Baumiller and Fordyce—New genus of feather star from Oligocene of New Zealand


877


other conometrid genera, and are highly variable, in the Waipati specimen of R. aotearoa n. comb., they are articulated to the primibrachials, and disappointingly, their facets remain con- cealed. Nevertheless, in its shape, arrangement of cirrus sockets, and sculpturing, Rautangaroa n. gen. most closely resembles other conometrids.


Discussion


Taphonomy.—The crinoids that have been recovered from the Otekaike Limestone occur in two states of preservation: most, including Eagle’s (2007, 2008) material, consist of dissociated elements that include brachials, pinnules, cirri, centrodorsals, and only in a few instances, centrodorsals with a radial circlet attached; the specimen of R. aotearoa n. comb. collected near Waipati described herein is remarkably complete and articu- lated, consisting of a centrodorsal, many cirri of several cirrals (none complete), with a radial circlet, radiating arms of as many as 21 brachials (none complete), and numerous pinnulars (Fig. 3, Supplemental Data 1, 2, 3). This dichotomous nature of pre- servation may indicate that different taphonomic processes were responsible: in the first instance, a period of postmortem decay, disarticulation, and burial, and in the second, rapid burial of an intact, perhaps live individual. For fossil feather stars, the high degree of disarticulation


Figure 3. Lateral view of Rautangaroa aotearoa n. gen. n. comb. from the Otekaike Limestone, Oligocene, ‘Waipati,’ North Otago, New Zealand, (OU46680). Micro-CT slices and a 3D rendering of the specimen are provided in the Supplemental Data 2 and 3. Scale bar as indicated.


compressed, reaching length-to-width ratio of 1.6 by about c12; no cirri intact beyond about c12; numerous disarticulated cirri ranging from cylindrical (0.3mm long by 0.3mm wide; length- to-width ratio=1) to long, compressed, hour-glass shaped; no spines, no swellings or ridges; claw not recovered (Fig. 5).


Remarks.—Assignment of R. aotearoa n. comb. to the Con- ometridae is based primarily on the centrodorsal morphology and arrangement, size, and shape of cirrus sockets. Given that the Waipati specimen of R. aotearoa n. comb. is largely intact, it may seem surprising that other skeletal elements were not useful in this regard, but this is in part a consequence of the highly incomplete preservation of the other six genera currently assigned to this family (Hess and Messing, 2011). Furthermore, the radials, which are often taxonomically important, proved of limited use in this case because whereas they are known in the


and incompleteness is by far the most common mode of preservation. This is perhaps not surprising given that their multiplated skeletons are not particularly resistant to postmor- tem processes and disarticulate easily (Meyer and Meyer, 1986). Most crinoid skeletal elements are only loosely held together by slender fibers of soft tissue (ligament and muscle) that decay quickly, whereas those articulations that are more tightly bound (e.g., syzygies) tend to be specialized for autotomy and fail even more quickly either due to the active response of the organism to the death-related stress or because they are not resistant to decay. The more frequent recovery of fossil centrodorsals or centrodorsals with a basal and radial ring is consistent with the fact that the centrodorsal is the largest element, and the articulation between it and the radials is nonmoveable, tightly sutured, and not specialized for autotomy. Experiments on extant feather stars confirm that postmortem disarticulation may be rapid, with high potential for differential sorting of elements soon after death even with minimal transport (Meyer, 1971; Liddell, 1975; Meyer and Meyer, 1986; Baumiller, 2003). The Otekaike feather stars described by Eagle (2007, 2008) had to experience some period of decay prior to burial given that they are highly disarticulated: centrodorsals were recovered either as single elements or, in a few instances, with articulated radials, but with no other elements attached. Yet the material appears autochthonous, given the absence of abrasion and the fact that other dissociated elements (brachials, pinnules, cirri) were also recovered. Eagle (2007) noted the presence of epibionts on some echinoid fragments at these localities, which is also consistent with rather slow sedimentation rates and the potential for exposure on the sediment–water interface of some duration prior to burial. The preservation of the highly articulated Waipati speci-


men of R. aotearoa n. comb. indicates that this specimen was buried while still intact, perhaps while still alive, and that the


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