NEW MICROPETASOS, A GENUS OF ANGIOSPERMS FROM MID-CRETACEOUS BURMESE AMBER George Kenton Chambers 0. Poinar, Joerg Wunderlich Jr. L. Department ofZoology Department ofBotany and Plant Pathology Oberer Hauselbergweg 24 Oregon State University Oregon State University Hirschberg 69493 Oregon 9733 Oregon 9733 GERMANY Corvallis, U.S.A. Corvallis, U.S.A. 1, 1, ABSTRACT RESUMEN INTRODUCTION Burmese amber has been mined since AD 100, when an amber trade route was established with China. Around 1896, it was noted that the amber contained insect remains. In 2001, a new amber mine was opened in the Hukawng Valley, southwest of Maingkhwan in the state of Kachin (Poinar et al. 2005). Amber-bearing strata in this mine, known Bum as the Noije 2001 Summit were initially assigned to the Upper Albian (97-110 Ma) Site, of the Early Cretaceous on (ammonite) and palynological evidence (Cruickshank the basis of paleontological & Ko 2003). More an Ma, based on U-Pb recently, Shi et (2012) give age of 98.79+/-0.62 analysis of zircons al. from Ma the volcanoclastic matrix of the amber. This slightly younger than the date of 100.5 assigned to the is end of the Albian by the International Commission on Stratigraphy (2013, http://www.stratigraphy.org). How- ever, Shi et al. (op. cit.) contradict themselves in claiming that the amber has not been re-deposited, yet stating been re-deposited, because amber is not formed in such an environment. Just when it was first formed in a ter- restrial forest is not known, leaving the true age of amber from Myanmar in question. With re-deposition, the amber must be by older than the zircon-based dates determined Shi et al. (op. cit.). The ancient age of amber from supported by the presence of primitive insects in the deposit. For this site is example, a bee was discovered possessed some characters of sphecid wasps, the taxon which, in tradi- that & tional An systematics, is considered to be ancestral to bees (Poinar Danforth 2006). elcanid grasshopper was also found, representing a group (Elcanoidea) that appeared in the Early Permian and continued only to first m e id-Cretaceous atomic and (Poinar Thus, paleontological evidence, dating, the insect inclu- 2005). et al. Bum in the amber favor an early mid-Cretaceous age for mines at the Noije 2001 Summit Site. In their °°k on Myanmar early flowers of the Cretaceous, Friis et al. (2011, p. 34) propose that amber is Late Creta- Ceous or Early Cenozoic; however, they provide no new evidence in support of this revised date. 746 Nuclear magnetic resonance (NMR) spectra of samples taken from this locality indicate an araucarian amber While dominate (possibly Agathis) source of the (Poinar et al. 2007b). insect fossils (Grimaldi et al. 2002), the deposits have revealed some interesting plants, including 2 early bambusoid grasses (Poinar 2004), & a staminate flower with affinities to the Monimiaceae (Poinar Chambers 2005), an epigynous flower similar Comaceae to (Poinar et al. 2007a), a pistillate, apetalous flower with possible connections to the rosid clade of modem eudicots (Poinar et 2008b), and an epigynous flower with characters paralleling some Cunoniaceae al. (Chambers Grimaldi et al. 2010, et al. 2002, fig. 13). The mixed present fossil consists of a basally bracteate fragment of a cymose-paniculate inflorescence, 9 mm long (Fig. 1), whose branches bear 3-7 flowers on glabrous, relatively stout pedicels (Fig. 3). Eighteen flow- ers are present, but only 10 are positioned well enough for study. The perianth lacks petals, consisting of a single whorl of five basally connate sepals spreading laterally at anthesis (Fig. The calyx lobes may be equal 2). or unequal in size. The numerous stamens are tightly clumped around the perhaps becoming aggregated pistil, On during preservation in the resin. four flowers, 1 or 2 unusually long stamens are separate from and visible, external to the others (Figs. 2, 3), and some of these appear to have a broadened, ribbon-like filament (Fig. 2). The gynoecium consists of a single carpel bearing a short, curved, attenuate style, the ovary being mostly hid- den by the surrounding mass of stamens (Fig. 3). Among eudicot flowers thus far described from this period (Friis et al. 2006, 2011), Micropetasos is distinctive in its combination of five connate, spreading sepals, no pet- numerous als, stamens with bisporangiate anthers, and a gynoecium comprising a single, superior carpel with MATERIALS AND METHODS The fossil inflorescence is preserved in a quadrilateral piece of amber with sides of 20, 15, 11, and 10 mm, which was initially part of a larger piece containing a fossil scorpion. It is in the amber collection of Wun- J. derlich, Oberer Hauselbergweg Germany Hirschberg, and 24, 69493, will eventually be deposited in the Museum Senckenberg and Research Institute, Frankfurt-am-Main. The amber was obtained from the Noije Bum 2001 Summit Hukawng Site in the Burma, Valley, as described above. Examination and photography made were with