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.
Computer simulation of water flow around Protocinctus mansillaensis, a fossil echinoderm from the Cambrian of Spain, Rahman et al. 2015
Three-dimensional computer reconstruction of Heropyrgus disterminus, a fossil echinoderm from the Silurian of Herefordshire, UK, Briggs et al. 2017
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.
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, IA, Waters, JA, Sumrall, CD, Astolfo, A
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.