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John Paterson

University of New England - Australia, Earth Sciences, Faculty Member

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John completed his Bachelor of Science majoring in geology and palaeontology at Macquarie University (Sydney) in 2000, and was awarded First Class Honours in 2001 for his research on Ordovician (470 million-year-old) fossils from western New South Wales. His PhD studies at Macquarie University (2002-2005) were centered on Cambrian to Ordovician (520 to 470 million-year-old) trilobites – an extinct group of marine arthropods that are distantly related to crustaceans and insects – from around Australia, including New South Wales, South Australia, Queensland and Victoria.

John’s research contributions have primarily focused on documenting the palaeo-biodiversity of Australian Cambrian and Ordovician biotas (ca. 444 to 541 million years ago) and using these key fossils to answer major questions relating to evolution, biogeography and palaeoecology during this critical time interval. He has also used these fossils in the relative dating and correlation of strata around the globe in order to refine the geologic timescale. The multidisciplinary nature of his work includes numerous publications on taxonomy, phylogeny, biostratigraphy, biogeography, taphonomy and palaeoecology.

John’s current research focuses on Cambrian (540-510 million-year-old) fossils, especially from the Flinders Ranges and the globally significant Emu Bay Shale Konservat-Lagerstätte on Kangaroo Island in South Australia. His main area of expertise lies in arthropods, although he also studies molluscs, brachiopods, “worms” and other enigmatic organisms. John is very active in the Australian and international palaeontological communities. He was the Secretary of the Association of Australasian Palaeontologists from 2006 to 2010, and is currently a Voting Member of the International Subcommission on Cambrian Stratigraphy.

Google Scholar profile: http://scholar.google.com.au/citations?user=aYcIfKwAAAAJ&hl=en
Address: Earth Sciences
University of New England
Armidale NSW 2351
Australia

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Papers by John Paterson

Jago, J.B., Bentley, C.J., Paterson, J.R., Holmes, J.D., Lin, T.-R. & Sun, X.-W., 2021. The stratigraphic significance of early Cambrian (Series 2, Stage 4) trilobites from the Smith Bay Shale near Freestone Creek, Kangaroo Island. Australian Journal of Earth Sciences, 68(2): 204–212.

Bicknell, R.D.C., Holmes, J.D., Edgecombe, G.D., Losso, S.R., Ortega-Hernández, J., Wroe, S. & Paterson, J.R., 2021. Biomechanical analyses of Cambrian euarthropod limbs reveal their effectiveness in mastication and durophagy. Proceedings of the Royal Society B, 288: 20202075.

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

Paterson, J.R., Edgecombe, G.D. & García-Bellido, D.C., 2020. Disparate compound eyes of Cambrian radiodonts reveal their developmental growth mode and diverse visual ecology. Science Advances, 6(49): eabc6721.

Radiodonts are nektonic stem-group euarthropods that played various trophic roles in Paleozoic ma... more Radiodonts are nektonic stem-group euarthropods that played various trophic roles in Paleozoic marine ecosystems, but information on their vision is limited. Optical details exist only in one species from the Cambrian Emu Bay Shale of Australia, here assigned to Anomalocaris aff. canadensis. We identify another type of radiodont compound eye from this deposit, belonging to 'Anomalocaris' briggsi. This ≤4-cm sessile eye has >13,000 lenses and a dorsally oriented acute zone. In both taxa, lenses were added marginally and increased in size and number throughout development, as in many crown-group euarthropods. Both species' eyes conform to their inferred lifestyles: The macro-phagous predator A. aff. canadensis has acute stalked eyes (>24,000 lenses each) adapted for hunting in well-lit waters, whereas the suspension-feeding 'A.' briggsi could detect plankton in dim down-welling light. Radiodont eyes further demonstrate the group's anatomical and ecological diversity and reinforce the crucial role of vision in early animal ecosystems.

Jago, J.B. et al., 2020. The Cambrian System in the Arrowie Basin, Flinders Ranges, South Australia. Australian Journal of Earth Sciences, 67(7): 923–948.

The lower to ?middle Cambrian rocks (Terreneuvian, Series 2 and possibly Miaolingian) of the Arro... more The lower to ?middle Cambrian rocks (Terreneuvian, Series 2 and possibly Miaolingian) of the Arrowie Basin are exposed superbly in the Flinders Ranges of South Australia. They comprise two major sedimentary packages: a lower carbonate-rich succession (Hawker Group and correlates) and an upper siliciclastic-dominated succession (Billy Creek Formation, Wirrealpa Limestone and Lake Frome Group). These rocks form one of the most complete lower Cambrian (Terreneuvian and Series 2) successions globally. They contain one of the most diverse known early Cambrian biotas in the world, with trilobites, archaeocyaths, bradoriides, brachiopods, some of the earliest known coralomorphs, small shelly fossils, molluscs, hyoliths, acritarchs and trace fossils. Series divisions, based on ranges of shelly fossils and archaeocyath biostratigraphy are currently being established. Ancient reef structures are prominent in several areas. Syndepositional faulting and diapiric activity affected sedimentation in places. The global significance of the region is enhanced by the presence of tuff horizons at some levels, which provide the opportunity to link the biostratigraphic zones with radiometric dates and carbon isotope curves. ARTICLE HISTORY

Holmes, J.D., Paterson, J.R. & García-Bellido, D.C., 2020. The trilobite Redlichia from the lower Cambrian Emu Bay Shale Konservat-Lagerstätte of South Australia: systematics, ontogeny and soft-part anatomy. Journal of Systematic Palaeontology, 18(4): 295–334.

The trilobite Redlichia Cossmann, 1902 is an abundant element of the lower Cambrian (Series 2, St... more The trilobite Redlichia Cossmann, 1902 is an abundant element of the lower Cambrian (Series 2, Stage 4) Emu Bay Shale (EBS) Konservat-Lagerst€ atte on Kangaroo Island, South Australia. Well-preserved, fully articulated specimens from this deposit are known to reach lengths of up to 25 cm, representing one of the largest known Cambrian trilobites. Until now, all Redlichia specimens from the EBS have been referred to Redlichia takooensis Lu, 1950, a species originally described from South China. Previous work recognized considerable differences in exoskeletal morphology among specimens of varying sizes, which was attributed to ontogeny. However, close examination of a large collection of recently acquired specimens shows that this variation actually represents two distinct morphs, interpreted here as separate species: R. takooensis, and a large, new species, Redlichia rex sp. nov. An analysis of morphological variation in holaspides ('adults') of the more common R. takooensis reveals considerable ontogenetic change occurred even during this later phase of growth. Some specimens of both Redlichia species from the EBS also exhibit exceptionally preserved soft-part anatomy, particularly the antennae and biramous appendages. Here, appendages (antenniform and biramous) and digestive structures are described, and biramous appendage reconstructions of R. rex sp. nov. are presented, which show a striking resemblance to some early Cambrian trilobites from South China. In particular, R. rex has a tripartite exopodite, as well as a dorsoventrally deep protopodite with gnathobasic spines used to shred or crush food items. Based on recent phylogenetic analyses, it is possible that an exopodite with tripartite subdivisions represents the plesiomorphic condition for Artiopoda (trilobites and kin). The digestive system of R. takooensis exhibits a series of paired digestive glands in the cephalon and anterior thorax, similar to those described for a number of other Cambrian and Ordovician trilobites. http://zoobank.org/urn:lsid:zoobank.org:pub:507BEAFC-4AFA-43F4-A5C4-49E4B58C658E

