The Middle Miocene Flora of the Chalk Mountain Formation, Warrumbungle Volcano Complex, NSW, Australia

1 2 HOLMES, W.B.K. AND ANDERSON, H.M.

1[[email protected]] 46 Kurrajong Street, Dorrigo, NSW 2453, Australia, University of New England, Armidale, NSW 2351 2[[email protected]], Evolutionary Studies Institute, University of the Witwatersrand, Johannesburg 20150, South Africa

Published on 8 August 2019 at https://openjournals.library.sydney.edu.au/index.php/LIN/index

Holmes, W.B.K. and Anderson, H.M. (2019). The Middle Miocene fl ora of the Chalk Mountain Formation, Warrumbungle Volcano Complex, NSW, Australia. Proceedings of the Linnean Society of 141, S19-S32.

A Miocene fl ora from the Chalk Mountain Formation occurring on a spur of the Warrumbungle Volcano Complex to the north-west of Coonabarabran, near Bugaldie is described. The fl ora consists of representatives in the families Equisetaceae (Equisetum sp. indet.), Isoetaceae and Araucariaceae (Agathis sp.). Among the angiosperm families are (Ceratopetalum priscum), Moraceae, Myrtaceae (Eucalyptus bugaldiensis), Urticaceae (Dendrocnide sp. A aff. D. excelsa). This paper describes the fi rst fossil record of Dendrocnide (Urticaceae) leaves from Australia and the second post-Cretaceous record of the genus Equisetum, the fi rst from the Miocene. The fl ora includes rainforest, swamp and sclerophyll forms and indicates a warming and drying climate as the Australian plate moved northwards during the Middle Miocene.

Manuscript received 18 February 2019, accepted for publication 22 July 2019.

Key Words: Chalk Mountain, Equisetum, Eucalyptus, fossil , Miocene, Warrumbungle volcano.

INTRODUCTION genera. This paper describes additional rainforest and sclerophyll macrofossil plant material and the second The Chalk Mountain Formation occurs on a post-Cretaceous record of the genus Equisetum, the spur of the Warrumbungle Volcano Complex to the fi rst record of Dendrocnide (Urticaceae) leaves from north-west of Coonabarabran, near Bugaldie. It is Australia. The diatomite and lignite beds of the Chalk a caldera deposit of diatomite, tuffs and a band of Mountain Formation are now weathered, overgrown lignite underlain by basalt dated at 17.2 million with weeds and natural regrowth. The location is years and overlain by basalt dated at 13.7 million closed to the public and further collecting is unlikely years, confi rming the Miocene age. The Formation to eventuate. was well-known for the numerous fossils of small Macquarie codfi sh (Hills 1946) and a fossil owlet- nightjar (Rich and McEvey 1977). The senior CHALK MOUNTAIN GEOLOGY author and his family visited Chalk Mountain in the 1970’s to collect plant fossils. Papers describing The Chalk Mountain Formation (Grid reference the eucalypt and Ceratopetalum collected material 199148 Gilgandra 1:250 000 Geological Series Sheet were published by Holmes et al. (1983), Holmes and SH 55–16) comprises 15–18 metres of lacustrine Holmes (1992). The eucalypt paper (Holmes et al. sediments of siltstone, mudstone, clay, tuff, lignite 1983) included a comprehensive palynological study and mostly of pure diatomite underlain and overlain by Dr Helene Martin of the spores and pollen from by volcanic fl ows (Griffi n 1961, Herbert 1968). the Chalk Mountain diatomite and lignite beds that The unit is exposed in the now abandoned revealed the presence of ferns, gymnosperms and quarry on Chalk Mountain (Fig. 1) situated on private angiosperms and evidence of still extant Australian property approximately 6 kilometres south of the MIDDLE MIOCENE FLORA OF THE CHALK MOUNTAIN FORMATION

