The Megafauna extinction in South América.

 

Megatherium americanum Cuvier, 1796. Museo Argentino de La Plata.

Megatherium americanum Cuvier, 1796. Museo Argentino de La Plata.

During the Pleistocene and the early Holocene,  most of the terrestrial megafauna became extinct. It was a deep global-scale event. The extinction was notably more selective for large-bodied animals than any other extinction interval in the last 65 million years. Multiple explanatory hypotheses have been proposed for this event: climatic change, over hunting, habitat alteration, and the introduction of a new disease. Traditionally, the focus of research and debate has been on the Eurasian and North American extinctions. In North America, two mammalian orders (Perissodactyla, Proboscidea) were eliminated completely. At the species level, the extinction was total for mammals larger than 1000 kg and greater than 50% for size classes between 1000 and 32 kg. Early observations confirm that extinctions could be severe even in relatively climatically stable regions where the vegetation changed little. In South America the event was  more severe, with the loss of 50 megafaunal genera. Three orders of mammals disappeared (Notoungulata, Proboscidea, Litopterna), as did all megafaunal xenarthrans and at the species level, the extinction was total for mammals larger than 320 kg (Koch and Barnosky, 2006).

“Descuartizando un gliptodonte. Escenas de la vida del hombre primitivo” (Quartering a glyptodont. Scenes from the life of primitive man). Painting by Luis de Servi. Museo de la Plata).

“Descuartizando un gliptodonte. Escenas de
la vida del hombre primitivo” (Quartering a
glyptodont. Scenes from the life of primitive man). Painting by Luis de Servi, Museo de la Plata.

Before the Great American Biotic Interchange, about 3 million years ago, the largest mammals in South America were mainly endemic notoungulates, litopterns and xenarthrans. But, during the interchange, many other megamammals and large mammals arrived to South America. The late Pleistocene in this region is first characterized by a rapid cooling. During the Pleistocene-Holocene transition pollen sequences suggest a change to sub-humid climatic conditions. In addition to rapid climate change, the extinctions are seen as the result of habitat loss, reduced carrying capacity for herbivores, resource fragmentation or disturbances in the co-evolutionary equilibrium between plants, herbivores, and carnivores. The death event of the gomphothere population in Águas de Araxá (Brazil)  about 55,000 years ago, is probably an example of individuals that were suffering with the climate changes during the Late Pleistocene.

Paleontological and archaeological data indicate that extinctions seem more common after the human arrival and during the rapid climate change between 11.200 and 13.500 years. This pattern suggests that a synergy of human impacts and rapid climate change—analogous to what is happening today — may enhance extinction probability (Prado et al., 2015).

 

References:

J.L. Prado et al. (2015). “Megafauna extinction in South America: A new chronology for the Argentine Pampas.” Palaeogeography, Palaeoclimatology, Palaeoecology 425: 41–49

Alroy, John. (2001). “A Multispecies Overkill Simulation of the End-Pleistocene Megafaunal Mass Extinction.” Science 292:1893-1896

Koch PL, Barnosky AD (2006) Late Quaternary extinctions: State of the debate. Annu Rev Ecol Evol Syst 37:215–250.

Prescott GW, Williams DR, Balmford A, Green RE, Manica A. (2012) Quantitative global analysis of the role of climate and people in explaining late Quaternary megafaunal extinctions. Proc. Natl Acad. Sci. USA 109,45274531

Barnosky AD, Lindsey EL.(2010) Timing of Quaternary megafaunal extinction in South America in relation to human arrival and climate change

 

Remembering Mary Anning.

BECHE_Mary_Annings

Sketch of Mary Anning by Henry De la Beche. From Wikimedia Commons.

Mary Anning, ‘the greatest fossilist the world ever knew’, died of breast cancer on 9 March, 1847, at the age of 47. She was buried in the cemetery of St. Michaels. In the last decade of her life, Mary received  three accolades. The first was an annuity of £25, in return for her many contributions to the science of geology. The second was in 1846, when the geologists of the Geological Society of London organized a further subscription for her. The third accolade was her election, in July 1846, as the first Honorary Member of the new Dorset County Museum in Dorchester (Torrens, 1995). After her death, Henry de la Beche, Director of the Geological Survey and President of the Geological Society of London, wrote a very affectionate obituary published in the Quarterly Journal of the Geological Society on February 14, 1848, the only case of a non Fellow who received that honour. In his presidential address, de la Beche summarized Mary’s work: “I cannot close this notice of our losses by death without adverting to that of one, who though not placed among even the easier classes of society, but who had to earn her daily bread by her labour, yet contributed by her talents and untiring researches in no small degree to our knowledge of the great Enalio-saurians, and other forms of organic life entombed in the vicinity of Lyme Regis. MARY ANNING was the daughter of Richard Anning, a cabinet-maker of that town, and was born in May, 1799. … From her father, who appears to have been the first to collect and sell fossils in that neighbourhood, she learnt to search for and obtain them. Her future life was dedicated to this pursuit, by which she gained her livelihood; and there are those among us in this room who know well how to appreciate the skill she employed (from her knowledge of the various works as they appeared on the subject), in developing the remains of the many fine skeletons of Ichthyosauri and Plesiosauri, which without her care would never have presented to comparative anatomists in the uninjured form so desirable for their examinations…”