Smith, P.M., Brock, G.A. & Paterson, J.R., 2020. Shelly fauna from the Cambrian (Miaolingian, Guzhangian) Shannon Formation and the SPICE event in the Amadeus Basin, Northern Territory. Alcheringa, 44(1): 1–24.

Paterson, J.R., 2020. The trouble with trilobites: classification, phylogeny and the cryptogenesis problem. Geological Magazine, 157(1): 35–46.

Trilobites are an iconic group of extinct arthropods that lived in Palaeozoic oceans for c. 270 M... more Trilobites are an iconic group of extinct arthropods that lived in Palaeozoic oceans for c. 270 Ma, before their demise at the end of the Permian Period. Despite their considerable diversity (> 22 000 species) and abundance, particularly in Cambrian and Ordovician rocks, as well as intensive study for well over 200 years, trilobite systematics remains in a state of flux. In this contribution, the complex history of trilobite classification over the last century is briefly reviewed, including the seminal scheme published by Henry Swinnerton in 1915. The cryptogenesis problem, which relates to the supposedly obscure phylogenetic links between major post-Cambrian trilobite clades and their Cambrian sister taxa, is also discussed. Previous studies have suggested that the cryptogenesis problem is largely a taxonomic artefact, but the Cambrian origins of some post-Cambrian groups, such as the orders Proetida and Odontopleurida, are still unclear. Future directions for research on trilobite systematics are outlined, from taxonomic studies involving comprehensive documentation and extensive illustration of morphology at the species level, through to broad-scale phylogenetic analyses that initiate or test hypotheses about relationships across the major groups. Other ongoing issues to be addressed include identifying the sister group of Trilobita, and determining whether certain taxa, such as the suborder Agnostina and Cambrian family Burlingiidae, represent trilobites.

Bicknell, R.D.C., Paterson, J.R. & Hopkins, M.J., 2019. A trilobite cluster from the Silurian Rochester Shale of New York: predation patterns and possible defensive behavior. American Museum Novitates, 3937: 1–16.

Evidence of predator-prey interactions in the fossil record offers important insights into extinc... more Evidence of predator-prey interactions in the fossil record offers important insights into extinct ecosystems. As direct predator-prey relationships are rarely preserved, records of failed predation upon prey species are often considered. The biomineralized exoskeleton of trilobites is exemplary for recording injuries that have resulted from predation. Despite the extensive documentation of trilobite injuries, abnormal specimens are often documented in isolation, with examples of injuries among clustered individuals being poorly known. Here we document a well-preserved body cluster of 18 individuals of the large lichid trilobite Arctinurus boltoni from the mid-Silurian (Wenlock) Rochester Shale of New York, with eight specimens showing injuries. Landmark geometric morphometrics of the specimens is used to explore possible patterns between injured and noninjured specimens. Results of the morphometric analysis indicate that injured and noninjured specimens do not show any systematic difference in overall shape of the exoskeleton, but many of the larger specimens have injuries. The majority of injuries are posteriorly located and right-side dominant, highlighting the possibility of predator or prey lateralization. Biostratinomic evidence suggests that the cluster represents a biological aggrega-tion that was rapidly buried in situ. Potential reasons for this gregarious behavior are discussed, including the possibility that individuals of A. boltoni grouped together to provide "safety in numbers" against predatory attack.

Betts, M.J., Claybourn, T.M., Brock, G.A., Jago, J.B., Skovsted, C.B. & Paterson, J.R., 2019. Shelly fossils from the lower Cambrian White Point Conglomerate, Kangaroo Island, South Australia. Acta Palaeontologica Polonica, 64(3): 489–522.

Yun, H., Brock, G.A., Zhang, X.L., Li, L.Y., García-Bellido, D.C. & Paterson, J.R., 2019. A new chancelloriid from the Emu Bay Shale (Cambrian Stage 4) of South Australia. Journal of Systematic Palaeontology, 17(13): 857–867.

Chancelloria australilonga sp. nov. is described from the Emu Bay Shale (Cambrian Series 2, Stage... more Chancelloria australilonga sp. nov. is described from the Emu Bay Shale (Cambrian Series 2, Stage 4) of Kangaroo Island, South Australia. The new species has a typical sac-like body, equipped with a meshwork of dozens of distinctive rosette-like sclerites. Each sclerite comprises one central ray and six or seven lateral rays, and is characterized by a pair of remarkably long and subparallel adapical rays. Chancelloria australilonga is one of the few chancelloriid species preserved with an apical orifice with an obvious peripheral tuft. The tuft consists of a series of single-rayed sclerites with inflated bases. The preservation of the specimens, coupled with sedimentological information and their general rarity in the Emu Bay Shale, suggests short-distance transport and subsequent deposition in a nearshore, low-oxygen preservational trap. Additionally, the known distribution of chancelloriids in the well-documented Konservat-Lagerst€ atten representing a variety of sedimentary environments, indicates that chancelloriids, especially the genus Chancelloria, were likely adapted to an extensive range of habitats. http://zoobank.org/urn:lsid:zoobank.org:pub:E46167B4-186A-4521-B3D7-DC3F48F72A30

Paterson, J.R., Edgecombe, G.D. & Lee, M.S.Y., 2019 Trilobite evolutionary rates constrain the duration of the Cambrian explosion. Proceedings of the National Academy of Sciences (USA), 116(10): 4394-4399.

