880


Journal of Paleontology 92(5):872–882


Schneider, 1988; Nichols, 1994; Oji, 1996; Baumiller, 2013a). However, as was previously discussed, fossils of intact feather stars are so rare that opportunities for recognizing regeneration are very few. Yet data on regeneration are crucial for evaluating hypotheses related to functional morphology and evolutionary history of crinoids. For example, today’s success of feather stars relative to stalked crinoids in terms of their bathymetric distribution, abundance, and diversity has often been linked to the various ways in which they have been able to cope with interactions with other organisms (Meyer and Macurda, 1977; Messing, 1997; Gorzelak et al., 2012). Several in situ observations have confirmed that such interactions do occur in the Recent (Magnus, 1963; Fishelson, 1972, 1974; Conan et al., 1981; Meyer and Ausich, 1983; Meyer et al., 1984; Vail, 1987; Messing et al., 1988; Baumiller et al., 1991; Nichols, 1994; Baumiller et al., 2008b; Bowden et al., 2011; Stevenson et al., 2017), often involving sublethal damage to the crinoid, including injuries to arms and/or pinnules. Consequently, regenerating arms have been assumed to represent repair of injuries and used as a proxy for antagonistic interactions (Meyer, 1985; Schneider, 1988; Oji, 1996; Aronson et al., 1997; Baumiller and Gahn, 2003, 2004, 2013; Gahn and Baumiller, 2005; Baumiller, 2013b). Using this logic, the regenerating arm in the Waipati specimen of R. aotearoa n. comb. not only provides the first fossil example of this phenomenon in a feather star, but supports the claim that they suffered sublethal predation in the geologic past. Another interesting feature of the intact specimen of


R. aotearoa n. comb. from Waipati relates to the position of the regenerating arm, more specifically to the articulation between the distal brachial of the remaining portion of the original arm (IIIBr1) and the proximal brachial of the regenerating portion (IIIBr2). This articulation, IIIBr1–2, is a syzygy, an articulation type that is generally thought to facilitate the shedding (autotomy) and regrowth of arms in some crinoids, including feather stars (Wilkie, 2001). In extant crinoids, autotomy at syzygies can occur in response to mechanical stimulation; in addition, syzygies are almost always the site of arm regeneration (Holland and Grimmer, 1981; Mladenov, 1983; Oji and Okamoto, 1994). Drawing on these observations, Oji and Okamoto (1994) presented a compelling argument that the function of syzygies is to reduce damage and mortality from predators, and presence and specific placement of syzygies have been linked to the success of feather stars in handling predation pressure (Oji and Okamoto, 1994; Baumiller, 1997, 2008). So whereas syzygies have been documented in fossil feather stars because of their distinct morphology, data on their placement, which is taxon specific and highly predictable (Hess and Messing, 2011), requires intact specimens, and confirming the autotomy function necessitates a regenerating arm. In this regard, the intact specimen of R. aotearoa n. comb. is of special importance as it: (1) provides data on the position of syzygies in Conometridae, a family with no extant representatives, and (2) confirms syzygial autotomy function in a Paleogene feather star.


Acknowledgments


We are grateful to the following for their assistance with museum specimens: N. Hudson, University of Auckland; C. del


Rio, Museo Argentino de Ciencias Naturales; J. Simes and M. Terezow, Geological and Nuclear Sciences; the late A.Grebneff,University ofOtago.Wethank the following for help withMāori names:M. Brunton, K. Cassidy, and theUniversity of Otago Office of Māori Affairs, and T. King and R. Donaldson, manager of Waihao Marae. Foveran Station and the Harvey family are thanked for access to localities.We thank M. Eleaume for help with translating de Loriol,M. Griffin for help in locating specimens of Cypelometra inhering,M.Lynch,A. Rountrey, J. Pang, J. Saulsbury for assistance with CT scan and 3D rendering, and two anonymous reviewers for comments and suggestions. Figures by C. Abraczinskas. Figure 4 by C. Abraczinskas and B. Miljour. T.K.B. was supported in part by the US and New Zealand Fulbright during his sabbatical at the University of Otago. This work was partially funded by grants to T.K.B. from the National Science Foundation (EAR 0824793; DEB 1036260) and the National Geographic Society (NGS 8505-08), and to R.E.F. from the National Geographic Society (NGS 4846-92).


Accessibility of supplemental data


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