Abstracts of recent talks given to Section C
Wednesday November 30th 2016
Xiaoya Ma (Dept Earth Sciences, NHM, London; & Yunnan Key Lab. for Palaeobiology, Yunnan Uni. Kunming, China)
Fossil Brains from the Cambrian Chengjiang biota.
Comparative studies of nervous systems and sensory organs are fundamental for understanding the evolutionary relationships between major animal groups and their ecological adaptation throughout evolutionary history. Exceptionally [well] preserved Cambrian panarthropod fossils provide a rich and underexploited source of data pertaining to neural and sensory organisation during the early sages of their radiation.
Recent reports of the brain and other neural structures of Cambrian pan arthropods demonstrate that these ancient animals had acquired complex central nervous systems (CNS) and sensory organs by 517 Ma, and that the two main configurations of the brain and eyes, observed in extant arthropods (Mandibulata & Chelicerata), had already evolved. The neural structures, identified in a Cambrian stem-euarthropod anomalocaridid, provide direct evidence for the segmental affinity of its frontal appendages, shedding light on the origin of the euarthropod CNS. However, scarcity of fossilised neural tissue has meant that most studies to date have been based on single specimens, hindering tests of fidelity of those structures, and [the] understanding [of] the diagenetic processes that led to their exceptional preservation. Geochemical analyses provide crucial insight into neural tissue preservation, revealing that the neural tissue was initially preserved as carbonaceous film, and subsequently pyritized. This mode of preservation is consistent with the taphonomic pathways of gross anatomy, indicating that no special mode is required for the fossilisation of labile neural tissue. Preliminary decay experiments also support the preservation potential of neural structures and their morphological interpretation after compression.