Flow chart outlining the identification and verification steps involved in the analysis of SEM images.

Citizen scientist (volunteers) microfossil identification reduced the SEM image dataset from 25,200 to 4192. Experts reviewed the 4192 images and verified microfossils in 448 images. Accounting for image overlap, the final pollen and spore count in these verified images was 383, of which 300 specimens were identifiable. Key for superscript lettering: a—An ‘agreement’ was reached by a minimum of three volunteers on questions set out in the questionnaire template; this category was then subdivided into images indicated as having ‘no microfossil/s’ and images indicated as having ‘microfossil/s’. b—These images were undisputed (i.e., not disputed by a fourth volunteer). c—These images were disputed by an additional (fourth) volunteer and had to be reviewed by an expert. d—These images were identified by three volunteers as containing other microfossils, that are not pollen or spores. e—If ‘no agreement’ was reached by a minimum of three volunteers on questions set out in the questionnaire template, these images were automatically marked by the system to be reviewed.</p

All raw citizen science expedition data (CSV files) and collated data.

All raw citizen science expedition data (CSV files) and collated data.</p

Breakdown of total number of images transcribed by volunteers and expert reviewed.

Total number of images in which volunteers reached agreement or did not reach agreement on the questionnaire template. Total number of images that needed expert review, as well as images verified to contain pollen/spores and final pollen/spore counts. (PDF)</p

Automated image acquisition.

(a) FEI QEM SCAN 650F scanning electron microscope (SEM). (b) A representative rock sample (AM F.147103) from McGraths Flat (approx. 50 × 60 mm) used for automated image acquisition; the photograph was taken using the microscope chamber’s digital camera. The flat surface of the rocks and their iron-rich composition makes it simple to maintain focus, as well as provide the conductivity needed for SEM operation without applying a conductive coating to the sample. (c) Schematic depiction of a 60 × 60 (3600) image montage; the area covered by 3600 images is 0.265 cm2 (note that neighbouring images have a 12.5% overlap). (d,e) SEM images that contain microfossils: d—image showing a single pollen (Nothofagidites emarcidus/heterus); and, e—two neighbouring images (dashed lines) showing an unknown spore. The images were electronically stitched together using Kolor Autopano Pro 4. The SEM images have not been adjusted for contrast and appear in the same format as viewed by volunteers.</p

Total pollen and spore counts (expert verified) from 25,200 SEM images analysed by citizen scientists and palynomorph density/cm².

Total pollen and spore counts (expert verified) from 25,200 SEM images analysed by citizen scientists and palynomorph density/cm2.</p

Reasons for no agreement on images.

Venn diagram illustrating the number of times that questions related to specimen count, occurrence, position, name, and image focus on the questionnaire template led to ‘no agreement’ among volunteer citizen scientists. The analysis is based on 275 images that were expert verified as containing pollen or spores (see Fig 3 for details). The top reasons that resulted in ‘no agreement’ included a combination of questions (count, occurrence, position, and name = 78 images), followed by identification of the specimen (75 images). Occurrence—whether or not a microfossil is present in an image; count—number of pollen or spores in an image; position—placement of microfossil on the edge or middle of the image; name—selected from a range of listed specimens; and focus—image is in focus or out of focus.</p

Microfossil identification, counts, and abundance.

(a) The total number of palynomorphs identified across 1.85cm2 of rock surface analysed. Note ‘Spores’ indicates that from ferns and mosses. (b) Pie chart showing the relative abundance (%) of palynomorphs, and in brackets, palynomorph density (number of specimens/cm2).</p

Pollen and spore types identified.

(a) Fungal spore. (b) Fern spore. (c) Nothofagidites. (d) Gymnospermous saccate pollen. (e) Myrtaceae/Cupanieae pollen. (f) Triporate pollen. (g) Porate angiosperm pollen. (h) Araucariaceae, gymnosperm pollen. (i) Angiosperm col(por)ate pollen; Quintinia. (j) Angiosperm colporate pollen; Margocolporites vanwijhei. (k) Angiosperm colpate pollen. Dashed lines indicate the overlap/stitching between neighbouring images. Scale bars, 15 μm. Arrows indicate the position of microfossils. Images have been adjusted slightly to improve contrast. Images appearing as they were viewed by volunteers can be found in S3 Fig.</p

Screenshots of the questionnaire template for the ‘Date a Fossil Project’ hosted on DigiVol.

Screenshots of the questionnaire template for the ‘Date a Fossil Project’ hosted on DigiVol.</p

Location and fossils of McGraths Flat.

(a) Map of Australia depicting the location of McGraths Flat (red star) near the town of Gulgong, Central Tablelands, New South Wales, Australia. (b) Field site. (c) Cross-section of the finely-bedded goethite-rich sedimentary rock from McGraths Flat. (d) Myrtaceous (eucalypt) leaf (AM F.146592). (e) Budding Malvales(?) flowers (AM F.146589). (f) Sawfly (Tenthredinoidea: Symphyta) (AM F.145093). (d-f) modified from McCurry et al., 2022. Note the variation in colour (yellow-red-brown) is dominantly due to grain size, the overall composition is homogeneous. Scale bars, c—1 cm, d—1 cm, e—1 mm, f—2 mm.</p