Figure 1. Chalk Mountain Formation exposure in the abandoned quarry ca 1980. village of Bugaldie and at the northern margin of very friable and breaks into tiny, granular fragments. the Warrumbungle Volcano complex (White 1994, Kenny 1924). The Formation covers an area of approximately 38 hectares. The rich deposit of pure SYSTEMATIC PALAEOBOTANY diatomite was worked from 1919 to 1968 by the Davis Gelatine Co. and produced over 85,000 tonnes to be Order Equisetales transported by rail to for use as an abrasive, Family Equisetaceae fi lter, insulation material and many other purposes. Genus Equisetum The Formation is underlain by a thick bed of volcanic Equisetum sp. indet. basalt, andesite and trachyte and overlain by a basalt Figs. 2A–E fl ow. K/Ar dating was carried out by Dr A. Ewart of the University of (Holmes and Holmes, Material. 1992). The underlying basalt was dated at 17.2 mya AMF 145067. and the overlying basalt at 13.7 mya, both results at ± 2%, thus confi rming the Middle Miocene age. Description This taxon is based on an impression of an equisetalean stem fragment. Length preserved 120 MATERIAL mm, base and apex missing; margins almost parallel; average width 6 mm with ca 15 longitudinal striations; The fossil fl ora is based on collections of past impressions of four nodes located from the stem base published material housed in the Australian Museum at 25 mm, 55 mm, 85 mm and 104 mm (Fig. 2A). (AMF) and the Geological and Mining Museum Branch scars are not well preserved (Figs 2D, C). One (MMF) and from private collections now also node shows fi ve scars each ca 1mm roundish-square registered with the Australian Museum. The fossils are (Fig. 2E). No leaf whorls or nodal diaphragms are preserved as impressions and no cuticles are available evident. for study. If carbonaceous material is present then it is

S20 Proc. Linn. Soc. N.S.W., 141, 2019 W.B.K. HOLMES AND H.M. ANDERSON

Figure 2. [A–E] Equisetum sp. indet. AMF 145067, [F, G] Leaf whorl Isoetaceae, AMF 145068, (scale bar = 10 mm).

