Journal of Paleontology, 92(5), 2018, p. 872–882 Copyright © 2018, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2018.17


Rautangaroa, a new genus of feather star (Echinodermata, Crinoidea) from the Oligocene of New Zealand


Tomasz K. Baumiller1 and R. Ewan Fordyce2


1Museum of Paleontology, University of Michigan, Ann Arbor, Michigan 48109, USA ⟨tomaszb@umich.edu⟩ 2Department of Geology, University of Otago, Dunedin 9054, New Zealand ⟨ewan.fordyce@otago.ac.nz⟩


cirri. It represents the first example of arm autotomy and regeneration in a fossil feather star and thus has bearing on the importance of predation to the evolutionary history of this group.


UUID: http://zoobank.org/c050dafd-93ba-4334-b11b-59209aabb588 Introduction


Feather stars dominate the diversity of extant crinoids and account for more than 80% of species (Rouse et al., 2013). Unlike other living crinoids, feather stars lose the postlarval stalk and sub- sequently remain free living and able to crawl and, in some instances, swim. Both behaviors may represent antipredatory strategies as well as a means of relocating to more favorable microhabitats (Meyer and Macurda, 1977). These adaptations have been considered important to the evolutionary success of feather stars. Although historically the terms ‘comatulids’ and ‘feather stars’ have been used interchangeably, the two are no longer equivalent as recent work indicates that the crinoid order Comatulida contains the feather stars, a nonmonophyletic group, as well as taxa that retain their stalk as adults (Hemery, 2011; Hess and Messing, 2011; Rouse et al., 2013; Summers et al., 2017). In this study, to avoid ambiguity, we use the term ‘feather star’ to refer only to taxa that lose their postlarval stalk and apply the term ‘comatulid’ to all members of the order Comatulida. The fossil record of feather stars extends back ~200 Myr


(Hess, 1951, 2014; Hagdorn and Campbell, 1993; Simms et al., 1993), but only 43 genera are known from fossils, and whereas today’s diversity approaches 140 genera, only six of those have a fossil record. Moreover, at no time in the geologic past did recorded diversity exceed a dozen genera (Hess and Messing, 2011). The paucity of feather star fossils is further illustrated by the fact that fewer than 100 occurrences appear in the Paleobiology Database (6 July 2017), which contains over 1,300 total Mesozoic and Cenozoic crinoid occurrences. The low number of described fossil feather stars could


represent a true biological signal and imply a very recent radiation, or, alternatively, it could be an artifact of their poor


fossil record that less accurately reflects their past biological diversity. Generally, the latter has been considered more likely (e.g., Howe, 1942; Baumiller and Gaździcki, 1996; Donovan, 2001). Some of the reasons for this include their low preserva- tion potential due to the gracile skeletons and the high-energy reef environments that feather stars prefer (Meyer and Meyer, 1986), taxonomic problems caused by the great rarity of even partially articulated specimens, and inadequate sampling due to the very small size and difficulty of retrieving disarticulated skeletal elements (Howe, 1942; Oyen and Portell, 2001). Eagle (2001, 2007, 2008) described a rich Oligocene


crinoid fauna from New Zealand, which illustrates the degree to which the fossil record of feather stars may be undersampled. The 11 included taxa were the first Cenozoic fossil feather stars recorded from New Zealand, and all were new to science. In addition, his specimens demonstrated the highly incomplete mode of preservation characteristic of fossil feather stars: all were either isolated centrodorsals or centrodorsals with basal and radial circlets attached. None had articulated brachials, pinnules, or cirri, which are critical to extant feather star taxonomy (Messing, 1997). This mode of preservation is a general feature of the feather star fossil record: for Cenozoic genera, ~70% are known only from centrodorsals or centrodorsals with a basal and radial circlet. The lack of data on brachials makes it exceptionally difficult to reconstruct the history of arm-branching transformations as well as the temporal trends in the distribution of various brachial articula- tions, both of which are deemed critical to this group’s ecology and evolution (e.g., Oji and Okamoto, 1994). New finds, espe- cially of intact fossils, are therefore crucial. Here we describe one such fossil from New Zealand of an age contemporaneous with those described by Eagle (2001, 2007, 2008) that provides


872


Abstract.—We describe a nearly complete, and thus extremely rare, feather star (Crinoidea, Comatulida) from Oligocene strata of North Otago/South Canterbury, New Zealand. A detailed analysis of this specimen, as well as newly recovered material and previously described fragmentary remains from nearby contemporaneous sedimentary units, in addition to relevant historical specimens, lead us to conclude that it cannot be placed in any currently established genus. A new genus, Rautangaroa, is proposed to accommodate it. This intact specimen of Rautangaroa aotearoa (Eagle, 2007), provides rare data on the morphology of arms and


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