The study of moulting behaviour in the fossil record is relatively well known in arthropods and this is especially true for trilobites. Nevertheless, while studies focusing on the style of moulting in social and semi-social groups of modern animals (e.g. arthropods) are common, very few works investigate moulting adaptations in deep time. Here we report a trilobite assemblage from the Cambrian Series 2 “Tsinghsutung” Formation of South China. Around 850 specimens were used for this study from three different levels across one section near Balang (SE Guizhou Province, South China). These levels preserve numerous trilobite clusters in some cases containing around 400 individual specimens. Up to four species have been found in these clusters, but two species are more common. Trilobite clusters bear a high percentage of disarticulated specimens that we interpret as moults. Additionally, measurements of bioclast orientation and the dorsoventral attitude suggests very quiet water conditions followed by rapid burial events, prior to scavenger disturbance. Together, this indicates that the fossil assemblages were a result of a biological phenomenon rather than mechanical processes, allowing us to interpret the position of the fossil parts as different moulting configurations. Since the trilobite assemblage seems to be in situ, the large number of exuviae suggests a local place of migration. This was triggered by the need for group protection while moulting, which is suggestive of gregarious behaviour, possibly synchronized. These trilobites from the Cambrian Epoch 2, Age 4 constitute one of the earliest known gregarious community of trilobites and has important implications for understanding the ecology of this group during their emergence in the Cambrian.
This study reports the salamander Oedipina complex (Dunn, 1924) in a tropical and relictual humid forest in the Magdalena Valley, Colombia. Previous records outline O. complex as a species associated with the pluvial forests of central and northern areas of the Chocó Biogeographic Region in Colombia, Ecuador, and Panama. Based on this new record, the geographic distribution of the species is expanded 257 km east.
Geophis nigroalbus Boulenger, 1908 is a fossorial and secretive colubrid snake endemic to the western Andes of Colombia. Here we report this species for the first time in the Cordillera Oriental in Middle Magdalena Valley. We expand the known distribution of G. nigroalbus 183 km east of its original range.
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