Wood of Oleaceae from the Latest Cretaceous of India – the Earliest Olive Branch?

Home , Chionanthus, Mohgaon, Nestegis, Noronhia, Schrebera

SrivastavaIAWA Journal et al. 36 – Oleoxylon(4), 2015: from443–451 India 443

Wood of Oleaceae from the latest Cretaceous of India – the earliest olive branch?

Rashmi Srivastava1,*, Elisabeth A. Wheeler2, Steven R. Manchester3, and Pieter Baas4 1Birbal Sahni Institute of Palaeobotany, 53 University Road, Lucknow 226 007, India 2Department of Forest Biomaterials, N.C. State University, Raleigh, NC 27695-8005, U.S.A. 3Florida Museum of Natural History, Gainesville, FL 32611-7800, U.S.A. 4Naturalis Biodioversity Center, PO Box 9517, 2300 RA Leiden, The Netherlands *Corresponding author; e-mail: [email protected]

Abstract The wood of Oleoxylon deccanense, reported informally in 1981 from the Dec- can Intertrappean Beds of central India, is re-examined. We provide a formal diagnosis for the species and a more detailed description. The similarity to wood from species groups of the modern genera Chionanthus and Olea leads us to infer that this fossil taxon probably belongs to the monophyletic drupaceous subtribe Oleinae of the olive family, Oleaceae (Lamiales), although affinities with Rhamnaceae and Rutaceae cannot be wholly excluded. Since the fossil is from a late Maastrichtian-Danian horizon (65–67 MY BP) this would imply that a member of the Oleaceae was part of the flora that inhabited India several million years prior to the tectonic impact of India with Asia. The seemingly modern appearance of this and other Deccan fossil woods is briefly discussed. Keywords: Deccan Intertrappean Beds, Maastrichtian, Paleocene, India, wood anatomy, Oleaceae, Rhamnaceae, Rutaceae.

Introduction In 1981, Trivedi and Srivastava reported a fossil wood Oleoxylon deccanensis (erron. for deccanense), showing resemblance with the genus Olea from the Deccan Intertrap- pean Beds of Jheria village about 3 km south-west of Mohgaon Kalan, Chhindwara District, Madhya Pradesh, India. However, they did not provide a diagnosis and holotype number for the fossil and thus, according to the rules of nomenclature, this name is not valid (McNeill et al. 2012). We recently had the opportunity to re-examine this fossil wood, and herein describe it in more detail and compare it with more recent comprehensive information on modern and fossil woods in general (InsideWood 2004-onwards; Wheeler 2011) and the Oleaceae family in particular (Baas & Zhang Xinying 1986; Baas et al. 1988). The original specific name assigned to this fossil is retained and validated in the present communication by providing a diagnosis and holotype number for the specimen. The collecting locality is close to the town of Keria, adjacent to which several petrified woods have been collected and described previously (reviewed in Kapgate

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2005). These sites are apparently continuous with the classic Mohgaon Kalan fossil forest horizon, which is treated as Late Maastrichtian based on stratigraphic correla- tion and palynology (Samant & Mohabey 2013). These are interbeds of the great sequence of basalt flows known as the Deccan Traps. The area occupied by the Dec- can Traps today is about 500,000 km2 in peninsular India while the original stretch may have been three times greater, including sediments found in the Arabian Sea to the west of Mumbai (Jay & Widdowson 2008). The outpourings of lava were as- sociated with the northward drifting of the Indian Plate after it was separated from Gondwana during the Early Cretaceous and moved over the volcanic hot spot over which Reunion island is now positioned in the Indian Ocean (Chatterjee et al. 2013). Recent studies based on radiometric dating and planktonic foraminifera, indicate that the age of the intertrappean sediments ranges from upper Maastrichtian to Danian (Keller et al. 2009). The precision of whole-rock basalt radiometric dating is insuf- ficient to resolve whether many of the sites are latest Maastrichtian or earliest Paleo- cene. However, palynological and faunal assemblages suggest a Maastrichtian age for most of the intertrappean exposures with few Paleocene indicators (Kar & Srinivasan 1998; Samant & Mohabey 2009, 2013). Smith et al. (2015) give an integrated review of the geology and paleobotany of the Late Cretaceous-Paleocene transitions of India that also highlights the remaining uncertainties of the precise dating of the macrofossils. Paleobotanical and biogeographical studies suggest that some angiosperm taxa might have an Indian origin because their earliest records are known from these Maastrichtian- Danian sediments. Numerous petrified woods have been reported from the Deccan intertrappean sediments since the 1920s (compiled in Lakhanpal et al. 1976; Srivastava 1991; Kapgate 2005; Srivastava & Guleria 2006; Srivastava 2011). We have recently re-examined many of the original prepared slides of silicified wood specimens stored at the Birbal Sahni Institute of Paleobotany as part of a collaborative project to facilitate access to data and images on the internet (via InsideWood). In this article we elaborate on the fossil record of Oleoxylon, analyze its anatomical character combination in comparison with a global dataset of modern and fossil woods, and discuss its signifi- cance in the context of the fossil record of Oleaceae and the floristic composition and biogeographic importance of the Deccan flora.

