Experimental precipitation of apatite pseudofossils resembling fossil embryos

Abstract

Certain phosphatic grains preserved in the rock record are interpreted as microfossils representing a diversity of microorganisms from bacteria to fossil embryos. In addition to bona fide primary biological features, phosphatic microfossils and fossil embryos commonly exhibit features that result from abiotic precipitation or diagenetic alteration. Distinguishing between abiotic and primary biological features can be difficult, and some features thought to represent biological tissue could instead be artifacts that are unrelated to the original morphology of a preserved organism. Here, we present experimentally generated, abiotically produced mineral precipitates that morphologically resemble biologically produced features, some of which may be observed in the rock record or noted in extant organisms, including embryos. These findings extend the diversity of biomorphic features known to result from abiotic precipitation.

Authigenesis of biomorphic apatite particles from Benguela upwelling zone sediments off Namibia: The role of organic matter in sedimentary apatite nucleation and growth

“…Beginning within ~30 hr of the start of the double‐diffusion experiments, the ion fronts began to interact and apatite began to precipitate out in a faint band that proceeded to separate into several distinct zones over the next 4–5 days. SEM micrographs reveal that within the gel environment, apatite precipitated in a wide variety of morphologies (Figure ; reviewed in Crosby & Bailey, ). Most of the structures represent either rod‐shaped particles (Figure a), variously intersecting dumbbells (Figure b,d,e) or closed spheres (Figure c).…”

“…Scanning electron microscope ( SEM ) images of apatite precipitated in organic matrices during double‐diffusion experiments (Crosby & Bailey, , ). The resultant apatite morphologies range from (a) spindle‐shaped to (b) dumbbells to (c) spherical microstructures.…”

“…A similar assemblage of microstructures termed “fluorapatite‐gelatin nanocomposites” has been reported to occur in double‐diffusion experiments using a variety of organic substrata (Busch et al., ; Kniep & Busch, ; Kniep & Simon, ; Wu, Tseng, & Chan, ). In double‐diffusion experiments investigating the influence of organic materials on the precipitation of apatite, numerous morphologies evolved from prismatic to dumbbell‐like to spherical amongst the precipitates that nucleated and grew within a polymeric gelatin gel (Crosby & Bailey, , ; Figure ). Interestingly, many have a distinctly biological appearance despite being abiological, and they resemble features described in the Namibian phosphate pellets.…”

“…The precipitates suspended in the gel were then removed from the diffusion setup, residue gel dissolved in water and concentrated precipitates mounted on an adhesive carbon film on top of an SEM stub. Imaging was done on a Hitachi TM1000 Tabletop ESEM operated at 15.0 kV accelerating voltage, and analysed by EDS using bruker quantax 50 software (Crosby & Bailey, 2018). well constrained, varying between 9.327 and 9.332 ± 0.002 Å and 6.885 and 6.889 ± 0.002 Å for a and c parameters, respectively ( Figure 3b).…”

Early fossil record of Euarthropoda and the Cambrian Explosion

“…The Doushantuo Formation of China (∼580 Ma) (117) was thought to contain animal embryos; however, these structures have now been shown to be nonmetazoan, containing algal thalli, acritarch vesicles, and nonmetazoan cell clusters (118). Some may even be nonbiological, as comparable structures can be generated during experimental precipitation of apatite (119). Other late Precambrian phosphate deposits contain a similar suite of single-celled/colonial eukarya and bacteria (81)(82)(83)117), and even in the Khesen Formation of Mongolia, which is immediately below the base of the Cambrian, no metazoan remains are found (120,121).…”