Trilobites are often considered exemplary for understanding the Cambrian explosion of animal life... more Trilobites are often considered exemplary for understanding the Cambrian explosion of animal life, due to their unsurpassed diversity and abundance. These biomineralized arthropods appear abruptly in the fossil record with an established diversity, phyloge-netic disparity, and provincialism at the beginning of Cambrian Series 2 (∼521 Ma), suggesting a protracted but cryptic earlier history that possibly extends into the Precambrian. However, recent analyses indicate elevated rates of phenotypic and genomic evolution for arthropods during the early Cambrian, thereby shortening the phylogenetic fuse. Furthermore, comparatively little research has been devoted to understanding the duration of the Cambrian explosion, after which normal Phanerozoic evolutionary rates were established. We test these hypotheses by applying Bayesian tip-dating methods to a comprehensive dataset of Cambrian trilobites. We show that trilobites have a Cambrian origin, as supported by the trace fossil record and molecular clocks. Surprisingly, they exhibit constant evolutionary rates across the entire Cambrian, for all aspects of the preserved phenotype: discrete, meristic, and continuous morphological traits. Our data therefore provide robust, quantitative evidence that by the time the typical Cambrian fossil record begins (∼521 Ma), the Cambrian explosion had already largely concluded. This suggests that a modern-style marine biosphere had rapidly emerged during the latest Ediacaran and earliest Cambrian (∼20 million years), followed by broad-scale evolutionary stasis throughout the remainder of the Cambrian.

Liu, J., Lerosey-Aubril, R., Steiner, M., Dunlop, J.A., Shu, D. & Paterson, J.R., 2018. Origin of raptorial feeding in juvenile euarthropods revealed by a Cambrian radiodontan. National Science Review, 5(6): 863-869.

Bicknell, R.D.C, Ledogar, J.A., Wroe, S., Gutzler, B.C., Watson III, W.H. & Paterson, J.R., 2018. Computational biomechanical analyses demonstrate similar shell-crushing abilities in modern and ancient arthropods. Proceedings of the Royal Society B, 285: 20181935.

The biology of the American horseshoe crab, Limulus polyphemus, is well documented-including its ... more The biology of the American horseshoe crab, Limulus polyphemus, is well documented-including its dietary habits, particularly the ability to crush shell with gnathobasic walking appendages-but virtually nothing is known about the feeding biomechanics of this iconic arthropod. Limulus polyphemus is also considered the archetypal functional analogue of various extinct groups with serial gnathobasic appendages, including eurypterids, tri-lobites and other early arthropods, especially Sidneyia inexpectans from the mid-Cambrian (508 Myr) Burgess Shale of Canada. Exceptionally preserved specimens of S. inexpectans show evidence suggestive of durophagous (shell-crushing) tendencies-including thick gnathobasic spine cuticle and shelly gut contents-but the masticatory capabilities of this fossil species have yet to be compared with modern durophagous arthropods. Here, we use advanced computational techniques, specifically a unique application of 3D finite-element analysis (FEA), to model the feeding mechanics of L. polyphemus and S. inexpectans: the first such analyses of a modern horseshoe crab and a fossil arthropod. Results show that mechanical performance of the feeding appendages in both arthropods is remarkably similar, suggesting that S. inexpectans had similar shell-crushing capabilities to L. polyphemus. This biomechanical solution to processing shelly food therefore has a history extending over 500 Myr, arising soon after the first shell-bearing animals. Arrival of durophagous predators during the early phase of animal evolution undoubtedly fuelled the Cambrian 'arms race' that involved a rapid increase in diversity, disparity and abundance of biomineralized prey species.

Betts, M.J., Paterson, J.R., et al., 2018. Early Cambrian chronostratigraphy and geochronology of South Australia. Earth-Science Reviews, 185: 498-543.

Bicknell, R.D.C. & Paterson, J.R., 2018. Reappraising the early evidence of durophagy and drilling predation in the fossil record: implications for escalation and the Cambrian Explosion. Biological Reviews, 93(2): 754-784.

The Cambrian Explosion is arguably the most extreme example of a biological radiation preserved i... more The Cambrian Explosion is arguably the most extreme example of a biological radiation preserved in the fossil record, and studies of Cambrian Lagerstätten have facilitated the exploration of many facets of this key evolutionary event. As predation was a major ecological driver behind the Explosion-particularly the radiation of biomineralising metazoans-the evidence for shell crushing (durophagy), drilling and puncturing predation in the Cambrian (and possibly the Ediacaran) is considered. Examples of durophagous predation on biomineralised taxa other than trilobites are apparently rare, reflecting predator preference, taphonomic and sampling biases, or simply lack of documentation. The oldest known example of durophagy is shell damage on the problematic taxon Mobergella holsti from the early Cambrian (possibly Terreneuvian) of Sweden. Using functional morphology to identify (or perhaps misidentify) durophagous predators is discussed, with emphasis on the toolkit used by Cambrian arthropods, specifically the radiodontan oral cone and the frontal and gnathobasic appendages of various taxa. Records of drill holes and possible puncture holes in Cambrian shells are mostly on brachiopods, but the lack of prey diversity may represent either a true biological signal or a result of various biases. The oldest drilled Cambrian shells occur in a variety of Terreneuvian-aged taxa, but specimens of the ubiquitous Ediacaran shelly fossil Cloudina also show putative drilling traces. Knowledge on Cambrian shell drillers is sorely lacking and there is little evidence or consensus concerning the taxonomic groups that made the holes, which often leads to the suggestion of an unknown 'soft bodied driller'. Useful methodologies for deciphering the identities and capabilities of shell drillers are outlined. Evidence for puncture holes in Cambrian shelly taxa is rare. Such holes are more jagged than drill holes and possibly made by a Cambrian 'puncher'. The Cambrian arthropod Yohoia may have used its frontal appendages in a jack-knifing manner, similar to Recent stomatopod crustaceans, to strike and puncture shells rapidly. Finally, Cambrian durophagous and shell-drilling predation is considered in the context of escalation-an evolutionary process that, amongst other scenarios, involves predators (and other 'enemies') as the predominant agents of natural selection. The rapid increase in diversity and abundance of biomineralised shells during the early Cambrian is often attributed to escalation: enemies placed selective pressure on prey, forcing phenotypic responses in prey and, by extension, in predator groups over time. Unfortunately, few case studies illustrate long-term patterns in shelly fossil morphologies that may reflect the influence of predation throughout the Cambrian. More studies on phenotypic change in hard-shelled lineages are needed to convincingly illustrate escalation and the responses of prey during the Cambrian.

Smith, P.M., Paterson, J.R. & Brock, G.A., 2018. Trilobites and agnostids from the Goyder Formation (Cambrian Series 3, Guzhangian; Mindyallan), Amadeus Basin, central Australia. Zootaxa, 4396(1): 1-67.

