Sclerosperma fossils from the late Oligocene of Chilga, north-western Ethiopia

Figures & data

Figure 1. Locality map. A. Location of Ethiopia in Africa. B. The study area, Gonder, and the current capital city, Addis Ababa. Major rivers are shown, including the Blue Nile and its source, Lake Tana, to the immediate south of the study area. C. Location of the Guang and Hauga Rivers, and measured section shown in Figure 2.

Figure 2. Stratigraphic section, measured along the Guang River. Stars indicate stratum that produced the Sclerosperma fossil pollen, and the fossil leaf locality, CH41, is labelled and marked by a leaf icon. Radioisotopic dates are shown near the base and top of the section.

Table I. Pollen morphology of extant and fossil Sclerosperma.

	S. mannii	S. protomannii sp. nov.	S. walkeri	S. profizianum (Type A)	S. protoprofizianum sp. nov.	S. profizianum (Type C)	S. profizianum (Type B)
Distribution	Liberia, Nigeria, Cameroon, Equatorial Guinea, Gabon, Angola, Democratic Republic of the Congo (DRC)	Chilga, north-western Ethiopia	Gabon, DRC	Ghana, Gabon, Republic of the Congo, DRC, Angola (species distibution)	Chilga, north-western Ethiopia	Ghana, Gabon, Republic of the Congo, DRC, Angola (species distibution)	Ghana, Gabon, Republic of the Congo, DRC, Angola (species distibution)
Age	Recent	Late Oligocene	Recent	Recent	Late Oligocene	Recent	Recent
Outline polar view	Straight-triangular to slightly concave-triangular	Straight-triangular to slightly concave-triangular	Straight-triangular to slightly concave-triangular	Straight-triangular to slightly concave-triangular	Straight-triangular; apices often infolded towards proximal side (hexagonal appearance)	Straight-triangular to slightly convex-triangular	Straight-triangular to slightly concave-triangular
Outline equatorial view	Bean-shaped	Bean-shaped	Bean-shaped	Bean-shaped	Bean-shaped	Bean-shaped	Bean-shaped
Equatorial diameter (µm in LM)	32–38	27–38	35–40	35–40	23–35	37–42	32–38
Equatorial diameter (µm in SEM)	27–34	24–35	30–35	29–35	21–29	31–39	30–34
Polar axis (µm in LM)	9–15	9–12	15–19	10–14	9–12	10–16	10–13
Aperture type	Triporate	Triporate	Triporate	Triporate	Triporate	Triporate	Triporate
Aperture position	Sub-apically, distal polar face	Sub-apically, distal polar face	Sub-apically, distal polar face	Sub-apically, distal polar face	Sub-apically, distal polar face	Sub-apically, distal polar face	Sub-apically, distal polar face
Aperture outline	Elliptic	Elliptic	Elliptic	Elliptic	Elliptic	Circular to elliptic	Circular to elliptic
Aperture diameter (µm in SEM)	4.5–6.0	5.5–8.0	5.0–8.0	5.0–8.5	6.0–8.0	4.0–6.5	4.0–5.5
Exine thickness (µm in LM)	1.7–2.5	1.7–2.5	1.7–2.5	1.7–2.5	1.7–2.5	1.7–2.5	1.7–2.5
Pollen wall (SEM)	Semitectate	Semitectate	Semitectate	Semitectate	Semitectate to tectate	Tectate	Tectate
Sculpture (LM)	Reticulate	Reticulate	Reticulate	Reticulate	Reticulate	Scabrate	Rugulate
Sculpture (SEM)	Reticulate to perforate	Reticulate to perforate	Reticulate to perforate	Microreticulate to perforate	Microreticulate to perforate	Perforate, rugulate/verrucate and fossulate	Fossulate, rugulate/verrucate, perforate
