Hou et al.—Lower Cambrian trilobite ontogeny southern China


relatively large numbers of holaspid thoracic segments (up to 17 or more), whereas others have substantial holaspid pygidia comprised of multiple segments (7 or more) and fewer mature thoracic segments (9 or fewer). Until a phylogenetic analysis of the group is completed, it will remain unclear as to whether the families currently recognized constitute monophyletic groups, whether changes in mature trunk segment allocation evolved multiple times within the group, and what the polarities of any such trends were. Nevertheless, the group does appear to offer a promising study system for exploring aspects of trunk evolution among early trilobites (seeMcNamara, 1986).


Family Gigantopygidae Harrington in Harrington et al., 1959


Remarks.—This group is among those redlichiid trilobites with relatively large pygidia and an intermediate number of mature thoracic segments. Gigantopygidae are considered by Jell and Adrain (2003) to include the type species, Gigantopygus papillatus Hupé 1953 from Morocco, along with several other species described from the same region; Bornemannaspis,a form known only from cranidia collected in Sardina (Rasetti, 1972); and various other genera that are here all considered to belong to the subfamily Yiliangellinae. Gigantopygus papillatus


differs from members of the Yiliangellinae in its prominent fixigenal bacculae, and Bornemannaspis, which is too poorly knowto be assigned to the familywith confidence andwas placed in Redlichiidae by Chang et al. (in Kaesler, 1997).


Subfamily Yiliangellinae Zhang and Lin, in Zhang et al., 1980


Remarks.—Chang et al. in Kaesler, 1997 considered the sub- family Yiliangellinae to include only three genera: Yiliangella, Yiliangellina, and Zhangshania, but two other giganotopygid genera mentioned by Jell and Adrain (2003, p. 471) fit within Chang et al.’s (in Kaesler, 1997) definition. These are Parayiliangella Luo in Luo et al., 1994 and Pseudoyiliangella Yin in Yin and Li, 1978. The latter is based on a single crani- dium and is not considered further below. Systematically important morphological differences within Yiliangellinae are discussed in the Remarks section for the genus. Zhangshania Li and Zhang in Li et al., 1990 was first


reported from the Yuxiansi Formation of Leshan in Sichuan (Fig. 1.1). It was considered similar to Yiliangella Chang, 1966 and Yiliangellina Chang, 1966, and thus placed in the subfamily Yiliangellinae Zhang and Lin in Zhang et al., 1980. Those authors also erected another genus, Parazhanshania Li and Zhang in Li et al., 1990, whose sole species we synonymize with Z. typica below.


Genus Zhangshania Li and Zhang in Li et al., 1990


Type species.—Zhangshania typica Li and Zhang in Li et al. (1990, pl. 2, figs. 1–6), collected from the lower Cambrian Yuxiansi Formation, Yiliangella-Zhangshania Biozone, in Leshan, Sichuan Province, China.


Remarks.—Li et al. (1990) distinguished Zhangshania from Parazhangshania on the basis of the latter having a small mature dorsal exoskeleton, a narrow brim, non-bifurcated eye


Holotype.—A complete specimen, Ly-312 (Chengdu Institute of Geology and Mineral Resources) (Li et al., 1990, pl. 2, fig. 1);


counterpart of the holotype Ly-313 (Li et al., 1990, pl. 2, fig. 2). Paratypes: a nearly complete hypostome, Ly-314 (Li et al., 1990, pl. 2, fig. 3); a nearly complete cranidium, Ly-315 (Li et al., 1990, pl. 2, fig. 4); a nearly complete pygidium, Ly-316 (Li et al., 1990, pl. 2, fig. 5); a complete pygidium, Ly-317 (Li et al., 1990, pl. 2, fig. 6). All of these specimens are here assigned to holaspid stage 4.


89


ridges, large palpebral lobes, a relatively narrow glabella with a rounded anterior end, a very short preglabellar field, and a wide and short axial lobe on the pygidium. However, these supposed differences between the two genera are characteristics of the holaspid phase 3 of Z. typica (see below). Accordingly, Parazhangshania is a junior subjective synonym of Zhangshania. Yiliangella is very similar to Zhangshania, but differs by


having a smaller palpebral lobe and a long eye ridge that is not bifurcated. In addition, there are sixteen holaspid thoracic segments and a pygidium with two pairs of pygidial spines in Yiliangella, whereas Zhangshania has fourteen holaspid thor- acic segments and one pair of pygidial spines. A conical glabella with weakly incised glabellar furrows and a long preglabellar field differentiates Yiliangellina from


Zhangshania. The holaspid thorax of the former is composed of fifteen segments, and it also has two pairs of spines on the pygidium. Parayiliangella differs from Zhangshania in the


former’s notably smaller palpebral lobes and the presence of fifteen holaspid thoracic segments. Several taxa outside the Yiliangellinae also closely


resemble Zhangshania, including several yinitid taxa. If phylogenetic analysis reveals a trend within Redlichioidea toward a more segment-rich pygidium, it is possible that giganotopygids are a paraphyletic sister group of Yinitidae. Yinites Lu, 1945 differs from Zhangshania in having a larger glabella, a non-bifurcated eye ridge, and a long anterior border. Yinites has thirteen holaspid thoracic segments, each with short pleural spines, and a pygidium with a single pair of long spines that are preceded by two pairs of small spines. The yinitid Drepanopyge Lu, 1961 (emended by Chang,


1966) is distinguished from Zhangshania in having ten holaspid thoracic segments, each with short pleural spines, and by a pygidium with five pairs of short and wide spines. Malungia Lu, 1961 (emended by Chang, 1966) is differentiated from Zhangshania by its long preglabellar field that is of similar length to the anterior border that curves forward strongly.


Malungia also has a small pygidium with a pair of long, wide, flat, and sharp spines. Zhangshania typica Li and Zhang in Li et al., 1990


Figures 3.1–3.9, 4.1–4.6, 5.1–5.6; Supplementary Data 1.1–1.6, 2.1–2.12, 3.1–3.9


1990 Zhangshania typica Li and Zhang in Li et al., p. 44, pl. 2, figs. 1–3, 5, 6.


1990 Parazhangshania sichuanensis Li and Zhang in Li et al., p. 47, pl. 3, figs. 1–4, 6, 7, 10, 11.


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