Mary Anning's Window, St. Michael's Church. From Wikimedia Commons.

Mary Anning’s Window, St. Michael’s Church. From Wikimedia Commons.

In February 1850 Mary was honoured by the unveiling of a new window in the parish church at Lyme, funded through another subscription among the Fellows of the Geological Society of London, with the following inscription: “This window is sacred to the memory of Mary Anning of this parish, who died 9 March AD 1847 and is erected by the vicar and some members of the Geological Society of London in commemoration of her usefulness in furthering the science of geology, as also of her benevolence of heart and integrity of life.”

In 1865, Charles Dickens wrote an article about Mary Anning’s life in his literary magazine “All the Year Round”, where emphasised the difficulties she had overcome: “Her history shows what humble people may do, if they have just purpose and courage enough, toward promoting the cause of science. The inscription under her memorial window commemorates “her usefulness in furthering the science of geology” (it was not a science when she began to discover, and so helped to make it one), “and also her benevolence of heart and integrity of life.” The carpenter’s daughter has won a name for herself, and has deserved to win it.”

References:

Davis, Larry E. (2012) “Mary Anning: Princess of Palaeontology and Geological Lioness,”The Compass: Earth Science Journal of Sigma Gamma Epsilon: Vol. 84: Iss. 1, Article 8.

Hugh Torrens, Mary Anning (1799-1847) of Lyme; ‘The Greatest Fossilist the World Ever Knew’, The British Journal for the History of Science Vol. 28, No. 3 (Sep., 1995), pp. 257-284. Published by: Cambridge University Press.

De la Beche, H., 1848a. Obituary notices. Quarterly Journal of the Geological Society of London, v. 4: xxiv–xxv.

Dickens, C., 1865. Mary Anning, the fossil finder. All the Year Round, 13 (Feb 11): 60–63.

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.

Darwin, Owen and the ‘London specimen’.

Portrait of Charles Darwin painted by George Richmond (1840)

Portrait of Charles Darwin painted by George Richmond (1840)

The Archaeopteryx story began in  the summer of 1861, two years after the publication of the first edition of Darwin’s Origin of Species, when workers in a limestone quarry in Germany discovered the impression of a single 145-million-year-old feather. On August 15, 1861, German paleontologist Hermann von Meyer wrote a letter to the editor of the journal Neues Jahrbuch für Mineralogie, Geologie und Palaeontologie, where he made the first description of the fossil. Later, on September 30, 1861, he wrote a new letter:  “I have inspected the feather from Solenhofen closely from all directions, and that I have come to the conclusion that this is a veritable fossilisation in the lithographic stone that fully corresponds with a birds’ feather. I heard from Mr. Obergerichtsrath Witte, that the almost complete skeleton of a feather-clad animals had been found in the lithographic stone. It is reported to show many differences with living birds. I will publish a report of the feather I inspected, along with a detailed illustration. As a denomination for the animal I consider Archaeopteryx lithographica to be a fitting name”. 

The near complete fossil skeleton found in a Langenaltheim quarry near Solnhofen – with clear impressions of wing and tail feathers –  was examined by Andreas Wagner, director of the Paleontology Collection of the State of Bavaria in Germany. He reached the conclusion that the fossil was a reptile, and gave it the name Griphosaurus. He wrote: “Darwin and his adherents will probably employ the new discovery as an exceedingly welcome occurrence for the justification of their strange views upon the transformations of animals.”

Archaeopteryx lithographica, Archaeopterygidae, Replica of the London specimen; Staatliches Museum für Naturkunde Karlsruhe, Germany. From Wikimedia Commons

Archaeopteryx lithographica, Archaeopterygidae, Replica of the London specimen; Staatliches Museum für Naturkunde Karlsruhe, Germany. From Wikimedia Commons

The fossil was later bought by the British Museum of Natural History in London. Richard Owen, head of the Museum, was the first to describe the fossil and named it Archaeopteryx macrura, arguing that its identity with Meyer’s specimen could not be satisfactorily established (Owen 1862a, p. 33 n.). This fossil is also know as the London specimen. Owen, a fervent opponent of the evolutionary theory of Charles Darwin, was convinced that all animals within each larger systematic group were only variations of a single theme, the ‘ideal archetype’.

