Identifying signatures of the earliest benthic bulldozers in emergent subaerial conditions during the colonization of land by animals.
Wang Z, Davies NS, Liu AG, Minter NJ, Rahman IA
November 2024
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Journal article
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Proceedings. Biological sciences
The colonization of land by animals was a milestone in the history of life. Approximately 100 million years before full terrestrialization, early animals sporadically traversed emergent subaerial substrates, leaving behind trace fossils recording their activities. However, identifying temporarily emergent environments and determining the affinities, motility and subaerial endurance of the trace-makers, and the timing and magnitude of their impacts on marginal-marine environments, are challenging. Here, we used semi-resolved computational fluid dynamics-discrete element method coupling to simulate trace formation on non-cohesive sediments in submerged and emergent subaerial conditions. This revealed instability-induced morphological signatures that allow us to identify the earliest terrestrial trace fossils. Quantitative metrics enable us to infer that the putative earliest terrestrial trace-makers were molluscs, and dimensional analysis suggests that their subaerial excursions could last at least 15 min. These organisms navigated emergent environments from the early Cambrian (stage 2), tens of millions of years earlier than arthropods. This quantitative paradigm provides new insights into the palaeobiology of the earliest subaerial bulldozers and highlights that mollusc-like animals were among the first ecosystem engineers to enter marginal-marine settings. They may thus have contributed to the establishment of marginal-marine biogeochemical cycles, laying the groundwork for subsequent terrestrialization by other animals.
Quantitative ichnology: a novel framework to determine the producers of locomotory trace fossils with the ichnogenus Gordia as a case study
Wang Z, Rahman IA
November 2023
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Journal article
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Palaeontology
31 Biological Sciences, 3103 Ecology, 3104 Evolutionary Biology, 37 Earth Sciences, 3705 Geology, 1.1 Normal biological development and functioning
Reconstructing the feeding ecology of Cambrian sponge reefs: the case for active suspension feeding in Archaeocyatha.
Gibson BM, Chipman M, Attanasio P, Qureshi Z, Darroch SAF, Rahman IA, Laflamme M
November 2023
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Journal article
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Royal Society open science
Sponge-grade Archaeocyatha were early Cambrian biomineralizing metazoans that constructed reefs globally. Despite decades of research, many facets of archaeocyath palaeobiology remain unclear, making it difficult to reconstruct the palaeoecology of Cambrian reef ecosystems. Of specific interest is how these organisms fed; previous experimental studies have suggested that archaeocyaths functioned as passive suspension feeders relying on ambient currents to transport nutrient-rich water into their central cavities. Here, we test this hypothesis using computational fluid dynamics (CFD) simulations of digital models of select archaeocyath species. Our results demonstrate that, given a range of plausible current velocities, there was very little fluid circulation through the skeleton, suggesting obligate passive suspension feeding was unlikely. Comparing our simulation data with exhalent velocities collected from extant sponges, we infer an active suspension feeding lifestyle for archaeocyaths. The combination of active suspension feeding and biomineralization in Archaeocyatha may have facilitated the creation of modern metazoan reef ecosystems.
Raptorial appendages of the Cambrian apex predator Anomalocaris canadensis are built for soft prey and speed.
Bicknell RDC, Schmidt M, Rahman IA, Edgecombe GD, Gutarra S, Daley AC, Melzer RR, Wroe S, Paterson JR
July 2023
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Journal article
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Proceedings. Biological sciences
The stem-group euarthropod <i>Anomalocaris canadensis</i> is one of the largest Cambrian animals and is often considered the quintessential apex predator of its time. This radiodont is commonly interpreted as a demersal hunter, responsible for inflicting injuries seen in benthic trilobites. However, controversy surrounds the ability of <i>A. canadensis</i> to use its spinose frontal appendages to masticate or even manipulate biomineralized prey. Here, we apply a new integrative computational approach, combining three-dimensional digital modelling, kinematics, finite-element analysis (FEA) and computational fluid dynamics (CFD) to rigorously analyse an <i>A. canadensis</i> feeding appendage and test its morphofunctional limits. These models corroborate a raptorial function, but expose inconsistencies with a capacity for durophagy. In particular, FEA results show that certain parts of the appendage would have experienced high degrees of plastic deformation, especially at the endites, the points of impact with prey. The CFD results demonstrate that outstretched appendages produced low drag and hence represented the optimal orientation for speed, permitting acceleration bursts to capture prey. These data, when combined with evidence regarding the functional morphology of its oral cone, eyes, body flaps and tail fan, suggest that <i>A. canadensis</i> was an agile nektonic predator that fed on soft-bodied animals swimming in a well-lit water column above the benthos. The lifestyle of <i>A. canadensis</i> and that of other radiodonts, including plausible durophages, suggests that niche partitioning across this clade influenced the dynamics of Cambrian food webs, impacting on a diverse array of organisms at different sizes, tiers and trophic levels.
Cambrian stem-group ambulacrarians and the nature of the ancestral deuterostome.
Li Y, Dunn FS, Murdock DJE, Guo J, Rahman IA, Cong P
June 2023
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Journal article
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Current biology : CB
Deuterostomes are characterized by some of the most widely divergent body plans in the animal kingdom. These striking morphological differences have hindered efforts to predict ancestral characters, with the origin and earliest evolution of the group remaining ambiguous. Several iconic Cambrian fossils have been suggested to be early deuterostomes and hence could help elucidate ancestral character states. However, their phylogenetic relationships are controversial. Here, we describe new, exceptionally preserved specimens of the discoidal metazoan Rotadiscus grandis from the early Cambrian Chengjiang biota of China. These reveal a previously unknown double spiral structure, which we interpret as a chordate-like covering to a coelomopore, located adjacent to a horseshoe-shaped tentacle complex. The tentacles differ in key aspects from those seen in lophophorates and are instead more similar to the tentacular systems of extant pterobranchs and echinoderms. Thus, Rotadiscus exhibits a chimeric combination of ambulacrarian and chordate characters. Phylogenetic analyses recover Rotadiscus and closely related fossil taxa as stem ambulacrarians, filling a significant morphological gap in the deuterostome tree of life. These results allow us to reconstruct the ancestral body plans of major clades of deuterostomes, revealing that key traits of extant forms, such as a post-anal region, gill bars, and a U-shaped gut, evolved through convergence.