Systematic description Core – Eudicots Order – Lamiales Family – Oleaceae Subfamily – Oleoideae Genus – Oleoxylon Dupéron 1973 emend. Heteroxylous wood with characters of the family Oleaceae. Diffuse porous wood. Vessels with tangential diameters < 200 µm, solitary and in radial multiples. Perfora- tions simple. Intervessel pits alternate, minute to medium-sized. Axial parenchyma not abundant (scanty paratracheal-vasicentric). Rays narrow and low, usually 2–3 cells wide, heterocellular. Fibers with simple pits, non-septate. Longitudinal canals, radial canals, storied structure, oil/mucilage cells, and cambial variants absent.

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The diagnosis is emended, broadening the size range of intervessel pitting so as to be similar to that of present-day Oleoideae, and specifying diffuse porous wood, scanty paratracheal to vasicentric axial parenchyma, nonseptate fibers, and heterocellular rays (features included in the original description of Oleoxylon), and adding vessel- parenchyma pits similar to intervessel pits, which is consistent with Dupéron’s “Bois hétéroxylé possédant les caractères de la famille de Oleaceae” and necessary for this generic diagnosis to be unique. Species – Oleoxylon deccanense Srivastava, Wheeler, Manchester & Baas ex Trivedi & Srivastava. Holotype – BSIP Museum No. 40570. Stratigraphic horizon – Deccan Intertrappean Beds, Dhuma Formation of Amarkan- tak Group. Locality – Jheria, about 3 km southwest of Mohgaon Kalan, Chhindwara District, Madhya Pradesh, India. Age – Maastrichtian-Danian. Material – The description is based on a well-preserved piece of petrified wood meas- uring about 4.9 cm in width and 15 cm long. Diagnosis – Diffuse porous. Vessels often in long radial multiples of >4. Perforation plates simple. Intervessel pits alternate, 8–10 µm; vessel-ray pits similar to intervessel pits. Fibers with inconspicuous pits, nonseptate. Parenchyma scanty paratracheal to vasicentric and marginal. Rays 1–3-seriate, heterocellular. Storied structure absent. Description (Fig. 1–6): Wood diffuse porous. Growth rings indistinct, but one (possibly traumatic?) ring boundary present and demarcated by marginal parenchyma preceded by weakly flattened latewood fibers and differential distribution of smaller vessels. Vessels diffuse, 25–55 (average 32)/mm2, 14–20% solitary, remainder in radial multiples of 2–8 (rarely up to 17), round to oval in cross section, those in multiples slightly angular and flattened at the place of contact, tangential diameter 20–118 (average 59, SD 21) µm, radial diameter 30–150 (average 76, SD 30) µm. Vessel member length 225–530 (mostly 350–450) µm; perforations simple and oblique, often tailed end walls; intervessel pits alternate, medium-sized, 8–10 µm in diameter. Vessel-ray pits poorly preserved, at places seemingly similar to intervessel pits in shape and size. Vascular tracheids intergrading with narrow vessel elements in radial multiples very infrequent- ly present. Fibers angular in cross section, thin-walled to medium thick-walled, walls 3–4 µm thick, pits not conspicuous, nonseptate, 12–18 µm in diameter. Axial parenchyma scanty paratracheal to vasicentric (only one, probably traumatic, seemingly marginal band of 2–4 or more cells wide present in the cross section examined), cells 20–32 µm in diameter, 3–4 cells per parenchyma strand. Rays heterocellular, 8–12 rays per mm, 1–3- (mostly 1–2-)seriate; 5–32 cells or 234–814 (mostly up to 580) µm high, made up of procumbent cells in the central portion with 1–4 marginal rows of upright or square cells at one or both ends; uniseriate rays made up of either upright or both procumbent and upright cells, about 3–10 cells or 134–580 µm tall. Codified description according to the IAWA Hardwood List (IAWA Committee 1989): 2 5 10 13 22 23v 26 30 41 42 48 49 60v 61 66 69 78 79 89? 92 97 106 107 115.