Nikon a stereoscopic microscope SMZ-10R 80X and Nikon at a Optiphot microscope 800X. at Flowers small, in groups of 3-7 on branches of a basally bracteate, glabrous, mixed cymose-paniculate inflo- rescence (Fig. pedicels 1), relatively stout, glabrous, ebracteate (Fig. flowers bisexual, hypogynous, calyx 3), 5-merous, regularly or irregularly actinomorphic, sepals glabrous, basally connate, lobes triangular, obtuse or acute, equal or unequal (Fig. petals none, stamens numerous, bunched 2), around the filaments pistil (Fig. 3), on linear, short outer stamens, on longer those near the pistil, sometimes 1-2 outer filaments elongated (Fig?. anthers 2, small, oblong-ovoid, 3), bisporangiate (Figs. 2, 3), connective not prolonged, gynoecium of carpel, 1 ovary conic or ovoid (hidden by mass the of appressed stamens), disc or nectaries, if any, not visible, style short, arcuate, attenuate, stigmatic area terminal, papillate, not enlarged. Micropetasos burmensis G ^ & O. Poinar, K.L. Chambers Wunderlich, MYANMAR ^ j. sp. nov. (Figs. 1-4). Tvph: j BUnl SUmmit amber mine Hukawn SW in the g Valley, of Maingkhwan, 26°20'N, 96°36'E, 2012, I unknown ambe^ 11011 eventually to be deposited in the Senckenberg Museum and Research Frat^^am-Ma^Gmllny)^ Institute, mm Flowers 0.8 in diameter anthpgjs, conn at mm, :alyx 0.13 mr lobes 0.26-0.30 filament length variable, anthers 0.06-0.10 n mm a long, 0.38 wide, pedicels style 0.1 t, mm, 0.26-0.64 pollen triaperturate (Fig. diameter 10-14 4), p T^- E T name rom e < ' he Greek “ micro ' >«**.• ‘ sma11 broad-brimmed from the l hat, - - imagined shape • of the flowers name Species from -sis- the country of origin of the fossil. 747 % m . 748 M modem Insome families withasingle superior carpel, such as Fabaceae, a curved may style be associated with ^ r ^ „e Side 2“ mIw *- «* to «*-. and^ be ^ ^ ^ ““ Ucn ° * P flattened formless mass An (Fig. 3). irregular feature of the andrn “ “"^ ^vte“;:^ hads,am sof An irregularity in the gynoecium is present in one flower of Micropetasos, where two styles are present, and one short, straight, appressed to the usual longer, curved one (Fig. In unclear whether 1). is this indicates a fully bicarpellate gynoecium. Our ability to detect these kinds of developmental variations due is to the rare example of a in which fossil several flowers of the species are connected an in inflorescence, as contrasted to the usual case where flowers are detached and only one or two can be assigned same to the taxon (but see Poinar 2008a and Chambers et al. et al. 2012, where six and four flowers, were respectively, available) In an example by cited Friis et al. (2011, p. 32), two coalified fossil flowers of Lasistemon, male and female, could be associated through the presence, in both, of pollen having a distinctive exine From pattern. the example of Micropetasos, one might speculate that floral development was more flexible, i.e. less canalized, in the early evolution in some angiosperm clades, but that this has gone undetected because the descriptions of fossil taxa have commonly been based on one or a few flowers. In deposits of coalified or lignified flowers, where numbers large of speci- mens are collected together (Friis et al. 2011), it is possible that this drawback can be overcome. The consistent curvature of the style, together with the relatively stout floral pedicels of Micropetasos, may have been associated with insect pollination, especially given the small size of the flowers. The presence of po en grams on the and style calyx but not in the surrounding amber may suggests that the grains have been adhesive. This would feature facilitate attachment to the body of visiting insects. Small insects would be the most likely pollinators of minute flowers such as those of Micropetasos burmensis. Melittosphex burmensis, a mm tiny bee just less than 3 & in length that lived in the Burmese amber forest (Danforth Poinar 2011) a ii possible candidate. A possible relationship modem of Micropetasos with a family in one of the redefined clades of eudicots (APGIII, Stevens 200! onwanl) problematic is Features such as hypogyny, a counate numerous calyx, sta- mens, a single and carpel, a curved style are suggestive of certain members of the Fabaceae. However the simi- larity only is superficial, because the inflorescence differs from the racemose type found in that family, and numerous stamens occur principally in the highly derived subfamily Mimosoideae. Furthermore, molecular P ylogenetic studies date the origin of Fabaceae to the Early Tertiary (Lavin et al. 2005). In terms of phyloge- netic systematics, Micropetasos appears an member to represent early of the Pentapetalae clade (Cantino et al known 2007), also We as core eudicots. prefer to leave the question of its exact familial relationships open at ACKNOWLEDGMENTS We thank James Doyle for his careful review and helpful suggestions. Cant.no, P.D., M J.A. Doyle, S.W. Graham, W.S. 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