The Evolution and Development of Cephalopod Chambers and Their Shape

The Ammonoidea is a group of extinct cephalopods ideal to study evolution through deep time. The evolution of the planispiral shell and complexly folded septa in ammonoids has been thought to have increased the functional surface area of the chambers permitting enhanced metabolic functions such as: chamber emptying, rate of mineralization and increased growth rates throughout ontogeny. Using nano-computed tomography and synchrotron radiation based micro-computed tomography, we present the first study of ontogenetic changes in surface area to volume ratios in the phragmocone chambers of several phylogenetically distant ammonoids and extant cephalopods. Contrary to the initial hypothesis, ammonoids do not possess a persistently high relative chamber surface area. Instead, the functional surface area of the chambers is higher in earliest ontogeny when compared to Spirula spirula. The higher the functional surface area the quicker the potential emptying rate of the chamber; quicker chamber emptying rates would theoretically permit faster growth. This is supported by the persistently higher siphuncular surface area to chamber volume ratio we collected for the ammonite Amauroceras sp. compared to either S. spirula or nautilids. We demonstrate that the curvature of the surface of the chamber increases with greater septal complexity increasing the potential refilling rates. We further show a unique relationship between ammonoid chamber shape and size that does not exist in S. spirula or nautilids. This view of chamber function also has implications for the evolution of the internal shell of coleoids, relating this event to the decoupling of soft-body growth and shell growth

Lessons from the Past: Sponges and the Geological Record

Sponges have been a major part of marine ecosystems, in both shallow and deep water, from the time of the earliest animal communities. The great shifts in climate that have occurred over the past 541 million years have affected all organisms, including sponges. Although patchy knowledge of the sponge fossil record hinders recognition of trends, some general patterns are apparent. Shallow-water siliceous sponges were severely affected by glacial intervals, whereas deeper-water siliceous sponges appear to have flourished during these times. Some groups of hypercalcified sponges (such as stromatoporoids) were abundant during times of global warming and high sea level, but other groups (archaeocyathans and sphinctozoans) had their acme during times of low sea level and relatively cool climate. Overall, sponge diversity appears to have been controlled more by sea level than by climate: large-scale sponge biotas occurred at times of high sea level, when there were large areas of shallow sea.Fil: Muir, Lucy. National Museum Wales; Reino UnidoFil: Botting, Joseph P.. National Museum Wales; Reino Unido. Nanjing Institute Of Geology And Palaeontology; ChinaFil: Beresi, Matilde Sylvia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin