Terminalioxylon mozambicense, Bamford & Pickford, 2021

Bamford, Marion & Pickford, Martin, 2021, Stratigraphy, Chronology And Palaeontology Of The Tertiary Rocks Of The Cheringoma Plateau, Mozambique, Fossil Imprint 77 (1), pp. 187-213 : 205

Terminalioxylon mozambicense sp. nov.

Text-fig. 16

H o l o t y p e. BP/16/1734 ( Text-fig. 16 ).

P l a n t F o s s i l N a m e s R e g i s t r y N u m b e r.

PFN002687 (for new species).

A d d i t i o n a l m a t e r i a l. BP/16/1731, 1735, 1736,

1737.

R e p o s i t o r y. Curated at the Palaeobotany Herbarium , Evolutionary Studies Institute (previously the Bernard Price Institute), University of the Witwatersrand, Johannesburg, South Africa (for both holotype and additional material) .

E t y m o l o g y. The species name is for Mozambique with the latin suffix ense meaning “from”.

T y p e l o c a l i t y. Mhengere Hill, Site 3 (18°56′02.0″S, 34°36′50.6″E). Fossil wood associated with palaeopan, lower northwest slope ( Text-fig. 8 ), probably late Eocene .

D i a g n o s i s. The wood is diffuse porous and growth rings are absent to indistinct. Vessels are arranged in short radial multiples, often solitary but with lines of two or three pores. Some vessels are tylosed, and range in diameter from 145–175 µm ( Text-fig. 16a–c ). Perforation plates are simple and horizontal. Inter-vessel pits are alternate and 6–8 µm and vessel-parenchyma pits are the same ( Text-fig. 16a, b ). Parenchyma is scanty paratracheal to vasicentric and also diffuse ( Text-fig. 16a ). There are 2–4 cells per parenchyma strand. Prismatic crystals occur in the diffuse parenchyma cells and the ray cells ( Text-fig. 16d–g ). Rays are exclusively uniseriate and up to 16 cells high (175-400-500 µm), and procumbent body cells with 1–2 rows of marginal, square or upright cells that are difficult to see because of the dark cell contents ( Text-fig. 16i ). No canals were seen.

C o m p a r i s o n s. The Gorongosa wood is very similar to Terminalioxylon tunesense DUPÉRON- LAUDOUEN. described from the late Oligocene to early Miocene of Tunisia (DelteilDesneux 1981) except that the vessels of the Gorongosa wood are smaller, it has rare diffuse parenchyma with prismatic crystals, as well as crystals in the ray cells (like the Tunisian specimen). Vessel size is not a reliable taxonomic feature and the presence of diffuse parenchyma is easy to miss. The geographic separation of the two sites is considerable so in order to avoid unreliable phytogeographic correlations, the Gorongosa wood has been placed in a new species.

There are 57 examples of fossil Terminalioxylon woods listed in the InsideWood database but none of them is compatible with the Gorongosa wood samples. For example, only ten of the listed woods have diffuse parenchyma. Of these ten, only three have rays with only one row of upright marginal cells ( Terminalioxylon chiedense , T. coriaceum and T. felixii ). Terminalioxylon chiedense has wider rays, 1–2 cells with the uniseriate portion as wide as the multiseriate portion ( Fessler-Vrolant 1980). Terminalioxylon coriaceum has some vessels more than 200 µm in diameter and confluent parenchyma ( Licht et al. 2014). Terminalioxylon felixii has intervessel pits that are 10 µm wide, some confluent parenchyma, terminal parenchyma bands and tyloses ( Lakhanpal et al. 1984). None of these described woods matches the Gorongosa woods.

Four other species of Terminalioxylon and one fossil Terminalia L. have been described from Tertiary rocks of Africa ( Terminalioxylon crystallinum M.K.BAMFORD and Terminalioxylon orangense M.K.BAMFORD from the middle Miocene of Namibia ( Bamford 2003); Terminalioxylon welkitii LEMOIGNE et J.BEAUCH. from the Miocene of Ethiopia ( Lemoigne and Beauchamp 1972); Terminalia preglaucescens BANDE, DECHAMPS, R.N.LAKH. et U.PRAKASH from the early Miocene of Zaire ( Bande et al. 1987)). The species vary slightly in average vessel diameters and degree of heterogeneity of the ray cells. None has diffuse parenchyma recorded.

Trees of the Combretaceae are common in southern Africa with members of Combretum and Terminalia being the most common. In Mozambique today there are about 11 species of Terminalia (out of a worldwide total of 150). Other genera include Lumnitzera , Meiostemon and Pteleopsis ( Burroughs et al. 2018) . Woods of the Combretaceae have been well studied ( van Vliet 1978) and the genera are distinguishable. In Mozambique today there are ten species of Terminalia , all trees or shrubs, and their habitats range from rocky hillsides and ravines, Miombo woodland and forest to low altitude woodland ( Burroughs et al. 2018). Extrapolating the environmental setting for the fossil wood from the modern analogues it is possible to infer that a tropical wooded environment was likely to be the setting.

Figures

Text-fig. 16. Photomicrographs of thin sections of specimen BP/16/1734, Terminalioxylon mozambicense sp. nov. from Mhengere Hill, Gorongosa, Mozambique. a: TS with round vessels, scanty paratracheal to vasicentric parenchyma, diffuse and narrow terminal or initial bands; b: TS at higher magnification, note the very narrow rays; c: TLS, vessels with small alternate pits, and partly tylosed; d–g: TLS with crystals (small white arrows) in the parenchyma cells, medium to thick-walled fibres and uniseriate, low rays; h: TLS, rays up to 20 cells high; i: RLS rays with procumbent body cells and 1–2 rows of marginal upright cells.

Text-fig. 8. Mhengere Hill fossiliferous localities (1–3). Silicified tree trunks and fragments of wood are abundant in the poorly indurated basal deposits (marly sand and conglomerate) as well as in the silicified lime-rich sandstones that form the hill, which is interpreted to be the remains of a palaeopan. Image modified from Google Earth.