Abstract

Extant arthropods comprise the most species-rich taxon hallmarked by stunning morphological diversity. However, just four central nervous system ground patterns typify Arthropoda (Onychophora, Myriapoda, Pancrustacea, Chelicerata). Neurocladistics resolves these arrangements as distinct, but for how long they have been distinct has been impossible to tell. This may find resolution in the fossil record. In the last six years, Cambrian Lagerstätten have provided data about brain diversity during early stages of arthropod radiation. Rare Chengjiang specimens resolve muscle, digestive tracts and glands vascular system, and also cerebral ganglia, optic lobes, and ventral nervous system (VNS) in addition to integumental features, such as eye structures and sensilla. With some exceptions1, such morphological features had been largely overlooked partly because nervous systems were considered unlikely to be preserved. This was challenged by observations of the late Cambrian stem arthropod Waptia fieldensis2. Observations of the earlier Fuxianhuiids from the Chengjiang early Cambrian demonstrated that 520 million years ago a brain3 and ventral cord4 typical of extant mandibulates equipped a morphologically simple stem arthropod. The identification of the brain, eyes and VNS of the megacheiran Allalcomenaeus demonstrated the coeval presence of the chelicerate ground pattern5. Subsequent identification of an onychophoran-like brain in a new anomalocaridid species Lyrarapax unguispinus6, resolved a long-standing dispute regarding the segmental affinity of “frontal appendages” versus “great appendages.” These discoveries impel considerations about the divergent evolution of arthropod morphologies, and hence sensory systems, and how these relate to ancestral brains and central nervous systems7.

References:

1. Vannier, J., García-Bellido, D.C., Hu, S-X. & Chen, A-L. Proc. R. Soc. B 2009 276 2567 -2574. 2009. 2. Strausfeld, N.J. Palaeo. Canadiana 31, 157–169. 2011. 3. Ma, X., Hou, X, Edgecombe, G. D. & Strausfeld, N. J. Nature 490, 258-261. 2012. 4. Yang, J., Ortega-Hernandez, J., Butterfield, N.J. & Zhang G. Nature 494, 468-471. 2013. 5. Tanaka, G. Hou, X., Ma, X., Edgecombe, G. D. & Strausfeld, N. J. Nature 502, 364-367. 2013. 6. Cong, P., Ma, X., Hou, X, Edgecombe, G. D. & Strausfeld, N.J. Nature doi:10.1038/nature13486. 2014. 7. Strausfeld, N.J. Arthropod Brains: Evolution, Functional Elegance, and Historical Significance (Belknap, Harvard University Press). 2012.

Host and contact person: Liria Masuda-Nakagawa (lm546@cam.ac.uk) Please let Liria know if you would like to meet Professor Strausfeld after the seminar.