Hugh Falconer, a Scottish geologist and paleontologist, saw the Archaeopteryx as a valid “transitional” fossil. At that time, he was in  a dispute with Owen, and pointed out that Owen’s description of the Archaeopteryx had missed some essential elements. On January 3, 1863, he wrote a letter to Darwin about the significance of this fossil:  “It is a much more astounding creature—than has entered into the the conception of the describer—who compares it with the Raptores & Passeres & Gallinaceæ, as a round winged (like the last) `Bird of flight.’ It actually had at least two long free digits to the fore limb—and those digits bearing claws as long and strong as those on the hind leg. Couple this with the long tail—and other odd things,—which I reserve for a jaw—and you will have the sort of misbegotten-bird-creature—the dawn of an oncoming conception `a la Darwin.”

Darwin answered that letter on January 20, 1863, and commented about Owen’s mistake: “Has God demented Owen, as a punishment for his crimes, that he should overlook such a point?. “

Richard Owen stands next to the largest of all moa, Dinornis maximus (now D. novaezealandiae). From Wikimedia Commons.

Richard Owen stands next to the largest of all moa, Dinornis maximus (now D. novaezealandiae). From Wikimedia Commons.

In later editions of The Origin of Species, Darwin mention the Archaeopteryx: “That strange bird, Archaeopteryx, with a long lizardlike tail, bearing a pair of feathers on each joint, and with its wings furnished with two free claws . . . Hardly any recent discovery shows more forcibly than this, how little we as yet know of the former inhabitants of the world.”

 

References:

MEYER v., H. (1861): Archaeopterix lithographica (Vogel-Feder) und Pterodactylus von Solenhofen. Neues Jahrbuch fur Mineralogie, Geognosie, Geologie und Petrefakten-Kunde. 6: 678-679

Falconer, H. letter of January 3, 1863 to Charles Darwin; The Correspondence of Charles Darwin Vol. 11, edited by F. Furkhardt, DM Porter, S. A Dean, J. R Tophan, and S. Wilmot.  Cambridge University Press, Cambridge, 1999

OWEN, R. (1863): On the Archaeopteryx of von Meyer, with a description of the fossil remains of a long-tailed species, from the lithographic stone of Solenhofen. Philosophical Transactions of the Royal Society of London 153: 33-47

Prothero, D. R.  Evolution: What the Fossils Say and Why it Matters. Columbia University Press, New York, 2007.

Peter Wellnhofer, A short history of research on Archaeopteryx and its relationship with dinosaurs, Geological Society, London, Special Publications, 343:237-250, doi:10.1144/SP343.14, 2010

 

Links:

Darwin Correspondence Project http://www.darwinproject.ac.uk/entry-3899

 

The Triassic Paleoclimate.

Early to Middle Triassic (240Ma) From Wikimedia Commons.

Early to Middle Triassic (240Ma) From Wikimedia Commons.

There are three basic states for Earth climate: Icehouse, Greenhouse (subdivided into Cool and Warm states), and Hothouse (Kidder & Worsley, 2010). The “Hothouse” condition is relatively short-lived and is consequence from the release of anomalously large inputs of CO2 into the atmosphere during the formation of Large Igneous Provinces (LIPs), when atmospheric CO2 concentrations may rise above 16 times (4,800 ppmv), while the “Icehouse” is characterized by polar ice, with alternating glacial–interglacial episodes in response to orbital forcing. The ‘Cool Greenhouse” displays  some polar ice and alpine glaciers,  with global average temperatures between 21° and 24°C. Finally, the ‘Warm Greenhouse’ lacked of any polar ice, and global average temperatures might have ranged from 24° to 30°C.

The rifting of Pangea during the Mesozoic modified the paleoposition and shoreline configuration of the land masses and generated huge epicontinental seas. This altered significantly the oceanic circulation and caused profound consequences for paleoclimates and for the evolution of life.

Siberian flood-basalt flows in Putorana, Taymyr Peninsula.(From Earth science: Lethal volcanism, Paul B. Wignall, 2011,  Nature 477, 285–286 )

Siberian flood-basalt flows in Putorana, Taymyr Peninsula.(From Earth science: Lethal volcanism, Paul B. Wignall, 2011, Nature 477, 285–286 )

During the Late Permian, massive volcanic eruptions in Siberia covered more than 2 millions of km 2 with lava flows, releasing more carbon in the atmosphere and high amounts of fluorine and chlorine increasing the climatic instability, which means that the Mesozoic began under extreme hothouse conditions.