The rangeomorph Pectinifrons abyssalis: hydrodynamic function at the dawn of animal life
Darroch SAF, Gutarra S, Masaki H, Olaru A, Gibson BM, Dunn FS, Mitchell EG, Racicot RA, Burzynski G, Rahman IA
January 2023
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Journal article
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iScience
Rangeomorphs are among the oldest putative eumetazoans known from the fossil record. Establishing how they fed is thus key to understanding the structure and function of the earliest animal ecosystems. Here, we use computational fluid dynamics to test hypothesized feeding modes for the fence-like rangeomorph Pectinifrons abyssalis, comparing this to the morphologically similar extant carnivorous sponge Chondrocladia lyra. Our results reveal complex patterns of flow around P. abyssalis unlike those previously reconstructed for any other Ediacaran taxon. Comparisons with C. lyra reveal substantial differences between the two organisms, suggesting they converged on a similar fence-like morphology for different functions. We argue that the flow patterns recovered for P. abyssalis do not support either a suspension feeding or osmotrophic feeding habit. Instead, our results indicate that rangeomorph fronds may represent organs adapted for gas exchange. If correct, this interpretation could require a dramatic reinterpretation of the oldest macroscopic animals
A new species of Nanhsiungchelys (Testudines: Cryptodira: Nanhsiungchelyidae) from the Upper Cretaceous of Nanxiong Basin, China, and the role of anterolateral processes on the carapace in drag reduction
Heterochrony and parallel evolution of echinoderm, hemichordate and cephalochordate internal bars.
Álvarez-Armada N, Cameron CB, Bauer JE, Rahman IA
May 2022
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Journal article
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Proceedings. Biological sciences
Deuterostomes comprise three phyla with radically different body plans. Phylogenetic bracketing of the living deuterostome clades suggests the latest common ancestor of echinoderms, hemichordates and chordates was a bilaterally symmetrical worm with pharyngeal openings, with these characters lost in echinoderms. Early fossil echinoderms with pharyngeal openings have been described, but their interpretation is highly controversial. Here, we critically evaluate the evidence for pharyngeal structures (gill bars) in the extinct stylophoran echinoderms <i>Lagynocystis pyramidalis</i> and <i>Jaekelocarpus oklahomensis</i> using virtual models based on high-resolution X-ray tomography scans of three-dimensionally preserved fossil specimens. Multivariate analyses of the size, spacing and arrangement of the internal bars in these fossils indicate they are substantially more similar to gill bars in modern enteropneust hemichordates and cephalochordates than to other internal bar-like structures in fossil blastozoan echinoderms. The close similarity between the internal bars of the stylophorans <i>L. pyramidalis</i> and <i>J. oklahomensis</i> and the gill bars of extant chordates and hemichordates is strong evidence for their homology. Differences between these internal bars and bar-like elements of the respiratory systems in blastozoans suggest these structures might have arisen through parallel evolution across deuterostomes, perhaps underpinned by a common developmental genetic mechanism.
Cambrian edrioasteroid reveals new mechanism for secondary reduction of the skeleton in echinoderms.
Zamora S, Rahman IA, Sumrall CD, Gibson AP, Thompson JR
March 2022
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Journal article
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Proceedings. Biological sciences
Echinoderms are characterized by a distinctive high-magnesium calcite endoskeleton as adults, but elements of this have been drastically reduced in some groups. Herein, we describe a new pentaradial echinoderm, <i>Yorkicystis haefneri</i> n. gen. n. sp., which provides, to our knowledge, the oldest evidence of secondary non-mineralization of the echinoderm skeleton. This material was collected from the Cambrian Kinzers Formation in York (Pennsylvania, USA) and is dated as <i>ca</i> 510 Ma. Detailed morphological observations demonstrate that the ambulacra (i.e. axial region) are composed of flooring and cover plates, but the rest of the body (i.e. extraxial region) is preserved as a dark film and lacks any evidence of skeletal plating. Moreover, X-ray fluorescence analysis reveals that the axial region is elevated in iron. Based on our morphological and chemical data and on taphonomic comparisons with other fossils from the Kinzers Formation, we infer that the axial region was originally calcified, while the extraxial region was non-mineralized. Phylogenetic analyses recover <i>Yorkicystis</i> as an edrioasteroid, indicating that this partial absence of skeleton resulted from a secondary reduction. We hypothesize that skeletal reduction resulted from lack of expression of the skeletogenic gene regulatory network in the extraxial body wall during development. Secondary reduction of the skeleton in <i>Yorkicystis</i> might have allowed for greater flexibility of the body wall.
The locomotion of extinct secondarily aquatic tetrapods.
Gutarra S, Rahman IA
February 2022
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Journal article
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Biological reviews of the Cambridge Philosophical Society
The colonisation of freshwater and marine ecosystems by land vertebrates has repeatedly occurred in amphibians, reptiles, birds and mammals over the course of 300 million years. Functional interpretations of the fossil record are crucial to understanding the forces shaping these evolutionary transitions. Secondarily aquatic tetrapods have acquired a suite of anatomical, physiological and behavioural adaptations to locomotion in water. However, much of this information is lost for extinct clades, with fossil evidence often restricted to osteological data and a few extraordinary specimens with soft tissue preservation. Traditionally, functional morphology in fossil secondarily aquatic tetrapods was investigated through comparative anatomy and correlation with living functional analogues. However, in the last two decades, biomechanics in palaeobiology has experienced a remarkable methodological shift. Anatomy-based approaches are increasingly rigorous, informed by quantitative techniques for analysing shape. Moreover, the incorporation of physics-based methods has enabled objective tests of functional hypotheses, revealing the importance of hydrodynamic forces as drivers of evolutionary innovation and adaptation. Here, we present an overview of the latest research on the locomotion of extinct secondarily aquatic tetrapods, with a focus on amniotes, highlighting the state-of-the-art experimental approaches used in this field. We discuss the suitability of these techniques for exploring different aspects of locomotory adaptation, analysing their advantages and limitations and laying out recommendations for their application, with the aim to inform future experimental strategies. Furthermore, we outline some unexplored research avenues that have been successfully deployed in other areas of palaeobiomechanical research, such as the use of dynamic models in feeding mechanics and terrestrial locomotion, thus providing a new methodological synthesis for the field of locomotory biomechanics in extinct secondarily aquatic vertebrates. Advances in imaging technology and three-dimensional modelling software, new developments in robotics, and increased availability and awareness of numerical methods like computational fluid dynamics make this an exciting time for analysing form and function in ancient vertebrates.
A Silurian ophiuroid with soft‐tissue preservation
Carter RP, Sutton MD, Briggs DEG, Rahman I, Siveter DJ, Siveter DJ
July 2021
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Journal article
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Papers in Palaeontology
Most Palaeozoic brittle stars lack the fused arm ossicles (vertebrae) that facilitate the remarkable mode of walking that characterizes living forms. Here we describe a stem ophiuroid from the Herefordshire Lagerstätte (Silurian, Wenlock Series), which is exceptional in preserving the body cavity uncompacted and the long tube feet. We assign the specimen to the order Oegophiurida. The morphology of the arms and attitude of the specimen suggest that locomotion may have been achieved by arm propulsion combined with podial walking. This ophiuroid increases the diversity of echinoderm higher taxa with preserved soft parts represented in the Herefordshire Lagerstätte.