Bicknell, R.D.C., Klinkhamer, A.J., Flavel, R.J., Wroe, S. & Paterson, J.R., 2018. A 3D anatomical atlas of appendage musculature in the chelicerate arthropod Limulus polyphemus. PLoS ONE, 13(2), e0191400.

by John Paterson and Stephen Wroe

Limulus polyphemus, an archetypal chelicerate taxon, has interested both biological and paleontol... more Limulus polyphemus, an archetypal chelicerate taxon, has interested both biological and paleontological researchers due to its unique suite of anatomical features and as a useful modern analogue for fossil arthropod groups. To assist the study and documentation of this iconic taxon, we present a 3D atlas on the appendage musculature, with specific focus on the muscles of the cephalothoracic appendages. As L. polyphemus appendage muscula-ture has been the focus of extensive study, depicting the muscles in 3D will facilitate a more complete understanding thereof for future researchers. A large museum specimen was CT scanned to illustrate the major exoskeletal features of L. polyphemus. Micro-CT scans of iodine-stained appendages from fresh, non-museum specimens were digitally dissected to interactively depict appendage sections and muscles. This study has revealed the presence of two new muscles: one within the pushing leg, located dorsally relative to all other patella muscles, and the other within the male pedipalp, located in the modified tibiotarsus. This atlas increases accessibility to important internal and external morphological features of L. polyphemus and reduces the need for destructive fresh tissue dissection of specimens. Scanning, digitally dissecting, and documenting taxa in 3D is a pivotal step towards creating permanent digital records of life on Earth.

Bicknell, R.D.C., Paterson, J.R., Caron, J.-B. & Skovsted, C.B., 2018. The gnathobasic spine microstructure of recent and Silurian chelicerates and the Cambrian artiopodan Sidneyia: Functional and evolutionary implications. Arthropod Structure & Development, 47(1): 12-24.

Gnathobasic spines are located on the protopodal segments of the appendages of various euarthropo... more Gnathobasic spines are located on the protopodal segments of the appendages of various euarthropod taxa, notably chelicerates. Although they are used to crush shells and masticate soft food items, the microstructure of these spines are relatively poorly known in both extant and extinct forms. Here we compare the gnathobasic spine microstructures of the Silurian eurypterid Eurypterus tetragonophthalmus from Estonia and the Cambrian artiopodan Sidneyia inexpectans from Canada with those of the Recent xiphosuran chelicerate Limulus polyphemus to infer potential variations in functional morphology through time. The thickened fibrous exocuticle in L. polyphemus spine tips enables effective prey mastication and shell crushing, while also reducing pressure on nerve endings that fill the spine cavities. The spine cuticle of E. tetragonophthalmus has a laminate structure and lacks the fibrous layers seen in L. polyphemus spines, suggesting that E. tetragonophthalmus may not have been capable of crushing thick shells, but a durophagous habit cannot be precluded. Conversely, the cuticle of S. inexpectans spines has a similar fibrous microstructure to L. polyphemus, suggesting that S. inexpectans was a competent shell crusher. This conclusion is consistent with specimens showing preserved gut contents containing various shelly fragments. The shape and arrangement of the gnathobasic spines is similar for both L. polyphemus and S. inexpectans, with stouter spines in the posterior cephalothoracic or trunk appendages, respectively. This differentiation indicates that crushing occurs posteriorly, while the gnathobases on anterior appendages continue mastication and push food towards and into the mouth. The results of recent phylogenetic analyses that considered both modern and fossil euarthropod clades show that xiphosurans and eurypterids are united as crown-group euchelicerates, with S. inexpectans placed within more basal artiopodan clades. These relationships suggest that gnathobases with thickened fibrous exocuticle, if not homoplasious, may be plesiomorphic for chelicerates and deeper relatives within Arachnomorpha. This study shows that the gnathobasic spine microstructure best adapted for durophagy has remained remarkably constant since the Cambrian.

Schroeder, N.I., Paterson, J.R. & Brock, G.A., 2018. Eldonioids with associated trace fossils from the lower Cambrian Emu Bay Shale Konservat-Lagerstätte of South Australia. Journal of Paleontology, 92(1): 80-86.

Rare specimens of eldonioids recovered from the lower Cambrian (Series 2, Stage 4) Emu Bay Shale ... more Rare specimens of eldonioids recovered from the lower Cambrian (Series 2, Stage 4) Emu Bay Shale (EBS) Konservat-Lagerstätte represent the first record of the group for the Cambrian of East Gondwana. The disc-shaped body of the EBS taxon bears fine concentric corrugations on the dorsal surface and, ventrally, a series of internal lobes that have primary and secondary bifurcations, as well as a coiled sac. It appears to be most similar to Rotadiscus and Pararotadiscus of the Cambrian Chengjiang and Kaili biotas of South China, respectively. While the structure of the internal lobes would indicate that this occurrence in the EBS represents a new taxon within the Rotadiscidae, lack of detail regarding the precise number of internal lobes and the condition of the circumoral tentacles warrants a more conservative approach in leaving the genus and species under open nomenclature. The EBS specimens also host trace fossils, including the remains of a burrow, which are generally lacking in the body-fossil-bearing layers of the Konservat-Lagerstätte interval. These traces appear to have been made by small organisms and are similar to traces associated with the discs of Pararotadiscus guizhouensis (Zhao and Zhu, 1994) from the Kaili Biota. The available taphonomic, paleoenvironmental, and ichnological evidence indicates that the EBS eldonioids are most likely vagrants that were transported or settled into the 'preservational trap' and subsequently exposed on the substrate for a brief period before burial, thereby allowing organisms to exploit their carcasses for nutrients or other purposes.

Betts, M.J., Paterson, J.R., Jago, J.B., Jacquet, S.M., Skovsted, C.B., Topper, T.P. & Brock, G.A., 2017. Global correlation of the early Cambrian of South Australia: Shelly fauna of the Dailyatia odyssei Zone. Gondwana Research, 46: 240-279.

A lack of well resolved biostratigraphic data has prevented robust regional and global correlatio... more A lack of well resolved biostratigraphic data has prevented robust regional and global correlation of lower Cam-brian successions from South Australia. A new early Cambrian biostratigraphy, based on data derived from 21 measured stratigraphic sections and drill cores (11 described herein) reveals the abundance and diversity of shelly fauna from the Arrowie Basin, and the value of early Cambrian "small shelly fossils" (SSF) for biostrati-graphic studies. Here we examine shelly fauna associated with the youngest of three recently established biozones, the Dailyatia odyssei Taxon Range Zone (hereafter D. odyssei Zone), and their correlative potential. The D. odyssei Zone features a diverse suite of tommotiids, organophosphatic brachiopods, bradoriid arthropods, molluscs and phosphatic problematica. This fauna permits strong correlation (often at species-level) with other major early Cambrian terranes, particularly Antarctica, South China and Laurentia, and suggest a Cambrian Series 2, Stages 3-4 age for the D. odyssei Zone. Bradoriids have proven to be useful biostratigraphic tools. Four new species and three new genera are described herein: Acutobalteus sinuosus gen. et sp. nov., Eozhexiella adnyamathanha gen. et sp. nov., Manawarra jonesi gen. et sp. nov. and Mongolitubulus descensus sp. nov. The description of Eohadrotreta sp. cf. zhenbaensis represents the first occurrence of the acrotretoid brachiopod Eohadrotreta from Australia.

