Synchrotron X-ray absorption spectroscopy of melanosomes in vertebrates and cephalopods: implications for the affinity of Tullimonstrum

Screening pigments are essential for vision in animals. Vertebrates use melanins bound in melanosomes as screening pigments, whereas cephalopods are assumed to use ommochromes. Preserved eye melanosomes in the controversial fossil Tullimonstrum (Mazon Creek, IL, USA) are partitioned by size and/or shape into distinct layers. These layers resemble tissue-specific melanosome populations considered unique to the vertebrate eye. Here, we show that extant cephalopod eyes also show tissue-specific size- and/or shape-specific partitioning of melanosomes; these differ from vertebrate melanosomes in the relative abundance of trace metals and in the binding environment of copper. Chemical signatures of melanosomes in the eyes of Tullimonstrum more closely resemble those of modern cephalopods than those of vertebrates, suggesting that an invertebrate affinity for Tullimonstrum is plausible. Melanosome chemistry may thus provide insights into the phylogenetic affinities of enigmatic fossils where melanosome size and/or shape are equivocal

Mechanical Properties of the Chitin-Calcium-Phosphate Clam Shrimp Carapace (Branchiopoda: Spinicaudata): Implications for Taphonomy and Fossilization

Spinicaudata (colloquially ‘the clam shrimp’) are freshwater branchiopod crustaceans that occur worldwide in lakes and temporary pools. The spinicaudatans are easily recognizable by their bivalved carapace which is unusual among arthropods in that it is subject to only partial molting. During ecdysis (molting), the outer surface of the carapace is not shed, resulting in the retention of the ontogenetic record of an individual through distinct growth-rings representing each molt. When this unusual feature is considered alongside the interesting chemical properties of the carapace, “clam shrimp” present an interesting biological material not seen anywhere else: a multi-laminar calcium-phosphate-chitin composite. In addition, the carapace survives numerous destructive taphonomic processes (including transport, decay, compaction, and desiccation) to become the dominant body component of Spinicaudata preserved in their 380 million year fossil record. Understanding the mechanical properties and chemical composition of this structure may not only aid in a better understanding of the evolutionary history of this group but also facilitate efforts to develop novel materials that retain functional material properties even in harsh aquatic conditions. Therefore, this study aims to provide quantitative information about the composition and mechanics of this unique and interesting biological material and help predict possible biases in the fossilization of different species of Spinicaudata to aid future palaeontological research

Autoecology of Wolfestheria smekali (Spinicaudata) from the Upper Jurassic (Cañadón Asfalto Formation), Patagonia, Argentina

Spinicaudatans are small branchiopod crustaceans also usually known as ‘Conchostraca’. They are easily recognizable by their short, laterally-compressed body inside of a characteristic bivalved, lightly-mineralized chitin carapace which is often the only preserved element of the group in the fossil record. The valves of the carapace are distinctive due to the presence of growth lines which are produced by the accumulation of successive cuticle layers retained after ecdysis. ‘Conchostracan’ paleoecology has been the subject of several previous studies—most focus on the paleoenvironment of the rock units in which the fossils were found. Few studies have been carried out on the paleoautecology of fossil taxa. In this work, an exploratory study was performed regarding the paleoautecology of the small clam shrimp Wolfestheria smekali Gallego and Monferran 2013, from the Cañadón Asfalto Formation (Upper Jurassic) in the Argentinean Chubut province in Patagonia, with the objective of understanding the ecological characteristics of individuals and populations within this species. Samples were collected from four stratigraphic levels in the Estancia La Sin Rumbo locality (in the Chubut River middle valley). W. smekali was found in association with the darwinuloid ostracod Penthesilenula sarytirmenensis Sharapova, mollusks assigned to the genus Diplodon Spix, and insects represented by larval cases from the order Trichoptera (caddisflies, Ostracindusia and Conchindusia). The population density of W. smekali in each sample was recorded and morphometric analyses were performed on a selected subsample of individuals. This technique allowed the discrimination of sexual dimorphism where males have a telliniform, ovate–elliptical shape, and females have a cycladiform, subcircular–subtriangular shape. Given the sex-ratio observed in the samples collected, it is likely that the species had a dioecious reproductive system (50% males, 50% females). It is hoped that the present work will give new insights into the dynamics of ancient ephemeral pools and serve as a foundation for future studies of fossil Spinicaudata.Fil: Monferran, Mateo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Centro de Ecologia Aplicada del Litoral (i); Argentina; Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura; Argentina;Fil: Gallego, Oscar Florencio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Nordeste. Centro de Ecologia Aplicada del Litoral (i); Argentina; Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura; Argentina;Fil: Astrop, Timothy I.. University of Akron; Estados Unidos;Fil: Cabaleri, Nora Graciela. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Geocronologia y Geologia Isotopica (i); Argentina