Vertically migrating Isoxys and the early Cambrian biological pump
Pates S, Daley AC, Legg DA, Rahman IA
June 2021
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Journal article
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Proceedings of the Royal Society B: Biological Sciences
<jats:p>
The biological pump is crucial for transporting nutrients fixed by surface-dwelling primary producers to demersal animal communities. Indeed, the establishment of an efficient biological pump was likely a key factor enabling the diversification of animals over 500 Myr ago during the Cambrian explosion. The modern biological pump operates through two main vectors: the passive sinking of aggregates of organic matter, and the active vertical migration of animals. The coevolution of eukaryotes and sinking aggregates is well understood for the Proterozoic and Cambrian; however, little attention has been paid to the establishment of the vertical migration of animals. Here we investigate the morphological variation and hydrodynamic performance of the Cambrian euarthropod
<jats:italic>Isoxys</jats:italic>
. We combine elliptical Fourier analysis of carapace shape with computational fluid dynamics simulations to demonstrate that
<jats:italic>Isoxys</jats:italic>
species likely occupied a variety of niches in Cambrian oceans, including vertical migrants, providing the first quantitative evidence that some Cambrian animals were adapted for vertical movement in the water column. Vertical migration was one of several early Cambrian metazoan innovations that led to the biological pump taking on a modern-style architecture over 500 Myr ago.
</jats:p>
Lack of support for Deuterostomia prompts reinterpretation of the first bilateria
Kapli P, Natsidis P, Leite DJ, Fursman M, Jeffrie N, Rahman IA, Philippe H, Copley RR, Telford MJ
March 2021
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Journal article
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Science Advances
The bilaterally symmetric animals (Bilateria) are considered to comprise two monophyletic groups, Protostomia (Ecdysozoa and the Lophotrochozoa) and Deuterostomia (Chordata and the Xenambulacraria). Recent molecular phylogenetic studies have not consistently supported deuterostome monophyly. Here, we compare support for Protostomia and Deuterostomia using multiple, independent phylogenomic datasets. As expected, Protostomia is always strongly supported, especially by longer and higher-quality genes. Support for Deuterostomia, however, is always equivocal and barely higher than support for paraphyletic alternatives. Conditions that cause tree reconstruction errors—inadequate models, short internal branches, faster evolving genes, and unequal branch lengths—coincide with support for monophyletic deuterostomes. Simulation experiments show that support for Deuterostomia could be explained by systematic error. The branch between bilaterian and deuterostome common ancestors is, at best, very short, supporting the idea that the bilaterian ancestor may have been deuterostome-like. Our findings have important implications for the understanding of early animal evolution.
Pentaradial eukaryote suggests expansion of suspension feeding in White Sea-aged Ediacaran communities
<jats:title>Abstract</jats:title><jats:p>Suspension feeding is a key ecological strategy in modern oceans that provides a link between pelagic and benthic systems. Establishing when suspension feeding first became widespread is thus a crucial research area in ecology and evolution, with implications for understanding the origins of the modern marine biosphere. Here, we use three-dimensional modelling and computational fluid dynamics to establish the feeding mode of the enigmatic Ediacaran pentaradial eukaryote <jats:italic>Arkarua</jats:italic>. Through comparisons with two Cambrian echinoderms, <jats:italic>Cambraster</jats:italic> and <jats:italic>Stromatocystites</jats:italic>, we show that flow patterns around <jats:italic>Arkarua</jats:italic> strongly support its interpretation as a passive suspension feeder. <jats:italic>Arkarua</jats:italic> is added to the growing number of Ediacaran benthic suspension feeders, suggesting that the energy link between pelagic and benthic ecosystems was likely expanding in the White Sea assemblage (~ 558–550 Ma). The advent of widespread suspension feeding could therefore have played an important role in the subsequent waves of ecological innovation and escalation that culminated with the Cambrian explosion.</jats:p>
Functional assessment of morphological homoplasy in stem-gnathostomes
Ferrón H, Martínez-Pérez C, Rahman I, Selles de Lucas V, Botella H, Donoghue P
January 2021
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Journal article
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Proceedings of the Royal Society B: Biological Sciences
Osteostraci and Galeaspida are stem-gnathostomes, occupying a key phylogenetic position for resolving the nature of the jawless ancestor from which jawed vertebrates evolved more than 400 million years ago. Both groups are characterized by the presence of rigid headshields that share a number of common morphological traits, in some cases hindering the resolution of their interrelationships and the exact nature of their affinities with jawed vertebrates. Here, we explore the morphological and functional diversity of osteostracan and galeaspid headshields using geometric morphometrics and computational fluid dynamics to constrain the factors that promoted the evolution of their similar morphologies and informing on the ecological scenario under which jawed vertebrates emerged. Phylomorphospace, Mantel analysis and Stayton metrics demonstrate a high degree of homoplasy. Computational fluid dynamics reveals similar hydrodynamic performance among morphologically convergent species, indicating the independent acquisition of the same morphofunctional traits and, potentially, equivalent lifestyles. These results confirm that a number of the characters typically used to infer the evolutionary relationships among galeaspids, osteostracans and jawed vertebrates are convergent in nature, potentially obscuring understanding of the assembly of the gnathostome bodyplan. Ultimately, our results reveal that while the jawless relatives of the earliest jawed vertebrates were ecologically diverse, widespread convergence on the same hydrodynamic adaptations suggests they had reached the limits of their potential ecological diversity—overcome by jawed vertebrates and their later innovations.
Computational fluid dynamics and its applications in echinoderm palaeobiology
Rahman I
October 2020
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Journal article
Computational fluid dynamics (CFD), which involves using computers to simulate fluid flow, is emerging as a powerful approach for elucidating the palaeobiology of ancient organisms. Here, Imran A. Rahman describes its applications for studying fossil echinoderms. When properly configured, CFD simulations can be used to test functional hypotheses in extinct species, informing on aspects such as feeding and stability. They also show great promise for addressing ecological questions related to the interaction between organisms and their environment. CFD has the potential to become an important tool in echinoderm palaeobiology over the coming years.
ecology, echinoderms, computational fluid dynamics, palaeobiology, function
Computational fluid dynamics suggests ecological diversification among stem-gnathostomes
Ferrón H, Martínez-Pérez C, Rahman I, Selles de Lucas V, Botella H, Donoghue P
October 2020
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Journal article
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Current Biology
The evolutionary assembly of the vertebrate bodyplan has been characterized as a long-term ecological trend toward increasingly active and predatory lifestyles, culminating in jawed vertebrates that dominate modern vertebrate biodiversity [1, 2, 3, 4, 5, 6, 7, 8]. This contrast is no more stark than between the earliest jawed vertebrates and their immediate relatives, the extinct jawless, dermal armor-encased osteostracans, which have conventionally been interpreted as benthic mud-grubbers with poor swimming capabilities and low maneuverability [9, 10, 11, 12]. Using computational fluid dynamics, we show that osteostracan headshield morphology is compatible with a diversity of hydrodynamic efficiencies including passive control of water flow around the body; these could have increased versatility for adopting diverse locomotor strategies. Hydrodynamic performance varies with morphology, proximity to the substrate, and angle of attack (inclination). Morphotypes with dorsoventrally oblate headshields are hydrodynamically more efficient when swimming close to the substrate, whereas those with dorsoventrally more prolate headshields exhibit maximum hydrodynamic efficiency when swimming free from substrate effects. These results suggest different hydrofoil functions among osteostracan headshield morphologies, compatible with ecological diversification and undermining the traditional view that jawless stem-gnathostomes were ecologically constrained [9, 10, 11, 12] with the origin of jaws as the key innovation that precipitated the ecological diversification of the group [13, 14].
