Transformative Paleobotany Companion Website Additional materials and information are available from the book’s companion website https://www.elsevier.com/books-and-journals/book-companion/9780128130124 Transformative Paleobotany Papers to Commemorate the Life and Legacy of Thomas N. Taylor Edited by Michael Krings SNSB-Bavarian State Collection for Palaeontology and Geology Munich, Germany Ludwig-Maximilians-Universita¨tMu¨nchen Munich, Germany The University of Kansas Lawrence, Kansas, United States Carla J. Harper The University of Kansas Lawrence, Kansas, United States SNSB-Bavarian State Collection for Palaeontology and Geology Munich, Germany Ne´ stor Rube´n Cu´ neo Museo Paleontolo´gico Egidio Feruglio, and National Research Council of Argentina Trelew, Chubut, Argentina Gar W. 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Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-813012-4 For information on all Academic Press publications visit our website at https://www.elsevier.com/books-and-journals Publisher: Andre Gerhard Wolff Acquisitions Editor: Anna Valutkevich Editorial Project Manager: Pat Gonzalez Production Project Manager: Sreejith Viswanathan Cover Designer: Mark Rogers Typeset by TNQ Technologies Chapter 24 Polar Regions of the MesozoicePaleogene Greenhouse World as Refugia for Relict Plant Groups Benjamin Bomfleur1, Patrick Blomenkemper1, Hans Kerp1 and Stephen McLoughlin2 1Westfälische Wilhelms-Universität Münster, Münster, Germany; 2Swedish Museum of Natural History, Stockholm, Sweden 1. INTRODUCTION presumed extinction of this iconic plant group of the Gondwanan Triassic. It appears that contrary to current Today, a prominent effect of the decreasing amount and assertions (Pattemore et al., 2015; Pattemore, 2016), increasing seasonality of solar energy input with increasing Dicroidium did not perish in the course of the end-Triassic latitude is the latitudinal gradient in species richness; that is, biotic crisis, but survived with relictual populations in polar the general decrease in biodiversity from the equator refugia well into the Jurassic. On this basis, we provide a toward the poles (Hillebrand, 2004; Gaston, 2000, 2007). review of case studies outlining the changing geographical Although this phenomenon has long been recognized distributions of both austral and boreal plant groups and has fascinated some of the most celebrated minds of to highlight a common pattern among archaic plant ecology and evolutionary theory (Von Humboldt, 1806; groupsdthat of retreat to the poles in the wake of biotic Darwin, 1859; Wallace, 1878), its underpinning mechanisms crises. remain poorly understood (Rohde, 1992; Gaston, 2000; Willig et al., 2003; Hillebrand, 2004). In recent decades, it has become increasingly clear that the latitudinal gradient 1.1 The Dicroidium Plants concept can be transposed to a much greater evolutionary Plants with Dicroidium-type foliage are the best-known scale and projected deep into geological time, revealing representatives of Umkomasiaceae (¼Corystospermaceae), biogeographical patterns in the origination and extinction of a group of extinct gymnosperms that were common clades (Crane and Lidgard, 1989; Jablonski, 1993; Jablonski elements in many early and mid-Mesozoic floras worldwide. et al., 2006; Mittelbach et al., 2007; Fig. 24.1). The cold Dicroidium plants constituted medium-sized to tall canopy deserts of the polar regions today are among the most trees producing distinctive forked fronds (the name-bringing inhospitable places on Earth. Global climates, however, have Dicroidium) and leafless fertile branching systems, either been changing throughout Earth history, and during warmer with terminal, recurved cupules (Umkomasia)orwithshort- periods of the Phanerozoic, large parts of landmasses in stalked, leafy microsporophylls with abaxial clusters high northern and southern latitudes were covered in lush of free pollen sacs (Pteruchus) containing non-taeniate vegetation (e.g., Heer, 1868; Halle, 1913; Taylor and Taylor, bisaccate pollen (Falcisporites)(Taylor et al., 2006, 2009). 1990; Cantrill and Poole, 2012). These past high-latitude Dicroidium foliage is highly variable in size, architecture terrestrial ecosystems have repeatedly been shown to host (simple to tripinnate), leaflet morphology (needle-like, entire, the youngest occurrences of plant taxa that had long to variably lobed or dissected), and venation (e.g., simple, disappeared from lower-latitude basins (e.g., McLoughlin taeniopteroid, odontopteroid, or alethopteroid; see Arch- et al., 2008, 2011). angelsky, 1968; Retallack, 1977; Anderson and Anderson, Here, we present Dicroidium cuticles from Jurassic 1983). All frond forms, however, possess the characteristic strata of East Antarctica that significantly postdate the basal bifurcation (see Anderson and Anderson, 1983), share Transformative Paleobotany. https://doi.org/10.1016/B978-0-12-813012-4.00024-3 593 Copyright © 2018 Elsevier Inc. All rights reserved. 594 SECTION j V Antarctic Paleobotany 1162°62° 1164°64° Shafer Peak Timber Peak Section Peak Section Peak N (74°02'S 162°34'E) (74°11'S 163°23'E) (73°14'S 161°55'E) Lichen Mesa Hills Range <198 ± 2 Ma . m SPP30b F SHC32 k SPL a . e P <191 ± 4 Ma m F n <214 ± 3 Ma o k i t a uunexposednexposed c e e P S Section Peak Fm. n o i t c SHB07 e <202 ± 3 Ma S Section Peak Fm. TI13/5 Shafer Peak EHT deposits 774°4° 188.2 ± 2.2 Ma Deep Freeze SHA13 Range SHA11 Main lithologies . SHA08/5 m SHA08/1 Sill intrusion F SHA06 Timber Peak k a e Pillow lava P n uunexposednexposed o Mafic volcaniclastic deposit i Eisenhower t c Range e S Section Peak Fm.uunexposednexposed Shafer Peak Fm. (Reworked) silicic tuff Coal 50 m Jang Bogo Dicroidium fossils Mudstone Gondwana Palynological sample Sandstone Mario Zucchelli Ross Radiometric age data Crystalline basement Sea FIGURE 24.1 Geographic and stratigraphic setting of the studied material. Modified from Bomfleur et al. (2014); radiometric age data adopted from Elsner (2010), Elsner et al. (2013), and Goodge and Fanning (2010). distinctive epidermal and cuticular features (e.g., Gothan, contain the latest Glossopteris survivors rather than 1912; Thomas, 1933; Jacob and Jacob, 1950; Townrow, 1957; precocious Dicroidium occurrences (see Section 4.3.2), Archangelsky, 1968; Bomfleur and Kerp, 2010), and are well-preserved Dicroidium fronds occur in reliably dated associated with similar reproductive organs (e.g., Thomas, Permian deposits of Jordan (Kerp et al., 2006; Abu Hamad 1933; Anderson and Anderson, 1983). The Dicroidium seed et al., 2008, 2017). Conversely, the possible occurrence ferns were the dominant gymnosperm group in temperate of Dicroidium in the Jurassic of Antarctica has also been forest and wetland environments across most of the reported (Rees and Cleal, 2004), but the fragments are Southern Hemisphere during the Middle and Late Triassic incomplete and assignment has been considered tentative. (e.g., Anderson et al., 1999; McLoughlin, 2001). Owing to their ubiquitous occurrence and sheer abundance in the 2. MATERIAL AND METHODS Gondwanan Triassic, the informal term “Dicroidium flora” is commonly used to describe their main geographic and This study is based primarily on new occurrences of biostratigraphic realm (e.g., Hirmer, 1936; Townrow, 1957; Dicroidium fossils in Jurassic deposits of the Victoria Group Barnard,