Deforestation: A Lesson from the Permian Extinction

Satellite photo of Amazon fires. Credit: NASA

The recent fires at Amazonas, Gran Canaria (Spain), Australia, and Indonesia sparked international outcry. Climate change makes forests hotter and drier, thus more likely to sustain uncontrolled fires. But fires are also linked with deforestation. Almost 1 million km2 of Amazon forest has already been deforested, and a recent study indicates that the number of active fires in this August was actually three times higher than 2018. Deforestation is a threat to biodiversity and ecosystems stability. It also leads to the loss of cultural diversity, the alteration of the hydrological cycle and climate systems.

The geological records show that large and rapid global warming events occurred repeatedly during the course of Earth history. The End-Permian extinction event (EPE) serves as a powerful deep-time analogue for modern deforestation and diversity loss, with as much as 95% of the marine animal species and a similarly high proportion of terrestrial plants and animals going extinct . This great crisis ocurred about 252 million years ago (Ma) during an episode of global warming. A recent study focussed on the Sydney Basin, Australia, shows how the typical Permian temperate forest communities disappeared abruptly, followed by a short ‘dead zone’ characterized only by charcoal, wood fragments, and fungi, signatures of an interval of wildfire and saprotrophic breakdown of organic matter.

Global paleogeographic map for the Permian-Triassic transition showing the location of the Siberian Traps Large Igneous Province. From Vajda et al., 2019

Two palynological events marked the end-Permian Event: the ‘algal/fungal/acritarch event’ (a bloom of Reduviasporonites, and of acritarchs in marine environments); and the ‘spore-spike event’. The first event in post-extinction continental deposits has contributed to a continuing debate as to whether the EPE interval was marked by eustatic sea-level rise. The ‘spore-spike event’ indicates that many plant groups survived in regional refugia, possibly at higher altitudes, or in coastal settings where conditions were consistently cooler or wetter. Some of those survivors constituted the pioneer vegetation during the Early Triassic.

During the EPE the woody gymnosperm vegetation (cordaitaleans and glossopterids) were replaced by spore-producing plants (mainly lycophytes) before the typical Mesozoic woody vegetation evolved. Glossopterids were the prime contributors of biomass to the vast Permian coal deposits of Gondwana, therefore their disappearance had major implications for ecosystem structure. The very rapid appearance of drought-tolerant plant associations (dominated by conifers and the seed fern Lepidopteris) in the macroflora of the Sydney Basin, may represent immigration of drought-adapted biota from other regions of Pangea.

Spores and pollen identified in the post-extinction mudstone at the Frazer Beach section. From Vajda et al., 2019

The palynological record suggests that wooded terrestrial ecosystems took four to five million years to reform stable ecosystems, while spore-producing lycopsids had an important ecological role in the post-extinction interval. The disappearance of the Glossopteris that dominated the cool Permian wetland forest of Gondwana, had  enormous consequences for landscape coverage, ecosystem structure, food webs, and caused substantial perturbations to the hydrological and carbon cycles of the entire biosphere.

Since the industrial revolution, the wave of animal and plant extinctions that began with the late Quaternary has accelerated. Australia has lost almost 40 percent of its forests, and almost 20% of the Amazon has disappeared in last five decades.Calculations suggest that the current rates of extinction are 100–1000 times above normal, or background levels. If we want to stop the degradation of our planet, we need to act now.

 

References:

V. Vajda et al. (2020), End-Permian(252Mya) deforestation, wildfires and flooding—An ancient biotic crisis with lessons for the present, Earth and Planetary Science Letters 529 (2020) 115875 https://doi.org/10.1016/j.epsl.2019.115875

Jos Barlow et al, Clarifying Amazonia’s burning crisis, Global Change Biology (2019). DOI: 10.1111/gcb.14872

Mutagenesis in land plants during the end-Triassic mass extinction

 

A basaltic lava flow section from the Middle Atlas, Morocco. From Wikimedia Commons.

During the last 540 million years five mass extinction events shaped the history of the Earth. The End-Triassic Extinction at 201.51 million years (Ma) is probably the least understood of these events. Most mammal-like reptiles and large amphibians disappeared, as well as early dinosaur groups. In the oceans, this event eliminated conodonts and nearly annihilated corals, ammonites, brachiopods and bivalves. In the Southern Hemisphere, the vegetation turnover consisted in the replacement to Alisporites (corystosperm)-dominated assemblage to a Classopollis (cheirolepidiacean)-dominated one.

The mass extinction event was likely caused by the eruption of the Central Atlantic Magmatic Province (CAMP), a large igneous province emplaced during the initial rifting of Pangea. Data indicates that magmatic activity started c. 100,000 years before the endTriassic event and continued in pulses for 700,000 years. The CO2 emissions caused global warming. The SO2 emissions on mixing with water vapour in the atmosphere, caused acid rain, which in turn killed land plants and caused soil erosion.