Gibson BM, Furbish DJ, Rahman IA, Schmeeckle MW, Laflamme M, Darroch SAF
September 2020
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Journal article
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Biological Reviews
Over 3.7 billion years of Earth history, life has evolved complex adaptations to help navigate and interact with the fluid environment. Consequently, fluid dynamics has become a powerful tool for studying ancient fossils, providing insights into the palaeobiology and palaeoecology of extinct organisms from across the tree of life. In recent years, this approach has been extended to the Ediacara biota, an enigmatic assemblage of Neoproterozoic soft‐bodied organisms that represent the first major radiation of macroscopic eukaryotes. Reconstructing the ways in which Ediacaran organisms interacted with the fluids provides new insights into how these organisms fed, moved, and interacted within communities. Here, we provide an in‐depth review of fluid physics aimed at palaeobiologists, in which we dispel misconceptions related to the Reynolds number and associated flow conditions, and specify the governing equations of fluid dynamics. We then review recent advances in Ediacaran palaeobiology resulting from the application of computational fluid dynamics (CFD). We provide a worked example and account of best practice in CFD analyses of fossils, including the first large eddy simulation (LES) experiment performed on extinct organisms. Lastly, we identify key questions, barriers, and emerging techniques in fluid dynamics, which will not only allow us to understand the earliest animal ecosystems better, but will also help to develop new palaeobiological tools for studying ancient life.
Potential evolutionary trade‐off between feeding and stability in Cambrian cinctan echinoderms
Rahman IA, O'Shea J, Lautenschlager S, Zamora S
June 2020
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Journal article
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Palaeontology
Reconstructing the function and behaviour of extinct groups of echinoderms is problematic because there are no modern analogues for their aberrant body plans. Cinctans, an enigmatic group of Cambrian echinoderms, exemplify this problem: their asymmetrical body plan differentiates them from all living species. Here, we used computational fluid dynamics to analyse the functional performance of cinctans without assuming an extant comparative model. Three‐dimensional models of six species from across cinctan phylogeny were used in computer simulations of water flow. The results demonstrate that cinctans with strongly flattened bodies produced much less drag than species characterized by dorsal protuberances or swellings, suggesting the former were more stable on the seafloor. However, unlike the flattened forms, cinctans with high‐relief bodies were able to passively direct flow towards the mouth and associated food grooves, indicating that they were capable of more efficient feeding on particles suspended in the water. This study provides evidence of a previously unknown evolutionary trade‐off between feeding and stability in Cambrian cinctan echinoderms.
Evolution and Development at the Origin of a Phylum
Deline B, Thompson JR, Smith NS, Zamora S, Rahman IA, Sheffield SL, Ausich WI, Kammer TW, Sumrall CD
May 2020
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Journal article
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Current Biology
Quantifying morphological evolution is key to determining the patterns and processes underlying the origin of phyla. We constructed a hierarchical morphological character matrix to characterize the radiation and establishment of echinoderm body plans during the early Paleozoic. This showed that subphylum-level clades diverged gradually through the Cambrian, and the distinctiveness of the resulting body plans was amplified by the extinction of transitional forms and obscured by convergent evolution during the Ordovician. Higher-order characters that define these body plans were not fixed at the origin of the phylum, countering hypotheses regarding developmental processes governing the early evolution of animals. Instead, these burdened characters were flexible, enabling continued evolutionary innovation throughout the clades’ history.
Re-evaluating the phylogenetic position of the enigmatic early Cambrian deuterostome Yanjiahella
Gregarious suspension feeding in a modular Ediacaran organism
Gibson BM, Rahman I, Maloney KM, Racicot RA, Mocke H, Laflamme M, Darroch SAF
June 2019
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Journal article
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Science Advances
A new ophiocistioid with soft-tissue preservation from the Silurian Herefordshire Lagerstätte, and the evolution of the holothurian body plan
Rahman I, Briggs DEG, Siveter D, Siveter D
April 2019
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Journal article
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Proceedings of the Royal Society B: Biological Sciences
Reconstructing the evolutionary assembly of animal body plans is challenging when there are large morphological gaps between extant sister taxa, as in the case of echinozoans (echinoids and holothurians). However, the inclusion of extinct taxa can help bridge these gaps. Here we describe a new species of echinozoan, Sollasina cthulhu, from the Silurian Herefordshire Lagerstätte, UK. Sollasina cthulhu belongs to the ophiocistioids, an extinct group that shares characters with both echinoids and holothurians. Using physical–optical tomography and computer reconstruction, we visualize the internal anatomy of S. cthulhu in three dimensions, revealing inner soft tissues that we interpret as the ring canal, a key part of the water vascular system that was previously unknown in fossil echinozoans. Phylogenetic analyses strongly suggest that Sollasina and other ophiocistioids represent a paraphyletic group of stem holothurians, as previously hypothesized. This allows us to reconstruct the stepwise reduction of the skeleton during the assembly of the holothurian body plan, which may have been controlled by changes in the expression of biomineralization genes.
Effects of body plan evolution on the hydrodynamic drag and energy requirements of swimming in ichthyosaurs
Proceedings of the Royal Society B: Biological Sciences
Ichthyosaurs are an extinct group of fully marine tetrapods that were well adapted to aquatic locomotion. During their approximately 160 Myr existence, they evolved from elongate and serpentine forms into stockier, fish-like animals, convergent with sharks and dolphins. Here, we use computational fluid dynamics (CFD) to quantify the impact of this transition on the energy demands of ichthyosaur swimming for the first time. We run computational simulations of water flow using three-dimensional digital models of nine ichthyosaurs and an extant functional analogue, a bottlenose dolphin, providing the first quantitative evaluation of ichthyosaur hydrodynamics across phylogeny. Our results show that morphology did not have a major effect on the drag coefficient or the energy cost of steady swimming through geological time. We show that even the early ichthyosaurs produced low levels of drag for a given volume, comparable to those of a modern dolphin, and that deep ‘torpedo-shaped’ bodies did not reduce the cost of locomotion. Our analysis also provides important insight into the choice of scaling parameters for CFD applied to swimming mechanics, and underlines the great influence of body size evolution on ichthyosaur locomotion. A combination of large bodies and efficient swimming modes lowered the cost of steady swimming as ichthyosaurs became increasingly adapted to a pelagic existence.