The Early Triassic transition is marked by a moderate oxygen depletion and by mass extinction of glossopterids, gigantopterids, tree lycopsids and cordaites, as major contributors to coal deposits in the southern hemisphere. That was accompanied  by unusually anoxic swamp soils (Retallack, 2013). The rifting of Gondwana began during the Early Triassic with the opening of the Indian Ocean and the separation of India and Australia, that modified shoreline configuration and enhanced platform areas inducing intense marine biodiversification. It was suggested that during that time there was a moderate oxygen depletion that caused the low body size of the amphibian and reptilian life-forms found in those rocks.

Fossil of Lystrosaurus, one of the few survivors of the Late Permian shows a variety of adaptations to low oxygen atmosphere. It was by far the most common terrestrial vertebrate of the Early Triassic (Staatliches Museum für Naturkunde Stuttgart; from Wikimedia Commons).

Fossil of Lystrosaurus, one of the few survivors of the Late Permian shows a variety of adaptations to low oxygen atmosphere. It was by far the most common terrestrial vertebrate of the Early Triassic (Staatliches Museum für Naturkunde Stuttgart; from Wikimedia Commons).

By the Mid Triassic, global temperature was still high – between 20°C and 30°C – and the atmospheric CO2 began to increase. There are reported episodes of humid climate registered by fossil vertebrates from the Molteno Formation in South Africa, and from Los Rastros Formation in central western Argentina.

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. Massive volcanic eruptions from a large region known as the Central Atlantic Magmatic Province (CAMP) release huge amounts of lava and gas, including carbon dioxide, sulfur and methane into the atmosphere which led to global warming and acidification of the oceans.

Light-microscope photographs of Classopollis pollen from the Late Triassic (Image adapted from Kürschner et al., 2013).

Light-microscope photographs of Classopollis pollen from the Late Triassic (Image adapted from Kürschner et al., 2013).

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. In the Southern Hemisphere, the vegetation turnover consisted in the replacement to Alisporites (corystosperm)-dominated assemblage to a Classopollis (cheirolepidiacean)-dominated one.

Most of scientists agree that the extinctions were caused by massive volcanic activity associated with the break-up of the super-continent Pangaea. 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).

References:

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

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

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

Retallack, G.J. 2009. Greenhouse crises of the past 300 million years. Geological Society of America Bulletin, 121:1441–1455.

The Great Acceleration.

 

Iron and Coal, 1855–60, by William Bell Scott illustrates the central place of coal and iron working in the industrial revolution (From Wikimedia Commons)

Iron and Coal, 1855–60, by William Bell Scott illustrates the central place of coal and iron working in the industrial revolution (From Wikimedia Commons)

During a meeting of the International Geosphere-Biosphere Programme (IGBP) celebrated in Mexico, in 2000, the Vice-Chair of IGBP, Paul Crutzen, proposed the use of the term Anthropocene to designate the last three centuries of human domination of earth’s ecosystems, and to mark the end of the current Holocene geological epoch. He suggested that the start date of the Anthropocene must be placed near the end of the 18th century, about the time that the industrial revolution began, and noted that such a start date would coincide with the invention of the steam engine by James Watt in 1784.

Although there is no agreement on when the Anthropocene started, researchers accept that the Anthropocene is a time span marked by human interaction with Earth’s biophysical system. It has been defined, primarily, by significant and measurable increases in anthropogenic greenhouse gas emissions from ice cores, and other geologic features including synthetic organic compounds and radionuclides. Eugene Stoermer, in an interview in 2012, proposed that the geological mark for the Anthropocene was the isotopic signature of the first atomic bomb tests. Hence,  Anthropocene deposits would be those that may include the globally distributed primary artificial radionuclide signal (Zalasiewicz et al, 2015).

 

anthropocene

Alternative temporal boundaries for the Holocene–Anthropocene boundary (calibrated in thousand of years before present) From Smith 2013

 

Human activity is a major driver of the dynamics of Earth system. After the World War II, the impact of human activity on the global environment dramatically increased. This period associated with very rapid growth in human population, resource consumption, energy use and pollution, has been called the Great Acceleration.

During the Great Acceleration, the atmospheric CO2 concentration grew, from 311 ppm in 1950 to 369 ppm in 2000 (W. Steffen et al., 2011). About one third of the carbon dioxide released by anthropogenic activity is absorbed by the oceans. When CO2 dissolves in seawater, it produce carbonic acid. The carbonic acid dissociates in the water releasing hydrogen ions and bicarbonate. Then, the formation of bicarbonate removes carbonate ions from the water, making them less available for use by organisms. Ocean acidification affects the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus in the ocean, and will directly impact in a wide range of marine organisms that build shells from calcium carbonate, like planktonic coccolithophores, molluscs,  echinoderms, corals, and coralline algae.