A normal fern spore compared with mutated ones from the end-Triassic mass extinction event. Image credit: S LINDSTRÖM, GEUS

Volcanoes are also a primary source of mercury (Hg) in the global atmosphere. Mercury can cause morphologically visible abnormalities in plants and their reproductive cells (spores and pollen). A new study led by Sofie Lindström of the Geological Survey of Denmark and Greenland analized various types of abnormalities in the reproductive cells of ferns, with focus in two morphogroups: LTT-spores (laevigate, trilete fern spores with thick exine), and LCT-spores (laevigate, circular, trilete spores). The LTT-spores were produced primarily by the fern families Dipteridaceae, Dicksoniaceae, and Matoniaceae, while LCT spores were primarily produced by ferns belonging to Osmundaceae and Marattiales.

The elevated concentrations of mercury (Hg) in sedimentary rocks in North America, Greenland, England, Austria, Morocco, and Peru are linked to CAMP eruptions. This pulse of mercury also correlate with high occurrences of abnormal fern spores, indicating severe environmental stress and genetic disturbance in the parent plants. Three negative organic C-isotope excursions (CIEs) have being recognized at the end-Triassic: the Marshi, the Spelae, and the top-Tilmanni CIEs. Malformations in LTT-spores first occur sporadically in the lower pre-Marshi interval. LCT-spores are present but are generally rare in this interval. During the Spelae CIE, the occurrences of moderate to severe malformations increased and aberrant forms can encompass as much as 56% of the counted LTT-spores. This interval is associated with marked global warming, recorded by stomatal proxy data.

 

 

References:

Sofie Lindström et al. Volcanic mercury and mutagenesis in land plants during the end-Triassic mass extinction, Science Advances (2019). DOI: 10.1126/sciadv.aaw4018}

Grasby, S. E., Them, T. R., Chen, Z., Yin, R., & Ardakani, O. H. (2019). Mercury as a proxy for volcanic emissions in the geologic record. Earth-Science Reviews, 102880. doi:10.1016/j.earscirev.2019.102880

On This Side of Paradise.

Stardate 3417.3. The Enterprise has arrived to the planet Omicron Ceti III to catalog the destruction suffered by an agricultural colony stablished in 2264. It was assumed that the colonists are dead because the planet was bathed in Berthold rays, a lethal form of radiation. Although there was no sign of animal life on the planet, the colonists were found alive and in excellent health. Mr. Spock, intrigued about the survival of the colony, is conducted by Leila Kalomi, a botanist he had met six years prior on Earth, to a field with very strange flowers which expelled some spores into his face. Spock begun to feel sick, and after a brief agonizing struggle, he smiled and confessed his love for Leila. Like Spock, all the members of the Enterprise that were exposed to the spores changed their behavior. The only one who resisted the effect of the spores was Captain Kirk.

Spock with Leila Kalomi (Image: CBS)

The key elements for the colony survival were the spores. The term ‘spores’ derived from the Greek word for seed. In a broad sense, spores are the reproductive structures of bacteria, fungi, algae, protists and land plants, adapted for dispersion and surviving for extended periods of time during unfavorable conditions.

The colonization of land by vascular plants in the Paleozoic was one of the most significant events in Earth’s history. We could hypothesize that terrestrial colonization was not possible prior to the evolution of the sporopollenin spore wall, and this adaptation is considered to be a synapomorphy of the embryophytes. Sporopollenin is the major component of the spore (and pollen) wall. This highly resistant biopolymer occurs in certain charophyceans, but is located in an inner layer of the zygote wall.

Cryptospores from the Early Middle Ordovician of Argentina (From Rubinstein et al., 2010)

Like their algal ancestors, all plant life cycle goes through both haploid (gametophyte) and diploid (sporophyte) stages. In vascular plants, the sporophyte generation predominates. The sporophyte produces the spores, which contain only a single copy of the chromosomes. The earliest dispersed spores attributable to terrestrial plants, termed cryptospores, are known from the Middle Ordovician. Cryptospores are believed to have been produced by bryophyte-like plants, but recently, they were interpreted as the product of a diverse group of mostly extinct plants, whose precise affinities to living clades remain unclear.

C. barrandei sp. nov., from Czech Republic (scale bar, 10 mm). From Libertín et al., 2018.

The description of Cooksonia barrandei (432 my, Czech Republic) shed light on the origins of the alternation of generations in land plants. The genus Cooksonia (named in honor of Isabel Cookson) is generally accepted as the oldest land plant, with a broad distribution in the Late Silurian and Early Devonian periods, including North America, North Africa, Europe, Asia and South America. Cooksonia barrandei (the species name is honoring Joachim Barrande, a famous French palaeontologist who lived in Prague), and is five million years older than the oldest previously described cooksonioids (427 mya). The plants were isosporous (produced only one kind of spore) and of small size, with a bent, isotomously branched axis with terminal branches completely preserved.

Star Trek has been a cult phenomenon for decades. The Original Series premiered on September 8, 1966, and has spawned five successor shows starting in the 1980s and several feature films , comic books, novels and an animated series. Star Trek also influenced generations of viewers about advanced science and engineering. “This side of Paradise” remains as one of the best episode of Star Trek. It was premiered on March 2, 1967. The title was taken by the final line of the poem “Tiare Tahiti” by Rupert Brooke: “Well this side of Paradise! …. There’s little comfort in the wise.”