Exploring the potential of neutron imaging for life sciences on IMAT
Burca G, Nagella S, Clark T, Tasev D, Rahman I, Garwood RJ, Spencer ART, Turner MJ, Kelleher JF
October 2018
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Journal article
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Journal of Microscopy
Neutron imaging has been employed in life sciences in recent years and has proven to be a viable technique for studying internal features without compromising integrity and internal structure of samples in addition to being complementary to other methods such as Xray or magnetic resonance imaging. Within the last decade, a neutron imaging beamline, IMAT, was designed and built at the ISIS Neutron and Muon Source, UK, to meet the increasing demand for neutron imaging applications in various fields spanning from materials engineering to biology. In this paper, we present the first neutron imaging experiments on different biological samples during the scientific commissioning of the IMAT beamline mainly intended to explore the beamline’s capabilities and its potential as a non-invasive investigation tool in fields such as agriculture (soil-plants systems), palaeontology and dentistry.
Whole-body photoreceptor networks are independent of ‘lenses’ in brittle stars
Sumner-Rooney L, Rahman I, Sigwart JD, Ullrich-Lüter E
January 2018
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Journal article
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Proceedings of the Royal Society B: Biological Sciences
Photoreception and vision are fundamental aspects of animal sensory biology and ecology, but important gaps remain in our understanding of these processes in many species. The colour-changing brittle star Ophiocoma wendtii is iconic in vision research, speculatively possessing a unique whole-body visual system that incorporates information from nerve bundles underlying thousands of crystalline ‘microlenses’. The hypothesis that these form a sophisticated compound eye-like system regulated by chromatophore movement has been extensively reiterated, with consequent investigations into biomimetic optics and similar ‘visual’ structures in living and fossil taxa. However, no photoreceptors or visual behaviours have ever been identified. We present the first evidence of photoreceptor networks in three Ophiocoma species, both with and without microlenses and colour-changing behaviour. High-resolution microscopy, immunohistochemistry and synchrotron tomography demonstrate that putative photoreceptors cover the animals’ oral, lateral, and aboral surfaces, but are absent at the hypothesised focal points of the microlenses. The structural optics of these crystal ‘lenses’ are an exaptation and do not fulfil any apparent visual role. This contradicts previous studies, yet the photoreceptor network in Ophiocoma appears even more widespread than previously anticipated, both taxonomically and anatomically.
An edrioasteroid from the Silurian Herefordshire Lagerstätte of England reveals the nature of the water vascular system in an extinct echinoderm
Briggs DEG, Siveter DJ, Siveter DJ, Rahman I
September 2017
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Journal article
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Proceedings of the Royal Society B: Biological Sciences
Echinoderms are unique in having a water vascular system with tube feet, which perform a variety of functions in living forms. Here, we report the first example of preserved tube feet in an extinct group of echinoderms. The material, from the Silurian Herefordshire Lagerstätte, UK, is assigned to a new genus and species of rhenopyrgid edrioasteroid, Heropyrgus disterminus. The tube feet attach to the inner surface of compound interradial plates and form two sets, an upper and a lower, an arrangement never reported previously in an extant or extinct echinoderm. Cover plates are absent and floor plates are separated along the perradial suture, creating a large permanent entrance to the interior of the oral area. The tube feet may have captured food particles that entered the oral area and/or enhanced respiration. The pentameral symmetry of the oral surface transitions to eight columns in which the plates are vertically offset resulting in a spiral appearance. This change in symmetry may reflect flexibility in the evolutionary development of the axial and extraxial zones in early echinoderm evolution.
Silurian, water vascular system, Echinodermata, Edrioasteroidea, Herefordshire Lagerstätte
The Cambrian Substrate Revolution and the early evolution of attachment in suspension-feeding echinoderms
Zamora S, Deline B, Alvaro JJ, Rahman I
July 2017
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Journal article
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Earth-Science Reviews
The Cambrian, characterized by the global appearance of diverse biomineralized metazoans in the fossil record for the first time, represents a pivotal point in the history of life. This period also documents a major change in the nature of the sea floor: Neoproterozoic-type substrates stabilized by microbial mats were replaced by unconsolidated soft substrates with a well-developed mixed layer. The effect of this transition on the ecology and evolution of benthic metazoans is termed the Cambrian Substrate Revolution (CSR), and this is thought to have impacted greatly on early suspension-feeding echinoderms in particular. According to this paradigm, most echinoderms rested directly on non-bioturbated soft substrates as sediment attachers and stickers during the Cambrian Epoch 2. As the substrates became increasingly disturbed by burrowing, forming a progressively thickening mixed layer, echinoderms developed new strategies for attaching to firm and hard substrates. To test this model, we evaluated the mode of attachment of 83 Cambrian suspension-feeding echinoderm species; attachment mode was inferred based on direct evidence in fossil specimens and interpretations of functional morphology. These data were analyzed quantitatively to explore trends in attachment throughout the Cambrian. In contrast to previous studies, the majority of Cambrian clades (eocrinoids, helicoplacoids, helicocystoids, isorophid edrioasteroids, and solutes) are now interpreted as hard (shelly) substrate attachers. Only early edrioasteroids attached directly to firm substrates stabilized by microbially induced sedimentary structures. Contrary to the predictions of the CSR paradigm, our study demonstrates that Cambrian echinoderms were morphologically pre-adapted to the substrate changes that occurred during the Cambrian, allowing them to fully exploit the appearance of hardgrounds in the Furongian. We find no support for the claim that the CSR explains the peak in echinoderm diversity during Cambrian Epochs 2–3, or that it caused the extinction of helicoplacoids.
palaeoecology, attachment, seafloor, evolution
Inference of facultative mobility in the enigmatic Ediacaran organism Parvancorina
Darroch SAF, Rahman I, Gibson B, Racicot RA, Laflamme M
May 2017
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Journal article
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Biology Letters
Establishing how Ediacaran organisms moved and fed is critical to deciphering their ecological and evolutionary significance, but has long been confounded by their non-analogue body plans. Here, we use computational fluid dynamics to quantitatively analyze water flow around the Ediacaran taxon Parvancorina, thereby testing between competing models for feeding mode and mobility. The results show that flow was not distributed evenly across the organism, but was directed towards localized areas; this allows us to reject osmotrophy, and instead supports either suspension feeding or detritivory. Moreover, the patterns of recirculating flow differ substantially with orientation to the current, suggesting that if Parvancorina was a suspension feeder, it would have been most efficient if it was able to re-orient itself with respect to current direction, and thus ensure flow was directed towards feeding structures. Our simulations also demonstrate that the amount of drag varied with orientation, indicating that Parvancorina would have greatly benefited from adjusting its position to minimize drag. Inference of facultative mobility in Parvancorina suggests that Ediacaran benthic ecosystems might have possessed a higher proportion of mobile taxa than currently appreciated from trace fossil studies. Furthermore, this inference of movement suggests the presence of musculature or appendages which aren’t preserved in fossils, supporting a bilaterian affinity for Parvancorina.
