Spiny fruits revealed by nano-CT scanning, from the early Oligocene Belén flora of Peru
Fossil fruits formerly described as cashews from the Oligocene of Peru are reinvestigated based on the original specimens and newly collected materials. The recovery of an outer spiny layer, preserved in the sedimentary molds surrounding the locule casts, indicates that these disseminules do not represent Anacardium. Imagery from nano-CT scans of the specimens documents a distinctive morphology which does not resemble any fruits or seeds of Anacardiaceae.
We describe the morphology in more detail and reassign the fossils to an extinct genus, Pseudoanacardium gen. nov., of uncertain familial affinity. Pseudoanacardium peruvianum (Berry) comb. nov. was a prominent member of the Belén carpoflora, which also included palms plus Annonaceae, Euphorbiaceae, Humiriaceae, Leeaceae, Icacinaceae, Rutaceae and Vitaceae.
Plate 1. 1–19. Disseminules of Pseudoanacardium peruvianum (Berry) comb. nov. 1–3. Locule casts by reflected light, originals of Berry (1924, 1927). Scale bar = 1 cm; 1. Lectotype from Berry 1924 in lateral view, with two wall layers exposed by fractures of the surface. USNM 320717; 2. Specimen in lateral view showing protruding ventral attachment scar or placenta and curved surface striations. USNM 320713; 3. Smooth interior cast, lateral view. USNM 320715; 4, 5. Locule cast, surface rendering from CT scan. UF 603-70621. Scale bar = 1 cm; 4. Ventral view showing keel in plane of bisymmetry; 5. Lateral view, showing con- vex dorsal surface and concave ventral surface; 6–15. Surface renderings and virtual sections of fruit with spiny ornamentation partially intact. UF 603-54895. Scale bar = 1 cm; 6. Lateral view showing exposed locule cast with peg protruding on ventral side, and remains of spiny endocarp; 7. Ventral view; 8. Dorsal view; 9. Apical view of locule cast with some adhering remains of spiny endocarp; 10. Basal view; 11. Lateral view as in fig. 6, but with external surface of “peg” rendered transparent, showing internal vascular strand (funicular or placental); 12. Digital longitudinal section approximately in plane of bisymmetry, showing placental strand or funicle (left). Black part is airspace (including deteriorated endocarp wall); 13. Transverse section at apical 1/3, showing spiny wall; 14. Transverse section transecting ventral peg and vascular strand; 15. Transverse section of specimen in figs 4, 5, showing thin wrinkled membrane of seed coat within. UF 603-70621; 16–19. Digital section and isosurface render- ings of UF603-54943; 16. Transverse slice showing thickness of spiny fruit wall; 17. Isosurface rendering, basal view; 18. Same, enlarged; 19. Lateral view, showing spines over lateral and dorsal surface, and relatively smooth ventral rib. Scale bar = 1 cm
Plate 2. 1–26. Disseminules of Pseudoanacardium peruvianum (Berry) comb. nov.; 1–10. Cast and mold of fruit. UF603-54881. Scale bar = 1 cm; 1. Dorsal surface of silica locule cast, still partially encased in sedimentary mold of fruit, reflected light; 2. Same specimen, with locule cast removed, showing concavity of mold with outline of ventral smooth ridge surrounded by punctate surface indicating protrusion of spines, reflected light; 3. Ventral view of virtual fruit cast partially covering silica endocarp cast. Surface rendering from CT scan; 4. Locule cast from fig. 1, removed from matrix and viewed laterally, reflected light. Note large circular scar on ventral side (arrow). Reflected light; 5. Same view of locule cast, surface rendering from X-ray data; 6. Same, rotated 90° to show ventral surface with keel and large circular scar (arrows); 7. Same as fig. 3, rotated 90°to show lateral view with portion of the spiny endocarp remaining, and smooth locule cast protruding; 8. Same, flipped 180°, showing distinction between spiny ornamentation over most of fruit and smooth ventral area; 9. Same with portion of endo- carp digitally removed, revealing circular scar of locule cast within (arrow); 10. Same specimen in apical view; (Supplemental Material: http://bomax.botany.pl/filmy/Acta_Palaeobot_58_1_Manchester_Suppl_UF_54881.mpg); 11–14. Isosurface rendering of fruit with partially intact spiny endocarp. UF603-54890. Scale bar = 1 cm; 11. Lateral view; 12. Basal view. Note keel in plan of bisymmetry; 13. Ventral view; 14. Dorsal view. UF603-54890; (Supplemental Material: http://bomax.botany.pl/filmy/ Acta_Palaeobot_58_1_Manchester_Suppl_Anac_54890.mpg) 15–17. Digital section and isosurface renderings of UF603-54941; 15. Transverse slice showing spines of endocarp protruding into sediment (left side). Space between locule cast and endocarp mold represents original thickness of endocarp; 16. Surface rendering with locule cast partially covered by remains of spiny endocarp, basal view; 17. Surface rendering, lateral view; 18–23. Surface renderings of UF603-54891; 18. Lateral view with somewhat eroded (spines rounded), endocarp over upper half, and smooth locule cast exposed in lower half; 19. Same view with covering portion of endocarp removed to reveal apical part of locule cast with its circular scar (arrow); 20. Oblique ventral view showing delimitation between smooth ventral surface and ornamented lateral and dorsal surface of endocarp; 21. Dorsal view of endocarp with eroded spines; 22. Dorsal view of locule cast; 23. Apical view of endocarp; 24. Sedimentary mold showing punctate surface indicative of spiny fruit, from which images in 15–17 were taken. Reflected light. UF603-54941. Scale bar = 1 cm; 25. Surface rendering of spiny fruit in ventral view with smooth, fusiform ventral rib showing median groove (arrow). UF603-54894. Scale bar = 1 cm; 26. Longitudinal fracture of sedimentary mold from fig. 24, revealing spines in longitudinal view. UF603-54941. Scale bar = 3 mm
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