References:

Libertín, Milan; Kvaček, Jiří; Bek, Jiří; Žárský, Viktor & Štorch, Petr (2018), “Sporophytes of polysporangiate land plants from the early Silurian period may have been photosynthetically autonomous”, Nature Plants, 4 (5): 269–271, doi:10.1038/s41477-018-0140-y

Rubinstein, C. V., Gerrienne, P., de la Puente, G. S., Astini, R. A., & Steemans, P. (2010). Early Middle Ordovician evidence for land plants in Argentina (eastern Gondwana). New Phytologist, 188(2), 365–369. doi:10.1111/j.1469-8137.2010.03433.x 

 

Terrestrial floras at the Triassic-Jurassic Boundary in Europe.

Proportions of range-through diversities of higher taxonomic categories of microfloral elements over the Middle Triassic–Early Jurassic interval (From Barbacka et al., 2017)

Over the last 3 decades, mass extinction events  have become the subject of increasingly detailed and multidisciplinary investigations. Most of those events are associated with global warming and proximal killers such as marine anoxia. Volcanogenic-atmospheric kill mechanisms include ocean acidification, toxic metal poisoning, acid rain, increased UV-B radiation, volcanic darkness, cooling and photosynthetic shutdown. The mass extinction at the Triassic-Jurassic Boundary (TJB) has been linked to the eruption of the Central Atlantic Magmatic Province (CAMP), a large igneous province emplaced during the initial rifting of Pangea. Another theory is that a huge impact was the trigger of the extinction event. At least two craters impact were reported by the end of the Triassic. The Manicouagan Impact crater in the Côte-Nord region of Québec, Canada was caused by the impact of a 5km diameter asteroid, and it was suggested that could be part of a multiple impact event which also formed the Rochechouart crater in France, Saint Martin crater in Canada, Obolon crater in Ukraine, and the Red Wing crater in USA (Spray et al., 1998).

Photographs of some Rhaetian–Hettangian spores and pollen from the Danish Basin (From Lindström, 2015)

Most mammal-like reptiles and large amphibians disappeared, as well as early dinosaur groups. In the oceans, this event eliminated conodonts and nearly annihilated corals, ammonites, brachiopods and bivalves. In the Southern Hemisphere, the vegetation turnover consisted in the replacement to Alisporites (corystosperm)-dominated assemblage to a Classopollis (cheirolepidiacean)-dominated one. But there was no mass extinction of European terrestrial plants during the TJB. The majority of genera and a high percentage of species still existed in its later stages, and replacement seems to have been local, explainable as a typical reaction to an environmental disturbance. In Greenland, for example, the replacement of Triassic wide-leaved forms with Jurassic narrow-leaved forms was linked to the reaction of plants to increased wildfire. In Sweden, wildfire in the late Rhaetian and early Hettangian caused large-scale burning of conifer forests and ferns, and the appearance of new swampy vegetation. In Austria and the United Kingdom, conifers and seed ferns were replaced by ferns, club mosses and liverworts. In Hungary, there was a high spike of ferns and conifers at the TJB, followed by a sudden decrease in the number of ferns along with an increasing share of swamp-inhabiting conifers.

Although certain taxa/families indeed became extinct by the end of the Triassic (e.g. Peltaspermales), the floral changes across Europe were rather a consequence of local changes in topography.

References:

Maria Barbacka, Grzegorz Pacyna, Ádam T. Kocsis, Agata Jarzynka, Jadwiga Ziaja, Emese Bodor , Changes in terrestrial floras at the TriassicJurassic Boundary in Europe, Palaeogeography, Palaeoclimatology, Palaeoecology (2017), doi: 10.1016/j.palaeo.2017.05.024

S. Lindström, Palynofloral patterns of terrestrial ecosystem change during the end-Triassic event — a review, Geol. Mag., 1–23 (2015) https://doi.org/10.1017/S0016756815000552

Van de Schootbrugge, B., Quan, T.M., Lindström, S., Püttmann, W., Heunisch, C., Pross, J., Fiebig, J., Petschick, R., Röhling, H.-G., Richoz, S., Rosenthal, Y., Falkowski, P. G., 2009. Floral changes across the Triassic/Jurassic boundary linked to flood basalt volcanism. Nat. Geosci. 2, 589–594. doi: 10.1038/NGEO577.

N.R. Bonis, W.M. Kürschner, Vegetation history, diversity patterns, and climate change across the Triassic/Jurassic boundary, Paleobiology, 8 (2) (2012), pp. 240–264 https://doi.org/10.1666/09071.1

A Tale of Two Exctintions.

The permian triassic boundary at Meishan, China (Photo: Shuzhong Shen)

The Permian Triassic boundary at Meishan, China (Photo: Shuzhong Shen)

Extinction is the ultimate fate of all species. The fossil record indicates that more than 95% of all species that ever lived are now extinct. Over the last 3 decades, mass extinction events  have become the subject of increasingly detailed and multidisciplinary investigations. In 1982, Jack Sepkoski and David M. Raup identified five major extinction events in Earth’s history: at the end of the Ordovician period, Late Devonian, End Permian, End Triassic and the End Cretaceous. These five events are know as the Big Five.

The end-Permian extinction is the most severe biotic crisis in the fossil record, with as much as 95% of the marine animal species and a similarly high proportion of terrestrial plants and animals going extinct . This great crisis occurred 252 million years ago (Ma) during an episode of global warming. The End-Triassic Extinction  is probably the least understood of the big five. Most mammal-like reptiles and large amphibians disappeared, as well as early dinosaur groups. In the oceans, this event eliminated conodonts and nearly annihilated corals, ammonites, brachiopods and bivalves. Although it’s almost impossible briefly summarize all the changes in biodiversity associated with both extinction events, we can describe their broad trends.

