666 J. Paleont., 81(4), 2007, pp. 666–683 Copyright  2007, The Paleontological Society 0022-3360/07/0081-666$03.00 EPIPUNCTAE AND PHOSPHATIZED SETAE IN LATE ORDOVICIAN PLAESIOMYID BRACHIOPODS FROM ANTICOSTI ISLAND, EASTERN CANADA JISUO JIN, 1 RENBIN ZHAN, 2 PAUL COPPER, 3 AND W. G. E. CALDWELL 1 1 Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7 Canada, jjin@uwo.ca, 2 State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China, rbzhan@nigpas.ac.cn, and 3 Department of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada, gcaldwel@uwo.ca ABSTRACT—Epipunctae, a new type of shell perforation, are well developed in typical taxa of the family Plaesiomyidae, a group of common orthide brachiopods from Laurentia and some other tropically located tectonic plates of Late Ordovician age. These minute, prominently elongate, tubular structures are similar to endopunctae in size and density, but differ in being oblique, intersecting the shell surface at a relatively low angle, and being confined largely to the outer portion of the shell wall. The tubules are similar in orientation to aditicules within the same shells but are much smaller and denser, usually aligned along fine growth lines and arranged in crude longitudinal columns. Exceptionally preserved phosphatic molds of bundled setal canals inside epipunctae and aditicules, described for the first time in this paper, are direct evidence that these two types of tubular structures of different sizes had the same function of housing sensory setae along the shell margin, but both the setae and the tubules became abandoned in the outer portion of the shell wall through burial by the secondary shell layer when the shell margin migrated forward. Epipunctae have been found so far only in plaesiomyid shells, but aditicules are common in many groups of the order Orthida. The taxonomic value of epipunctae is shown by a reassessment of Pionorthis Schuchert and Cooper, 1932. The hypotype previously regarded widely, but erroneously, as the archetype of ‘Orthis sola’ Billings, 1866, the type species of Pionorthis, is allied to Plaesiomys Hall and Clarke, 1892. It bears the characteristic epipunctae. The holotype of Orthis sola is a dalmanelloid shell with true punctae, assignable to Mendacella Cooper, 1930. This warrants rejection of the genus Pionorthis. INTRODUCTION I N CLASSIFICATION of the order Orthida, the presence or absence of endopunctae has been regarded as diagnostic at the subor- dinal and superfamilial levels (see, for example, Williams and Harper, 2000). Within the orthide groups that have impunctate shells, however, various microscopic pits and tubules (e.g., adi- ticules and exopunctae) have not been shown to be of much tax- onomic value except at the generic and specific levels in some groups. In his study of the well-known meshwork ornaments of Dictyonella Hall, 1867 (subsequently changed to Eodictyonella Wright, 1994 as a correction of homonymy), Wright (1981) car- ried out a broad survey of brachiopod shells with surface pits. He recognized that aditicules and arrugiae associated with ribs (costae or costellae) are different from the dense pits of Eodictyonella. The term arrugia, used by Wright (1981) for the fine aditicules of Paurorthis Schuchert and Cooper, 1931 and Plectorthis Hall and Clarke, 1892, has become obsolete (Williams and Brunton, 1997), as the perforations in these two genera have been regarded as exopunctae by Williams and Harper (2000). As far as the or- thides are concerned, Wright’s (1981) study clearly demonstrated that the shell surface pits and nonpenetrating microtubules are widespread in impunctate orthide brachiopods, although the func- tional morphology and evolutionary implications of these struc- tures have been subjects of some speculation. In the course of a monographic treatment of exceptionally well- preserved orthide brachiopods from the Upper Ordovician Vau- real and Ellis Bay formations of Anticosti Island, eastern Canada, it has become evident that the details of microstructures in some orthide shells are more complex than previously realized, espe- cially in the development of surface pits, tubules, capillae, and papillae (tubercles). The family Plaesiomyidae, for example, has been known for its prominent aditicules, but several common gen- era (e.g., Dinorthis Hall and Clarke, 1892, Plaesiomys Hall and Clarke, 1892, and Retrorsirostra Schuchert and Cooper, 1931) have much finer, denser, and punctalike tubules in the outer por- tion of the shell wall (Figs. 1.6–1.9, 2.5–2.8), which have not been recorded for this group of impunctate brachiopods until the present study. The plaesiomyids are a group of relatively large-shelled orthide brachiopods that thrived in the shelf and epicontinental seas of North America (Laurentia) during the Late Ordovician. Despite their long history of study (e.g., Hall and Clarke, 1892; Schuchert and Cooper, 1932; Cooper, 1956; Howe, 1988), the plaesiomyids have not been examined in detail with regards to their shell mi- crostructures. This is partly because the abundant shells from the upper Caradoc and Ashgill rocks of the American midcontinent, particularly those from the Cincinnati area, are covered commonly by encrusting epibionts (e.g., bryozoans) or a micritic-microspar- ry matrix, and partly because few studies have involved micros- copy and serial sectioning. The abundant, exquisitely preserved, calcitic shells from the Upper Ordovician rocks of Anticosti Is- land, therefore, provide a rare opportunity for studying the mi- crostructures of this group. Formally named ‘‘epipunctae’’ in this study, the tubular micro- structures found in the family Plaesiomyidae may have important taxonomic and evolutionary significance for the orthide brachio- pods. Several specimens of Plaesiomys from the Ellis Bay For- mation have exceptionally preserved epipunctae and aditicules, which exhibit soft tissue permineralized by calcium phosphate and soft-tissue structures in the form of phosphatic molds that clearly resemble setae (chitinous sensory bristles) of modern bra- chiopods. This appears to be the first record of fossilized setae in brachiopods. The main objectives of this study are to provide a preliminary account of the morphology and functions of epipunc- tae, to compare them with aditicules and other shell surface pits or perforations, and to survey their occurrences in various taxa. MATERIAL AND METHODS Brachiopod shells used in this study were mainly from the P. Copper Collection (with contributions from J. Jin) from the Upper Ordovician Vaureal and Ellis Bay formations of Anticosti Island, eastern Canada. The material is currently housed partly in the Geological Survey of Canada, Ottawa, and partly in the Depart- ment of Earth Sciences, the University of Western Ontario. Types and figured specimens are in the repositories of the Geological Survey of Canada (GSC), Ottawa, the Peabody Museum of Nat- ural History of Yale University (YPM), or the Department of Earth Sciences of the University of Western Ontario (W). Sample locality numbers prefixed with the letter A denote the Copper Collection from Anticosti Island, and detailed stratigraphic and geographic information of each locality is available from the au- thors. For general geology and stratigraphy of the Vaureal and