Exuviation of trilobite Nangaops danzhaiensis Zhou in Lu et al., 1974 from the Cambrian “Tsinghsutung Formation” of Balang, Guizhou
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Abstract:
Nangaops danzaoensis (Zhou in Lu et al., 1974) is a trilobite that was collected from Tsinghsutung Formation in Balang Village, Jianhe County, Guizhou Province. In total, 36 specimens in Songshan Section, were productive for this study. We identified three preservation states from the specimens: 32 specimens were completely preserved without displacement; free cheeks are not preserved in three specimens; one specimen has no free cheeks, whereas they appeared from the fourth to eleventh thoracic segments. The free cheeks overlaps with the thoracic segments and under the carapace. The genal spine of free cheeks pointed to head, shows 180 degrees of flipping. According to the preserved state, four molting specimens were identified. The mechanism of the molting process is interpreted as follows: facial suture separated with seawater entering, followed by free cheek and epistomal plate turning downwards, and finally the postecdysial trilobite struggled to get rid of proecdysial exuvia. Such information gives an important insight into in-situ burial, and provides evidence that the Jiianhe bi-ota were autochthonous.