Jago, J.B., Bentley, C.J., Paterson, J.R., Holmes, J.D., Lin, T.-R. & Sun, X.-W., 2021. The stratigraphic significance of early Cambrian (Series 2, Stage 4) trilobites from the Smith Bay Shale near Freestone Creek, Kangaroo Island. Australian Journal of Earth Sciences, 68(2): 204–212.

Bicknell, R.D.C., Holmes, J.D., Edgecombe, G.D., Losso, S.R., Ortega-Hernández, J., Wroe, S. & Paterson, J.R., 2021. Biomechanical analyses of Cambrian euarthropod limbs reveal their effectiveness in mastication and durophagy. Proceedings of the Royal Society B, 288: 20202075.

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

Paterson, J.R., Edgecombe, G.D. & García-Bellido, D.C., 2020. Disparate compound eyes of Cambrian radiodonts reveal their developmental growth mode and diverse visual ecology. Science Advances, 6(49): eabc6721.

Radiodonts are nektonic stem-group euarthropods that played various trophic roles in Paleozoic ma... more Radiodonts are nektonic stem-group euarthropods that played various trophic roles in Paleozoic marine ecosystems, but information on their vision is limited. Optical details exist only in one species from the Cambrian Emu Bay Shale of Australia, here assigned to Anomalocaris aff. canadensis. We identify another type of radiodont compound eye from this deposit, belonging to 'Anomalocaris' briggsi. This ≤4-cm sessile eye has >13,000 lenses and a dorsally oriented acute zone. In both taxa, lenses were added marginally and increased in size and number throughout development, as in many crown-group euarthropods. Both species' eyes conform to their inferred lifestyles: The macro-phagous predator A. aff. canadensis has acute stalked eyes (>24,000 lenses each) adapted for hunting in well-lit waters, whereas the suspension-feeding 'A.' briggsi could detect plankton in dim down-welling light. Radiodont eyes further demonstrate the group's anatomical and ecological diversity and reinforce the crucial role of vision in early animal ecosystems.

Jago, J.B. et al., 2020. The Cambrian System in the Arrowie Basin, Flinders Ranges, South Australia. Australian Journal of Earth Sciences, 67(7): 923–948.

The lower to ?middle Cambrian rocks (Terreneuvian, Series 2 and possibly Miaolingian) of the Arro... more The lower to ?middle Cambrian rocks (Terreneuvian, Series 2 and possibly Miaolingian) of the Arrowie Basin are exposed superbly in the Flinders Ranges of South Australia. They comprise two major sedimentary packages: a lower carbonate-rich succession (Hawker Group and correlates) and an upper siliciclastic-dominated succession (Billy Creek Formation, Wirrealpa Limestone and Lake Frome Group). These rocks form one of the most complete lower Cambrian (Terreneuvian and Series 2) successions globally. They contain one of the most diverse known early Cambrian biotas in the world, with trilobites, archaeocyaths, bradoriides, brachiopods, some of the earliest known coralomorphs, small shelly fossils, molluscs, hyoliths, acritarchs and trace fossils. Series divisions, based on ranges of shelly fossils and archaeocyath biostratigraphy are currently being established. Ancient reef structures are prominent in several areas. Syndepositional faulting and diapiric activity affected sedimentation in places. The global significance of the region is enhanced by the presence of tuff horizons at some levels, which provide the opportunity to link the biostratigraphic zones with radiometric dates and carbon isotope curves. ARTICLE HISTORY

Holmes, J.D., Paterson, J.R. & García-Bellido, D.C., 2020. The trilobite Redlichia from the lower Cambrian Emu Bay Shale Konservat-Lagerstätte of South Australia: systematics, ontogeny and soft-part anatomy. Journal of Systematic Palaeontology, 18(4): 295–334.

The trilobite Redlichia Cossmann, 1902 is an abundant element of the lower Cambrian (Series 2, St... more The trilobite Redlichia Cossmann, 1902 is an abundant element of the lower Cambrian (Series 2, Stage 4) Emu Bay Shale (EBS) Konservat-Lagerst€ atte on Kangaroo Island, South Australia. Well-preserved, fully articulated specimens from this deposit are known to reach lengths of up to 25 cm, representing one of the largest known Cambrian trilobites. Until now, all Redlichia specimens from the EBS have been referred to Redlichia takooensis Lu, 1950, a species originally described from South China. Previous work recognized considerable differences in exoskeletal morphology among specimens of varying sizes, which was attributed to ontogeny. However, close examination of a large collection of recently acquired specimens shows that this variation actually represents two distinct morphs, interpreted here as separate species: R. takooensis, and a large, new species, Redlichia rex sp. nov. An analysis of morphological variation in holaspides ('adults') of the more common R. takooensis reveals considerable ontogenetic change occurred even during this later phase of growth. Some specimens of both Redlichia species from the EBS also exhibit exceptionally preserved soft-part anatomy, particularly the antennae and biramous appendages. Here, appendages (antenniform and biramous) and digestive structures are described, and biramous appendage reconstructions of R. rex sp. nov. are presented, which show a striking resemblance to some early Cambrian trilobites from South China. In particular, R. rex has a tripartite exopodite, as well as a dorsoventrally deep protopodite with gnathobasic spines used to shred or crush food items. Based on recent phylogenetic analyses, it is possible that an exopodite with tripartite subdivisions represents the plesiomorphic condition for Artiopoda (trilobites and kin). The digestive system of R. takooensis exhibits a series of paired digestive glands in the cephalon and anterior thorax, similar to those described for a number of other Cambrian and Ordovician trilobites. http://zoobank.org/urn:lsid:zoobank.org:pub:507BEAFC-4AFA-43F4-A5C4-49E4B58C658E

Smith, P.M., Brock, G.A. & Paterson, J.R., 2020. Shelly fauna from the Cambrian (Miaolingian, Guzhangian) Shannon Formation and the SPICE event in the Amadeus Basin, Northern Territory. Alcheringa, 44(1): 1–24.