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1 2 3

4 5 6

Figure 1–6. Oleoxylon deccanense. – 1–3: Diffuse porous wood, TS. – 1 & 2: Radial multiples of 4 or more common, axial parenchyma scanty paratracheal. – 3: Region where vessel multiples of 4 or more are not common (post-injury?). – 4: Rays 1–3-seriate, mostly 2-seriate, TLS. – 5: Simple perforation plate and ray composition, RLS. – 6: Crowded alternate intervessel pits, TLS. — Scale bars: 200 µm in 1 & 3; 100 µm in 2, 4 & 5; 20 µm in 6.

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Discussion Affinities of the fossil We used the InsideWood database, the literature, and the Leiden slide collection (Lw) for searching the best matches of the fossil. We searched InsideWood for the follow- ing combination of features: Presence of diffuse porous wood (5p) with commonly occurring radial multiples of >4 vessels (10 p), exclusively simple perforation plates (13 p 14 a), medium-sized alternate pits (22 p 26 p), vessel-ray pitting similar to intervessel pits (30 p), non-septate fibers with inconspicuous pits (61p 66 p), presence of scanty paratracheal parenchyma present (78 p), rays 1–3-seriate (97p). Absence of aliform, confluent and banded parenchyma (80a 83a 84a 85a 86a), rays >1 mm high and of two size classes (102a 103a), rays not homocellular and not with many marginal rows (104a 105a 108a 109a), storied structure (118a 119a 120a), oil cells (124a 125a 126a), canals (127a 128a 129a 130a), and cambial variant structure (133a 134a). This search yielded Nestegis and Olea (Oleaceae) as direct matches. Alternative searches also indicated strong similarities with some Rhamnaceae and Rutaceae, but differing by one or more characters hence matching less perfectly than these Oleaceae genera (cf. Schirarend 1991; Appelhans et al. 2012; InsideWood 2004-onwards). Table 1 compares some salient features of these genera (Baas & Zhang Xinying 1986; Baas et al. 1988), this Deccan wood, and Oleoxylon aginnense Dupéron (1973) from the Tertiary of France. Chionanthus is included because it overlaps in wood anatomy with Olea (Baas et al. 1988). Nestegis has a pronounced dendritic vessel pattern, a feature not present in the Deccan wood. Olea types B & C show the greatest similarities with Oleoxylon deccanense.

Table 1. Comparison of Oleoxylon with Chionanthus, Olea and Nestegis. RM > 4 = radial multiples of over 4 vessels common. RM > 4 Dendritic Intervessel pit size vessel pattern (µm) Oleoxylon deccanense + – 8–10 Oleoxylon aginnense + – 3–4 Olea A +/– – 3–5 (2–7) Olea B +/– – 6–8 (4–11) Olea C + +/– 7–8 (5–10) Chionanthus A +/– – 3–5 (2–6) Chionanthus B – + 6–10 Nestegis +/– + 6–7 (5–8)