Computational fluid dynamics as a tool for testing functional and ecological hypotheses in fossil taxa
Rahman I
May 2017
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Journal article
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Palaeontology
Computational fluid dynamics is a method for simulating fluid flows that has been widely used in engineering for decades, and which also has applications for studying function and ecology in fossil taxa. However, despite the possible benefits of this approach, computational fluid dynamics has been used only rarely in palaeontology to date. In this article, I outline the theoretical basis underlying the technique and detail the main steps involved in carrying out computer simulations of fluid flows. I also describe previous studies that have applied the method to fossils and discuss their potential for informing future research directions in palaeontology. Computational fluid dynamics can enable large-scale comparative analyses, as well as exacting tests of hypotheses related to the function and ecology of ancient organisms. In this way, it could transform our understanding of many extinct fossil groups.
computational fluid dynamics, hypothesis testing, ecology, fossils, function
Modelling enrolment in Cambrian trilobites
Esteve J, Rubio P, Zamora S, Rahman I
April 2017
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Journal article
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Palaeontology
Trilobites were capable of enrolling in different ways based on the flexible articulation of thoracic segments and associated interlocking devices; the type of enrolment (spiral or sphaeroidal) is thought to have largely depended on the coaptative devices that each trilobite used to enclose the body. Based on X-ray microtomography scans of complete enrolled specimens from the Cambrian, we created three-dimensional (3-D) computer models to assess the kinematics needed to achieve both enrolment types. We demonstrate that closely related trilobites with little morphological variation (Bailiaspis?, Conocoryphe and Parabailiella) developed different enrolment types as a result of small variations in the number of thoracic segments and the angle between adjacent segments. Moreover, our models indicate that sphaeroidal enrolment, which is associated with a smaller number of thoracic segments, enabled faster encapsulation. This supports the hypothesis that there was a trend in the evolution of trilobites towards reduction in the number of thoracic segments in phylogenetically derived taxa in order to enhance the efficiency of enrolment.
Proceedings of the Royal Society B: Biological Sciences
Over the past two decades, the development of methods for visualizing and analysing specimens digitally, in three and even four dimensions, has transformed the study of living and fossil organisms. However, the initial promise, that the widespread application of such methods would facilitate access to the underlying digital data, has not been fully achieved. The underlying datasets for many published studies are not readily or freely available, introducing a barrier to verification and reproducibility, and the reuse of data. There is no current agreement or policy on the amount and type of data that should be made available alongside studies that use, and in some cases are wholly reliant on, digital morphology. Here, we propose a set of recommendations for minimum standards and additional best practice for 3D digital data publication, and review the issues around data storage, management and accessibility.
phenotype, functional analysis, digital data, visualization, computed tomography, 3D models
Towards a better understanding of the origins of microlens arrays in Mesozoic ophiuroids and asteroids
Gorzelak P, Rahman I, Zamora S, Gąsiński A, Trzciński J, Brachaniec T, Salamon MA
February 2017
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Journal article
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Evolutionary Biology
Echinoderms are characterized by a calcite endoskeleton with a unique microstructure, which is optimized for multiple functions. For instance, some light-sensitive ophiuroids (Ophiuroidea) and asteroids (Asteroidea) possess skeletal plates with multi-lens arrays that are thought to act as photosensory organs. The origins of these lens-like microstructures have long been unclear. It was recently proposed that the complex photosensory systems in certain modern ophiuroids and asteroids could be traced back to at least the Late Cretaceous (ca. 79 Ma). Here, we document similar structures in ophiuroids and asteroids from the Early Cretaceous of Poland (ca. 136 Ma) that are approximately 57 million years older than the oldest asterozoans with lens-like microstructures described thus far. We use scanning electron microscopy, synchrotron tomography, and electron backscatter diffraction combined with focused ion beam microscopy to describe the morphology and crystallography of these structures in exceptional detail. The results indicate that, similar to Recent light-sensitive ophiuroids, putative microlenses in Cretaceous ophiuroids and asteroids exhibit a shape and crystal orientation that would have minimized spherical aberration and birefringence. We suggest that these lens-like microstructures evolved by secondary deposition of calcite on pre-existing porous tubercles that were already present in ancestral Jurassic forms.
Palaeontology: Tiny fossils in the animal family tree
Rahman I
January 2017
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Journal article
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Nature
Newly discovered microscopic fossils might shed light on the early evolution of the deuterostomes, the animal group that includes vertebrates. But more work is needed to resolve the fossils' place in the deuterostome tree.
Applications of three-dimensional box modeling to paleontological functional analysis
Rahman I, Lautenschlager S
January 2017
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Journal article
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Paleontological Society Papers
Functional analysis through computer modeling can inform on how extinct organisms moved and fed, allowing us to test long-standing paleobiological hypotheses. Many such studies are based on digital models derived from computed tomography or surface scanning, but these methods are not appropriate for all fossils. Here, we show that box modeling — 3-D modeling of complex shapes based on simple objects — can be used to reconstruct the morphology of various fossil specimens. Moreover, the results of computational functional analyses utilizing such models are very similar to those for models derived from tomographic or surface-based techniques. Box modeling is more broadly applicable than alternative methods for digitizing specimens, and hence there is great potential for this approach in paleontological functional analysis. Possible applications include large-scale comparative studies, analyses of hypothetical morphologies, and virtually restoring incomplete/distorted specimens.
Virtual paleontology – An overview
Sutton M, Rahman I, Garwood R
April 2016
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Journal article
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Paleontological Society Papers
Virtual paleontology is the study of fossils through three-dimensional digital visualizations; it represents a powerful and well-established set of tools for the analysis and dissemination of fossil-data. Techniques are divisible into tomographic (i.e. slice-based) and surface-based types. Tomography has a long pre-digital history, but the recent explosion of virtual paleontology has resulted primarily from developments in X-ray computed tomography (CT), and of surface-based technologies such as laser scanning. Destructive tomographic methods include forms of physical-optical tomography (e.g. serial grinding); these are powerful but problematic techniques. Focused Ion Beam (FIB) tomography is a modern alternative for microfossils, also destructive but capable of extremely high resolutions. Non-destructive tomographic methods include the many forms of CT; these are the most widely used data-capture techniques at present, but are not universally applicable. Where CT is inappropriate, other non-destructive technologies (neutron tomography, magnetic resonance imaging, optical tomography) may prove suitable. Surface-based methods provide portable and convenient data capture for surface topography and texture, and may be appropriate when internal morphology is not of interest; technologies include laser scanning, photogrammetry, and mechanical digitization. Reconstruction methods that produce visualizations from raw data are many and various; selection of an appropriate workflow will depend on many factors, but is an important consideration that should be addressed prior to any study. The vast majority of three-dimensional fossils can now be studied using some form of virtual paleontology, and barriers to broader uptake are being eroded. Technical issues regarding data-sharing, however, remain problematic. Technological developments continue; those promising tomographic recovery of compositional data are of particular relevance to paleontology.