Paterson, J.R., 2020. The trouble with trilobites: classification, phylogeny and the cryptogenesis problem. Geological Magazine, 157(1): 35–46.

Trilobites are an iconic group of extinct arthropods that lived in Palaeozoic oceans for c. 270 M... more Trilobites are an iconic group of extinct arthropods that lived in Palaeozoic oceans for c. 270 Ma, before their demise at the end of the Permian Period. Despite their considerable diversity (> 22 000 species) and abundance, particularly in Cambrian and Ordovician rocks, as well as intensive study for well over 200 years, trilobite systematics remains in a state of flux. In this contribution, the complex history of trilobite classification over the last century is briefly reviewed, including the seminal scheme published by Henry Swinnerton in 1915. The cryptogenesis problem, which relates to the supposedly obscure phylogenetic links between major post-Cambrian trilobite clades and their Cambrian sister taxa, is also discussed. Previous studies have suggested that the cryptogenesis problem is largely a taxonomic artefact, but the Cambrian origins of some post-Cambrian groups, such as the orders Proetida and Odontopleurida, are still unclear. Future directions for research on trilobite systematics are outlined, from taxonomic studies involving comprehensive documentation and extensive illustration of morphology at the species level, through to broad-scale phylogenetic analyses that initiate or test hypotheses about relationships across the major groups. Other ongoing issues to be addressed include identifying the sister group of Trilobita, and determining whether certain taxa, such as the suborder Agnostina and Cambrian family Burlingiidae, represent trilobites.

Bicknell, R.D.C., Paterson, J.R. & Hopkins, M.J., 2019. A trilobite cluster from the Silurian Rochester Shale of New York: predation patterns and possible defensive behavior. American Museum Novitates, 3937: 1–16.

Evidence of predator-prey interactions in the fossil record offers important insights into extinc... more Evidence of predator-prey interactions in the fossil record offers important insights into extinct ecosystems. As direct predator-prey relationships are rarely preserved, records of failed predation upon prey species are often considered. The biomineralized exoskeleton of trilobites is exemplary for recording injuries that have resulted from predation. Despite the extensive documentation of trilobite injuries, abnormal specimens are often documented in isolation, with examples of injuries among clustered individuals being poorly known. Here we document a well-preserved body cluster of 18 individuals of the large lichid trilobite Arctinurus boltoni from the mid-Silurian (Wenlock) Rochester Shale of New York, with eight specimens showing injuries. Landmark geometric morphometrics of the specimens is used to explore possible patterns between injured and noninjured specimens. Results of the morphometric analysis indicate that injured and noninjured specimens do not show any systematic difference in overall shape of the exoskeleton, but many of the larger specimens have injuries. The majority of injuries are posteriorly located and right-side dominant, highlighting the possibility of predator or prey lateralization. Biostratinomic evidence suggests that the cluster represents a biological aggrega-tion that was rapidly buried in situ. Potential reasons for this gregarious behavior are discussed, including the possibility that individuals of A. boltoni grouped together to provide "safety in numbers" against predatory attack.

Betts, M.J., Claybourn, T.M., Brock, G.A., Jago, J.B., Skovsted, C.B. & Paterson, J.R., 2019. Shelly fossils from the lower Cambrian White Point Conglomerate, Kangaroo Island, South Australia. Acta Palaeontologica Polonica, 64(3): 489–522.

Yun, H., Brock, G.A., Zhang, X.L., Li, L.Y., García-Bellido, D.C. & Paterson, J.R., 2019. A new chancelloriid from the Emu Bay Shale (Cambrian Stage 4) of South Australia. Journal of Systematic Palaeontology, 17(13): 857–867.

Chancelloria australilonga sp. nov. is described from the Emu Bay Shale (Cambrian Series 2, Stage... more Chancelloria australilonga sp. nov. is described from the Emu Bay Shale (Cambrian Series 2, Stage 4) of Kangaroo Island, South Australia. The new species has a typical sac-like body, equipped with a meshwork of dozens of distinctive rosette-like sclerites. Each sclerite comprises one central ray and six or seven lateral rays, and is characterized by a pair of remarkably long and subparallel adapical rays. Chancelloria australilonga is one of the few chancelloriid species preserved with an apical orifice with an obvious peripheral tuft. The tuft consists of a series of single-rayed sclerites with inflated bases. The preservation of the specimens, coupled with sedimentological information and their general rarity in the Emu Bay Shale, suggests short-distance transport and subsequent deposition in a nearshore, low-oxygen preservational trap. Additionally, the known distribution of chancelloriids in the well-documented Konservat-Lagerst€ atten representing a variety of sedimentary environments, indicates that chancelloriids, especially the genus Chancelloria, were likely adapted to an extensive range of habitats. http://zoobank.org/urn:lsid:zoobank.org:pub:E46167B4-186A-4521-B3D7-DC3F48F72A30

Paterson, J.R., Edgecombe, G.D. & Lee, M.S.Y., 2019 Trilobite evolutionary rates constrain the duration of the Cambrian explosion. Proceedings of the National Academy of Sciences (USA), 116(10): 4394-4399.

Trilobites are often considered exemplary for understanding the Cambrian explosion of animal life... more Trilobites are often considered exemplary for understanding the Cambrian explosion of animal life, due to their unsurpassed diversity and abundance. These biomineralized arthropods appear abruptly in the fossil record with an established diversity, phyloge-netic disparity, and provincialism at the beginning of Cambrian Series 2 (∼521 Ma), suggesting a protracted but cryptic earlier history that possibly extends into the Precambrian. However, recent analyses indicate elevated rates of phenotypic and genomic evolution for arthropods during the early Cambrian, thereby shortening the phylogenetic fuse. Furthermore, comparatively little research has been devoted to understanding the duration of the Cambrian explosion, after which normal Phanerozoic evolutionary rates were established. We test these hypotheses by applying Bayesian tip-dating methods to a comprehensive dataset of Cambrian trilobites. We show that trilobites have a Cambrian origin, as supported by the trace fossil record and molecular clocks. Surprisingly, they exhibit constant evolutionary rates across the entire Cambrian, for all aspects of the preserved phenotype: discrete, meristic, and continuous morphological traits. Our data therefore provide robust, quantitative evidence that by the time the typical Cambrian fossil record begins (∼521 Ma), the Cambrian explosion had already largely concluded. This suggests that a modern-style marine biosphere had rapidly emerged during the latest Ediacaran and earliest Cambrian (∼20 million years), followed by broad-scale evolutionary stasis throughout the remainder of the Cambrian.