Proc. Linn. Soc. N.S.W., 141, 2019 S21 MIDDLE MIOCENE FLORA OF THE CHALK MOUNTAIN FORMATION

Discussion. by Rozefelds et al. (2019) who described the fi rst Based on the gross form of AMF 145067 (Fig. Equisetum from the late Eocene or early Oligocene, 2A) this stem with nodal scars (Figs 2B–E) closely Makowata, Queensland, Australia. The fossil here resembles the New Zealand Miocene Equisetum sp. described from the Chalk Mountain is signifi cant in described by Pole and McLoughlin (2017) but differs that it now extends the range for Australia into the by the generally narrower stem with less branch scars Miocene. The cause of extinction of Equisetum from at the node. The characters preserved are considered Australia and New Zealand remains obscure but Pole insuffi cient to warrant the erection of a new specifi c and McLoughlin (2017) suggest it may have been name. The only other Australian Cenozoic Equisetum related to substantial environmental changes. was described recently by Rozefelds et al. (2019) Given the age of the fl ora it could be argued that from Makowata, Queensland. This consists of a short this fossil may be more closely compared to some stem (ca 9 x 2.5 mm) with a slightly detached node, angiosperm genus. However, it is most unlikely that to which are attached, in a whorl, numerous leaves this fossil belongs to Casuarina or Allocasuarina (24–30), joined at the base into a sheath and distally even though such plants have branchlets with free. No nodes are evident on this stem but the large whorls of leaves (tiny teeth) with regular articles number of leaves clearly sets it apart from the low (internodes) and bear a superfi cial resemblance to number of about fi ve leaf or branch scars in the Equisetum. Their branchlets (stems) in all species are Chalk Mountain fossil. The Makowata fossil is rather about 1 mm in diameter or less, (this fossil stem is unique in showing a whorl of leaves conjoined in a 6 mm in diameter) the articles are very short about sheath with distal free leaves (not short teeth) similar 10 mm (this fossil internode is from 25 mm up to to some genera occurring in the Triassic of Gondwana 104 mm in length). Vegetative Casuarinaceae fossils such as Townroviamites (Holmes 2001, Anderson and are well known from the Paleocene of Australia Anderson 2018) which have more numerous and (Scriven & Hill 1995) and the Miocene of New much longer leaves. Zealand (Campbell & Holden 1984) and these show The sphenophyte family Equisetaceae (which the typical tiny stems occurring in branchlets. includes the genus Equisetum with about 15 extant species commonly known as horsetails) is an ancient group of plants fi rst appearing in the Devonian Order Lycopodiales Period ca 300 million years ago (Taylor et al. 2009). Family Isoetaceae By the Carboniferous Period they had evolved into Leaf whorl, genus and species uncertain many diverse forms including -sized plants. In Gondwana during the Permian Period, sphenophytes Fig. 2F, G formed an understory association with glossopterids that produced some of the World’s greatest coal beds Material. (Beeston 1991, McLoughlin 1993). Following the AMF. 145068. End-Permian extinction event many sphenophyte forms recovered and regained a cosmopolitan Description. distribution (Taylor et al. 2009) and a great diversity A diatomite block shows three whorls of linear in the Triassic of Gondwana (Anderson and Anderson leaves on one surface and on the reverse side a poorly 2018). They are well documented from the Australian preserved whorl surrounding a stem, possibly a and New Zealand Gondwana fossil plant collections continuation of the stem on the other surface bearing (Rigby 1966, Gould 1968, Retallack 1980, Holmes the large leaf whorl. The main leaf whorl shows 1982, 2000, 2001). However during Cretaceous time about 16 linear leaves with parallel margins and faint the sphenophytes declined in frequency and diversity parallel striations, to >40 mm in length and 4 mm in throughout the World. Equisetum, the only width surrounding a circular depression of a stem ca surviving sphenophyte genus has an almost world- 12 mm in circumference. Point of attachment of leaves wide, natural distribution except for Australia and to the stem is not clearly preserved. The second whorl New Zealand where it was previously considered (lower left of main whorl) is smaller with narrower extinct by the Cenomanian (Cretaceous) with the last leaves and the third whorl (close to lower right of records being from the Winton Flora as reported by main whorl) is partially obscured. McLoughlin et al. (2010). However this view has been changed by Pole and McLoughlin (2017) who Discussion. reported a Miocene (Cenozoic) Equisetum from The Chalk Mountain whorl of linear leaves two localities in central Otago, New Zealand and resembles that of Isoetes beestonii (Retallack 1997

