Journal of Paleontology, 92(1), 2018, p. 33–39 Copyright © 2017, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2017.76


The attachment strategies of Cambrian kutorginate brachiopods: the curious case of two pedicle openings and their phylogenetic significance


Lars E. Holmer,1,2 Zhifei Zhang,1 Timothy P. Topper,3 Leonid Popov,4 and Thomas M. Claybourn2


1Early Life Institute and Department of Geology, State Key Laboratory for Continental Dynamics, Northwest University, Xi’an 710069, China ⟨elizf@nwu.edu.cn⟩ 2Uppsala University, Department of Earth Sciences, Palaeobiology, Villav 16, S-75236 Uppsala, Sweden ⟨lars.holmer@pal.uu.se⟩,


⟨thomas.claybourn@geo.uu.se⟩ 3Palaeoecosystems Group, Department of Earth Sciences,Durham University,DurhamDH1 3LE, United Kingdom⟨timothy.topper@durham.ac.uk⟩ 4Department of Geology, NationalMuseum ofWales,Cathays Park,Cardiff CF10 3NP,Wales, UnitedKingdom ⟨leonid.popov@museumwales.ac.uk⟩


Abstract.—The kutorginates are commonly the most abundant rhynchonelliform brachiopod found in the early Cambrian; they are also some of the oldest known rhynchonelliforms, first appearing in the Unnamed Series 2 (Atdabanian equivalent) and becoming extinct sometime in Cambrian Series 3 (Amgaian equivalent). Moreover, kutorgi- nates are the first known member of the rhynchonelliforms for which we have a detailed knowledge of their soft-part anatomy, including the lophophore, digestive tract, and pedicle—all exceptionally preserved in Kutorgina chengjiangensis Zhang et al., 2007 from the early Cambrian Chengjiang Lagerstätte of southern China. The stout and annulated pedicle in the original report was described as protruding between the valves; however, newly collected better-preserved material now clearly shows that the pedicle actually protrudes from the apical perforation of Kutorgina chengjiangensis. This type of apical pedicle has also been described from other early Cambrian rhynchonelliforms, including the problematic chileate Longtancunella chengjiangensis (Zhang et al., 2011a). Exceptionally preserved similar pedicles are also known to emerge apically from the Silurian chileate dictyonellid Eichwaldia subtrigonalis Billings, 1858, as well as from the recently descri- bed Silurian chileate Trifissura rigida Holmer, Popov, and Bassett, 2014. However, it is clear that the only other exceptionally preserved kutorginate—a silicified Nisusia—was provided with an adult pedicle emerging between the valves from a posterior gap; thus, Nisusia has two pedicle openings. However, the apical foramen may represent the earliest attachment of the larvae, which subsequently became nonfunctional through ontogeny. It is suggested that both types of attachment strategies may have appeared early in the stem lineage of the Rhynchonelliformea.


Introduction


The class Kutorginata Williams et al., 1996 includes both the kutorginids and the nisusiids, which are some of the oldest known Cambrian rhynchonelliform brachiopods with a shell composed of calcium carbonate and primitive types of articu- lation (Popov et al., 1996; Williams et al., 1996; Popov and Williams, 2000; Bassett et al., 2001). The Kutorginata first appeared in the Atdabanian (Unnamed Series 2), rapidly diver- sified, and attained a cosmopolitan distribution before becoming extinct by the end of the Unnamed Cambrian Series 3. Perhaps the most unusual morphological feature of the


kutorginates is that they are provided with both a ventral apical perforation and a widely triangular posterior notothyrial and delthyrial opening between the outer margins of the notothy- rium and pseudodeltidium (Fig. 1), and both openings have at some time been interpreted as accommodating the pedicle (see discussions and reviews in Williams and Carlson, 2007 and Popov et al., 2007, 2010). To date, the best exceptionally pre- served record of a kutorginate with soft anatomy, including the attachment structures, is Kutorgina chengjiangensis Zhang et al., 2007 from the early Cambrian Chengjiang Lagerstätte of


33


southern China, and the original report (Zhang et al., 2007, 2008) described the pedicle as emerging from the posterior notothyrial and delthyrial opening (Fig. 1.1). Here we show that additional better-preserved material


clearly illustrates that the pedicle emerges from the apical perforation of Kutorgina chengjiangensis, while the notothyrial and delthyrial opening lacks any evidence for having been associated with any adult attachment structure. This new infor- mation has important phylogenetic connotations for our under- standing of brachiopod evolution. The known record of early Paleozoic rhynchonelliform brachiopods with exceptionally preserved attachment structures (variously termed) emerging from apical perforations have increased recently, mainly recor- ded from the enigmatic chileates, but also from the obolellates (Zhang et al., 2011a, 2011b; Holmer et al., 2014). This type of attachment may have been widespread in early rhynchonelli- forms, representing a potential plesiomorphic feature that possibly was lost repeatedly. However, critical exceptionally preserved silicified material of another kutorginate—Nisusia sulcata Rowell and Caruso, 1985—shows that the complete shells in this species have preserved cylindroid protrusions,which are here interpreted as the adult attachment (Popov et al., 2007,


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124