Palaeontologia Electronica http://palaeo-electronica.org MONOCOT MACROFOSSILS FROM THE MIOCENE OF SOUTHERN NEW ZEALAND Mike Pole Mike Pole. Queensland Herbarium, Toowong, Qld 4066, Australia [email protected] ABSTRACT Monocot cuticle is an uncommon component of dispersed cuticle samples in the New Zealand Miocene, a fact most likely due to its generally fragile nature. Neverthe- less, 120 fossiliferous samples from two regions, the interior Manuherikia Basin in Cen- tral Otago, and the paleo-coastal delta of the Southland Coalfield, have produced 17 morphological types of cuticle, 15 of which are clearly monocot. These are described as parataxa and are regarded as including Astelia, Arecaceae, Rhipogonum, Pandan- aceae, and Typhaceae. Most of the fossils remain unidentified, but are probably semi- aquatic swamp plants. Six forms of fossil Typha seeds are also illustrated. KEY WORDS: Early Miocene, cuticle, biodiversity, stomata, monocot INTRODUCTION differences from New Zealand’s single extant spe- cies of palm, Rhopalostylis sapida, which is the New Zealand’s Miocene sediments have pro- most southerly palm in the world (Wardle 1991). vided a small number of monocot macrofossils. Impressions of the distinctive net-veined monocot, One of the earliest to be described was a palm Rhipogonum, were also described from the same frond, Seaforthia zeelandica (von Ettingshausen region (Pole 1993b), and Rhipogonum leaves with 1887, 1891). This probably came from the same cuticle were later documented from the Miocene of locality (near Cromwell) from which Pole (1993a) the Foulden Hills Diatomite near Middlemarch described palm fronds, fruits, and flowers and (Pole 1996). Holden’s (1982) Cinnamomum mioce- redescribed S. zealandica as Phoenicites zeeland- nicum from Murchison, and Oliver’s (1936) Coriaria ica. Phoenicites is a morphogenus, the usage of latepetiolata from Dunedin are likely to also be which was clarified by Read and Hickey (1972) to Rhipogonum. Fossil “coconuts” from the far north apply to one of the limited range of palm frond of the North Island were identified as Cocos by shapes. As such, it is not a genus in any compara- Berry (1926), but have since been suggested to ble way to extant genera, and I would no longer have a closer relationship with Parajubaea (Endt use the concept. Phoenicites zeelandica has small and Hayward 1997). PE Article Number: 10.3.15A Copyright: Society of Vertebrate Paleontology December 2007 Submission: 30 January 2007. Acceptance: 8 November 2007 Pole, Mike, 2007. Monocot Macrofossils from the Miocene of Southern New Zealand. Palaeontologia Electronica Vol. 10, Issue 3; 15A:21p. http://palaeo-electronica.org/2007_3/125/index.html POLE: MIOCENE MONOCOTS OF NEW ZEALAND These fossils are ‘macrofossils’-in the classic been found, as well as some seeds. The purpose sense that they are apparent to the naked eye on of this paper is to describe the cuticle and seed the bedding surfaces of splitting sediment, or in the types as a basis for further studies of past biodiver- case of the ‘coconuts’, can be picked from the sed- sity, ecology, and biogeography. iment or even, in the case of the fossil “coconuts” can be picked up from strand lines on the present MATERIALS AND METHODS beach. But another collecting rationale, in the Fossils were collected from two geological appropriate sediments, involves searching for leaf basins of which the sedimentary fill is now repre- cuticle, the resistant material which covers the leaf sented by two stratigraphic groups (Figure 1). The epidermis and which preserves an impression of Manuherikia Group (MG) is an extensive (>5600 the epidermal cell morphology. Although fragments 2 of cuticle can be large (as large as the original km ) deposit of Miocene fluvial (Dunstan Forma- leaf), the essential features can only be observed tion) to lacustrine (Bannockburn Formation) basin with a microscope. fill in Central Otago, southern N.Z. The stratigraphy Stebbins and Khush (1961) were probably the and sedimentology has been detailed by Douglas first to present a broad review of extant monocot (1986), the palynology by Mildenhall (1989) and cuticle but by far the greatest contribution has been Mildenhall and Pocknall (1989), who dated the that of Tomlinson (1960, 1961, 1965, 1969, 1971, Group as Early-Late Miocene, and the macropale- 1974, 1982), who included descriptions of epider- obotany by Pole (1993c and references therein). mal features as part of his broader treatment of the The sediments which yield dispersed cuticle come monocots. Dahlgren and Clifford (1982) included a from outcrops in the oldest unit, the incised valley useful comparative treatment of monocot stomatal fill of the St Bathans Member (sample numbers construction. Typical monocot epidermis