[Palaeontology, Vol. 59, Part 3, 2016, pp. 463–479]
UNVEILING BIASES IN SOFT-TISSUE PHOSPHATIZATION: EXTENSIVE PRESERVATION OF MUSCULATURE IN THE CRETACEOUS (CENOMANIAN) POLYCHAETE ROLLINSCHAETA MYOPLENA (ANNELIDA: AMPHINOMIDAE) by PAUL WILSON 1 , LUKE A. PARRY 1 , 2 , JAKOB VINTHER 1 , 3 * and GREGORY D. EDGECOMBE 2 * 1 School of Earth Sciences, Bristol Life Sciences Building, Tyndall Avenue, Bristol, UK; e-mails:
[email protected],
[email protected],
[email protected] 2 Department of Earth Sciences, Natural History Museum, Cromwell Road, London, UK; e-mail:
[email protected] 3 School of Biological Sciences, Bristol Life Sciences Building, Tyndall Avenue, Bristol, UK *Corresponding authors
Typescript received 27 October 2015; accepted in revised form 19 February 2016
tion: (1) a taxonomic bias restricted to R. myoplena that triggers unusually extensive phosphatization; and (2) a tissue bias whereby longitudinal and parapodial musculature show markedly higher fidelity in comparison to the musculature of the intestine and body wall circular muscles. Potential explanations for these biases include internal phosphateenrichment by relative muscle density, the relative rate of decay and the physiology of musculature. Incongruence between experimental decay series for polychaetes and the prevalence of labile tissue preservation over recalcitrant tissues in R. myoplena exposes the limits of decay experiments for understanding exceptional preservation.
Abstract: The process of soft-tissue phosphatization (the replication of labile tissues by calcium phosphate) is responsible for many instances of high-resolution soft tissue preservation, often revealing anatomical insights into the animals that so preserved. However, while much work has gone into exploring key issues such as biases and micro-controls, phosphatization remains poorly understood as a taphonomic process. Here, using camera lucida, plain-light microscopy and SEM imagery, we address this issue by describing the taphonomy and fidelity of the musculature of Rollinschaeta myoplena Parry et al., a phosphatized annelid from the Cretaceous Konservat-Lagerst€atten of Hakel and Hjoula, Lebanon, with an unprecedented quantity of three-dimensional soft-tissue preservation. Analysis highlights two strong, previously recognized biases affecting the process of phosphatiza-
Key words: phosphatization, taphonomy, soft tissue.
T H E fossil record depicts an overwhelming bias towards the preservation of recalcitrant tissues, those materials that are resistant to decay and diagenesis. Instances in which more labile tissues such as skin or muscle are preserved, termed ‘Konservat-Lagerst€atten’, are considerably rarer (Seilacher 1970) and commonly provide important windows into evolutionary history and yield key insights into the diversification of life (Gabbott et al. 1995; Li et al. 1998; Zhou et al. 2003; Parry et al. 2014; Paterson et al. 2016; Wang et al. 2016). Among a variety of different taphonomic modes by which these tissues can be lithified, phosphatization (the permineralization, replacement or infilling of organic material with calcium phosphates) is one of the most informative, commonly yielding soft-tissues with sub-cellular details, such as the
putative embryos of the Doushantuo Formation (Xiao et al. 1998; Butterfield 2003; Donoghue et al. 2006; Yin & Zhu 2012) and the fish of the Santana Formation (Martill 1990). As it stands, a number of different modes of phosphatization are recognized. Doushantuo-type embryos and Orsten-type cuticular impregnations bear many similarities, both being derived from a shared bias towards cuticular phosphatization (Butterfield 2003; Donoghue et al. 2006). However, small shelly fossil-type (SSF-type) is characterized by phosphatic steinkerns and moulds of a variety of small (