Sculpture distal face (SEM)	Reticulate with broad muri and elliptic to triangular to polygonal lumina, 0–6 nanogemmae free-standing columellae per lumina	Reticulate with broad muri and elliptic to polygonal lumina	Reticulate with broad muri and elliptic to triangular to polygonal lumina, 0–6 nanogemmae free-standing columellae per lumina	Microreticulate with broad muri and elliptic to triangular to polygonal lumina	Microreticulate to perforate with broad muri and elliptic to polygonal lumina or circular to slit-like perforations, free-standing columellae rare, up to 4 nanogemmae free-standing columellae per lumina when present	Perforate, perforations elliptic to slit-like, perforations often aligned in sinuous rows, rows of perforations outlining irregular shaped rugulae/verrucae	Fossulate with tiny circular to slit-like perforations aligned within the fossulae, sinuous fossulae outlining irregular shaped rugulae/verrucae
Number of lumina/perforations at central distal face (SEM)	18–25 per 100 µm^2	10–20 per 100 µm^2	16–25 per 100 µm^2	30–35 per 100 µm^2	50–65 per 100 µm^2	45–55 per 100 µm^2	Not applicable
Sculpture proximal face (SEM)	Reticulate central polar area and mesoporium with elliptic to triangular to polygonal lumina, 0–6 nanogemmae free-standing columellae per lumina; becoming microreticulate to perforate towards apices	Reticulate central polar area and mesoporium with elliptic to polygonal lumina, nanogemmae free-standing columellae extremely rare and singular; becoming microreticulate to perforate towards apices	Reticulate central polar area and mesoporium with elliptic to triangular to polygonal lumina, 0–6 nanogemmae free-standing columellae per lumina; becoming microreticulate to perforate towards apices	Microreticulate central polar area and mesoporium with elliptic to circular or slit-like lumina; becoming nanoreticulate to perforate towards apices	Microreticulate to perforate central polar area and mesoporium with elliptic to circular to polygonal or slit-like lumina/perforations, free-standing columellae rare, up to 4 nanogemmae free-standing columellae per lumina when present; becoming nanoreticulate to perforate towards apices	Perforate and fossulate central polar area and mesoporium, perforations elliptic to slit-like, perforations often aligned in sinuous rows, rows of perforations and fossulae outlining irregular shaped rugulae/verrucae; becoming micro- to nanorugulate/verrucate and perforate towards apices	Fossulate central polar area and mesoporium with tiny circular to slit-like perforations aligned within the fossulae, sinuous fossulae outlining irregular shaped rugulae/verrucae; becoming micro- to nanorugulate/verrucate and perforate towards apices
Opercula (SEM)	Nanoverrucate to granulate sublayer and microreticulate supra-layer	Sublayer not observed, but with reticulate supra-layer	Nanoverrucate to granulate sublayer and microreticulate supra-layer	Nanoverrucate to granulate sublayer and reticulate supra-layer	Nanoverrucate to granulate sublayer and microreticulate supra-layer	Nanoverrucate to granulate sublayer and perforate supra-layer	Nanoverrucate to granulate sublayer and perforate supra-layer