Liu, J., Lerosey-Aubril, R., Steiner, M., Dunlop, J.A., Shu, D. & Paterson, J.R., 2018. Origin of raptorial feeding in juvenile euarthropods revealed by a Cambrian radiodontan. National Science Review, 5(6): 863-869.

Bicknell, R.D.C, Ledogar, J.A., Wroe, S., Gutzler, B.C., Watson III, W.H. & Paterson, J.R., 2018. Computational biomechanical analyses demonstrate similar shell-crushing abilities in modern and ancient arthropods. Proceedings of the Royal Society B, 285: 20181935.

The biology of the American horseshoe crab, Limulus polyphemus, is well documented-including its ... more The biology of the American horseshoe crab, Limulus polyphemus, is well documented-including its dietary habits, particularly the ability to crush shell with gnathobasic walking appendages-but virtually nothing is known about the feeding biomechanics of this iconic arthropod. Limulus polyphemus is also considered the archetypal functional analogue of various extinct groups with serial gnathobasic appendages, including eurypterids, tri-lobites and other early arthropods, especially Sidneyia inexpectans from the mid-Cambrian (508 Myr) Burgess Shale of Canada. Exceptionally preserved specimens of S. inexpectans show evidence suggestive of durophagous (shell-crushing) tendencies-including thick gnathobasic spine cuticle and shelly gut contents-but the masticatory capabilities of this fossil species have yet to be compared with modern durophagous arthropods. Here, we use advanced computational techniques, specifically a unique application of 3D finite-element analysis (FEA), to model the feeding mechanics of L. polyphemus and S. inexpectans: the first such analyses of a modern horseshoe crab and a fossil arthropod. Results show that mechanical performance of the feeding appendages in both arthropods is remarkably similar, suggesting that S. inexpectans had similar shell-crushing capabilities to L. polyphemus. This biomechanical solution to processing shelly food therefore has a history extending over 500 Myr, arising soon after the first shell-bearing animals. Arrival of durophagous predators during the early phase of animal evolution undoubtedly fuelled the Cambrian 'arms race' that involved a rapid increase in diversity, disparity and abundance of biomineralized prey species.

Betts, M.J., Paterson, J.R., et al., 2018. Early Cambrian chronostratigraphy and geochronology of South Australia. Earth-Science Reviews, 185: 498-543.

Bicknell, R.D.C. & Paterson, J.R., 2018. Reappraising the early evidence of durophagy and drilling predation in the fossil record: implications for escalation and the Cambrian Explosion. Biological Reviews, 93(2): 754-784.

The Cambrian Explosion is arguably the most extreme example of a biological radiation preserved i... more The Cambrian Explosion is arguably the most extreme example of a biological radiation preserved in the fossil record, and studies of Cambrian Lagerstätten have facilitated the exploration of many facets of this key evolutionary event. As predation was a major ecological driver behind the Explosion-particularly the radiation of biomineralising metazoans-the evidence for shell crushing (durophagy), drilling and puncturing predation in the Cambrian (and possibly the Ediacaran) is considered. Examples of durophagous predation on biomineralised taxa other than trilobites are apparently rare, reflecting predator preference, taphonomic and sampling biases, or simply lack of documentation. The oldest known example of durophagy is shell damage on the problematic taxon Mobergella holsti from the early Cambrian (possibly Terreneuvian) of Sweden. Using functional morphology to identify (or perhaps misidentify) durophagous predators is discussed, with emphasis on the toolkit used by Cambrian arthropods, specifically the radiodontan oral cone and the frontal and gnathobasic appendages of various taxa. Records of drill holes and possible puncture holes in Cambrian shells are mostly on brachiopods, but the lack of prey diversity may represent either a true biological signal or a result of various biases. The oldest drilled Cambrian shells occur in a variety of Terreneuvian-aged taxa, but specimens of the ubiquitous Ediacaran shelly fossil Cloudina also show putative drilling traces. Knowledge on Cambrian shell drillers is sorely lacking and there is little evidence or consensus concerning the taxonomic groups that made the holes, which often leads to the suggestion of an unknown 'soft bodied driller'. Useful methodologies for deciphering the identities and capabilities of shell drillers are outlined. Evidence for puncture holes in Cambrian shelly taxa is rare. Such holes are more jagged than drill holes and possibly made by a Cambrian 'puncher'. The Cambrian arthropod Yohoia may have used its frontal appendages in a jack-knifing manner, similar to Recent stomatopod crustaceans, to strike and puncture shells rapidly. Finally, Cambrian durophagous and shell-drilling predation is considered in the context of escalation-an evolutionary process that, amongst other scenarios, involves predators (and other 'enemies') as the predominant agents of natural selection. The rapid increase in diversity and abundance of biomineralised shells during the early Cambrian is often attributed to escalation: enemies placed selective pressure on prey, forcing phenotypic responses in prey and, by extension, in predator groups over time. Unfortunately, few case studies illustrate long-term patterns in shelly fossil morphologies that may reflect the influence of predation throughout the Cambrian. More studies on phenotypic change in hard-shelled lineages are needed to convincingly illustrate escalation and the responses of prey during the Cambrian.

Smith, P.M., Paterson, J.R. & Brock, G.A., 2018. Trilobites and agnostids from the Goyder Formation (Cambrian Series 3, Guzhangian; Mindyallan), Amadeus Basin, central Australia. Zootaxa, 4396(1): 1-67.

Bicknell, R.D.C., Klinkhamer, A.J., Flavel, R.J., Wroe, S. & Paterson, J.R., 2018. A 3D anatomical atlas of appendage musculature in the chelicerate arthropod Limulus polyphemus. PLoS ONE, 13(2), e0191400.

by John Paterson and Stephen Wroe

Limulus polyphemus, an archetypal chelicerate taxon, has interested both biological and paleontol... more Limulus polyphemus, an archetypal chelicerate taxon, has interested both biological and paleontological researchers due to its unique suite of anatomical features and as a useful modern analogue for fossil arthropod groups. To assist the study and documentation of this iconic taxon, we present a 3D atlas on the appendage musculature, with specific focus on the muscles of the cephalothoracic appendages. As L. polyphemus appendage muscula-ture has been the focus of extensive study, depicting the muscles in 3D will facilitate a more complete understanding thereof for future researchers. A large museum specimen was CT scanned to illustrate the major exoskeletal features of L. polyphemus. Micro-CT scans of iodine-stained appendages from fresh, non-museum specimens were digitally dissected to interactively depict appendage sections and muscles. This study has revealed the presence of two new muscles: one within the pushing leg, located dorsally relative to all other patella muscles, and the other within the male pedipalp, located in the modified tibiotarsus. This atlas increases accessibility to important internal and external morphological features of L. polyphemus and reduces the need for destructive fresh tissue dissection of specimens. Scanning, digitally dissecting, and documenting taxa in 3D is a pivotal step towards creating permanent digital records of life on Earth.

