Coryloides, S.R.Manchester, 1994

Tiffney, Bruce H. & Manchester, Steven R., 2022, The Early Middle Eocene Wagon Bed Carpoflora Of Central Wyoming, U. S. A., Fossil Imprint 78 (1), pp. 51-79 : 57

Genus Coryloides MANCHESTER

Text-fig. 2o–r

M a t e r i a l. One specimen, chalcedony cast. USNM

PAL 772345.

D e s c r i p t i o n. Distorted sphere, 20.5 mm high, 18.9 mm on one equatorial axis, 21.7 mm on the opposite axis. One end surmounted by a very clearly demarcated disk, 11 × 12.5 mm in diameter, distorted on the same axes as the larger specimen. The center of the disk is smoother than the surface of the sphere as a whole, and tapers to a conical point ( Text-fig. 2o–q ). There is a suggestion that the surface of the sphere laps up against the margin of the terminal disk in one or more layers, the innermost exhibiting an undulating margin ( Text-fig. 2p ). The surface of the rest of the sphere is unevenly rumpled, and is traversed by eight faint, equidistant, longitudinal striations.

D i s c u s s i o n. We interpret this fossil as a locule cast or seed of Coryloides MANCHESTER, first described from the Clarno flora ( Manchester 1994). Initially we thought that this was the exterior of a poorly preserved fruit of some form. However, at least one Clarno specimen of Coryloides (pl. 7, fig. 12 in Manchester 1994) exhibits a broken nut, exposing a contained locule cast or seed. Re-examination of this latter specimen reveals that the locule cast/seed exhibits a large, circular, scar with a central pointed tip. This scar is not aligned with the basal cupule scar of the fruit ( Manchester 1994: pl. 7, figs 7, 9, 10). It is unclear from present data if this scar and point represents the micropylar end of the seed, or more plausibly due to its complexity, the chalaza.

The unevenly distorted surface of the Wagon Bed specimen suggests that the living structure had a flexible surface with a degree of plasticity that could be easily deformed in the preservational process; if the fossil represents a seed, it could well have been deformed in preservation, much as the specimen in pl. 7, fig. 12 of Manchester (1994). The surface of the Wagon Bed specimen is traversed by widely spaced, equidistant, longitudinal grooves. As with other Wagon Bed taxa, the presence of Coryloides suggests a geographic link with the Clarno flora.

Although the external surface of Coryloides nuts resembles that of extant Corylus L. in the Betulaceae , the locule morphology as seen in the Nut Beds and Wagon Bed specimens does not match that of the extant genus; whether this reflects true relationship or a convergent morphology within the Betulaceae ( Manchester 1994) is unclear. Corylus is currently represented by about 18 species of deciduous trees and shrubs of the Northern Hemisphere (Mabberly 2008).

Figures

Text-fig. 2. Salicaceae (a–g), Cannabaceae (h–n), cf. Betulaceae (o–r). a–g: Saxifragispermum, USNM PAL 772341. Scale bar = 5mm except as indicated. a–b: Lateral, c: apical, and d: basal views of fruit, reflected light, palladium coated; apex at top of (a, b). e: Equatorial transverse section reflected light; arrows indicate presumed seeds, scale bar = 2mm. f: Detail of locule contents extracted from (e), transmitted light, scale bar = 200 Μm. g: Interwoven trichomes or fibers from locule, transmitted light, scale bar = 5 Μm. h–j: Celtis. h, i: USNM PAL 772342, reflected light, palladium coated, scale bar = 5mm. h: Lateral view parallel with plane of dehiscence. i: Lateral view perpendicular to plane of dehiscence. j: DMNH EPI.47809, Celtis in lateral view; showing reticulate sculpture and the vertically-oriented, plane of dehiscence (arrow), scale bar = 5mm. k–m: Aphananthe. USNM PAL 772344, reflected light, palladium coated, scale bar = 5mm. k: Apical view, note triangular cross section and apical plug (arrow). l: Lateral view, apex up. m: Lateral view at 90° to (l). n: Detail of cellular pattern at surface of endocarp, scale bar = 0.5 mm. o–r: