Journal of Paleontology, 91(6), 2017, p. 1296–1305 Copyright © 2017, The Paleontological Society 0022-3360/17/0088-0906 doi: 10.1017/jpa.2017.80
Taxonomic Note
A quantitative taxonomic review of Fusichonetes and Tethyochonetes (Chonetidina, Brachiopoda)
Hui-ting Wu,1,2 G. R. Shi,2 and Wei-hong He1,3 1School of Earth Sciences, China University of Geosciences, Wuhan 430074, China 2School of Life and Environmental Sciences, Deakin University, Melbourne Burwood Campus, 221 Burwood Highway, Burwood, Victoria 3125,
Australia ⟨
guang.shi@
deakin.edu.au⟩ 3StateKey Laboratory of Biogeology and Environmental Geology, China University of Geosciences,Wuhan 430074, China ⟨
whzhang@cug.edu.cn⟩
Abstract.—Two middle Permian (Capitanian) to Early Triassic (Griesbachian) rugosochonetidae brachiopod genera, Fusichonetes Liao in Zhao et al., 1981 and Tethyochonetes Chen et al., 2000, have been regarded as two distinct taxa and used as such for a wide range of discussions including biostratigraphy, paleoecology, paleobiogeography, and the Permian-Triassic boundary mass extinction. However, the supposed morphological distinctions between the two taxa are subtle at best and appear to represent two end members of a continuum of morphological variations. In this study, we applied a range of quantitative and analytical procedures (bivariate plots, Kolmogorov-Smirnov test, categorical principle component analysis, and cladistic analysis) to a dataset of 15 quantified morphological variables, integrating both key external and internal characters, measured from 141 specimens of all well-known Fusichonetes and Tethyochonetes in order to test whether or not these two genera could be distinguished in view of the chosen characters. The results indicate that these two genera are morphologically indistinguishable and that the species classification previously applied to these two genera appears to represent polyphyletic groupings within the genus Fusichonetes. Consequently, Tethyochonetes is concluded to be a junior synonym of Fusichonetes. The diagnosis and key characteristics of Fusichonetes are clarified and refined based on a new suite of well-preserved specimens from the Permian − Triassic Xinmin section in South China.
Introduction
Fusichonetes Liao in Zhao et al., 1981 and Tethyochonetes Chen et al., 2000 both belong to the Rugosochonetidae, the most species-rich family among chonetidine brachiopods (Racheboeuf, 2000). As a genus, Fusichonetes was first mentioned in Liao (1979), without description. Later, Liao in Zhao et al. (1981) formally proposed and defined this genus, with Plicochonetes nayongensis Liao, 1980a from the Changhsingian strata at the Zhongling section, Nayong,Guizhou, South China as the type species (Fig. 1). Tethyochonetes was proposed by Chen et al. (2000) withWaagenites soochowensis quadrata Zhan, 1979 from the Late Permian of Lianxian, Guangdong, South China as the type species (Fig. 1). Since Fusichonetes was proposed, only two species have
been recorded, F. nayongensis (type species) and F. pygmaea (Liao, 1980a), both designated to this genus originally by Liao (1981), and both restricted to Lopingian (late Permian) and Griesbachian (earliest Triassic) strata in South China (Fig. 2.3). In contrast, at least 14 species of Tethyochonetes have been recognized (online supporting data: Appendix 1), most of which had been assigned to either Chonetes Fischer von Waldheim, 1830 or Waagenites Paeckelmann, 1930 in the old literature.
The collective stratigraphical range of these 14 Tethyochonetes species is from the Capitanian (middle Permian) to Griesbachian (Early Triassic), while their paleogeographic ranges spread across the Paleo-Tethys and Neo-Tethys (Fig. 2.3). Notably, both genera apparently survived the Permian-Triassic boundary mass extinction (PTBME), accounting for 11.8% of the Permian brachiopod genera that persisted into the Griesbachian before their final extinction at the Griesbachian-Dienerian boundary (Liao, 1980b; Yang et al., 1987; Chen et al., 2005; Clapham et al., 2013). As such, these two taxa, especially Tethyochonetes, have attracted much attention in recent years, especially in connection to their extinction, paleobiogeo- graphical distribution, and body-size change patterns (Chen et al., 2009; He et al., 2010; Wuet al., 2016; Zhang et al., 2016). However, despite their close connection to the PTBME and
potential significance for a better understanding of this major bio-crisis, the identity of these two genera and their mutual relationship have been problematic and never properly been investigated. Significantly, the problem arose because when Liao in Zhao et al. (1981) proposed Fusichonetes, he appears to have based the definition of his new genus primarily on a combination of external characteristics, including a very trans- verse outline, acute cardinal extremities, and coarse and angular
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