Bicknell, R.D.C., Paterson, J.R., Caron, J.-B. & Skovsted, C.B., 2018. The gnathobasic spine microstructure of recent and Silurian chelicerates and the Cambrian artiopodan Sidneyia: Functional and evolutionary implications. Arthropod Structure & Development, 47(1): 12-24.

Gnathobasic spines are located on the protopodal segments of the appendages of various euarthropo... more Gnathobasic spines are located on the protopodal segments of the appendages of various euarthropod taxa, notably chelicerates. Although they are used to crush shells and masticate soft food items, the microstructure of these spines are relatively poorly known in both extant and extinct forms. Here we compare the gnathobasic spine microstructures of the Silurian eurypterid Eurypterus tetragonophthalmus from Estonia and the Cambrian artiopodan Sidneyia inexpectans from Canada with those of the Recent xiphosuran chelicerate Limulus polyphemus to infer potential variations in functional morphology through time. The thickened fibrous exocuticle in L. polyphemus spine tips enables effective prey mastication and shell crushing, while also reducing pressure on nerve endings that fill the spine cavities. The spine cuticle of E. tetragonophthalmus has a laminate structure and lacks the fibrous layers seen in L. polyphemus spines, suggesting that E. tetragonophthalmus may not have been capable of crushing thick shells, but a durophagous habit cannot be precluded. Conversely, the cuticle of S. inexpectans spines has a similar fibrous microstructure to L. polyphemus, suggesting that S. inexpectans was a competent shell crusher. This conclusion is consistent with specimens showing preserved gut contents containing various shelly fragments. The shape and arrangement of the gnathobasic spines is similar for both L. polyphemus and S. inexpectans, with stouter spines in the posterior cephalothoracic or trunk appendages, respectively. This differentiation indicates that crushing occurs posteriorly, while the gnathobases on anterior appendages continue mastication and push food towards and into the mouth. The results of recent phylogenetic analyses that considered both modern and fossil euarthropod clades show that xiphosurans and eurypterids are united as crown-group euchelicerates, with S. inexpectans placed within more basal artiopodan clades. These relationships suggest that gnathobases with thickened fibrous exocuticle, if not homoplasious, may be plesiomorphic for chelicerates and deeper relatives within Arachnomorpha. This study shows that the gnathobasic spine microstructure best adapted for durophagy has remained remarkably constant since the Cambrian.

Schroeder, N.I., Paterson, J.R. & Brock, G.A., 2018. Eldonioids with associated trace fossils from the lower Cambrian Emu Bay Shale Konservat-Lagerstätte of South Australia. Journal of Paleontology, 92(1): 80-86.

Rare specimens of eldonioids recovered from the lower Cambrian (Series 2, Stage 4) Emu Bay Shale ... more Rare specimens of eldonioids recovered from the lower Cambrian (Series 2, Stage 4) Emu Bay Shale (EBS) Konservat-Lagerstätte represent the first record of the group for the Cambrian of East Gondwana. The disc-shaped body of the EBS taxon bears fine concentric corrugations on the dorsal surface and, ventrally, a series of internal lobes that have primary and secondary bifurcations, as well as a coiled sac. It appears to be most similar to Rotadiscus and Pararotadiscus of the Cambrian Chengjiang and Kaili biotas of South China, respectively. While the structure of the internal lobes would indicate that this occurrence in the EBS represents a new taxon within the Rotadiscidae, lack of detail regarding the precise number of internal lobes and the condition of the circumoral tentacles warrants a more conservative approach in leaving the genus and species under open nomenclature. The EBS specimens also host trace fossils, including the remains of a burrow, which are generally lacking in the body-fossil-bearing layers of the Konservat-Lagerstätte interval. These traces appear to have been made by small organisms and are similar to traces associated with the discs of Pararotadiscus guizhouensis (Zhao and Zhu, 1994) from the Kaili Biota. The available taphonomic, paleoenvironmental, and ichnological evidence indicates that the EBS eldonioids are most likely vagrants that were transported or settled into the 'preservational trap' and subsequently exposed on the substrate for a brief period before burial, thereby allowing organisms to exploit their carcasses for nutrients or other purposes.

Betts, M.J., Paterson, J.R., Jago, J.B., Jacquet, S.M., Skovsted, C.B., Topper, T.P. & Brock, G.A., 2017. Global correlation of the early Cambrian of South Australia: Shelly fauna of the Dailyatia odyssei Zone. Gondwana Research, 46: 240-279.

A lack of well resolved biostratigraphic data has prevented robust regional and global correlatio... more A lack of well resolved biostratigraphic data has prevented robust regional and global correlation of lower Cam-brian successions from South Australia. A new early Cambrian biostratigraphy, based on data derived from 21 measured stratigraphic sections and drill cores (11 described herein) reveals the abundance and diversity of shelly fauna from the Arrowie Basin, and the value of early Cambrian "small shelly fossils" (SSF) for biostrati-graphic studies. Here we examine shelly fauna associated with the youngest of three recently established biozones, the Dailyatia odyssei Taxon Range Zone (hereafter D. odyssei Zone), and their correlative potential. The D. odyssei Zone features a diverse suite of tommotiids, organophosphatic brachiopods, bradoriid arthropods, molluscs and phosphatic problematica. This fauna permits strong correlation (often at species-level) with other major early Cambrian terranes, particularly Antarctica, South China and Laurentia, and suggest a Cambrian Series 2, Stages 3-4 age for the D. odyssei Zone. Bradoriids have proven to be useful biostratigraphic tools. Four new species and three new genera are described herein: Acutobalteus sinuosus gen. et sp. nov., Eozhexiella adnyamathanha gen. et sp. nov., Manawarra jonesi gen. et sp. nov. and Mongolitubulus descensus sp. nov. The description of Eohadrotreta sp. cf. zhenbaensis represents the first occurrence of the acrotretoid brachiopod Eohadrotreta from Australia.

Lee, M.S.Y. Jago, J.B., García-Bellido, D.C., Edgecombe, G.D., Gehling, J.G., Paterson, J.R. 2011. Modern optics in exceptionally preserved eyes of Early Cambrian arthropods from Australia. Nature 474: 631-634

by John Paterson, Michael Lee, and Gregory D Edgecombe

Nature, Jan 1, 2011