Clastic plastiglomerate containing molten plastic and basalt and coral fragments (Image adapted from P. Corcoran et al., 2014)

Clastic plastiglomerate containing molten plastic and basalt and coral fragments (Image adapted from P. Corcoran et al., 2013)

One important marker for the future geological record is a new type of rock formed by anthropogenically derived materials. This type of rock has been named plastiglomerate, and has been originally described on Kamilo Beach, Hawaii. This anthropogenically influenced material has great potential to form a marker horizon of human pollution, signaling the occurrence of the Anthropocene epoch (Corcoran et al., 2013).

Climate change, shifts in oceanic pH, loss of biodiversity and widespread pollution have all been identified as potential planetary tipping point. Since the industrial revolution, the wave of animal and plant extinctions that began with the late Quaternary has accelerated. Calculations suggest that the current rates of extinction are 100–1000 times above normal, or background levels. We are in the midst of  the so called “Sixth Mass Extinction”.

Dealing with the transition into the Anthropocene requires careful consideration of its social, economic and biotic effects. In his master book L’Evolution Créatrice (1907), French philosopher Henri Bergson, wrote:  “A century has elapsed since the invention of the steam engine, and we are only just beginning to feel the depths of the shock it gave us.”

 

References:

Will Steffen, Wendy Broadgate, Lisa Deutsch, Owen Gaffney, and Cornelia Ludwig. The trajectory of the Anthropocene: The Great Acceleration. The Anthropocene Review, January 16, 2015 DOI: 10.1177/2053019614564785

Jan Zalasiewicz et al. When did the Anthropocene begin? A mid-twentieth century boundary level is stratigraphically optimal. Quaternary International, published online January 12, 2015; doi: 10.1016/j.quaint.2014.11.045

Smith, B.D., Zeder, M.A., The onset of the Anthropocene. Anthropocene (2013),http://dx.doi.org/10.1016/j.ancene.2013.05.001

Ellis, E.C., 2011. Anthropogenic transformation of the terrestrial biosphere. Philosophical Transactions of the Royal Society A 369, 1010–1035.

 

A brief introduction to the origin of Birds.

Archaeopteryx lithographica, specimen displayed at the Museum für Naturkunde in Berlin. (From Wikimedia Commons)

Archaeopteryx lithographica, specimen displayed at the Museum für Naturkunde in Berlin. (From Wikimedia Commons)

Birds originated from a theropod lineage more than 150 million years ago. Their evolutionary history is one of the most enduring and fascinating debates in paleontology. In recent years, several discovered fossils of theropods and early birds have filled the morphological, functional, and temporal gaps along the line to modern birds. The discovered fossils demonstrate that distinctive bird characteristics such as feathers, flight, endothermic physiology, unique strategies for reproduction and growth, and a novel pulmonary system have a sequential and stepwise transformational pattern, with many arising early in dinosaur evolution, like the unusually crouched hindlimb for bipedal locomotion,the furcula and the “semilunate” carpal that appeared early in the theropod lineage (Allen et al., 2013; Xu et al., 2014).  Also, the discovery of Mahakala – a basal dromaeosaurid dinosaur named for one of the eight protector deities in Tibetan Buddhism – suggests that extreme miniaturization and laterally movable arms necessary for flapping flight are ancestral for paravian theropods. In contrast, a number of basal birds resemble theropods in many features.

Sin título

Sciurumimus (A); the basal coelurosaur Sinosauropteryx (B) with filamentous feathers; the deinonychosaurs Anchiornis (C) and Microraptor (D). Adapted from Xu et al., 2014.

Anatomical features like aspects of egg shape, ornamentation, microstructure, and porosity of living birds trace their origin to the maniraptoran theropods, such as oviraptorosaurs and troodontids. In addition, some preserving brooding postures, are known for four oviraptorosaurs, two troodontids, a dromaeosaur, and one basal bird providing clear evidence for parental care of eggs.

In birds, particularly their forebrains, are expanded relative to body size. The volumetric expansion of the avian endocranium began relatively early in theropod evolution. Archaeopteryx lithographica is volumetrically intermediate between those of more basal theropods and crown birds (Balanoff et al., 2013). The digital brain cast of Archaeopteryx also present an indentation that could be from the wulst, a neurological structure present in living birds used in information processing and motor control with two primary inputs: somatosensory and visual. Birds also exhibit the most advanced vertebrate visual system, with a highly developed ability to distinguish colors over a wide range of wavelengths.