Note: Data on extant pollen from Grímsson et al. (2018). The fossil Sclerosperma pollen types are placed between those extant taxa they mostly compare to.

All measurements are given in micrometres (µm). Most diagnostic features separating the fossil pollen appear in bold font.

Figure 3. Light microscopy (LM) (A) and scanning electron microscopy (SEM) (B–I) micrographs of Sclerosperma protomannii sp. nov. (holotype: IPUW 7513/223). A. Pollen grain in polar view (upper in high focus and middle in optical cross-section) and equatorial view (lower). B. Pollen grain in polar view, distal side. C. Pollen grain in polar view, proximal side. D. Close-up of apex with aperture, distal side. E. Close-up of apex, proximal side. F. Close-up of central polar area, distal side. G. Close-up of central polar area, proximal side. H. Close-up of interapertural area, distal side. G. Close-up of interapertural area, proximal side. Scale bars – 10 µm (A–C), 1 µm (D–I).

Figure 4. Light microscopy (LM) (A) and scanning electron microscopy (SEM) (B–E) micrographs of Sclerosperma protomannii sp. nov. (paratype: IPUW 7513/224). A. Pollen grain in polar view (optical cross-section). B. Pollen grain in polar view, distal side. C. Pollen grain in polar view, proximal side. D. Close-up of central polar area, distal side. E. Close-up of interapertural area, proximal side. LM (F) and SEM (G–J) micrographs of S. protomannii sp. nov. (paratype: IPUW 7513/225). F. Pollen grain in polar view (high focus). G. Pollen grain in polar view, distal side. H. Pollen grain in polar view, proximal side. I. Close-up of apex with aperture, distal side. J. Close-up of apex, proximal side. Scale bars – 10 µm (A–C, F–H), 1 µm (D, E, I, J).

Figure 5. Light microscopy (LM) (A) and scanning electron microscopy (SEM) (B–E) micrographs of Sclerosperma protomannii sp. nov. (paratype: IPUW 7513/226). A. Pollen grain in polar view (upper, high focus) and equatorial view (lower). B. Pollen grain in polar view, distal side. C. Pollen grain in polar view, proximal side. D. Close-up of apex with aperture, distal side. E. Close-up of central polar area, distal side. LM (F) and SEM (G–J) micrographs of S. protoprofizianum sp. nov. (holotype: IPUW 7513/227). F. Pollen grain in polar view (high focus). G. Pollen grain in polar view, distal side. H. Pollen grain in polar view, proximal side. I. Close-up of apex with aperture, distal side. J. Close-up of central polar area, distal side. Scale bars – 10 µm (A–C, F–H), 1 µm (D, E, I, J).

Table II. Fossil record of Sclerosperma

Taxon	Organ	Locality	Age	Country	Reference
Scleropserma sp.	Pollen	Bignona borehole	Late Miocene (10–5 Ma)	Senegal	Medus (1975, plate 4, figures 2–3)
Sclerosperma safiannikoffii	Leaves, cuticle	Mero camp	?Miocene	Democratic Republic of the Congo	Lakhanpal (1966, plate 1, figure 1; plate 2, figure 1; plate 3, figures 1–2)

Note: This list includes allSclerosperma records verified using illustrated material (pollen, leaves, and cuticle).

All other records have been excluded.

Figure 6. Light microscopy (LM) (A) and scanning electron microscopy (SEM) (B–E) micrographs of Sclerosperma protoprofizianum sp. nov. (paratype: IPUW 7513/228). A. Pollen grain in polar view (high focus). B. Pollen grain in polar view, distal side. C. Pollen grain in polar view, proximal side. D. Close-up of apex with aperture, distal side. E. Close-up of central polar area, distal side. LM (F) and SEM (G–J) micrographs of S. protoprofizianum sp. nov. (paratype: IPUW 7513/229). F. Pollen grain in polar view (high focus). G. Pollen grain in polar view, distal side. H. Pollen grain in polar view, proximal side. I. Close-up of apex, proximal side. J. Close-up of central polar area, distal side. Scale bars – 10 µm (A–C, F–H), 1 µm (D, E, I, J).

Figure 7. Fossil leaf fragment from locality CH41, specimen 9A (CH41-9A), collected at 74 m above the base of the measured Guang River section (Figure 2).

Grímsson F, van Valkenburg JLCH, Wieringa JJ, Xafis A, Jacobs BF, Zetter R. 2018. Pollen morphology of the African Sclerosperma (Arecaceae). Grana. doi:10.1080/00173134.2018.1519033.

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Medus J. 1975. Palynologie de sédiments Tertiaires du Sénégal méridional. Pollen et Spores 17: 545–601.

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Lakhanpal RN. 1966. Some middle Tertiary plant remains from South Kivu, Congo. Annales du Musée Royal de l’Afrique Centrale Serie 8(52): 21–30.

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