The closest match to Oleoxylon deccanense seems to be with Olea B, a wood- anatomically uniform group of three Olea species living today in India, China and Indo-China (Baas & Zhang Xinying 1986; Baas et al. 1988). The only differences are gradational: O. deccanense has more frequent long vessel multiples of > 4 and has slightly larger intervessel pits than the recent species. With its small intervessel pits,

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Dupéron’s European fossil, O. aginnense, is closer to the Olea A. group, a widely dis- tributed group with species living today in Europe, Africa, Australia and the Hima- layas. Since Olea is probably polyphyletic, and very closely related to other genera, especially Chionanthus, of the Oleinae – the drupaceous clade of the subfamily Oleoi- deae – it is in need of revision (Wallander & Albert 2000; Besnard et al. 2009; Yuan et al. 2010; Hong-Wa & Besnard 2013). Meanwhile it seems prudent and reasonable to attribute Oleoxylon to this subtribe with close phylogenetic affinities to the modern genus Olea. The subtribe as a whole is heterogeneous for the presence or absence of oblique to dendritic vessel patterns and this character should be viewed in the light of frequent parallel origins of this feature in a number of families in response to strong climate seasonality (Appelhans et al. 2012). The absence of oblique to dendritic vessel patterns in Oleoxylon fits with the lack of seasonality expected for the more or less equatorial position of Late Cretaceous India (Smith et al. 2015). The fact that only one irregular and possibly traumatic marginal parenchyma band was found over a large transverse sectional area of O. deccanense, also suggests that climatic seasonality was weak or absent.

Age of the Oleaceae Oleinae constitute the most derived clade of the Oleaceae (Wallander & Albert 2000), a position strongly supported by wood anatomy (Baas et al. 1988). Extant genera included within this clade include Olea itself, well known as the source of olives (O. europaea), and several other genera with drupaceous fruits: Chionanthus, Osman- thus, Nestegis, Noronhia, and Phillyrea. On the basis of molecular clock analysis, Besnard et al. (2009) hypothesized that the Oleinae diverged about 36 million years ago (late Eocene /early Oligocene). The attribution of Oleoxylon to this subtribe would date it much earlier, i.e., to the Maastrichtian-Danian, c. 66 million years ago. Fossil pollen attributable to Oleaceae has been recorded from the early Campanian (late Cretaceous) of the Elk Basin, Wyoming (USA), about 14 million years older than the Deccan fossil wood (Manchester et al. 2015). Otherwise, the fossil record of Oleaceae is best known from the Cenozoic of the Northern Hemisphere, including records of Fraxinus confirmed by distinctive winged fruits as early as middle Eocene in North America (Call & Dilcher 1992), and entire-margined leaves of “laurophyllous” Oleaceae confirmed by epidermal anatomical characters, together with dispers- ed pollen corresponding to the family from the Oligocene and Miocene of Europe (Sachse 2001). If the attribution of Schreberoxylon, another fossil from the Deccan Intertrappean Beds, to Oleaceae by Trivedi and Srivastava (1982) is correct, the presumably older Schreberinae (Schrebera and Comoranthus), and sister to [Fraxinus plus Oleinae], would have been sympatric with an early representative of the Oleinae, suggesting an important role of the Indian tectonic plate in the evolution of the olive family. Oleoxylon is one of the Deccan fossil woods that can be fairly convincingly attrib- uted to a modern plant family (Srivastava 2011; Wheeler et al. in preparation). This is unusual compared to other late Cretaceous wood assemblages where primitive woods (in the Baileyan sense, e.g. with high frequencies of scalariform perforation plates)

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Acknowledgements

PB, SM and EAW wish to thank Prof. Sunil Bajpai, director of the Birbal Sahni Institute of Palaeo- botany, Lucknow, India, for granting permission for collaborative work on the institute’s collections, and for hospitality during the Christmas season of 2014. RS is thankful to the director for providing infrastructural facilities and permission to publish the paper (Ref. BSIP/RDCC/Publication no 98/2014-2015), and also to Zlatko Kvaček for advice on nomenclature. This project was supported in part by the US National Science Foundation, grant EAR 1338285.

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Accepted: 9 July 2015 Associate Editor: Imogen Poole

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