Dr Imran Rahman
Email: imran.rahman@oum.ox.ac.uk
Phone: +44 (0)1865 272 996
College profile page: Junior Research Fellow, St Cross College
Twitter: @VirtualPalaeo
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Research summary
Dr Rahman’s research uses echinoderms as a model group for uncovering the origin and early evolution of animals more broadly. His work is focused on Palaeozoic fossils, which document the earliest steps in the evolution of the echinoderm body plan. Fossils are analysed with the aid of high-resolution X-ray tomography and computer simulations (e.g. computational fluid dynamics), providing new insights into their morphology, systematics and function. This has informed rigorous tests of long-standing hypotheses concerning the mode of life, phylogenetic relationships and evolutionary history of early echinoderms, with implications for understanding the Cambrian explosion and the emergence of animals more generally.
Related research interests include Ediacaran organisms and their ecosystems, the anatomy and development of deuterostomes and techniques for three-dimensional visualization and analysis of fossil and modern specimens.
CV
Imran Rahman is Deputy Head of Research at Oxford University Museum of Natural History, and is currently supported by a Museum Research Fellowship. He is also a Junior Research Fellow at St Cross College. Prior to this, Imran was supported by an 1851 Research Fellowship split between the University of Bristol and the Oxford University Museum of Natural History.
Imran obtained an MSc in Palaeobiology from University College London and a PhD on Palaeozoic fossil echinoderms from Imperial College London under the supervision of Dr Mark Sutton. After his PhD, Imran undertook an MSc in Evolutionary Genetics and Genomics at the University of Manchester to gain practical experience in molecular biology and bioinformatics. This was followed by a NERC Postdoctoral Research Fellowship split between the Universities of Birmingham and Bristol.
Featured publications
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A new ophiocistioid with soft-tissue preservation from the Silurian Herefordshire Lagerstätte, and the evolution of the holothurian body plan.
Rahman, IA, Thompson, JR, Briggs, DEG, Siveter, DJ, Siveter, DJ, Sutton, MD2019|Journal article|Proc Biol SciReconstructing 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.Echinodermata, Herefordshire Lagerstätte, Holothuroidea, Ophiocistioidea, Silurian, water vascular system -
The Cambrian Substrate Revolution and the early evolution of attachment in suspension-feeding echinoderms
Zamora, S, Deline, B, Javier Álvaro, J, Rahman, IA2017|Journal article|Earth-Science Reviews© 2017 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. -
Cambrian cinctan echinoderms shed light on feeding in the ancestral deuterostome.
Rahman, IA, Zamora, S, Falkingham, PL, Phillips, JC2015|Journal article|Proc Biol SciReconstructing 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.computational fluid dynamics, deuterostomes, echinoderms, evolution, feeding, functional morphology, Animals, Biological Evolution, Computer Simulation, Echinodermata, Feeding Behavior, Fossils, Hydrodynamics -
Suspension feeding in the enigmatic Ediacaran organism Tribrachidium demonstrates complexity of Neoproterozoic ecosystems
Rahman, IA, Darroch, SAF, Racicot, RA, Laflamme, M2015|Journal article|Science Advances<jats:p>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 <jats:italic>Tribrachidium heraldicum</jats:italic> using computational fluid dynamics. We show that the external morphology of <jats:italic>Tribrachidium</jats:italic> 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 <jats:italic>Tribrachidium</jats:italic> 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.</jats:p> -
Early post-metamorphic, Carboniferous blastoid reveals the evolution and development of the digestive system in echinoderms.
Rahman, IA, Waters, JA, Sumrall, CD, Astolfo, A2015|Journal article|Biol LettInferring 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.blastoids, development, echinoderms, evolution, synchrotron tomography, Animals, Biological Evolution, China, Echinodermata, Fossils, Gastrointestinal Tract, Phylogeny
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