Palaeogeographic implications of a new iocrinid crinoid (Disparida) from the Ordovician (Darriwillian) of Morocco
Zamora S, Rahman I, Ausich WI
December 2015
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Journal article
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PeerJ
Complete, articulated crinoids from the Ordovician peri-Gondwanan margin are rare. Here, we describe a new species, Iocrinus africanus sp. nov., from the Darriwilian-age Taddrist Formation of Morocco. The anatomy of this species was studied using a combination of traditional palaeontological methods and non-destructive X-ray micro-tomography (micro-CT). This revealed critical features of the column, distal arms, and aboral cup, which were hidden in the surrounding rock and would have been inaccessible without the application of micro-CT. Iocrinus africanus sp. nov. is characterized by the presence of seven to thirteen tertibrachials, three in-line bifurcations per ray, and an anal sac that is predominantly unplated or very lightly plated. Iocrinus is a common genus in North America (Laurentia) and has also been reported from the United Kingdom (Avalonia) and Oman (middle east Gondwana). Together with Merocrinus, it represents one of the few geographically widespread crinoids during the Ordovician and serves to demonstrate that faunal exchanges between Laurentia and Gondwana occurred at this time. This study highlights the advantages of using both conventional and cutting-edge techniques (such as micro-CT) to describe the morphology of new fossil specimens.
Suspension feeding in the enigmatic Ediacaran organism Tribrachidium demonstrates complexity of Neoproterozoic ecosystems
Rahman I, Darroch SAF, Racicot RA, Laflamme M
November 2015
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Journal article
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Science Advances
<p style="text-align:justify;">The first diverse and morphologically complex macroscopic communities appear in the late Ediacaran period, 575 to 541 million years ago (Ma). The enigmatic organisms that make up these communities are thought to have formed simple ecosystems characterized by a narrow range of feeding modes, with most restricted to the passive absorption of organic particles (osmotrophy). We test between competing feeding models for the iconic Ediacaran organism Tribrachidium heraldicum using computational fluid dynamics. We show that the external morphology of Tribrachidium passively directs water flow toward the apex of the organism and generates low-velocity eddies above apical “pits.” These patterns of fluid flow are inconsistent with osmotrophy and instead support the interpretation of Tribrachidium as a passive suspension feeder. This finding provides the oldest empirical evidence for suspension feeding at 555 to 550 Ma, ~10 million years before the Cambrian explosion, and demonstrates that Ediacaran organisms formed more complex ecosystems in the latest Precambrian, involving a larger number of ecological guilds, than currently appreciated.</p>
Cambrian cinctan echinoderms shed light on feeding in the ancestral deuterostome
Rahman I, Zamora S, Falkingham PL, Phillips JC
November 2015
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Journal article
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Proceedings of the Royal Society B: Biological Sciences
Reconstructing the feeding mode of the latest common ancestor of deuterostomes is key to elucidating the early evolution of feeding in chordates and allied phyla; however, it is debated whether the ancestral deuterostome was a tentaculate feeder or a pharyngeal filter feeder. To address this, we evaluated the hydrodynamics of feeding in a group of fossil stem-group echinoderms (cinctans) using computational fluid dynamics. We simulated water flow past three-dimensional digital models of a Cambrian fossil cinctan in a range of possible life positions, adopting both passive tentacular feeding and active pharyngeal filter feeding. The results demonstrate that an orientation with the mouth facing downstream of the current was optimal for drag and lift reduction. Moreover, they show that there was almost no flow to the mouth and associated marginal groove under simulations of passive feeding, whereas considerable flow towards the animal was observed for active feeding, which would have enhanced the transport of suspended particles to the mouth. This strongly suggests that cinctans were active pharyngeal filter feeders, like modern enteropneust hemichordates and urochordates, indicating that the ancestral deuterostome employed a similar feeding strategy.
Early post-metamorphic, Carboniferous blastoid reveals the evolution and development of the digestive system in echinoderms
Rahman I, Waters JA, Sumrall CD, Astolfo A
October 2015
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Journal article
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Biology Letters
Inferring the development of the earliest echinoderms is critical to uncovering the evolutionary assembly of the phylum-level body plan but has long proven problematic because early ontogenetic stages are rarely preserved as fossils. Here, we use synchrotron tomography to describe a new early post-metamorphic blastoid echinoderm from the Carboniferous (approx. 323 Ma) of China. The resulting three-dimensional reconstruction reveals a U-shaped tubular structure in the fossil interior, which is interpreted as the digestive tract. Comparisons with the developing gut of modern crinoids demonstrate that crinoids are an imperfect analogue for many extinct groups. Furthermore, consideration of our findings in a phylogenetic context allows us to reconstruct the evolution and development of the digestive system in echinoderms more broadly; there was a transition from a straight to a simple curved gut early in the phylum's evolution, but additional loops and coils of the digestive tract (as seen in crinoids) were not acquired until much later.
SBTMR, echinoderms, synchrotron tomography, evolution, blastoids, development
Miocene Clypeaster from Valencia (E Spain): Insights into the taphonomy and ichnology of bioeroded echinoids using X-ray micro-tomography
Taphonomic analysis and X-ray micro-tomography (μCT) were applied to Clypeaster specimens from the Miocene of Fuente del Jarro (Valencia, Spain). This enabled the identification of various preservational features, including encrustation, bioerosion, abrasion and post-depositional cracking. Approximately 15% of the studied specimens were affected by encrusters and/or borers. Of particular interest was a single intensely-bored specimen preserving numerous cross-cutting bioerosion structures. These structures exhibit a distinctive morphology consisting of clavate or flask-shaped chambers with a circular to oval cross-section, a narrow neck region near the figure-of-eight-shaped aperture and a chimney extending outside the Clypeaster test. The excellent preservation and characteristic morphology, as revealed by the μCT scan, coupled with the observation that (in some cases) articulated bivalve shells are still present within the chambers, allows for the identification of the tracemaker as the boring bivalve Rocellaria, reaffirming these tube-dwelling animals as borers, burrowers and crypt-builders. The trace fossils described herein are semi-endoskeletal dwellings, representing a combination of bioerosion through the plates of the echinoids, bioturbation in the form of burrowing into the sediment infill of the Clypeaster specimen and carbonate secretion resulting in a crypt. The morphologies of the different dwellings are influenced by the limited available space within the echinoid tests. This study confirms the importance of the relatively stable and thick Clypeaster shells as benthic islands in Cenozoic sandy littoral settings. The high degree of multiple colonizations, as well as the uniform orientation of the burrows, suggests a long-term stable position of this secondary substrate at or near the sediment surface.
Experimental reduction of intromittent organ length reduces male reproductive success in a bug
Dougherty LR, Rahman I, Burdfield-Steel ER, Greenway EVG, Shuker DM
June 2015
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Journal article
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Proceedings of the Royal Society B: Biological Sciences
It is now clear in many species that male and female genital evolution has been shaped by sexual selection. However, it has historically been difficult to confirm correlations between morphology and fitness, as genital traits are complex and manipulation tends to impair function significantly. In this study, we investigate the functional morphology of the elongate male intromittent organ (or processus) of the seed bug Lygaeus simulans, in two ways. We first use micro-computed tomography (micro-CT) and flash-freezing to reconstruct in high resolution the interaction between the male intromittent organ and the female internal reproductive anatomy during mating. We successfully trace the path of the male processus inside the female reproductive tract. We then confirm that male processus length influences sperm transfer by experimental ablation and show that males with shortened processi have significantly reduced post-copulatory reproductive success. Importantly, male insemination function is not affected by this manipulation per se. We thus present rare, direct experimental evidence that an internal genital trait functions to increase reproductive success and show that, with appropriate staining, micro-CT is an excellent tool for investigating the functional morphology of insect genitalia during copulation.