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Fig. 6.3) a lycopod from the earliest Gondwana Material Triassic of Australia, previously known as Cylomeia Based on two specimens, a terminal undulata (White 1981c, 1986 fi gs 193, 201) branch fragment AMF145071 and a single leaf These differ from the Chalk Mountain whorls by AMF145070. the leaves emerging from a common area and the base of the leaves being fl ared to cordate (Retallack 1997, Description. p. 502, fi g. 7A). In the Chalk Mountain specimen the AMF145071 is a distal portion of a slender leaves appear to arise from different levels of the stem branch ca 25 mm in length as preserved, with four and in this aspect are more like the Triassic lycopod pairs of sub-opposite sessile elliptic leaves to 10 mm Pleuromeia or Cyclostrobus as described by Retallack wide and 25 mm long, apices acute. Veins numerous, (1997). Other records of Isoetes in Australia are from rising at base, fi ne, closely spaced and running ±ca the Tertiary of Tasmania based on megaspores and parallel to the margin. leaves described as I. reticulata (Hill 1988) and from The second specimen, AMF145070 is a portion the Cretaceous of I. bulbiformis (Drinnan of a larger single leaf, with base and apex missing, and Chambers 1986) is a corm with leaves. estimated original length ca 6.5 mm, width 15 mm The Chalk Mountain whorl of linear leaves also with fi ne closely spaced parallel venation. superfi cially resemble that of some equisetaleans from the Permian attributed by White (1986, fi g. 181) to Discussion. Phyllotheca australis. Similar whorls of linear leaves A number of extant conifers have leaves with (Zonulamites nymboidensis) were described from the parallel veins and in the absence of reproductive Australian Triassic by Holmes (2000). But the Chalk structures or cuticles it is diffi cult to make a fi rm Mountain whorls of leaves show no evidence of being identifi cation. In the Podocapaceae is Nageia with an attached to the stem in a clear whorl or of conjoining extant distribution beyond Australia. Araucariaceae at their base to form an encircling sheath around the is a family restricted to three genera – Araucaria, stem as occurs in Equisetum. Agathis and Wollemia which still grow in Eastern Given the age of the fl ora it could be argued that Australia. The fi rst records of this ancient conifer this fossil may be more closely compared to some family are from the Triassic Period (Taylor et al. 2009) angiosperm genus. However, it is most unlikely while their greatest diversity and widest distribution that this fossil belongs to a plant with a superfi cial was during the Jurassic Period (White 1981a, b, resemblance like Galium aparine (Rubiaceae). This Anderson et al. 2007 pp 56–59, 135). They are also has leaves in whorls that at fi rst glance look similar well known from Tertiary localities in south-eastern to this Chalk Mountain fossil or like a Permian Australia (Bigwood and Hill 1985, Hill and Bigwood Sphenophyllum (Equisetaceae) but a prominent 1987, Hill et al. 2008). midrib and reticulate venation clearly set it apart. Based on details of macro leaf form and venation, The identity of these whorls remains uncertain the Chalk Mountain fossils are placed in Agathis with but appear to be best placed in the Family Isoetaceae a close affi nity to A. robusta as illustrated in Harden et and possibly belong in a new genus. These leaf al. (2006). In the palynological study of diatomite and whorls are probably preserved in situ due to the lignite from Chalk Mountain undertaken by Helene stem continuing in 3D through the sediment and the Martin (in Holmes et al. 1983) Araucarites australis presence of further whorls on the same slab. The Cookson, attributed to Agathis and Araucaria extant genus of Isoetes (known as Quillworts) with comprised 18.1% of the pollen in the lignite and 10.7% some 192 species in the world (8 species in Australia) in the diatomite. Agathis robusta is today restricted grow in or close to water and the leaves arise closely to populations in rainforests of northern Queensland packed together from a central corm. and south-eastern Queensland. These leaves also show some similarity to the Tertiary fossils of early Oligocene to early Miocene age named Agathis Order Pinales tasmanica known from macro and cuticular remains Family Araucariaceae as described by Hill and Bigwood (1987) from Little Genus Agathis Rapid River locality in Tasmania. Agathis sp. aff. Agathis robusta (More ex Mueller) Bailey Genus ?Agathis, sp. indet. Figs 3C–E Figures 3A, B.

Proc. Linn. Soc. N.S.W., 141, 2019 S23 MIDDLE MIOCENE FLORA OF THE CHALK MOUNTAIN FORMATION

Figure 3. [A, B] ?Agathis species indet. AMF 145069; [C–E] Agathis sp. aff. A. robusta, [C] AMF 145070, [D,E] 145071 [F, G] Foliar conifer-like twig, AMF 145072, (scale bar = 10 mm).

