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Journal of Paleontology 92(1):33–39
and the clitambonitoid Antigonambonites (Popov et al., 2007). In all these taxa, the delthyrial opening was completely covered by the pseudodeltidium at all growth stages, which is unlike the kutorginate ontogeny. The dorsal metamorphic shell (see Bassett and Popov, 2017) in Coolinia, Salanygolina, and Pelmanotreta (the last paterinate being the second-oldest brachiopod yet documented), in addition to the protegulum and two to three pairs of lobes in all these taxa, shows the
position of larval setal sacs and, moreover, preserves a posterior flange, which indicates the presence of a larval pedicle emerged between valves, which presumably was used for the attachment on a settlement (Popov et al., 2007). This larval pedicle probably developed from the larval posterior pedicle lobe. If so, the larval pedicle of these brachiopods was homologous to the pedicle of the orthides and all crown group rhynchonellate brachiopods, as well as the pedicle of more derived paterinides, such as Dictyonina and Micromitra. The transition to the encrusting attachment by the surface of the ventral valve may have been due to the poorly developed mechanical properties of the body wall, which was lacking in dermal muscles. In the crown group rhynchonelliforms, there is invariably a cartilage-like tissue in the pedicle, which is clearly an apomorphic character that evolved later in brachiopod evolution. Thus, the pedicle of the nisusiids was probably also
developed from the larval posterior lobe, such as in the crown group rhynchonelliforms, and retained its function as a result of paedomorphic alteration; secretion of the ventral valve was delayed until the end of metamorphosis, which is indicated by the presence of the ventral umbonal perforation, although the ‘adult attachment’ by the surface of the ventral mantle in some groups became nonfunctional, as demonstrated by the specimens of Nisusia? burgessensis. Moreover, it is possible that connective-like tissue was present in the pedicle of nisusiids, which is supported by the fact that it is occasionally preserved.
Acknowledgments
Financial support from the National Natural Science Foundation of China (NSFC 41425008, 41720104002 and 41621003 to Z. Zhang) for the long-term collection of Chinese material is acknowledged. The work of L. Holmer was supported by a grant from the Swedish Research Council (VR 2012-1658), and his research visits in Xi’an for work with this paper were financially supported by the C.C. Yang Professor Scholarship from the Department of Geology, Northwest University, Xi’an. L. Popov acknowledges logistical and financial support from the National Museum of Wales. T. Topper was supported by a Marie Curie COFUND fellowship, Durham University. Fossil collection was partly financed by the National 973 Program (2013CB835002) and 111 Project of China (P201102007). Thanks are also extended to J.-P. Zhai for fossil preparation and to X. Liu for artistic reconstruction of fossils in this paper. We are also grateful to the editors J. Jin (Canada) and G. Brock (Australia) for assistance with the manuscript and to two referees for their helpful reviews, which greatly improved the paper.
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