Deciphering the early evolution of echinoderms with Cambrian fossils
Zamora S, Rahman I
November 2014
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Journal article
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Palaeontology
Echinoderms are a major group of invertebrate deuterostomes that have been an important component of marine ecosystems throughout the Phanerozoic. Their fossil record extends back to the Cambrian, when several disparate groups appear in different palaeocontinents at about the same time. Many of these early forms exhibit character combinations that differ radically from extant taxa, and thus their anatomy and phylogeny have long been controversial. Deciphering the earliest evolution of echinoderms therefore requires a detailed understanding of the morphology of Cambrian fossils, as well as the selection of an appropriate root and the identification of homologies for use in phylogenetic analysis. Based on the sister‐group relationships and ontogeny of modern species and new fossil discoveries, we now know that the first echinoderms were bilaterally symmetrical, represented in the fossil record by Ctenoimbricata and some early ctenocystoids. The next branch in echinoderm phylogeny is represented by the asymmetrical cinctans and solutes, with an echinoderm‐type ambulacral system originating in the more crownward of these groups (solutes). The first radial echinoderms are the helicoplacoids, which possess a triradial body plan with three ambulacra radiating from a lateral mouth. Helicocystoids represent the first pentaradial echinoderms and have the mouth facing upwards with five radiating recumbent ambulacra. Pentaradial echinoderms diversified rapidly from the beginning of their history, and the most significant differences between groups are recorded in the construction of the oral area and ambulacra, as well as the nature of their feeding appendages. Taken together, this provides a clear narrative of the early evolution of the echinoderm body plan.
Virtual paleontology: computer-aided analysis of fossil form and function
Rahman I, Smith SY
July 2014
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Journal article
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Journal of Paleontology
SBTMR
A virtual world of paleontology
Cunningham JA, Rahman I, Lautenschlager S, Rayfield EJ, Donoghue PCJ
May 2014
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Journal article
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Trends in Ecology and Evolution
Computer-aided visualization and analysis of fossils has revolutionized the study of extinct organisms. Novel techniques allow fossils to be characterized in three dimensions and in unprecedented detail. This has enabled paleontologists to gain important insights into their anatomy, development, and preservation. New protocols allow more objective reconstructions of fossil organisms, including soft tissues, from incomplete remains. The resulting digital reconstructions can be used in functional analyses, rigorously testing long-standing hypotheses regarding the paleobiology of extinct organisms. These approaches are transforming our understanding of long-studied fossil groups, and of the narratives of organismal and ecological evolution that have been built upon them.
functional analysis, digital visualization, SBTMR, paleontology, computed tomography, computer modeling
The youngest ctenocystoids from the Upper Ordovician of the United Kingdom and the evolution of the bilateral body plan in echinoderms
Rahman I, Stewart S, Zamora S
March 2014
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Journal article
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Acta Palaeontologica Polonica
During the early Palaeozoic, echinoderm body plans were much more diverse than they are today, displaying four distinct types of symmetry. This included the bilateral ctenocystoids, which were long thought to be restricted to the Cambrian. Here, we describe a new species of ctenocystoid from the Upper Ordovician of Scotland (Conollia sporranoides sp. nov.). This allows us to revise the genus Conollia, which was previously based on a single poorly-known species from the Upper Ordovician of Wales (Conollia staffordi). Both these species are characterized by a unique morphology consisting of an elongate-ovoid body covered in spines, which clearly distinguishes them from their better-known Cambrian relatives; they are interpreted as infaunal or semi-infaunal burrowers from deep-water environments. This indicates that the ctenocystoid body plan was not fixed early in the evolution of the group, and they most likely modified their structure as an adaptation to a new mode of life in the Ordovician.
echinodermata, ctenocystoidea, SBTMR, body plans, United Kingdom, ordovician, bilateral symmetry, evolution
Techniques for Virtual Palaeontology
Edited by:
Sutton, MD, Rahman, IA, Garwood, RJ
November 2013
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Book
Taphonomy and ontogeny of early pelmatozoan echinoderms: A case study of a mass-mortality assemblage of Gogia from the Cambrian of North America
Plated Cambrian bilaterians reveal the earliest stages of echinoderm evolution.
Zamora S, Rahman IA, Smith AB
January 2012
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Journal article
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PloS one
Echinoderms are unique in being pentaradiate, having diverged from the ancestral bilaterian body plan more radically than any other animal phylum. This transformation arises during ontogeny, as echinoderm larvae are initially bilateral, then pass through an asymmetric phase, before giving rise to the pentaradiate adult. Many fossil echinoderms are radial and a few are asymmetric, but until now none have been described that show the original bilaterian stage in echinoderm evolution. Here we report new fossils from the early middle Cambrian of southern Europe that are the first echinoderms with a fully bilaterian body plan as adults. Morphologically they are intermediate between two of the most basal classes, the Ctenocystoidea and Cincta. This provides a root for all echinoderms and confirms that the earliest members were deposit feeders not suspension feeders.
Animals, Echinodermata, Species Specificity, Body Patterning, Fossils, History, Ancient, Spain, X-Ray Microtomography, Biological Evolution
Bioturbation in Burgess Shale-type Lagerstätten — Case study of trace fossil–body fossil association from the Kaili Biota (Cambrian Series 3), Guizhou, China
New data on the genus Sucocystis (Cincta, Echinodermata) from the middle Cambrian of Spain: biostratigraphic and phylogenetic implications
Rahman I, Zamora S
December 2008
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Journal article
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Revista Española de Paleontología
New material of the carpoid class Cincta is described from the middle Cambrian of the Iberian Chains (Spain). Material consists of the dorsal surface of a well preserved individual belonging to the genus Sucocystis; this spe¬cimen comprises a complete theca and a partial stele. The marginal ring (cinctus) is composed of twelve margi¬nal plates (M6r-M5l). Two well-defined grooves run from the mouth around the outer face of the marginal ring: the right groove is short, terminating in M2r; the left one is longer, ending in the medial part of M2l. The lintel is composed of four suropercular plates, which are larger than other supracentral ossicles. The shape of the the¬ca, length of the left marginal groove and structure of the lintel allow Sucocystis sp. A to be differentiated from other members of the Sucocystidae. The specimen was found in Mesones de Isuela (Zaragoza, Spain), in levels from the upper part of the Murero Formation (lower Languedocian), which correspond to the Solenopleuropsis thorali zone. It is one of the oldest representatives of the genus and expands the stratigraphic range of Sucocys¬tis in the middle Cambrian of Spain. Sucocystis sp. A is unique among the Sucocystidae in the length of the left marginal groove, which reaches plate M2l. Comparisons with other species of Sucocystis (sensu Friedrich, 1993) demonstrate that there was considerable variation in the length and number of food grooves within the genus, suggesting that Sucocystis may be a paraphyletic group.