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Material Description AMF145069. A terminal portion of a foliar twig, 22 mm long as preserved, with ca 24 linear-oblong sessile leaves Description 1 mm in width and 8 mm long, decreasing distally Leaf elongate elliptic, length 130 mm, central in length towards the apex. Each leaf with a distinct portion with parallel margins 13 mm wide, with central vein, secondary veins absent. ca 20 faint longitudinal ribs or striations; tapering proximally and distally; transverse scars across the Discussion stem at 25, 50 and 85 mm from the assumed base. This foliar twig and leaf form is found in many extant conifer families and we restrict our comparison Discussion to two Australian possibilities. It resembles that of Superfi cially this specimen resembles an Podocarpus lawrencei, an extant conifer growing as Equisetum stem but differs by the proximal and a tall or tree in Victorian Eminundra rainforest distal tapering and appears more leaf-like. Branch and in heathlands in northern Victoria and southern or leaf scars on these apparent nodal scars are not NSW (Harden et al. 2006). It is also comparable to a evident. These irregular transverse scars (Fig. 3B) larger fossil twig named P. cupressinoides from the may be insect tunnels or physical damage during Eocene of Penrose NSW (White 1986, fi g. 365). In preservation. In form and the fi ne parallel venation gross morphology the twig is also similar in form to this leaf falls within the extreme limits of Agathis some extant angiosperms in the family Epacridaceae. robusta (Harden et al. 2006) but differs in the greater length from the Chalk Mountain leaves referred to Angiosperm Families (listed alphabetically) that species above. It can also be compared to the much larger Tertiary leaf described by Bigwood Family Cunoniaceae and Hill (1985) as Araucarioides linearis which is Genus Ceratopetalum Sm. based on an incomplete leaf, base and tip unknown, Ceratopetalum priscum Holmes and Holmes, 1992 160 mm length (as preserved) and to 15 mm wide. Fig. 4A As cuticles are not preserved on the Chalk Mountain fossils no further comparisons can be made with the Material latter species or others based largely on cuticular Holotype MMF25501, paratypes AMF 3975, differences as described by Hill and Bigwood (1987) (illustrated in White 1990, p. 197), AMF78245 (c.p. and Hill et al. (2008). AMF78246), all from Chalk Mountain Formation. This leaf may also be compared with extant Cycadales leafl ets (Hill and Osborne 2002) as it has an Description elongated linear form with fi ne parallel venation. Most Flower-fruit with fi ve narrow-oblong sepals; Australian genera Cycas, Lepidozamia, Macrozamia apices obtuse, bases not contracted, petals, if present, have very long leafl ets with a length/width ratio far with a single vein trifurcating distally. greater than the Chalk Mountain leaf. However, the leafl ets of Bowenia come closer being 70–150 mm Discussion long and 15–40 mm broad with the margins smooth The three detached fl ower-fruits of Ceratopetalum and occasionally toothed. B. spectabilis is unusual priscum from the Chalk Mountain locality are for a cycad in bearing bipinnate leaves and its present preserved as limonite or colourless impressions distribution is restricted to the tropical coastal ranges (Holmes and Holmes 1992, White 1990, p. 197). of north-eastern Queensland. Macrozamia heteromera They are differentiated from other fossil and extant occurs in the Warrumbungle region growing in dry Ceratopetalum species by the sepal bases not being sclerophyll woodlands and the extremely long linear contracted and the petals with a single vein trifurcating leafl ets are usually forked one to three times. distally (Barnes and Hill 1999). In Ceratopetalum the sepals of the fl ower grow larger after fertilisation and Family and Genus uncertain remain attached as part of the dehisced fruit. Foliar conifer-like twig A more widespread distribution of this extant Figures 3F, G genus during the Cenozoic is indicated by Holmes and Holmes (1992) who also describe C. wilkinsonii from Material near Emmaville, New South Wales from Late Eocene AMF145069. to Early Oligocene and Barnes and Hill (1999) who listed occurrences placed in Ceratopetalum from the

Proc. Linn. Soc. N.S.W., 141, 2019 S25 MIDDLE MIOCENE FLORA OF THE CHALK MOUNTAIN FORMATION

Figure 4. [A] Ceratopetalum priscum from Holmes and Holmes (1992, Fig. 1) MMF25501. [B] ?Myrtaceae leaf form [C] AMF 145073. [C, D] ?Moraceae leaf form [D] AMF 145074. [E] from Holmes et al. (1983, Fig.1). [E](A) Eucalyptus bugaldiensis AMF61713. [E](B) Eucalyptus leaf form A, AMF61721, [E](C) Eucalyptus leaf form B, AMF61724, (scale bar = 10 mm).

