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Hyoliths and the Pace of the Cambrian Explosion 1

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Hyoliths and the Pace of the Cambrian Explosion 1 DEPARTMENT OF EARTH SCIENCES- DURHAM UNIVERSITY Dr Martin Smith: [email protected] Hyoliths and the Pace of the Cambrian Explosion 1. Background The distinctive conical shells of hyoliths are some of the earliest remains of biomineralizing animals to enter the Cambrian fossil record, and hyoliths remain an important part of marine com- munities through the 290 million year duration of the Palaeozoic era. Long thought to represent an extinct body plan and a separate phylum, recent study of exceptional- ly preserved material from the Burgess Shale and Chengjiang has allied hyoliths with Brachiopods [1]. Unpublished observations indicate that hyoliths occupy a derived position within this group. Haplophrentis carinatus, a hyolithid from the Key aims Burgess Shale • To critically reappraise the fossil record of early pre-mineralization history in the Brachiopod line- “hyoliths” age – and thus permitting a long ‘fuse’ to the Cam- • To establish whether the stratigraphic history of brian explosion; (iii), hyoliths and brachiopods are the group can be reconciled with a gradualistic not, after all, closely related. evolutionary model On this view, brachiopod fossils should occur 3. Scientific benefits before the first hyoliths. But on the contrary, the first hyoliths occur some 10–20 million years be- Whereas the fossil record points to a relatively fore brachiopod fossils [2]. This raises the question abrupt appearance of complex animal-dominated of whether these early ‘orthothecids’ truly belong ecosystems early in the Cambrian period, estimates to the hyolith group; many of these fossils are based on evolutionary models (molecular and simply elongate conical shells, and lack muscle morphological clocks) point to a cryptic origin of scars, opercula, detailed shell mineralogy or other many animal phyla long before their first features that would conclusively align them with appearance in the fossil record. This project’s hyoliths. stratigraphic test of these competing hypotheses will help to illuminate the true nature of the Cambrian ‘explosion’, one of the defining events in 2. Aims and methods life history. This project will undertake a systematic review of hyolith fossils in order to establish a suite of char- 4. Training acteristics that robustly denote membership of the hyolith group. These criteria will be applied to the The student will be trained in systematics and Cambrian fossil record in order to re-evaluate early taxonomy and stratigraphic methods, and in the conical shells and reappraise (i) their membership application of appropriate statistical techniques and of Hyolitha; (ii) their position within the group. their implementation in R. This revised taxonomic framework will be in- References & reading tegrated with stratigraphic information to provide 1. Moysiuk, J., Smith, M.R., and Caron, J.-B. (2017). robust temporal constraint on hyolith evolution, in Hyoliths are Palaeozoic lophophorates. Nature 541, the context of occurrence data from Brachiopoda. 394–397. http://doi.org/10.1038/nature20804. Statistical tools will be applied to discriminate be- 2. Kouchinsky, A. V., Bengtson, S., Runnegar, B.N., tween three hypotheses: (i), the shelly fossil record Skovsted, C.B., Steiner, M., and Vendrasco, M.J. (2012). Chronology of early Cambrian provides a fundamentally accurate chronicle of bio- biomineralization. Geol. Mag. 149, 221–251. logical evolution in the brachiopod + hyolith line- http://journals.cambridge.org/action/displayAbstract?f age; (ii), hyoliths and brachiopods gained bio- romPage=online&aid=8483287. mineralization independently, pointing to a long MSc-by-Research STUDENTSHIP PROPOSAL — 2018 http://www.dur.ac.uk/earth.sciences/postgraduate/ .
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