Reconstruction of pulmonary components [cervical air-sac system (green), lung (orange), and abdominal air-sac system (blue)] in the theropod Majungatholus (From Xu et al., 2014)

Reconstruction of pulmonary components [cervical air-sac system (green), lung (orange), and abdominal air-sac system (blue)] in the theropod Majungatholus (From Xu et al., 2014)

Feathers were once considered to be unique avialan structures. The megalosaurus Sciurumimus, the compsognathus Sinosauropteryx, and a few other dinosaurs, document the appearance of primitive feathers. More recent studies indicated that non avian dinosaurs, as part of Archosauria, possessed the entirety of the known non keratin protein-coding toolkit for making feathers (Lowe et al., 2015)

The evolution of flight involved a series of adaptive changes at the morphological and molecular levels,like the fusion and elimination of some bones and the pneumatization of the remaining ones. The extensive skeletal pneumaticity in theropods such as Majungasaurus demonstrates that a complex air-sac system and birdlike respiration evolved in birds’ theropod ancestors. The increased metabolism associated with homeothermy and powered flight requires an efficient gas exchange process during pulmonary ventilation. Moreover, recent anatomical and physiological studies show that alligators, and monitor lizards exhibit respiratory systems and unidirectional breathing akin to those of birds, which indicate that unidirectional breathing is a primitive characteristic of archosaurs or an even more inclusive group with the complex air-sac system evolving later within Archosauria.

The earliest diversification of extant birds (Neornithes) occurred during the Cretaceous period and after the mass extinction event at the Cretaceous-Paleogene (K-Pg) boundary, the Neoaves, the most diverse avian clade, suffered a rapid global expansion and radiation. Today, with more than 10500 living species, birds are the most species-rich class of tetrapod vertebrates.

 

References:

Xing Xu, Zhonghe Zhou, Robert Dudley, Susan Mackem, Cheng-Ming Chuong, Gregory M. Erickson, David J. Varricchio, An integrative approach to understanding bird origins, Science, Vol. 346 no. 6215, DOI: 10.1126/science.1253293.

Puttick, M. N., Thomas, G. H. and Benton, M. J. (2014), HIGH RATES OF EVOLUTION PRECEDED THE ORIGIN OF BIRDS. Evolution, 68: 1497–1510. doi: 10.1111/evo.12363 A.

H. Turner, D. Pol, J. A. Clarke, G. M. Erickson, M. A. Norell, A basal dromaeosaurid and size evolution preceding avian flight. Science 317, 1378–1381 (2007).pmid: 17823350.

V. Allen, K. T. Bates, Z. Li, J. R. Hutchinson, Linking the evolution of body shape and locomotor biomechanics in bird-line archosaurs. Nature 497, 104–107 (2013). doi: 10.1038/nature12059; pmid: 23615616

A. M. Balanoff, G. S. Bever, T. B. Rowe, M. A. Norell, Evolutionary origins of the avian brain. Nature 501, 93–96 (2013). doi: 10.1038/nature12424; pmid: 23903660

M. S. Y. Lee, A. Cau, D. Naish, G. J. Dyke, Sustained miniaturization and anatomical innovation in the dinosaurian ancestors of birds. Science 345, 562–566 (2014). doi: 10.1126/science.1252243; pmid: 25082702

Craig B. Lowe, Julia A. Clarke, Allan J. Baker, David Haussler and Scott V. Edwards, Feather Development Genes and Associated Regulatory Innovation Predate the Origin of Dinosauria, Mol Biol Evol (2015) 32 (1): 23-28. doi: 10.1093/molbev/msu309

A Christmas Carol: Dickens and the Little Ice Age

Scrooge's third visitor,  by John Leech. London: Chapman & Hall, 1843. First edition. (From Wikimedia Commons)

Scrooge’s third visitor, by John Leech, 1843. (From Wikimedia Commons)

Charles Dickens was born on 7 February 1812. He had only 31, when began to write A Christmas Carol in September 1843. The book was published on 19 December 1843. The novella tells the story of  Ebenezer Scrooge, a bitter old man who finds salvation through the visits of the three Ghosts of Christmas (Ghost of Christmas Past, Ghost of Christmas Present, and Ghost of Christmas Yet to Come). Dickens divided the story in five “staves”, where he describes the brutal winter and the horrors of social inequality. Scrooge is considered to be the very embodiment of winter: “No wind that blew was bitterer than he, no falling snow was more intent upon its purpose, no pelting rain less open to entreaty.”