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Middle Eocene Beds of Maslin Bay, South Australia. Eucalyptus bugaldiensis Holmes and Holmes, 1983 The oldest known radially symmetrical fi ve Fig. 4E(A) from Holmes et al.1983 winged fossil fruits with unique characters supporting their inclusion in Ceratopetalum are from the Early Material. Eocene of Patagonia, Argentina (Gandolfo and AMF61713–61720. Hermsen 2017). Because the affi nities, provenance and age of those fossils is so well established, their Description. new fossil species C. edgardoromeroi Gandolfo Based on three umbellasters attached at a common and Hermsen, is an excellent candidate for use as a point to a stem, each umbellaster is composed of seven calibration point in divergence dating studies of the or fewer fruit. Fruit hemispherical with the external family Cunoniaceae. It represents the only record surface ornamented by 7–10 longitudinal ribs. The of Ceratopetalum outside Australasia and further rim is fl at and exerted valves form a low triangular corroborates the biogeographic connection between projection 0.5 mm above the rim. the Argentina Laguna del Hunco fl ora and ancient and modern fl oras of the Australasian region. Jud and Discussion. Gondalfo (2018) suggest that although Australasia This material was described in detail by Holmes is currently the centre of diversity of the family, the et al. (1983) and illustrated in colour by White (1990 Argentinian fi ndings suggest that west Gondwana pp 58, 59). Due to lack of cuticle and attached or had an important role in their diversifi cation. closely associated foliage it is diffi cult to compare According to Barnes et al. (2001) a Cretaceous origin these fertile organs with extant Eucalyptus species. In of Cunoniaceae is possible, and may account for its gross morphology there is a similarity with the extant widespread distribution on Southern Hemisphere Coolabah tree, Eucalypus microtheca (subgenus landmasses. Symphyomyrtus section adnataris) a widespread species often growing on ground subject to fl ooding. Family ?Moraceae Christophel (1989) considered the Chalk Mountain Genus and Species uncertain. leaf and fruit impressions as defi nitely eucalyptoid as Leaf Form D was also noted by Hill et al. (2016). Figures 4C, D Eucalyptus sp. Leaf Form A. Material. Fig.4 E(B) from Holmes et al. 1983 AMF145074. Material. Description. AMF61721–3 Upper portion of a broad ovate leaf 40 mm wide and 85 mm long, as preserved. Apex bluntly Description. pointed. Distinct narrow midvein terminating at Leaf lamina lanceolate to narrow falcate, apex. Secondary lateral veins irregularly alternate, asymmetrical about lamina base; secondary veins ca departing from midrib at ca 60°, decurving across 1 mm apart, parallel and running at 50° to 60° to the lamina to reach margin at ca 30°, occasionally forking intramarginal vein which runs close and parallel to the at 2/3 distance to margin. leaf margin. Tertiary veins form an irregular network of about 4 rows between the secondary veins. Discussion As the leaf base and tertiary venation are Discussion. not preserved to allow certain identifi cation, this The venation pattern of Leaf Form A resembles specimen is listed as Leaf Form D. From the features that of various eucalypt species now placed that are present it appears to be of rainforest origin in Corymbia and Angophora and Eucalyptus and in particular details of the leaf it resembles some trachyphloia, a bloodwood growing in the sandy extant native Ficus species (Harden et al. 2006). Note soils of the nearby Pilliga region. See Holmes et al. that the Ficus rubiginosa, Rusty Fig, still grows in the (1983) for further discussion on the venation pattern Warrumbungle region (Mackay 2017). and classifi cation.

Family Myrtaceae Eucalyptus sp. Leaf Form B Genus Eucalyptus Fig. 4E(C) from Holmes et al. 1983

