The earliest evidence of deep-sea vertebrates.

Vertebrate macroevolution has been punctuated by fundamental habitat transitions from shallow marine origins to terrestrial, freshwater, and aerial environments. Invasion of the deep sea is a less well-known ecological shift because of low fossilization potential and continual loss of abyssal fossil record by ocean floor subduction. Therefore, there has been a lack of convincing evidence of bottom-living vertebrates from pre-Paleogene deep seas. Here, we describe trace fossils from abyssal plain turbidites of the Tethys Ocean, which, combined with nannofossil dating, indicate that fishes have occupied the deep seafloor since at least the Early Cretaceous (Hauterivian-Barremian). These structures are identical to those produced by modern demersal fishes that feed by either scratching the substrate or expose their prey by water flow generated by suction or jetting. The trace fossils suggest activity of at least three fish species exploiting a productive abyssal invertebrate sediment fauna. These observations are consistent with Early Cretaceous vertebrate transition to the deep sea triggered by the availability of new food sources. Our results anticipate the appearance of deep-seafloor fishes in the fossil record by over 80 My while reassessing the mode of vertebrate colonization of the deep sea.

How Much Can We Trust Major Element Quantification in Bioapatite Investigation?

Bioapatite is probably the key factor in the unreplicated success of vertebrates. Chemical data on bioapatite composition can be achieved on a solid sample by using different analytical tools such as spectroscopic and spectrometric methods. As analytical outputs can be affected by the physical-chemical characteristics of the sample matrix, an internal standard is usually required to correct and validate the results. Bioapatite lattice can accommodate iso- and heterovalent substitutions during life or diagenesis varying its chemical composition through (geological) time. If on the one hand, this makes bioapatite a unique archive of physical and chemical information for both the living cycle and the events occurring after death, on the other, it excludes the identification of a sole internal standard. Here, we propose a method to measure major element concentration with specific care for P, Ca, Mg, Na, K, Si, Al, and Fe, which are the main substituent atoms in bioapatite, through homemade matrix-matched external calibration standards for laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). We tested the method on living and fossil shark teeth, critically comparing the results obtained using other analytical techniques and certified external standards. We demonstrated that matrix-matched calibration in LA-ICPMS is mandatory for obtaining a reliable chemical characterization even if factors such as matrix aggregation variability, diverse presence of volatile compounds, the fossilization footprint, and the instrumental variability can represent further variability parameters.

Modern Iron Ooids of Hydrothermal Origin as a Proxy for Ancient Deposits.

We constrained the origin and genetic environment of modern iron ooids (sand-sized grains with a core and external cortex of concentric laminae) providing new tools for the interpretation of their fossil counterparts as well as the analogous particles discovered on Mars. Here, we report an exceptional, unique finding of a still active deposit of submillimetric iron ooids, under formation at the seabed at a depth of 80 m over an area characterized by intense hydrothermal activity off Panarea, a volcanic island north of Sicily (Italy). An integrated analysis, carried out by X-ray Powder Diffraction, Environmental Scanning Electron Microscopy, X-ray Fluorescence and Raman spectroscopy reveals that Panarea ooids are deposited at the seafloor as concentric laminae of primary goethite around existing nuclei. The process is rapid, and driven by hydrothermal fluids as iron source. A sub-spherical, laminated structure resulted from constant agitation and by degassing of CO2-dominated fluids through seafloor sediments. Our investigations point the hydrothermal processes as responsible for the generation of the Panarea ooids, which are neither diagenetic nor reworked. The presence of ooids at the seawater-sediments interface, in fact, highlights how their development and growth is still ongoing. The proposed results show a new process responsible for ooids formation and gain a new insight into the genesis of iron ooids deposits that are distributed at global scale in both modern and past sediments.

Diagenesis does not invent anything new: Precise replication of conodont structures by secondary apatite.

Conodont elements are important archives of sea/pore water chemistry yet they often exhibit evidence of diagenetic mineral overgrowth which may be biasing measurents. We decided to investigate this phenomenon by characterising chemically and crystallographically, the original biomineral tissue and the diagenetic mineral nature of conodont elements from the Ordovician of Normandy. Diagenetic apatite crystals observed on the surface of conodont elements show distinctive large columnar, blocky or web-like microtextures. We demonstrate that these apatite neo-crystals exhibit the same chemical composition as the original fossil structure. X-ray microdiffraction has been applied herein for the first time to conodont structural investigation. Analyses of the entire conodont element surface of a variety of species have revealed the existence of a clear pattern of crystal preferred orientation. No significant difference in unit cell parameters was documented between the newly formed apatite crystals and those of the smooth conodont surfaces, thus it emerges from our research that diagenesis has strictly replicated the unit cell signature of the older crystals.