 

Flow chart summarizing proposed cause-and-effect relationships during the end-Permian extinction (From Bond and Wignall, 2014)

Flow chart summarizing proposed cause-and-effect relationships during the end-Permian extinction (From Bond and Wignall, 2014)

Both extinction events are commonly linked to the emplacement of the large igneous provinces of the Siberian Traps and the Central Atlantic Magmatic Province. Massive volcanic eruptions with lava flows, released large quantities of sulphur dioxide, carbon dioxide, thermogenic methane and large amounts of HF, HCl, halocarbons and toxic aromatics and heavy metals into the atmosphere. Furthermore, volcanism contribute gases to the atmosphere, such as Cl, F, and CH3Cl from coal combustion, that suppress ozone formation. Acid rain likely had an impact on freshwater ecosystems and may have triggered forest dieback. Mutagenesis observed in the Lower Triassic herbaceous lycopsid Isoetales has been attributed to increased levels of UV-radiation. Charcoal records point to forest fires as a common denominator during both events. Forest dieback was accompanied by the proliferation of opportunists and pioneers, including ferns and fern allies. Moreover, both events led to major schisms in the dominant terrestrial herbivores  and apex predators, including the late Permian extinction of the pariaeosaurs and many dicynodonts and the end-Triassic loss of crurotarsans (van de Schootbrugge and Wignall, 2016).

Aberrant pollen and spores from the end-Triassic extinction interval (scale bars are 20 μm). (a) Ricciisporites tuberculatus from the uppermost Rhaetian deposits at Northern Ireland (adapted from van de Schootbrugge and Wignall, 2016)

Aberrant pollen and spores from the end-Triassic extinction interval (scale bars are 20 μm). (a) Ricciisporites
tuberculatus and b) Kraeuselisporites reissingerii (adapted from van de Schootbrugge and Wignall, 2016)

During the end-Permian Event, the woody gymnosperm vegetation (cordaitaleans and glossopterids) were replaced by spore-producing plants (mainly lycophytes) before the typical Mesozoic woody vegetation evolved. The palynological record suggests that wooded terrestrial ecosystems took four to five million years to reform stable ecosystems, while spore-producing lycopsids had an important ecological role in the post-extinction interval. A key factor for plant resilience is the time-scale: if the duration of the ecological disruption did not exceed that of the viability of seeds and spores, those plant taxa have the potential to recover (Traverse, 1988). Palynological records from across Europe provide evidence for complete loss of tree-bearing vegetation reflected in a strong decline in pollen abundance at the end of the Triassic. In the Southern Hemisphere, the vegetation turnover consisted in the replacement to Alisporites (corystosperm)-dominated assemblage to a Classopollis (cheirolepidiacean)-dominated one.

Comparison of extinction rates for calcareous organisms during the end-Permian and end-Triassic extinction event (from van de Schootbrugge and Wignall, 2016)

Comparison of extinction rates for calcareous organisms during the end-Permian and end-Triassic extinction event (from van de Schootbrugge and Wignall, 2016)

Rapid additions of carbon dioxide during extreme events may have driven surface waters to undersaturation. Acidification affects the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus in the ocean and interferes with a range of processes, including growth, calcification, development, reproduction and behaviour in a wide range of marine organisms like foraminifera, planktonic coccolithophores, pteropods and other molluscs,  echinoderms, corals, and coralline algae. Both extinction events led to near-annihilation of cnidarian clades and other taxa responsible for reef construction, resulting in ‘reef gaps’ that lasted millions of years. Black shales deposited across both extinction events also contain increased concentrations of the biomarker isorenieratane, a pigment from green sulphur bacteria, suggesting that the photic zone underwent prolonged periods of high concentrations of hydrogen sulphide. Following the end-Triassic extinction, Early Jurassic shallow seas witnessed recurrent euxinia over a time span of 25 million years, culminating in the Toarcian Oceanic Anoxic Event.

 

References:

BAS VAN DE SCHOOTBRUGGE and PAUL B. WIGNALL (2016). A tale of two extinctions: converging end-Permian and end-Triassic scenarios. Geological Magazine, 153, pp 332-354. doi:10.1017/S0016756815000643.

BACHAN, A. & PAYNE, J. L. 2015. Modelling the impact of pulsed CAMP volcanism on pCO2 and δ13C across the Triassic-Jurassic transition. Geological Magazine, published online

Retallack, G.J. 2013. Permian and Triassic greenhouse crises. Gondwana Research 24:90–103.

 

Palynology of the Ischigualasto Formation.

Ischigualasto-perfil-gusano-montañas

Image from Ischigualasto Park (http://www.ischigualasto.gob.ar/)

Ischigualasto is an arid, sculpted valley, in northwest Argentina (San Juan Province), limiting to the north with the Talampaya National Park, in La Rioja Province. Both areas belong to the same geological formation: the Ischigualasto-Villa Unión Basin which is centered on a rift zone that accumulated thick terrestrial deposits during the Triassic. This basin preserves a complete and continuous fossiliferous succession of continental Triassic rocks.