can be prefixed with “BL” and “GL”). recognised primarily by having rows of longitudi- The second geological unit is the Gore Lignite nally oriented stomatal complexes (although But- Measures, of the East Southland Group, which terfass 1987, included some monocots in his list of accumulated on a coastal delta (Isaac and plants with transversely oriented stomata) and epi- Lindqvist 1990). Palynology of this unit has been dermal cells, a result of the typically parallel-veined detailed by Pocknall (1982) and Pocknall and leaves. The stomatal complex morphology, in the Mildenhall (1984). Samples were taken from drill sense that they typically have a pair of distinct core housed in the Crown Minerals Dunedin core polar and lateral subsidiary cells, overlaps that of library (sample number prefixed with “Sthd”). Full many conifers, although the topography and other sample details for both basins are provided in Pole details are quite different. For instance, in conifers (2007) including precise grid references for the MG the guard cells are typically embedded below over- samples and drill core depths for the East South- arching subsidiary cells, and the ends of the guard land Group. Detailed stratigraphic sections of the cells are often partially surrounded by distinct ‘polar East Southland Group are present in Isaac and extensions’. Like other angiosperms, monocots Lindqvist (1990). Precise stratigraphic relationships have outer stomatal ledges, projecting from the within the St Bathans Member, where there is com- guard cells, which are absent in conifers. Conifer plex fluvial channel cross-cutting, are still being cuticle is mostly much more robust, and tends to resolved and cannot be shown on a simple section. be preserved as recognizable leaves (often small Stratigraphic details at that resolution are not rele- and single-veined). Dunn et al. (1965) also pointed vant at this stage. The only additional sample here out that monocot stomatal complexes within a leaf is Bannockburn-1, which is the only sample found are of equal size, or at least do not fall into distinct in the Bannockburn region, which has good cuticu- size classes, which they often do in non-monocot lar preservation. It was collected at F41 087626 angiosperms. The epidermis of the reticulate- (grid reference based on the New Zealand 1:50 veined monocots is distinct from typical monocots, 000 Topographic Map 260 series). The outcrop has because the stomata and epidermal cells are not since been covered over by lake-shore develop- arranged in rows. Identification of taxa in this group ment after the completion of the Clyde Hydroelec- relies on direct comparison of the fossils with an tric scheme. extant species. Cuticle preparation followed a standard Over some 15 years of research on Miocene method whereby sediment was disaggregated by cuticle in southern New Zealand, some small and covering with hot water and adding some 40% typically rare fragments of monocot cuticle have hydrogen peroxide. The organic fraction was removed by sieving and cuticle further cleaned by 2 PALAEO-ELECTRONICA.ORG NEW ZEALAND Grey Lake St Bathans + Blue Lake 45S˚ Mata Ck 45S Bannockburn-1 170E 50 km 46S˚ 170E˚ DUNEDIN Chatton d1324 46S˚ d1027 d1115 d1051 d1026 d1057 GORE d1108 d1024 Waimumu d1052 d1109 d1110 Hedgehope d1243 d1121 d1124 MATAURA d1077 d1053 d1246 d1078 d1049 Makarewa d1107 Morton d1106 Mains INVERCARGILL d1105 d1297 Kapuka d1104 d1298 Waimatua d1102 d1299 d1141 d1101 d1142 d1143 d1144 d1296 d1294 10 km d1295 169E˚ Figure 1. Locality maps. The upper map shows the position of Blue Lake (the location of sample numbers prefixed with “BL-“, Grey Lake (the location of sample numbers prefixed with “GL-“), and Bannockburn-1. The grey circle is a schematic indication of the extent of the Manuherikia Group. The lower map shows the position of all drill-cores in Southland (the location of sample numbers prefixed with “Sthd-“) from which fossils were obtained. For precise loca- tions of all samples, see Pole (2007).. immersion for several hours in warm aqueous Material is lodged in the State Herbarium of chromium trioxide. After washing a staining in Queensland. Crystal Violet or Safranin, cuticle fragments were Cuticle morphologies are described as mounted on microscope slides (specimen numbers parataxa. They are given a non-hierarchical prefixed with “SB” or “SL”) in Thymol Glycerine parataxon code. For pragmatism this consists of Jelly for Transmitted Light Microscopy (TLM), or on the prefix ‘CUT-Mo-’ (for “cuticle-monocot”) fol- aluminium stubs (specimen numbers prefixed with lowed by a string of three letters. These letters “S-“) with double-sided tape and coated with plati- have no meaning, but together with the prefix, form num for Scanning Electron Microscopy (SEM).