Biology subjects

Pates, S.

Publications and source records attributed to Pates, S..

8 recordsLinked to original sources

bioRxiv2026

Healed predation scar on a Cambrian apex predator

Predation is considered a key driver of the rapid diversification of animals during the Cambrian explosion. While the fossil record documents a plethora of evidence of successful and failed predation on biomineralized invertebrates at low trophic levels, no previous evidence of predation on larger, often soft-bodied, animals at higher trophic levels has been reported. This means that the modeled links between higher trophic levels in Cambrian food webs lack supporting fossil evidence, hindering understanding of the complexity of Cambrian trophic relationships. Here, we report a healed injury on the swimming flap of the radiodont apex predator Amplectobelua symbrachiata-- one of the largest animals in the Cambrian oceans. The diagnostic W-shape with a healed margin supports interpretation of this wound as predatory in origin, with likely attackers including larger contemporaneous radiodonts - possibly members of the same species -- or the giant lobopodian Omnidens. Evidence that apex predators were attacked provides critical empirical data informing the complexity of Cambrian food webs. This finding provides empirical support for the existence of high-level feeding loops, analogous to those in modern marine ecosystems, documenting the rapid increase in trophic complexity during the latter stages of the Ediacaran-Cambrian Transition.

paleontology↗

bioRxiv2026

Possible planktonic lifestyle of the Silurian trilobite Deiphon evaluated through 3D modelling

Zooplankton are a crucial part of modern oceans, feeding on primary producers and moving nutrients vertically and horizontally. Many euarthropods have evolved planktonic lifestyles, but evaluating extinct taxa were planktonic relies on documenting a broad distribution in diverse lithologies, occurrence across multiple paleobiogeographic regions, and morphological comparisons to modern analogues. Trilobites living in the water column have been proposed to take two forms, well-streamlined and poorly-streamlined, reflecting different lifestyles and behaviors in the water column. Both are believed to go extinct at the end of the Ordovician. A planktonic lifestyle was suggested for Deiphon based on its highly inflated, spherical glabella and reduced body, but this is not supported by recent workers. The purpose of the glabellar bubble is also debated, having been both suggested to store low density lipids to increase the buoyancy or host a highly expanded gut. We use a three-dimensional model of Deiphon to estimate volume and density of different tissue types (exoskeleton, gut, body, limbs) to calculate its specific gravity. To investigate the impact of the bubble and its contents, we tested the impact on buoyancy by varying presence of the inflated glabella, content of the bubble, and exoskeletal thickness. The sedimentological and geographical information for this animal is poor, making morphology the only proxy available to test its life mode. Exoskeletal thickness has a large impact on the buoyancy of Deiphon, suggesting plankton trilobites may have required thin exoskeleton to remain buoyant in the water. Our results support a pelagic lifestyle for Deiphon, if its bubble was filled with lipids, which we consider the most likely of the possibilities when the rest of the animals morphology is considered.

paleontology↗

bioRxiv2025

A morphometric approach to the taxonomic dilemma of Zonozoe drabowiensis Barrande, 1872 and Zonoscutum solum Chlup&aacute&ccaron, 1999 (Upper Ordovician, Czech Republic)

Zonozoe drabowiensis Barrande, 1872 and Zonoscutum solum Chlupa[c], 1999 are rare and incompletely preserved arthropods from the Upper Ordovician of the Czech Republic. Their classification has been a subject of debate for over a century due to the limited number of specimens and the absence of clear diagnostic features. They were previously thought to belong to Aglaspidida, an extinct group of arthropods from the Cambrian and Ordovician, within Vicissicaudata, a branch of the larger arthropod clade Artiopoda that also includes trilobites. Herein, we used analyses of cephalic outline to quantify whether Zonozoe and Zonoscutum are morphologically more similar to vicissicaudates than other early Palaeozoic arthropods. We assembled a dataset of twenty-six cephalic outlines representing twenty-six early Palaeozoic species, including Zonozoe, Zonoscutum, five euchelicerates, six aglaspidids, three cheloniellids, and a selection of other artiopodans. We quantified their shape using elliptical Fourier analysis. Principal component analysis (PCA) and linear discriminant analysis (LDA) place Zonozoe and Zonoscutum within and close to the vicissicaudatan morphospace, clearly distinguishing them from euchelicerates and non-vicissicaudatan artiopodans. These data support the most conservative classification of Zonozoe and Zonoscutum within Artiopoda, while strengthening the case for a more specific affinity with Vicissicaudata, helping to resolve a 150-year-old taxonomic uncertainty. More broadly, this study demonstrates the value of outline-based morphometrics in testing systematic hypotheses when discrete characters are unavailable or scarce, offering a reproducible tool for re-evaluating other problematic fossils.