The Ischigualasto Formation is known worldwide for its tetrapod assemblage, which included the oldest known record of dinosaurs. Adolf Stelzner in 1889 published the first data on the geology of Ischigualasto, but it was not until 1911, that Bondenbender briefly refers to the fossils of the site. Several thin volcanic ash horizons, indicates that the deposition of the Ischigualasto Formation began at the Carnian Stage (approximately 228 mya), and consists of four lithostratigraphic members which in ascending order include the La Peña Member, the Cancha de Bochas Member, the Valle de la Luna Member, and the Quebrada de la Sal Member.

1–3. Retusotriletes herbstii sp. nov; 4–5. Rogalskaisporites cicatricosus; 6. Rugulatisporites

1–3. Retusotriletes herbstii sp. nov; 4–5. Rogalskaisporites cicatricosus; 6. Rugulatisporites

During the Late Triassic two distinct microfloras have been recognised in the southern hemisphere: the Ipswich microflora and the Onslow microflora. The Ipswich province, characterized by the abundance of bisaccate pollen, monosulcate pollen and trilete spores, evolved in southern and eastern Australia, Transantarctic Mountains region, South Africa and Argentina. The Onslow province is a mixture of Gondwanan and European taxa recognized in of north-western Australia, Madagascar, East Africa, Indian, and East Antarctic (Cesari and Colombi; 2013).

The recognition of Carnian European species in the Valle de la Luna Member of the Ishchigualasto Formation expands the distribution of the Onslow-type palynofloras. This assemblage was recovered from the site known as “El Hongo” in the Provincial Park, and contain the diagnostic “Onslow” species: Samaropollenites speciosus, Enzonalasporites vigens, Patinasporites densus, Vallatisporites ignacii, Ovalipollis pseudoalatus and Cycadopites stonei. This assemblage indicates that the Valle de la Luna Member was likely deposited under more humid conditions. It also implies the existence of a latitudinal floral belt from Timor (through the Circum-Mediterranean area) to western Argentina.

 

References:

Cesari, Silvia N., Colombi, Carina, Palynology of the late Triassic ischigualasto formation, Argentina: Paleoecological and paleogeographic implications, Palaeogeography, Palaeoclimatology, Palaeoecology (2016), doi: 10.1016/j.palaeo.2016.02.023

Césari, S. N., Colombi, C. E., 2013. A new Late Triassic phytogeographical scenario in westernmost Gondwana. Nature communications, 4.

Spalletti, L. A. Artabe, A. E. & Morel, E. M. Geological factors and evolution of southwestern Gondwana Triassic plants. Gondwana Res. 6, 119–134 (2003).

 

Darwin and the flowering plant evolution in South America.

pollen

Retimonocolpites sp. (Adapted from Llorens and Loinaze, 2015)

Charles Darwin’s fascination and frustration with the evolutionary events associated with the origin and early radiation of flowering plants are legendary. In a letter to Oswald Heer, a famous Swiss botanist, and paleontologist, Darwin wrote: “the sudden appearance of so many Dicotyledons in the Upper Chalk appears to me a most perplexing phenomenon to all who believe in any form of evolution, especially to those who believe in extremely gradual evolution, to which view I know that you are strongly opposed”. Heer discussed about the early angiosperm fossil record with Darwin, in a letter dated 1 March 1875: “if we say that the Dicotyledons begin with the Upper Cretaceous, we must still concede that this section of the vegetable kingdom, which forms the bulk of modern vegetation, appears relatively late and that, in geological terms, it underwent a substantial transformation within a brief period of time.” 

Darwin’s defense of a gradualist perspective led him to suggest that prior to the Cretaceous record of flowering plants, angiosperms had slowly evolved and diversified on a remote landmass. On 22 July 1879, in a letter to Joseph Dalton Hooker, Darwin refers to the early evolution of flowering plants as an “abominable mystery”. Nearing the end of his life, he wrote to Hooker another letter about a lost fossil record in the earliest phases of angiosperm diversification:  “Nothing is more extraordinary in the history of the Vegetable Kingdom, as it seems to me, than the apparently very sudden or abrupt development of the higher plants. I have sometimes speculated whether there did not exist somewhere during long ages an extremely isolated continent, perhaps near the South Pole.”

Letter from Charles Darwin to Joseph Dalton Hooker, written 22 July 1879 (provenance: Cambridge University Library DAR 95: 485–488)

Letter from Charles Darwin to Joseph Dalton Hooker, written 22 July 1879 (provenance: Cambridge University Library DAR 95: 485–488)

While the oldest records of the different groups of angiosperms are still in discussion, the outcrops of the Baquero Group, located in Argentinean Patagonia, contain one of the richest and most diverse Early Cretaceous floras in the Southern Hemisphere. The unit comprises three formations: Anfiteatro de Tico, Bajo Tigre and Punta del Barco. The first reports of angiosperm remains for the Anfiteatro de Tico Formation were made in 1967. The dominant types are Clavatipollenites, and Retimonocolpites.

