latest part of the Cretaceous (C29r) in this continent and probably in the world.     

Conodont chronostratigraphical resolution and Declinognathodus evolution close to the Mid‐Carboniferous Boundary in the Barcaliente Formation type section,NW Spain

The Barcaliente Formation in its type section provides significant conodont occurrences in the Mid‐Carboniferous Boundary interval (between the Mississippian and Pennsylvanian sub‐periods). A sequence of Declinognathodus morphotype appearances (considered here as species) is recognized from the uppermost Serpukhovian to the lower Bashkirian. These morphotypes belong to Declinognathodus noduliferus (Ellison & Graves) sensu lato, the primary marker for the worldwide correlation of the Mid‐Carboniferous Boundary. Among them, D. inaequalis (Higgins) appears to have been the first species to occur at the Mid‐Carboniferous Boundary bed in the Arrow Canyon GSSP. A morphocline between D. bernesgae (Sanz‐López et al.) and D. inaequalis is studied here to identify the bed correlated with the GSSP. Other diagnostic first occurrences of conodonts (Rachistognathus minutus (Higgins & Bouckaert), D. noduliferus, D. lateralis (Higgins & Bouckaert), Idiognathoides asiaticus Nigmadganov & Nemirovskaya and I. corrugatus (Harris & Hollingsworth)) are evaluated as chrono‐markers throughout their worldwide distribution, particularly for the Eurasian faunas. The available secondary markers provide a better resolution and support chrono‐correlation in sections other than that at the GSSP. The worldwide first and late occurrences of studied taxa are considered within the background of the Mid‐Carboniferous Extinction Event and the conodont overturn, where crises progenitor Declinognathodus gave rise to members of the Family Idiognathodontidae. Firstly, progenitor taxa are good biostratigraphic tools, whereas local extinction of genera considered Mississippian in age and new taxa arising later in the post‐crises radiation suggest an early Bashkirian palaeogeography and climatic conditions confining temporarily the biogeographic distribution of conodonts.     

THE SYSTEMATIC POSITION OF EOGINKGOITES

Eoginkgoites is a fan-shaped, imparipinnate leaf with a short rachis and long petiole. It was first described from the Upper Triassic Newark Group of Pennsylvania by Bock who assigned the fossil to the Ginkgoales. The fossil has also been found in the Upper Triassic Chinle Formation in Utah and Arizona and in the Newark Group in North Carolina. Investigation of the well-preserved specimens found in the Chinle Formation shows that the leaf has anastomosing venation, a marginal vein and paracytic (syndetocheilic) stomata. These characters indicate that the leaf is bennettitalean and Eoginkgoites is reassigned to the Bennettitales although its shape is perplexing. Eoginkgoites may be an important index fossil to the lower Upper Triassic (middle Carnian) rocks of North America.     

Revision of Iquius nipponicus Jordan 1919 (Teleostei: Cyprinidae) from the Miocene of Iki Island, Nagasaki, Japan and its phylogenetic position

Iquius nipponicus Jordan 1919 was described on the basis of a single specimen from the Miocene of Iki Island, Nagasaki, Japan, and was tentatively assigned to the family Clupeidae. The holotype consists of the anterior portion of the body (lacking the anal and caudal fins and most of the caudal vertebrae), and is re-examined. The species is re-described based on additional specimens from the type locality. This species possesses an extremely stout third dorsal spine-like fin ray with a smooth posterior edge, an expanded anterior portion of the maxilla covering approximately half of the bone, 13 branched anal fin rays, and 22 abdominal and 16 caudal vertebrae. A phylogenetic study using the character matrix from a previous study suggests that the species forms a clade with xenocyprinins, but it differs from xenocyprinins in the form of the maxilla and the dentary and the numbers of branched anal fin rays and vertebrae. The present study concludes that the genus Iquius does not belong to the family Clupeidae. Iquius is a distinct and valid genus that is closely related to cultrins and xenocyprinins of the family Cyprinidae.     

A carboniferous chondrichthyan assemblage from residues within a Triassic karst system at Cromhall quarry,Gloucestershire, England

Abstract. Sixteen different Lower Carboniferous (Tournaisian Courceyan to Chadian age, Mississippian) chondrichthyan teeth types have been extracted from Triassic erosional/aeolian fills in shallow karst systems found in the limestone quarry at Cromhall, Gloucestershire, England. These Carboniferous teeth have been found within a much larger assemblage of disarticulated bones and teeth belonging to small late Triassic terrestrial reptiles, for which Cromhall quarry is famous. The Carboniferous teeth are derived fossils, released during subaerial dissolution of the surrounding limestones. Owing to low specimen numbers and uncertainty of intraspecific character, 10 types of teeth are left in open nomenclature, although it is likely they represent new taxa. They belong to Jalodus, Ctenacanthiformes, Protacrodus, Orodus, Chomatodus, Petalodontidae, Euchondrocephali?, Helodus and Psephodus. A new genus and species, Cromhallia parvunda, of indeterminate phylogenetic relationships, is also erected. The assemblage includes also an identified suite comprising Thrinacodus ferox, Bransonella cf. nebraskensis and Stethacanthus cf. altonensis. The identification of all fish teeth found in the Cromhall assemblages as derived fossils from the Carboniferous removes any ambiguity regarding the fully terrestrial nature of the late Triassic fauna preserved in the residue‐bearing karst systems.     

New trace fossil evidence for eurypterid swimming behaviour

We describe a recently discovered trace fossil from a eurypterid Konservat‐Lagerstätte in the upper Silurian Tonoloway Formation of Pennsylvania, and formally describe contemporaneous traces from the Williamsville Formation Lagerstätte of Ontario. The traces from both localities are assigned here to Arcuites bertiensis igen. et isp. nov. Based on comparisons with previously described eurypterid trackways, neoichnological experiments, and the co‐occurrence with eurypterid remains, Arcuites is interpreted as having been made by the swimming leg (sixth prosomal appendage) of swimming juvenile to adult eurypteroid eurypterids, and represents the first unambiguous trace fossil evidence for eurypterid swimming behaviour. The morphology of Arcuites indicates that eurypteroid eurypterids swam using drag‐based rowing, whereby the animal propelled itself forward by moving its oar blade‐like swimming paddles in an in‐phase backstroke. Arcuites morphology also indicates that the eurypteroid swimming appendage had a greater degree of movement than was previously suggested, and a revised rowing model is proposed. Differences in the abundance of A. bertiensis in the Tonoloway and Williamsville formations suggest a bathymetric control on eurypterid swimming behaviour and trace production. The association of Arcuites with eurypterid body fossils in both units indicates that these Lagerstätten were autochthonous assemblages and provides additional evidence for eurypterid inhabitation of shallow subtidal marine environments in the late Silurian.