Wu et al.—Chinese Permian–Triassic chonetid taxonomy


distinct genera with consistency and rigor. Instead, as particu- larly demonstrated by the cladistic analysis (Fig. 9), they appear to constitute a highly coherent monophyletic clade evolved from Neochonetes. Consequently, we conclude that Tethyochonetes should be considered as a junior synonym of Fusichonetes and, as such, be suppressed as an invalid genus name. Following from this, it is necessary to provide an updated


and refined diagnosis for Fusichonetes. In part, this is essential because the original genus diagnosis given by Liao contained little information about the internal features. On the other hand,


1303


merging Tethyochonetes with Fusichonetes by suppressing the former means that all previously recognized Tethyochonetes species need to be transferred to Fusichonetes, thus substantially increasing the species composition of this genus. Another strong reason for updating and expanding the genus diagnosis of Fusichonetes is due to the availability of a large number of exceptionally well-preserved materials from the Xinmin section, including both dorsal and ventral interiors that show important internal features unknown to previous studies.


Emended genus diagnosis for Fusichonetes.—Small to medium in size, 1.47–11.77mm long and 2.22–20.14mm wide (online supporting data: Appendix 5); transversely rectangular to reverse trapezoidal in outline, width/length ratio 1.13–3.26, and lateral margin angle 14°–101° (online supporting data: Appendix 5); concavoconvex to almost planoconvex in lateral profile; ears normally smooth, flattened or slightly swollen; external surface ornamented by simple costellae, occasionally with micro- ornament of tubes; sulcus and fold variable. Ventral interior with median septum; dorsal interior with median septum, lateral septa (possibly) and brachial scars, cardinal process quadrilobate; internal surface of both valves with radially distributed papillae.


Figure 9. A strict consensus tree of three most parsimonious trees (TL: 29.2; CI: 0.543; RI: 0.602). Code number 3 represents variable LMA (lateral margin angle), 14 represents variable URW (umbonal region width).


Distinguishing Fusichonetes from similar chonetid genera.— As defined, Fusichonetes bears some similarities with several other rugosochonetid genera (Fig. 10). The genus is similar to Quinquenella Waterhouse, 1975, because both have a sub- quadrate outline, amoderately concavoconvex profile, and similar ventral interior, but differ in the latter having concentric stria, a long accessory septa in the dorsal interior, and lacking costellae. Rugaria Cooper andGrant, 1969 can be easily distinguished from


Figure 10. Comparison of Fusichonetes and Tethyochonetes with selected other morphologically similar chonetid genera. Gray blocks show the distinctive characteristics dividing genera from each other. Question marks indicate information that was not provided by the original authors when the genera were proposed. Holotype specimens of all genera are from the original references (Cooper and Cooper, 1969; Waterhouse, 1975; Jin and Hu, 1978; Zhan, 1979; Liao, 1980a; Waterhouse, 1982; Campi and Shi, 2002), except for Neochonetes from Racheboeuf (2000) and holotype specimens of Waagenites and Waterhouseiella separately from Waagen (1884) and Waterhouse and Piyasin (1970). Scale bars=5mm.


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