Pollen grains  could enter into the fossil record by falling directly into swamps or lakes, or being washed into them or into the rivers and seas. The ones which are not buried in reducing sediments will tend to become oxidized and be destroyed. They reflects the ecology of their parent plants and their habitats and provide a continuous record of their evolutionary history. Gymnosperms pollen often is saccate (grains with two or three air sacs attached to the central body), while Angiosperm pollen shows more variation and covers a multitude of combinations of features: they could be  in groups of four (tetrads),  in pairs (dyads),  or single (monads). The individual grains can be inaperturate, or have one or more pores, or slit-like apertures or colpi (monocolpate, tricolpate).

pollen

Clavatipollenites sp. SEM (Adapted from Archangelsky 2013)

Clavatipollenites pollen grains are interpreted as related to the modern family Chloranthaceae. The genus was established by Couper for dispersed monosulcate pollen grains recovered from the Early Cretaceous of Britain. Currently, the genus has a very broad definition. The genus Retimonocolpites include elongated to subcircular semitectate, columellate and microreticulate pollen grains with well defined monocolpate aperture (Llorens and Loinaze, 2015). The new species Jusinghipollisticoensis sp. nov. represents one of the oldest records of trichotomosulcate, and extends the geographical distribution of Early Cretaceous trichotomosulcate pollen grains to southern South America.

The data also indicates strong similarities between the Baquero Group assemblages and other coeval units from Argentina, Australia and United States.

References:

M. Llorens, V.S. Perez Loinaze, Late Aptian angiosperm pollen grains from Patagonia: Earliest steps in flowering plant evolution at middle latitudes in southern South America, Cretaceous Research 57 (2016) 66-78

Archangelsky, S.,et al. (2009). Early angiosperm diversification: evidence from southern South America. Cretaceous Research, 30, 1073-1082.

Doyle, J. A., & Endress, P. K. (2014). Integrating Early Cretaceous fossils into the phylogeny of living Angiosperms: ANITA. Lines and relatives of Chloranthaceae. International Journal of Plant Sciences, 175, 555-560.

A Brief Introduction to The Hell Creek Formation.

Hell Creek e Fort Union contact, as seen at Mountain Goat Lake Butte, southwestern North Dakota (Adapted from Fastovsky and Bercovici, 2015)

Hell Creek- Fort Union contact, as seen at Mountain Goat Lake Butte, southwestern North Dakota (Adapted from Fastovsky and Bercovici, 2015)

The Hell Creek Formation (HCF), in the northern Great Plains of the United States, is the most studied source for understanding the changes in the terrestrial biota across the Cretaceous-Paleogene boundary, because preserves an extraordinary record comprised of fossil flora, vertebrates, invertebrates, microfossils, a range of trace fossils, and critical geochemical markers such as multiple iridium anomalies associated with the Chicxulub impact event. The HCF is a fine-grained, fluvially derived, siliciclastic unit, that occupies part of the western Williston Basin, and overlies the Fox Hills Formation (Clemens and Hartman, 2014).
The history of research focused on the Hell Creek Formation and its biota started in October 1901, when William T. Hornaday, director of the New York Zoological Society, travelled to northeastern Montana and discovered three fragments of the nasal horn of a Triceratops in the valley of Hell Creek. He showed the fossils to Henry Fairfield Osborn who decided to include the valley of Hell Creek on the list of areas to be prospected by Barnum Brown the following year.
braun

Barnum Brown working in a quarry in 1902.

In July 1902, B. Brown arrived to Hell Creek. His field crew included Dr. Richard Swann Lull, and Phillip Brooks. Brown recounted that after their arrival, he found the partial skeleton that would become the type specimen of Tyrannosaurus rex. In 1904, William H. Utterback, preparator and collector for the Carnegie Museum of Natural History, collected a fragment of a jaw of Tyrannosaurus and two skulls of Triceratops. In the summer of 1906, B. Brown returned to Montana, and a year later he published a complete manuscript about the valley of Hell Creek. The field expeditions of 1908 and 1909 were crowned by the discovery of another skeleton of T-rex. Between 1902 and 1910, Osborn, Brown, and Lull published the analysis of some of the fossil vertebrates discovered in the Hell Creek Formation, including Tyrannosaurus rex, Triceratops, and Ankylosaurus.
Micrograph of Wodehouseia spinata and a specimenBisonia niemi, from the upper part of the Hell Creek Formation (Adapted from Fastovsky and Bercovici, 2015).

Micrograph of Wodehouseia spinata and a specimen Bisonia niemi, from the upper part of the Hell Creek Formation (Adapted from Fastovsky and Bercovici, 2015).

Plants are represented by fossil leaves, seeds and cones. Fossil wood is also commonly found in the HCF as permineralized fragments. The Hell Creek macroflora is largely dominated by angiosperms including palms, associated with several ferns, conifers, and single species of cycads and Ginkgo. The study of pollen and spores has played a very important role in the identification of the K/Pg boundary in the HCF. Palynologists were the first scientists to recognize that a major, abrupt change occurred at the end of the Cretaceous. Unlike the Permian-Triassic and Triassic-Jurassic boundaries, the palynologically defined K/Pg boundary is based on the extinction of Cretaceous taxa rather than the appearance of Paleocene taxa. Intimately associated with the K/Pg boundary globally, is the so-called “fern spike”, occurring exclusively at localities where the iridium anomaly is present. (Fastovsky and Bercovici, 2015; Vajda & Bercovici, 2014.)

