The past month has seen the publication of two exciting studies focusing on the preservation and evolutionary significance of fossilized central nervous systems. First, a collaboration with Dr. Russell Bicknell (University of New England) and colleagues, on the discovery of an exceptionally preserved brain in the extinct horseshoe crab Euproops danae from the Carboniferous Mazon Creek deposit in Illinois. The study published in Geology shows that the synganglion (the prosomal central nervous system) of horseshoe crabs has not changed significantly in terms of its overall morphology over the last 300 million years! Furthermore, the neurological structures of Euproops danae are replicated in clay minerals (e.g. kaolinite), suggesting a complex diagenetic history, and expanding the possible modes for nervous system fossilization. The story has been covered by various avenues online, including the The Conversation, New York Times, and the Natural History Museum. Thanks to the Wetmore Colles Grant for supporting the Open Access publication of this work.
Nervous system preservation in the Carboniferous horseshoe crab Euproops danae. A. YPM 168040, fossil specimen in dorsal view. B. Magnification of fossilized brain (synganglion) in prosoma). C. Morphological reconstruction of Euproops danae by Russell Bicknell.
In a second Open Access study published in iScience, Rudy and Javier joined forces with Dr. Luke Parry (University of Oxford) and Dr. James Weaver (Wyss Institute) to describe two new species of extinct comb jellies - or ctenophores - from the mid-Cambrian Marjum Formation in Utah. The new species increase the diversity of Cambrian comb jellies, and reveal surprising details of the internal anatomy such as fossilized longitudinal nerve tracts and and oral ring preserved as carbonaceous films. The new Marjum taxa illuminate the early evolution of comb jellies, and suggest that modern species have lost several characters relative to their Cambrian counterparts, including parts of the nervous system, a rigid skeleton and a mouth-like oral skirt. The study has been covered by New Scientist and EurekAlert! We thank our colleagues at the Natural History Museum of Utah for facilitating access to this fascinating material, and the Bureau of Land Management for donating the specimens for their formal study.
New species of fossil comb jellies from the mid-Cambrian Marjum Formation of Utah. Top row: Ctenorhabdotus campanelliformis with nervous system preserved as delicate carbon films, visible through elemental mapping. Other important characters include the presence of a well developed oral skirt, and rigid capsule covering the apical organ. Bottom row: Thalassostaphylos elegans showing the presence of polar fields, and the loss of the apical capsule. Morphological reconstruction courtesy of Holly Sullivan (https://www.sulscientific.com/).