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Material. Discussion. AMF61724–5, MMF15284. This small leaf fragment is distinguished by its three veins and the pattern of the lateral veins at an Description. acute angle. The extant rainforest genus Rhodamnia Leaf lanceolate, slightly falcate, base has similar three veins from the base but the lateral asymmetrical, secondary veins sub-parallel, spaced veins are closely spaced and run at an obtuse angle irregularly and running a slightly undulate course to >45o towards the leaf margin (Floyd 1989, Harden et the intra-marginal vein. al. 2006). The three main veins are somewhat similar to those in the much smaller sepals of Ceratopetallum Discussion. (Figure 4A) but the lateral veins differ by being at an Eucalyptus Leaf Form B differs from Eucalyptus acute angle. Leaf Form A by the wider spacing and irregular course of the secondary veins. In form and venation Leaf Family Urticaceae Form B is similar to the leaves of extant Eucalyptus Genus Dendrocnide raveretiana, Black Ironbark, that grows along inland Dendrocnide sp. A aff. D. excelsa watercourses, river fl ats and open woodland (Halford Figs 5 A–D 1997). See Holmes et al. (1983) for further discussion on the venation pattern and for a colour illustration of Material. the attached leaves White (1990 p. 197). AMF145075, 145076 and counterpart 145077, Lange (1980) commented on the absence of 154078. eucalypt cuticles from mid-Tertiary fl oras around the margin of the Australian Plate that were dominated Description. by rainforest. The presence of eucalypt fruit and Based on the macro features of two closely leaves in the Chalk Mountain fl ora indicates that the similar ovate leaves, almost complete but with base warming and drying of the region was occurring in missing, to 80 mm wide. Margin slightly undulate, the Warrumbungle region by the mid Miocene and entire to slightly toothed. Midvein to 2 mm in width, resulted in the introduction of a sclerophyll fl ora into decreasing gradually to leaf apex. Secondary veins a previous rainforest dominated environment. prominent, leaving midrib as opposite pairs closer The earliest Eucalyptus fossils were described by to base, sub-opposite to alternate distally as angle of Gandolfo et al. (2011) from the Eocene Laguna del attachment decreases from ca 80° to ca 40° upwards; Hunco palaeofl ora of Patagonia, Argentina and from decurving slightly but close to margin curving New Zealand by Pole (1993) indicating the genus may upwards to run parallel to leaf margin; rarely forking. have occurred around the Southern Hemisphere at that Tertiary veins joining secondary veins at right angles time which suggests that the rich extant Australian 2–3 mm apart. Quaternary veins form an irregular population of eucalypts may be a relic from an Early network of very fi ne lines between the tertiary veins. Cenozoic time. The cause of extinction of Eucalyptus from South America (Hermsen et al. 2012) and New Discussion. Zealand remains obscure (Hill et al. 2016). The venation pattern of the fossil leaves is identical to that in the mature foliage of extant Family ?Myrtaceae Dendrocnide excelsa (Fig. 5E) and D. moroides Genus and Species uncertain (Floyd 1989, Harden et al. 2006). In Australia Leaf Form C these two species have very similar leaves with D. Figure 4B excelsa having a cordate base while D. moroides is a peltate leaf with the base truncate to cordate. None of Material. the fossil leaves have their base preserved and their AMF145073. identity is thus uncertain. D. excelsa is commonly known as the Giant Stinging Tree and has numerous Description silica spines on the leaf surface. When touched by A small ovate-elliptic leaf, apex rounded-acute: humans the spines enter the skin causing severe and base missing: length as preserved 25 mm, total length prolonged pain. The silica spines are not evident on the probably ca 35 mm, width 10 mm: tri-veined, outer fossils. The Giant Stinging Tree is a pioneer species veins running parallel 1mm in from leaf margin. in eastern Australian rainforests following openings Lateral veins widely spaced, leaving midvein at ca of the canopy as a result of severe storms. The young 20° and running almost straight to outer vein. trees show vigorous growth with very large juvenile

S28 Proc. Linn. Soc. N.S.W., 141, 2019 W.B.K. HOLMES AND H.M. ANDERSON

Figure 5. [A–D] Dendrocnide sp. A aff. D. excelsa. [A, B] AMF 145075. [C] AMF 145076. [D] AMF 145077 (counter part of 145076). [E] D. excelsa extant leaf from Dorrigo Rainforest, (scale bar = 10 mm).