 

References:

Fastovsky, D. E., & Bercovici, A., The Hell Creek Formation and its contribution to the CretaceousePaleogene extinction: A short primer, Cretaceous Research (2015), http://dx.doi.org/10.1016/j.cretres.2015.07.007
Clemens, W. A., Jr., & Hartman, J. H. (2014). From Tyrannosaurus rex to asteroid impact: early studies (1901- 1980) of the Hell Creek Formation in its type area. In J. Hartman, K. R. Johnson, & D. J. Nichols (Eds.), Geological society of America special paper: 361. The Hell Creek Formation and the Cretaceous-tertiary boundary in the northern great plains (pp. 217-245).
Husson, D., Galbrun, B., Laskar, J., Hinnov, L. A., Thibault, N., Gardin, S., & Locklair, R. E. (2011). “Astronomical calibration of the Maastrichtian (late Cretaceous)”. Earth and Planetary Science Letters 305 (3): 328–340.doi:10.1016/j.epsl.2011.03.008
Johnson, K. R., Nichols, D. J., & Hartman, J. H. (2002). Hell Creek Formation: A 2001 synthesis. The Hell Creek Formation and the Cretaceous-Tertiary Boundary in the northern Great Plains: Geological Society of America Special Paper, 361, 503-510.

Ecosystem instability in the Late Triassic and the early evolution of dinosaurs.

The Late Triassic Petrified Forest Member of the Chinle Formation (Photo from AASG)

The Late Triassic Petrified Forest Member of the Chinle Formation (Photo from AASG)

Dinosaurs likely originated in the Middle Triassic and the first unequivocal dinosaur fossils are known from the late Carnian, but much about the geological and temporal backdrop of early dinosaur history remains poorly understood. A key question is why early dinosaurs were rare and species-poor at low paleolatitudes throughout the Late Triassic Period, for at least 30 million years after their origin.

The oldest well-dated identified dinosaurs are from the late Carnian (approx. 230 Ma) of the lower Ischigualasto Formation in northwestern Argentina. Similarly, the Santa Maria and Caturrita formations in southern Brazil preserve basal dinosauromorphs, basal saurischians, and early sauropodomorphs. In North America, the oldest dated occurrences of vertebrate assemblages with dinosaurs are from the Chinle Formation, but are less abundant and species rich compared to those from South America. The fact that those assemblages were at moderately high paleolatitudes during the Late Triassic, and the North American assemblages were near the paleoequator supports the hypotheses for a diachronous rise of dinosaurs across paleolatitudes (Irmis et al., 2011).

A reconstructed scene from the Late Triassic (Norian) of central Pangea. (Credit: image from Brusatte, S. L. 2008)

A reconstructed scene from the Late Triassic (Norian) of central Pangea. (Image from Brusatte, S. L. 2008, Dinosaurs, Quercus Publishing, London).

The Late Triassic is marked by a return to the “hothouse” condition of the Early Triassic, with two greenhouse crisis that may also have played a role in mass extinctions and long-term evolutionary trends (Retallack, 2013). The paleoclimate was a very arid with intense evaporation rate. Although there was at least one time of significant increase in rainfall known as the “Carnian Pluvial Event”, possibly related to the rifting of Pangea. Now, a multiproxy study  suggests  that fluctuating aridity in tropical and subtropical Pangea could explain why Triassic dinosaur faunas at low latitudes are restricted to small, slower growing carnivorous forms, whereas large-bodied herbivores, including sauropodomorph dinosaurs, are absent at low paleolatitudes during the Late Triassic “hothouse.” The palynomorphs recovered from sediments of the Chinle Formation indicate a major change from a seed fern-dominated (Alisporites) assemblage with accessory gymnosperms to one dominated by conifers and seed ferns in the lower portion of the Petrified Forest Member. In addition, the extensive charcoal record in the Petrified Forest Member provides evidence of paleo-environmental variability and aridity. 

 

References:

Jessica H. Whiteside, Sofie Lindström, Randall B. Irmis, Ian J. Glasspool, Morgan F. Schaller, Maria Dunlavey, Sterling J. Nesbitt, Nathan D. Smith, and Alan H. Turner. 2015. Extreme ecosystem instability suppressed tropical dinosaur dominance for 30 million years. PNAS: doi:10.1073/pnas.1505252112

Brusatte, S. L., Nesbitt, S. J., Irmis, R. B., Butler, R. J., Benton, M. J., and Norell, M. A. 2010. The origin and early radiation of dinosaurs. Earth-Science Reviews, 101, 68-100

Holz, M., Mesozoic paleogeography and paleoclimates – a discussion of the diverse greenhouse and hothouse conditions of an alien world, Journal of South American Earth Sciences (2015), doi: 10.1016/j.jsames.2015.01.001

Nesbitt,  S. J., Irmis,  R. B, Parker,  W. G. (2007) A critical re-evaluation of the Late Triassic di-nosaur taxa of North America. J Syst Palaeontology 5(2):209243

Sellwood, B.W. & Valdes, P.J. 2006. Mesozoic climates: General circulation models and the rock Record. Sedimentary Geology 190:269–287.

 

Response of marine ecosystems to the PETM.

