Insight Paleobotany

The Conquest

Assoc. Prof. of Land Wiesław Trela (PhD, DSc) works at the Polish Geological Institute – National Research in the Ordovician Institute. For over 20 years he has been conducting sedimentological and stratigraphic research Plant fossils discovered in Poland’s Holy Cross on the Paleozoic of Poland’s Holy Mountains are estimated to be 445 million years old, Cross Mountains. His research activity which changes our view of plant evolution, concentrates on studies of depositional and above all proves that they appeared on land environments and paleoecological much earlier than we thought. conditions in the Ordovician period. [email protected] Wiesław Trela global biogeochemical cycle, weathering process- Zbigniew Szczepanik es, soil structure, and, consequently, the state of the Earth’s climate. With the appearance of terrestrial Polish Geological Institute plants, carbon binding began, both in the gradually – National Research Institute in Warsaw growing plant cover and the organic matter accumu- lated in the soil. The colonization of land by plants is Paweł Filipiak, Mariusz Salamon

Dr. Zbigniew Faculty of Natural Sciences, Institute of Earth Szczepanik (PhD) Sciences, University of Silesia in Katowice works at the Holy Cross Mountains Przemysław Gorzelak Branch of the Polish Geological Institute Institute of Paleobiology – National Research of the Polish Academy of Sciences in Warsaw Institute. He studies the stratigraphic, environmental and palaeogeographic aspects of acritrach microflora, as well as the thermal maturity ne of the most important issues in the evo- of the organic matter O lution of life on Earth is how terrestrial of Lower Paleozoic habitats were colonized by plants. Molecular studies, palynomorphs. as well as morphological, cytological and biochem- zbigniew.szczepanik ical features show a great similarity between plants @pgi.gov.pl and certain green algae (Chara), indicating that they share a close relationship and common ancestor. Ac- cording to paleontological data, plants first began to colonize land in the Ordovician period, between 475 and 450 million years ago. The terrestrialization of Trichotomously branching plant axis (A) and oval sporangium (B) plants had a fundamental impact on changing the from the Upper Ordovician (Hirnantian) in the HCM

t h e m a g a z i n e o f t h e p a s 82 3–4/63–64/2019 Siberia Asst. Prof. Paweł Filipiak (PhD, DSc) works at the Faculty of Natural Sciences, Laurentia Baltica Institute of Earth Sweden Sciences, University Iapetus O. of Silesia. He studies Avalonia HCM Saudi Arabia Argentina the palynology Rheic Ocean Oman of Devonian and Gondwana Carboniferous deposits Czechia and macroflora. Member of the editorial board of the journal Cryptospores: Trilete spores: Plant fossils: Annales Societatis Middle Ordovincian Sandbian Katian Geologorum Poloniae. Upper Ordovincian Katian Hirnantian [email protected]

Occurrence of spores and plant fossils on the paleogeographic map of the Late Ordovician (445 million years ago); HCM – the Holy Cross Mountains

currently considered to be one of the most important senting the transition from algae. However, the oldest factors (if not the key factor) responsible for the cool- definite fossils of terrestrial plants are cryptospores ing of the Ordovician climate, through their effect on found in the Ordovician period, which have many reducing CO2 concentration and increasing O2 in the features in common with modern liverwort spores. atmosphere. This process ended about 445 million Their presence has been documented in deposits of the years ago, when the CO2 concentration dropped to 8 Middle Ordovician period, in Argentina (470 million times today’s level (or less). This triggered the forma- years ago) and Saudi Arabia (460 million years ago). Assoc. Prof. tion of the ice sheet in the southern part of the Gond- In addition, in the Upper Ordovician (Katian stage), Mariusz Salamon wana continent, which lasted from 0.5 to 1 million sedimentary records of Oman sporangium fragments (PhD, DSc) years, which in turn resulted in a global sea level fall were found together with cryptospores, which are sim- is a Professor at the Institute of Earth (the Hirnantian regression) and a biotic crisis, which ilar to modern liverworts. This is why liverworts were Sciences, Faculty finished the Great Ordovician Biodiversity. It should considered to have been the first plants which colo- of Natural Sciences, be noted, however, that other important factors con- nized land. The Late Ordovician period was also time at the University tributing to the reduction of CO2 in the atmosphere span when the first trilete spores appeared, which are if Silesia. His studies could also be responsible for the Ordovician climate regarded to be a spore morphology typical for vascu- the taphonomy, cooling, such as: 1) declining volcanic activity associ- lar plants, although these type forms are also found paleoecology, ated with the super mantle plume, 2) mass blooming among some bryophytes. However, unequivocal mac- systematics and evolution of fossil of phytoplankton (the Ordovician planktonic revolu- rofossils of vascular plants are known from the Middle crinoids. Member tion) and the related increasing supply of organic car- Silurian period (430 million years ago) and are repre- of the editorial board bon in bottom sediments, and 3) increased weathering sented by the fossil-genus Cooksonia, characterized by of the journal Annales of siliciclastic rocks. bifurcating axes and more than one sporangium. In Societatis Geologorum the late Silurian, colonization of land by plants was so Poloniae. First plants advanced that it left a signature of wildfires. [email protected] According to some researchers, the presence of per- The oldest fossils manent tetrads and dyadas in Middle Cambrian sed- iments, or sporomorphs (forms morphologically re- In 2018, an international team of researchers published sembling spores), permanently linked together into the results of a study in the journal New Phytologist biologically undivided aggregates, point to the Cam- regarding the oldest macrofossils presumably of ter- brian colonization of land by pioneer plants repre- restrial plants from 445 million years ago found in Po-

