1024


Journal of Paleontology


Figure 6. Reconstruction of protaspid and early meraspid stages of Ellipsostrenua granulosa (Ahlberg, 1984) from the Fånån area (Jämtland, Sweden): (1) early protaspid stage, dorsal view; (2) early protaspid stage, posterior view; (3) late protaspid stage, dorsal view; (4) late protaspid stage, posterior view; (5) early meraspid cranidium, dorsal view; (6) early meraspid hypostome, ventral view; (7, 8) early meraspid pygidia, dorsal view.


northern Sweden. The early stages ofE. gripi aremorphologically nearly equivalent to the stages of E. granulosa described herein. Themain difference is the comparatively longer intergenal spines


in some meraspid cranidia of E. gripi (cf., Kautsky, 1945, pl. 16, fig. 8, pl. 18, fig. 1). This difference can be attributed either to interspecific differences or,more likely, to the fragmentary nature of the early meraspid cranidia of E. granulosa resulting in fre- quent breakage of such spines. Indeed, the absence of intergenal spines in numerous other cranidia of E. gripi (cf., Kautsky, 1945, pl. 16, figs. 4–7, 9, pl. 17, figs. 5–7) favors the latter possibility. Cederström et al. (2012) described disarticulated meraspid and holaspid sclerites of S.? spinosa from the Grammajukku Forma- tion (Stage 4) in the Storuman and Laisvall areas, Lapland, Swe- den. These meraspid cranidia are comparable to those of E. granulosa and E. gripi, but they have a slightly more pointed intergenal angle, a more rounded anterior border, and longer intergenal spines. Sufficient developmental data, including numerous protaspid


and earlymeraspid stages, are also known fromsome members of the Estaingiidae, which is believed to be phylogenetically closely related to Ellipsocephalidae (Paterson and Edgecombe, 2006); both families are classified in the Ellipsocephaloidea Matthew, 1887 (cf., Adrain, 2011). Superbly preserved phosphatized sclerites of Ichangia ichangensis fromthe Shuigoukou Formation (Henan Province, South China plate) were described by Zhang and Pratt (1999) and Zhang and Clarkson (2012). The protaspid period of I. ichangensis can be divided into two stages (stages 0 and 1 sensu Zhang and Pratt, 1999). Dai and Zhang (2012) described protaspides andmeraspid cranidia of Estaingia sinensis from the Shuijingtuo Formation (Hubei Province, South China plate) and synonymized phosphatized material described by Zhang and Pratt (1999, p. 125) as “genus and species indeterminate 2” with E. sinensis. If the specimens described by both Zhang and Pratt (1999) and Dai and Zhang (2012) are conspecific, the protaspid period of E. sinensis comprises an early


stage (stage 0 sensu Zhang and Pratt, 1999) and one (stage 1 sensu Zang and Pratt, 1999) or two (anaprotaspid and metaprotaspid stages sensu Dai and Zhang, 2012) later stages. The earliest known protaspid stages of Ellipsostrenua,


orientation of the fixigenal spines is identical: the anterior fixigenal spine is pointed laterally; the intergenal spine is directed postero-ventrally. The differences between early protaspides of these genera are minor and mainly include the shape of the LA and the length of the fixigenal spines (Fig. 7.1). Late protaspides of Ellipsostrenua, Ichangia, and Estangia


(Fig. 7.1) are similar in their basic body plan. They have circular to sub-hexagonal protocranidia with a posterior border furrow curved forward abaxially, so that it reaches the posterior tip of the palpebral lobe. The protocranidia also share distinct bacullae, a prominent preglabellar field, and genal swellings. Protocranidia of Ellipsostrenua and Ichangia still bear two pairs of the fixigenal spines (the anterior fixigenal spines and the intergenal spines). The protocranidium in the late protaspid stage of Estaingia is, however, slightly different from those of Ellipsostrenua and Ichangia (e.g., it has a more parallel-sided glabella and lacks the anterior fixigenal spines). Because such a morphology is typical for later stages (meraspides) of Ellipsostrenua and Ichangia, the cranidial development of Estaingia was probably slightly accelerated in comparison with


Ichangia,and Estaingia share a narrow axis with the same number of dorsally expressed segments (LA–LO). All of them have the same number of fixigenal spines in comparable positions. The trunk portion is not distinguishable. Hence, these earliest protaspides seem to represent homologous stages in all taxa discussed. Othermorphological similarities (Fig. 7.1) are: (1) the early protaspides of these genera are all circular to elliptical and have distinct bacullae, (2) their palpebral lobes reach the exoskeletal mid-length, (3) the anterior parts of the fixigenae are gently swollen, (4) there is a short but distinct preglabellar field, and (5) there is an anteriorly curved posterior border furrow. The


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