Biotic change among foraminifera during and after the PETM. (From Speijer et al., 2012)

Biotic change during and after the PETM. (From Speijer et al., 2012)

The Paleocene-Eocene Thermal Maximum (PETM; 55.8 million years ago), was a short-lived (~ 200,000 years) global warming event attributed to a rapid rise in the concentration of greenhouse gases in the atmosphere. It was suggested that this warming was initiated by the melting of methane hydrates on the seafloor and permafrost at high latitudes. During the PETM, around 5 billion tons of CO2 was released into the atmosphere per year, and temperatures increased by 5 – 9°C. This event was accompanied by other large-scale changes in the climate system, for example, the patterns of atmospheric circulation, vapor transport, precipitation, intermediate and deep-sea circulation and a rise in global sea level.

Dinoflagellate cysts: Adnatosphaeridium robustum and Apectodinium augustum (From Sluijs and Brinkhuis, 2009)

Dinoflagellate cysts: Adnatosphaeridium robustum and Apectodinium augustum (From Sluijs and Brinkhuis, 2009)

The rapid warming at the beginning of the Eocene has been inferred from the widespread distribution of dinoflagellate cysts. One taxon in particularly, Apectodinium, spans the entire carbon isotope excursion (CIE) of the PETM. The distribution of Apectodinium is linked to high temperatures and increased food availability.

The most disruptive impact during the PETM was likely the exceptional ocean acidification and the rise of the calcite dissolution depth, affecting marine organisms with calcareous shells (Zachos et al., 2005). When CO2 dissolves in seawater, it produce carbonic acid. The carbonic acid dissociates in the water releasing hydrogen ions and bicarbonate. The formation of bicarbonate then removes carbonate ions from the water, making them less available for use by organisms.

Nannofossil abundance changes during the PETM. (From Kump, 2009.)

Nannofossil abundance changes during the PETM. (From Kump, 2009.)

The PETM onset is also marked by the largest deep-sea mass extinction among calcareous benthic foraminifera (including calcareous agglutinated taxa) in the last 93 million years. Similarly, planktonic foraminifera communities at low and high latitudes show reductions in diversity, while larger foraminifera are the most common constituents of late Paleocene–early Eocene carbonate platforms.

The response of most marine invertebrates (mollusks, echinoderms, brachiopods) to paleoclimatic change during the PETM is poorly documented.

Coccolithus bownii and Toweius pertusus

Coccolithus bownii and Toweius pertusus (Adapted from Bown and Pearson, 2009)

The PETM is also associated with dramatic changes among the calcareous plankton,characterized by the appearance of transient nanoplankton taxa of heavily calcified forms of Rhomboaster spp., Discoaster araneus, and D. anartios as well as Coccolithus bownii, a more delicate form.

The combination of global warming and the release of large amounts of carbon to the ocean-atmosphere system during the PETM has encouraged analogies to be drawn with modern anthropogenic climate change. The current rate of the anthropogenic carbon input  is probably greater than during the PETM, causing a more severe decline in ocean pH and saturation state. Also the biotic consequences of the PETM were fairly minor, while the current rate of species extinction is already 100–1000 times higher than would be considered natural. This underlines the urgency for immediate action on global carbon emission reductions.

Comparison of the effects of anthropogenic emissions (total of 5000 Pg C over 500 years) and PETM carbon release (3000 Pg C over 6 kyr) on the surface ocean saturation state of calcite. From Zeebe, 2013

Comparison of the effects of anthropogenic emissions (total of 5000 Pg C over 500 years) and PETM carbon release (3000 Pg C over 6 kyr) on the surface ocean saturation state of calcite. From Zeebe, 2013

 

References:

Maria Rose Petrizzo, The onset of the Paleocene–Eocene Thermal Maximum (PETM) at Sites 1209 and 1210 (Shatsky Rise, Pacific Ocean) as recorded by planktonic foraminifera, Marine Micropaleontology, Volume 63, Issues 3–4, 13 June 2007, Pages 187-200

Zeebe RE and Zachos JC. 2013 Long-term legacy ofmassive carbon input to the Earth system: Anthropocene versus Eocene. Phil Trans R Soc A 371: 20120006. http://dx.doi.org/10.1098/rsta.2012.0006.

Wright JD, Schaller MF (2013) Evidence for a rapid release of carbon at the Paleocene-Eocene thermal maximum. Proc Natl Acad Sci USA 110(40):15908–15913.

Kump, L.R., T.J. Bralower, and A. Ridgwell. 2009. Ocean acidification in deep time. Oceanography 22(4):94–107, http://dx.doi.org/10.5670/oceanog.2009.100

Raffi, I. and de Bernardi, B.: Response of calcareous nannofossils to the Paleocene-Eocene Thermal Maximum: observations on composition, preservation and calcification in sediments from ODP Site 1263 (Walvis Ridge – SW Atlantic), Mar. Micropaleontol., 69, 119–138, 2008.

Robert P. SPEIJER, Christian SCHEIBNER, Peter STASSEN & Abdel-Mohsen M. MORSI; Response of marine ecosystems to deep-time global warming: a synthesis of biotic patterns across the Paleocene-Eocene thermal maximum (PETM), Austrian Journal of Earth Sciences. Vienna. 2012. Volume 105/1.