paleontology↗

bioRxiv2025

Hierarchical importance of factors impacting trilobite cephalic disparity

1Trilobite cephala show high disparity owing to their supporting of key functional ecological structures, such as sensory and feeding structures, and those enabling important behaviours like enrollment and exoskeleton moulting. Previous studies analysed associations between cephalic morphometry, trends through time and with diversity, and these behaviours. However, no studies have yet quantitatively compared the importance of these different varied factors on cephalic morphometry. Here, we explore the association between trilobite cephalic morphometry and taxonomic variables, moulting behaviour, and facial suture type in Principal Components Analysis morphospace, and assess whether these variables can predict cephalic morphometry using Linear Discriminant Analyses. We employed Linear Mixed-Effects Models (LMMs) to quantify the hierarchical importance of these variables for determining cephalic disparity. The dataset used comprises cephalon outlines for 762 species of trilobites from across the globe and through the entire Palaeozoic. We found that variation in cephalic morphometry is not clearly associated with moulting behaviour, nor is moulting behaviour linked to facial suture type. Trilobite moulting behaviour is evidently too phenotypically plastic, and/or preservationally impacted, to produce clear signals across broad datasets. Results demonstrate the utility of LMMs for palaeontological datasets; we found that family-level assignment overall well explains cephalic morphometry, more so than order-level assignment which shows significant overlap in morphospace. Geological Period, facial suture type, and moulting behaviour had little impact on cephalic morphometry. We thereby demonstrate that trilobite cephalic outline morphometry is generally in accordance with trilobite family-level systematics and highlight the use of LMMs for interrogating broad-scale fossil morphological data.

paleontology↗

bioRxiv2024

Hydrodynamic function of genal prolongations in trinucleimorph trilobites revealed by computational fluid dynamics

Trilobites, a diverse clade of Palaeozoic arthropods, repeatedly converged on the trinucleimorph morphology. Trinucleimorphs possessed vaulted cephala with a broad anterior fringe and prominent posteriorly orientated genal prolongations. Various functional hypotheses have been proposed for the fringe, however the possible function of the genal prolongations has received less attention. Here we use a computational fluid dynamics approach to test whether these prolongations served a hydrodynamic function: generating negative lift to allow trinucleimorphs to remain in place on the seafloor and prevent overturning within fast flowing water. We simulated the performance of cephala with broad, narrow, and absent genal prolongations in a benthic environment with flow speeds ranging from 0.05-0.5 m s-1, in two cephalic postures. The first posture had the anterior of the cephalon parallel to the seafloor, while for the second the genal prolongations were parallel to the seafloor. Posture and presence of genal prolongations were found to be important for generating negative lift, with performance improving under faster flow speeds. No significant difference between narrow and broad genal prolongations was detected. This study provides support for genal prolongations serving a hydrodynamic function, similar to the femurs of some insect larvae, however, it does not preclude prolongations also serving additional functions as snowshoes or antipredatory deterrents.