Dickens describe the severe weather in many parts of the book: “…and they stood in the city streets on Christmas morning, where (for the weather was severe) the people made a rough, but brisk and not unpleasant kind of music in scraping the snow from the pavement in front of their dwellings, and from the tops of their houses, whence it was mad delight to the boys to see it come plumping down into the road below, and splitting into artificial little snow-storms.

A Frost Fair on the Thames at Temple Stairs by Abraham Danielsz Hondius (Abraham de Hondt), circa 1684 (From Wikimedia Commons)

Dickens grew up during the coldest years of the Little Ice Age, between 1805 to 1820. Many of the Christmas stories that are popular today were written during that period and winter landscapes were commonly depicted by artists like Pieter Bruegel, Hendrick Avercamp,  and Abraham Hondius.

The Little Ice Age (LIA) was a period that extends from the early 14th century through the mid-19th century, during which the Northern Hemisphere suffered from severe and prolonged cold winters. The period between 1600 and 1800 marks the height of the Little Ice Age.

Volcanoes are a possible cause for the LIA. The Tambora eruption on April 10, 1815, released two million tons of debris and  sulphur components into the atmosphere.  The following year was known as “the year without summer”. Charles Lyell describes the eruption in his Principles of Geology: “Great tracts of land were covered by lava, several streams of which, issuing from the crater of the Tomboro Mountain, reached the sea. So heavy was the fall of ashes, that they broke into the Resident’s house at Bima, forty miles east of the volcano, and rendered it, as well as many other dwellings… The darkness occasioned in the daytime by the ashes in Java was so profound, that nothing equal to it was ever witnessed in the darkest night.”

Reconstructed depth of the Little Ice Age varies between different studies  (From Wikimedia Commons)

Reconstructed depth of the Little Ice Age varies between different studies (From Wikimedia Commons)

Dickens revitalized the traditions of Christmas and to Victorian England, Dickens was Christmas. But he also contributed to the popularity of geology with the creation of ideas and images for public consumption, such as he did in Bleak House, with the description of the streets of London where ancient lizards roamed, and volcanoes and quakes shocked the earth.

 

References:

Charles Dickens, A Christmas Carol, Chapman & Hall, 1843.

BOER, de J.Z. & SANDERS, D.T. (2002): Volcanoes in Human History: The Far-Reaching Effects of Major Eruptions. Princeton University Press: 295

Brian M. Fagan, The Little Ice Age: How Climate Made History 1300-1850 (2001), Basic Books.

Buckland, Adelene , ‘“The Poetry of Science”: Charles Dickens, Geology and Visual and Material Culture in Victorian London’, Victorian Literature and Culture, 35 (2007), 679–94 (p. 680).

 

Early studies of South American Fossils.

 

Megatherium americanum, MACN.

Megatherium americanum on display at the MACN.

The first notices of South American fossils were reported by early Spanish explorers. These fossils were interpreted as the remains of an ancestral race of giant humans erased from the face of the Earth by a divine intervention. In the second half of the sixteenth century, Fray Reginaldo de Lizarraga (1540-1609), referred in his writings to those “graves of giants” found in Córdoba, Argentina. In 1760, the English Jesuit Thomas Falkner, discovered the first remains of a glyptodon. He wrote: “I myself found the shell of an animal, composed of little hexagonal bones, each bone an inch in diameter at least; and the shell was near three yards over. It seemed in all respects, except it’s size, to be the upper part of the shell of the armadillo; which, in these times, is not above a span in breadth.” (1774, p. 54-55).  However, the first formal description of a gliptodonte was performed in 1838, by English naturalist Sir Richard Owen.

In 1766, by order of Juan de Lezica y Torrezuri (1709-1783), Mayor of Buenos Aires, fossil remains recovered in Arrecifes, were sent to Spain. Previously to the trip, three surgeons, Matías Grimau, Juan Parán and Ángel Casteli, analyzed the bones to determine if these were humans. In Spain, scholars of the Real Academia de la Historia, stated that the remains were not human, conjecturing that those bones resembled those of a quadruped, and perhaps an Elephant. The scholars were right, the remains in question belonged to mastodons, extinct relatives of elephants.

Portrait of  Manuel Torres by Francisco Fortuny.

Portrait of Manuel Torres by Francisco Fortuny.

In 1787, Fray Manuel de Torres found near the banks of the Lujan River,  the skeletal remains of a gigantic mammal. He carefully documented this extraordinary finding. On April 29, 1787, he sent a letter to the Viceroy Francisco Nicolás Cristóbal del Campo, Marqués de Loreto, with details of his work. In 1789, the specimen was sent to the Cabinet of Natural History in Madrid where was illustrated by Juan Bautista Brú de Ramón (1740-1799). This is the real starting point of paleontological studies in the Rio de la Plata.