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mil. yrs 443.8 HIRNANTIAN plant fossils (Poland’s HCM) sporangium fragments with KATIAN cryptospores (Oman) trilete spores (Saudi Arabia) Asst. Prof. Przemysław UPPER Gorzelak SANDBIAN cryptospores (Sweden) (PhD, DSc) 458.4 works at the PAS Institute cryptospores (Czechia, Saudi Arabia) of Paleobiology DARRIWILIAN in Warsaw. He studies cryptospores (Saudi Arabia) the paleoecology, functional morphology, MIDDLE DAPINGIAN cryptospores (Argentina) evolution and 470.0

biomineralization ORDOVINCIAN of contemporary and fossil echinoderms. FLOIAN He has received scholarships from the Foundation for Polish Science and the Minister of LOWER TREMADOCIAN Science and Higher Stratigraphic location of Ordovician spores and plant fossils Education. 477.7 (HCM – the Holy Cross Mountains) [email protected]

land’s Holy Cross Mountains (HCM). They occurred ago). Thus the Hirnantian plant fossils from the HCM in the latest Ordovician (the Hirnantian stage) mud- are the oldest macrofossils of polysporangiophytes in stones, shales and marls with sandstone interbeds, the sedimentary record. which are a regional record of sea level fall, forced by In the late Ordovician the HCM were located close Further reading: glaciation in Gondwana. The stratigraphic position of to the southwestern margin of the Baltica, between these deposits was determined on the basis of trilobite 30° and 40° southern latitude. The latest research on Porębski S.J., Anczkiewicz fossils of Mucronaspis and brachiopods of the Hirnan- Hirnantian sediments on the Polish side of the Baltic R., Paszkowski M., Skompski S., Kędzior A., Mazur S., tia Fauna. In addition, these sediments yielded a typi- Sea indicates that at that time icebergs from Gondwa- Szczepański J., Buniak A., cal Upper Ordovician microfossil assemblage, includ- na were reaching its southwestern shelf, from which Mikołajewski Z., Hirnantian ing chitinozoa and acritarchs. Particularly noteworthy thicker terrigenous material, such as sand and fine icebergs in the subtropical is acritarch microflora consisting of Hirnantian forms, gravel, was melted. It is likely that the Late Ordovi- shelf of Baltica: Evidence from accompanied by Cambrian and Middle Ordovician cian icebergs also influenced the HCM region. In this sedimentology and detrital zircon provenance, Geology redeposited taxa, such as the genus Frankea, typical context, the presence of Frankea in the Hirnantian 2019, 47: 284–288. for the Middle Ordovician in Gondwana. acritarch assemblage of the HCM may be interpreted The plant fragments found in the HCM have di- in two ways, as a result of 1) redeposition from the Rubinstein C.V., Vajda V., Baltica cradle of early land chotomously branched axes. These specimens are collision zone of the Avalonia microcontinent with plants? Oldest record of trilete small, only 2‒3 mm long and about 3 mm wide. One Baltica, or 2) transport by icebergs from the marginal spores and diverse cryptospore specimen with a trichotomous axis division (3.2 mm zone of Gondwana. Therefore, it cannot be rule out assemblages; evidence long and 0.3 mm wide) was also documented, which that fossils of terrestrial plants found in the HCM may from Ordovician successions is a feature noted in some late Silurian and Early De- have been redeposited and in fact are older than the of Sweden, GFF 2019, 141: 181–190. vonian plants (430‒410 million years ago). The single Hirnantian age. not branched specimens end in cup-shaped and oval A recently reported assemblage of sporomorphs Salamon M.A., Gerrienne P., Steemans P., Gorzelak P., sporangia (about 0.4‒0.8 mm long and 0.3‒1.1 mm from the Middle and Upper Ordovician in Sweden Filipiak P., Le Hérissé A., wide), which in form, size and morphology are similar is noteworthy in that it consists of cryptospores and Florentin P., to the Silurian genus Cooksonia, and resemble struc- trilete spores. These data challenge the current opin- Cascales-Miňnana B., tures found in Triassic liverworts. In addition, sporo- ion that the first plants originated in Gondwana. They Brachaniec T., Misz-Kennan M., morphs morphologically similar to trilete spores were also suggest that vascular plants may have appeared Niedźwiedzki R., Trela W., Putative Late Ordovician land identified in samples from the HCM, and stomatal on Baltica as early as the Late Ordovician, although plants, New Phytologist 2018, apparatus resembling that in Akdalophyton caradocki, according to some researchers, trilete spores may also 218: 1305–1309. a plant from the late Sandbian (453‒455 million years occur in some bryophytes.

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