paleontology↗

bioRxiv2024

Distinct causes underlie double-peaked trilobite morphological disparity

Trilobite cephalic morphology impacted the autecology of individuals, and is critical for high- and low-level taxonomic assignments. Disparity in trilobite cephalon shape varied through time and was integral to the occupation of a diversity of ecological niches. To fully appreciate trilobite cephalic evolution, we must understand how this disparity varies, and what factors control cephalon morphometry. We explore the disparity of trilobite cephala through the Palaeozoic, and analyse the associations between cephalic morphometry and taxonomic assignment and geological Period, using a dataset of 983 2D trilobite cephalon outlines. Elliptical Fourier transformation visualised as a Principal Components Analysis suggests significant differences in morphospace occupation for order and Period groups, and comparisons of disparity measures also suggest significantly different disparities between the groups. Trilobite cephalic disparity peaks in the Ordovician and Devonian. The Cambrian-Ordovician expansion of morphospace occupation appears a result of radiation to new niches, and thus all trilobite orders were established by the late Ordovician. In comparison, the morphospace expansion from the Silurian to Devonian seems solely a result of within-niche diversification rather than novel niche occupation. However, analyses interrogating the regions of morphospace occupied, including centroid distances, average pairwise shape comparisons and Linear Discriminant Analysis demonstrate that, except for the order Harpida and the Cambrian and Ordovician Periods, order and geological Period could not be robustly predicted for an unknown trilobite. Further, Kmeans clustering analyses suggest the total dataset naturally subdivides into only seven groups that do not correspond with taxonomic orders, though Kmeans clusters do decrease in number through the Palaeozoic, aligning with findings of decreasing disparity.

paleontology↗

bioRxiv2023

Multiple origins of cephalic sutures in trilobites and their relatives

Euarthropods are an extremely diverse phylum in the modern, and have been since their origination in the early Palaeozoic. They grow through moulting the exoskeleton (ecdysis) facilitated by breaking along lines of weakness (sutures). Artiopodans, a group that includes trilobites and their non-biomineralizing relatives, dominated arthropod diversity in benthic communities during the Palaeozoic. Most trilobites - a hyperdiverse group of tens of thousands of species - moult by breaking the exoskeleton along cephalic sutures, a strategy that has contributed to their high diversity during the Palaeozoic. However, the recent description of similar sutures in early diverging non-trilobite artiopodans mean that it is unclear whether these sutures evolved deep within Artiopoda, or convergently appeared multiple times within the group. Here we describe new well-preserved material of Acanthomeridion, a putative early diverging artiopodan, including hitherto unknown details of its ventral anatomy and appendages revealed through CT scanning, highlighting additional possible homologous features between the ventral plates of this taxon and trilobite free cheeks. We used three coding strategies treating ventral plates as homologous to trilobite free cheeks, to trilobite cephalic doublure, or independently derived. If ventral plates are considered homologous to free cheeks, Acanthomeridion is recovered sister to trilobites however dorsal ecdysial sutures are still recovered at many places within Artiopoda. If ventral plates are considered homologous to doublure or non-homologous, then Acanthomeridion is not recovered as sister to trilobites, and thus the ventral plates represent a distinct feature to trilobite doublure/free cheeks.

paleontology↗

bioRxiv2021

New opabiniid diversifies the weirdest wonders of the euarthropod lower stem group

Once considered weird wonders of the Cambrian, the emblematic Burgess Shale animals Anomalocaris and Opabinia are now recognized as lower stem-group euarthropods. Anomalocaris and its relatives (radiodonts) had a worldwide distribution and survived until at least the Devonian, whereas - despite intense study - Opabinia remains the only formally described opabiniid to date. Here we reinterpret a fossil from the Wheeler Formation of Utah as a new opabiniid, KUMIP 314087. By visualizing the sample of phylogenetic topologies in treespace, our results fortify support for the position of KUMIP 314087 beyond the nodal support traditionally applied. Our phylogenetic evidence expands opabiniids to multiple Cambrian Stages spanning approximately five million years. Our results underscore the power of treespace visualization for resolving imperfectly preserved fossils and expanding the known diversity and spatiotemporal ranges within the euarthropod lower stem group. Additional noteThis work contains a new biological name. New names in preprints are not considered available by the ICZN. To avoid ambiguity, the new biological name is not included in this preprint, and the specimen number (KUMIP 314087) is used as a placeholder. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=150 SRC="FIGDIR/small/434726v1_ufig1.gif" ALT="Figure 1"> View larger version (98K): org.highwire.dtl.DTLVardef@e770aaorg.highwire.dtl.DTLVardef@95bbd3org.highwire.dtl.DTLVardef@5e460eorg.highwire.dtl.DTLVardef@1494152_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOCover image.C_FLOATNO Artistic reconstruction of the new opabiniid from the Wheeler Formation, Utah, USA (Cambrian: Drumian). Artwork by F. Anthony. C_FIG

paleontology↗