In 1795, Philippe-Rose Roume (1724-1804), a French officer, sent Bru’s illustrations to the Institut de France, with a little description of the skeleton. A year later, George Cuvier (1769-1832) published the first scientific work on a South American fossil. He assigned the fossil the scientific name Megatherium americanum. Cuvier also studied fossils from Bolivia, Chile, Colombia, and Ecuador, among which he recognized three morphotypes, designated informally as “mastodonte a dents étroites”, “mastodonte Cordillierès” and “mastodonte humboldien”. Cuvier (1823) later formally named them Mastodon angustidens, Mastodon andium and Mastodon humboldti, respectively (Fernicola et al, 2009).

References:

PASQUALI, Ricardo C  y  TONNI, Eduardo P. Los hallazgos de mamíferos fósiles durante el período colonial en el actual territorio de la Argentina. Ser. correl. geol.[online]. 2008, n.24 [citado  2014-12-08], pp. 35-43 . Disponible en: . ISSN 1666-9479.

Fernicola, J. C., Vizcaino, F, and de Iuliis, G. (2009), ‘The Fossil Mammals collected by Charles Darwin in South America during his travels on board the HMS Beagle’, Revista de la Asociatión Geológica Argentina. 64 (1), 147-59.

Fariña, Richard A.; Vizcaíno, Sergio F.; De Iuliis, Gerry (2013). Megafauna. Giant Beasts of Pleistocene South America. Indiana University Press.

The Anthropocene defaunation process.

 

Richard Owen stands next to the largest of all moa, Dinornis maximus (now D. novaezealandiae). From Wikimedia Commons.

Richard Owen stands next to the largest of all moa, Dinornis maximus (now D. novaezealandiae). From Wikimedia Commons.

In 2000,  Paul Crutzen proposed use the term Anthropocene to designate the last two hundred years of human history and to mark the end of the current Holocene geological epoch. Although there is no agreement on when the Anthropocene started, it has been defined, primarily, by significant and measurable increases in anthropogenic greenhouse gas emissions from ice cores and other geologic features including synthetic organic compounds, radionuclides and ocean acidification.

Another marker for the Anthropocene is the current biodiversity crisis. The term defaunation was created to designate the declining of top predators and herbivores triggered by human activity, that results in a lack of agents that control the components of the ecosystems vegetation.

Global population declines in mammals and birds represented in numbers of individuals per 10,000 km2 for mammals and birds (From Dirzo et al., 2014)

Global population declines in mammals and birds (From Dirzo et al., 2014).

Since the industrial revolution, the wave of animal and plant extinctions that began with the late Quaternary has accelerated. Calculations suggest that the current rates of extinction are 100–1000 times above normal, or background levels. We are in the midst of  the so called “Sixth Mass Extinction”.

Although anthropogenic climate change is playing a growing role, the primary drivers of modern extinctions seem to be habitat loss, human predation, and introduced species (Briggs, 2011). The same drivers that contributed to ancient megafaunal and island extinctions.

SConsequences of defaunation (From Dirzo et al., 2014)

The consequences of defaunation (From Dirzo et al., 2014)

 

One of the most famous and well-documented extinctions come from Madagascar. Pygmy hippos, giant tortoises, and large lemurs went extinct due to human hunting or habitat disturbance.  A very interesting study by Burney et al. (2003) tracked the decline of coprophilous Sporormiella fungus spores in sediments due to reduced megafaunal densities after the human arrival on the island. Another well documented case is the Moa extinction in New Zealand. Recent radiocarbon dating and population modeling suggests that their disappearance occurred within 100 years of first human arrival. A large number of  land birds across Oceania suffered a similar fate beginning about 3500 years ago.

Some biologist predict that the sixth extinction  may result in a 50% loss of the plants and animals on our planet by AD 2100, which would cause not only the collapse of ecosystems but also the loss of food economies, and medicinal resources.

References:

Richard N. Holdaway, Morten E. Allentoft, Christopher Jacomb, Charlotte L. Oskam, Nancy R. Beavan, Michael Bunce. An extremely low-density human population exterminated New Zealand moa. Nature Communications, 2014; 5: 5436 DOI: 10.1038/ncomms6436

Rodolfo Dirzo et al., Defaunation in the Anthropocene, Science 345, 401 (2014); DOI: 10.1126/science.1251817

Braje, T.J., Erlandson, J.M., Human acceleration of animal and plant extinctions: A Late Pleistocene, Holocene, and Anthropocene continuum. Anthropocene (2013), http://dx.doi.org/10.1016/j.ancene.2013.08.003