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Spinicaudata Look for this name in NCBI Wikipedia Animal Diversity Web
Wolfe et al. 2016
node minimum age |
D. mandalgobiensis is from the Eedemt Formation, Khootiin Khotgor coal mine region, Dundgobi Province, southeast Mongolia (Li et al., 2014). The spinicaudatan genus Triglypta (co-occurring with D. mandalgobiensis) provides a biostratigraphic constraint on the Eedemt Formation, as Triglypta species also occur in both the (older) Euestheria ziliujingensis fauna and (younger) Sinokontikia fauna in lacustrine sequences of northwestern China (Li et al., 2014; Li and Matsuoka, 2012). First, the E. ziliujingensis fauna is distributed throughout east Asia, dated to a Bajocian-Bathonian (Jurassic) age by the occurrence of Euestheria trotternishensis (Chen et al., 2007). E. trotternishensis co-occurs in the Skyestheria spinicaudatan fauna of Skye, Scotland; the Bajocian-Bathonian date for this locality comes fromammonite and palynological index fossils (Chen and Hudson, 1991). Although the Sinokontikia fauna was once thought stratigraphically equal to the late E. ziliujingensis fauna (Chen et al., 2007; Li and Matsuoka, 2012), Sinokontikia has been determined to be younger based on occurrence in the Qiketai Formation of the Turpan Basin, northwest China. The Qiketai Formation is constrained only to the Callovian. As Chinese Triglypta (the index genus for the Eedemt Formation) is absent from any higher strata, a minimum age comes from the upper boundary of the Sinokontikia fauna (Li et al., 2014). The upper boundary of the Callovian is 163.5 Ma ± 1.0 Myr, giving a minimum age for the Eedemt Formation of 162.5 Ma.
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A soft maximum age is obtained from the oldest mandibulate, Y. dianensis, which was recovered from the Yu'anshan Formation at Xiaotan section, Yongshan, Yunnan Province, attributed to the Eoredlichia–Wutingaspis Biozone (Zhang et al., 2007). Chinese Cambrian stratigraphy has been revised substantially and the Eoredlichia –Wutingaspis Biozone is no longer recognized (Peng, 2003, 2009). However, Eoredlichia is known to co-occur with Hupeidiscus, which is diagnostic of the Hupeidiscus-Sinodiscus Biozone, which is formally recognized as the second biozone of the Nangaoan Stage of the Qiandongian Series of the Cambrian of China (Peng and Babcock,2008). The Nangaoan is the proposed third stage of the Cambrian System for the International Geologic Timescale (Peng et al., 2012a).Thus, a soft maximum constraint can be established on the age of the lower boundary of the Nangaoan, which has been dated to 521 Ma (Peng et al., 2012a; Peng and Babcock, 2008).
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Phylogenetic analysis of spinicaudatan fossils is rare, owing to difficulty in character identification (Astrop and Hegna, 2015). Members of Leptestheriidae appear to share emergence of dendritic reticulation and anastomizing ridge ornamentation with the fossil spinicaudatan family Loxomegaglyptidae (Astrop and Hegna, 2015; Shen, 1994). D. mandalgobiensis is perhaps the oldest definitive Loxomegaglyptidae, based on large-sized reticulate ornamentation and weakly defined growth lines, shared with other members of the family (Li et al., 2014). Due to the above ornamentation characters (Astrop and Hegna, 2015; T. Astrop, pers. comm.), it can be placed on the stem lineage of Leptestheriidae, and thus within crown Spinicaudata.
Li, G., Ando, H., Hasegawa, H., Yamamoto, M., Hasegawa, T., Ohta, T., Hasebe, N., Ichinnorov, N., 2014. Confirmation of a Middle Jurassic age for the Eedemt Formation in Dundgobi Province, southeast Mongolia: constraints from the discovery of new spinicaudatans (clam shrimps). Alcheringa 38, 305–316.
Astrop, T.I., Hegna, T.A. 2015. Phylogenetic relationships between living and fossil spinicaudatan taxa (Branchiopoda Spinicaudata): reconsidering the evidence. J. Crustac. Biol. 35, 339–354.
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