The Record of Precambrian Steroidal HydrocarbonsThe record of sterane and triterpane hydrocarbon biomarkers in Archean and Proterozoic sedimentary rocks has come under extremely thorough scrutiny in recent times. Concerns about contamination, and doubts about reports of steroidal hydrocarbons in the 2.7 billion year-old Fortescue Group sediments of the Pilbara Craton (Brocks et al., 1999), were initially raised in 2003(Brocks et al., 2003. These potential problems became increasingly difficult to dismiss when new and improved types of geochemical analyses were devised and applied. For example, Brocks and colleagues showed that a selection of rock and sediment samples from a range of localities were ubiquitously contaminated with petroleum-and plastic-derived organic compounds . Analyses of thin slices of sediment core showed that spatial distributions of hydrocarbons could be used to distinguish indigenous hydrocarbons from surface contaminants in Archean shales (Brocks, 2011). In another example, the carbon isotopic data values of in situ and insoluble kerogen and pyrobitumen in rock formations that had previously yielded biomarkers were discrepant from those of the extractable hydrocarbons, meaning that the latter could not be indigenous (Rasmussen et al., 2008).

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Brain anatomy provides key evidence for ray-finned fish relationships 1 , but two key limitations obscure our understanding of neuroanatomical evolution in this major vertebrate group. First, the deepest branching living lineages are separated from the group's common ancestor by hundreds of millions of years, with indications that aspects of .

Brain anatomy provides key evidence for ray-finned fish relationships, but two key limitations obscure our understanding of neuroanatomical evolution in this major vertebrate group. First, the deepest branching living lineages are separated from the group's common ancestor by hundreds of millions of years, with indications that aspects of their brain morphology--like other aspects of their anatomy--are specialised relative to primitive conditions. Second, there are no direct constraints on brain morphology in the earliest ray-finned fishes beyond the coarse picture provided by cranial endocasts: natural or virtual infillings of void spaces within the skull. Here we report brain and cranial nerve soft-tissue preservation in Coccocephalichthys wildi, a ~319-million-year-old (Myr) ray-finned fish. This oldest example of a well-preserved vertebrate brain provides a unique window into neural anatomy deep within ray-finned fish phylogeny. Coccocephalichthys indicates a more complicated pattern of brain evolution than suggested by living species alone, highlighting cladistian apomorphies and providing temporal constraints on the origin of traits uniting all extant ray-finned fishes. Our findings, along with a growing set of studies in other animal groups, point to the significance of ancient soft tissue preservation in understanding the deep evolutionary assembly of major anatomical systems outside of the narrow subset of skeletal tissues.