Proc. Linn. Soc. N.S.W., 141, 2019 S29 MIDDLE MIOCENE FLORA OF THE CHALK MOUNTAIN FORMATION leaves that are frequently eaten by insects. On older leaves (Martin in Holmes et al. 1983) indicates that trees the leaves reduce in size identical to the fossils the Warrumbungle region vegetation was responding described above. Extant mature trees may reach 44 m to a warming and drying climate as the Australian in height and to 6.4 m in diameter at breast height (see plate moved northwards during the Middle Miocene www.nationalregisterofbigtrees). (Wilford and Brown 1994). This resulted in the Fossil pollen attributed to the Urticaceae family introduction of a sclerophyll fl ora possibly due to has been recorded from the Upper Oligocene and an increasing fi re frequency that altered the previous Miocene deposits in Australia (Martin 1994). There are rainforest dominated vegetation (Hill et al. 2016, no previous macrofossil records of Dendrocnide from Kershaw et al. 1994). Australia which makes these leaves from the Chalk Mountains very signifi cant. The world macrofossil record of Urticaceae is scattered and largely based on ACKNOWLEDGEMENTS fossil achenes from the Late Cretaceous of Central Europe (Friis et al. 2010). The authors wish to thank: the G. Hawker family, An additional fragmentary leaf (AMF154078 previous owners of the Chalk Mountain property for not illustrated) shows generally similar venation to information and allowing access to the diatomite workings the two illustrated specimens but with two unusual many years ago; Mr Neil Percival who donated additional secondary veins. material; Mr Wolfgang and Mrs Nola Bredereck of the Crystal Kingdom in Coonabarabran for early photos of the Chalk Mountain workings; Dr Maria Gandolfo at Dublin EPPC 2019 Conference in Dublin for discussion RECONSTRUCTING THE CHALK MOUNTAIN on her Patagonian fossil fl oras; the organisers of the 2018 FLORA Linnean Society of NSW Symposium on “The Volcanoes of Northwest New South Wales: Exploring Relationships In reconstructing a fl ora based on limited preserved among Geology, Flora, Fauna and Fires” that inspired our remains, one must accept that the fossil material further research on the Chalk Mountain fossil fl ora. may have been transported from varying distances and from diverse vegetation types. The macrofossil remains described above and the palynological REFERENCES records of Martin (in Holmes et al. 1983) of swamp, riverside, rainforest and sclerophyll type vegetation preserved in the Chalk Mountain diatomite indicates Anderson, H.M. and Anderson, J.M. (2018). Molteno sphenophytes: late Triassic biodiversity in southern a variety of sources. Greenwood (1994) noted that Africa. Palaeontologia africana 53 (Special Volume), fossil leaf accumulations constitute a biased but 1–391, http://wiredspace.wits.ac.za/10539/24672 often detailed record of the parent vegetation. In the Anderson, J.M., Anderson, H.M. and Cleal, C.J. (2007). Chalk Mountain Formation, except for a thin basal Brief history of the gymnosperms: classifi cation, lignite horizon (Fig. 1) the pure diatomite of the biodiversity, phytogeography and ecology. Strelitzia lake deposit clearly demonstrates that there were no 20, 1–280. incoming streams depositing sediments in the caldera Barnes R.W. and Hill R.S. (1999). Ceratopetalum (White 1994). The fossil plant material was therefore fruits from Australian Cainozoic sediments and deposited mainly by gravity or carried from a distance their signifi cance for petal evolution in the genus. Australian Systematic Botany 12, 635–645. by wind storms. There is some evidence of in situ Barnes, R.W., Hill, R.S. and Bradford, S.C. (2001). The preservation based on the whorls of leaves assigned to History of Cunoniaceae in Australia from macrofossil the ?Isoetaceae which possibly grew around the lake evidence. Australian Journal of Botany 49, 301– margin. The occurrence of Equisetum also indicates 320. a moist possible swamp environment. The presence Beeston, J.W. (1991). Coal facies depositional models. of eucalypt material with rainforest remains does not Denison Trough area, Bowen Basin. Queensland necessarily refl ect a common rainforest origin. The Geology 2, 1–34. eucalypts were probably from a sclerophyll forest Bigwood, A. J. and Hill, R. S. (1985). Tertiary araucarian adapted for growth on the sandy soils derived from macrofossils from Tasmania. Australian Journal of Botany 33, 645–656. the adjacent and underlying Jurassic Pilliga Sandstone Campbell, J.D. and Holden, A.M. (1984). Miocene beds and the rainforest species from sheltered and casuarinacean fossils from Southland and Central moist gully situations. Otago, New Zealand. New Zealand Journal of Botany The low Nothofagus pollen content and the high 22, 159–167. myrtaceous content including Eucalyptus fruit and Christophel, D.C. (1989). Evolution of the Australian fl ora

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