Mao et al.—New Silurian Petalocrinidae
Brassfield Formation, Ohio and Kentucky (various publications noted above); the East Point, Goéland, and Richardsonmembers of the Jupiter Formation, Quebec (Ausich and Copper, 2010); the La Chute and Mc Giluray members of the Gun River Formation, Quebec (Ausich and Copper, 2010); and the Hickory and Wallington members of the Reynales Formation, New York (Eckert, 1990; Eckert and Brett, 2001). In the United Kingdom, this new fauna is approximately equivalent to the Mulloch Hill Sandstone, Scotland (Fearnhead and Donovan, 2007a, 2007b).
Materials and methods
The specimens described herein were collected from the Shuiba- tang, Baisha, and Fengxiang sections. 13 specimens were collected fromthe Shuibatang section, including the holotypes of Spirocrinus circularis n. sp. and Spirocrinus dextrosus n. sp.; seven specimens were from the Baisha section, including Petalocrinus inferior with all the arms intact, and the holotype Petalocrinus stenopetalus n. sp.; and three specimens were from the Fengxiang section. In addition, thirteen specimens fromMu and Lin (1987) are illustrated herein, including two specimens of Petalocrinus inferior and 11 type specimens of Sinopetalocrinus. The phylogenetic analysis presented here was completed in
PAUP 4.0a142 (Swofford, 2002) using the maximum parsimony criterion. All characters were equally weighted and unordered, and a heuristic search with the tree-bisection reconnection (TBR) algorithm was conducted with random addition repeated 1000 times. A 50% majority-rule tree with bootstrap values is presented. The consistency index (CI), retention index (RI), and rescaled-consistency index (RC) are listed. Bootstrap and jackknife support were also calculated in PAUP 4.0a142. As noted elsewhere, the oldest known petalocrinid is
Eopetalocrinus from the Ordovician of China, and all other studied taxa are from the Llandovery (Aeronian) of China. Thus, Eopetalocrinus is used as the outgroup. All but one of the taxa considered in this study are known exclusively from the second primibrachial plate. Although the brachial plates among petalocrinids have distinctive characteristics, with only eleven second primibrachial characters known (Appendices 1 and 2) to delineate relationships among nine taxa, a highly resolved tree should not be expected. Thus, we illustrate the 50% majority-rule tree with bootstrap and jackknife values. Terminology and classification follows Weller and Davidson
(1896), Bather (1898), Lane and Moore (1978), Mu and Lin (1987), and Mao et al. (2015). All measurements are in mm (millimeters).
Repository and institutional abbreviation.—All specimens are deposited in the Nanjing Institute of Geology of Paleontology, Chinese Academy of Sciences (NIGP). Specific locations are listed in the occurrence sections for each species (see below).
Systematic paleontology Class Crinoidea Miller, 1821
Subclass Cladida Moore and Laudon, 1943 Order Cyathocrinina Bather, 1899
Superfamily Gasterocomacea Roemer, 1854 Family Petalocrinidae Weller and Davidson, 1896
Remarks.—According to Mao et al. (2015), the Petalocrinidae has a relatively small aboral cup with arms, each presumably a series of fused brachials. These specialized arm plates are robust and can be transported as isolated plates after death. Although relatively common in many settings, very few specimens of any petalocrinid are known from the entire crown. Instead, their fossil record is almost entirely known from the large fused secundibrachial plates. Thus, the genera and species of the Petalocrinidae are based on the morphology of fused arm plates instead of aboral cup plates (Fearnhead and Donovan, 2007a), which is unusual among crinoids. In the few specimens preserved with complete crowns, the second primibrachial characters are consistent within an individual. Therefore, until demonstrated otherwise, one must assume that arm characters are consistent within an individual and within a taxon. Despite the fact that only second secundibrachials are evaluated and relatively few characters can be identified to differentiate among taxa, the characters that do exist are varied, distinctive, and directly linked to suspension-feeding behavior. So, the second primibrachials provide critical infor- mation about these crinoids. The Ordovician to Devonian family Petalocrinidae
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includes 28 species belonging to five genera. Paleobiogeo- graphic occurrences of this family include Laurentia, Baltica, Avalonia, South China, Sibumasu, and Perunica blocks. Among these, the South China Block contains the most diversified forms during the Llandovery.
Genus Petalocrinus Weller and Davidson, 1896
Type species.—Petalocrinus mirabilis Weller and Davidson, 1896.
Other species.—Petalocrinus inferior Bather, 1898.
Petalocrinus inferior Bather, 1898 Figure 2
1949 (1950) Petalocrinus inferior;Mu, p. 94, pl. 3, figs. 1–3, 12. 1955
1898 1987 Petalocrinus inferior Bather, p. 426, pl. 26, fig. 57.
Petalocrinus inferior; Tien and Mu, p. 91–92, pl. 48, figs. 6–10.
Petalocrinus inferior; Mu and Lin, p. 7–8, pl. 1, figs. 1–2.
Occurrence.—Leijiatun Formation, Aeronian (Llandovery, Silurian), Sigou section, Shiqian County, Guizhou Province, China; Leijiatun Formation, Aeronian (Llandovery, Silurian), Baisha section, Shiqian County, Guizhou Province, China.
Materials.—NIGP 73928, NIGP 73929, and NIGP 163722.
Remarks.—NIGP 73928 and NIGP 73929 are two scattered arm plates from Mu and Lin (1987). NIGP 163722 is the first specimen known from the Upper Yangtze Platform, South China Block with all the arms intact. The entire specimen is
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