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

 

 

The plant fossil record and the extinction events.

Odontopteris lingulata, seed fern from the Late  Late Pennsylvanian to Early Permian. (Image Credit: Taylor et al, 2009)

Odontopteris lingulata, seed fern from the Late Late Pennsylvanian to Early Permian. (Image Credit: Taylor et al, 2009)

Mass extinctions has shaped the global diversity of our planet several times during the geological ages. They were originally identified in the marine fossil record and have been interpreted as a result of catastrophic events or major environmental changes that occurred too rapidly for organisms to adapt.

In 1982, Jack Sepkoski and David M. Raup used a simple form of time series analysis at the rank of family to distinguish between background extinction levels and mass extinctions in marine faunas, and identified five major extinction events in Earth’s history: at the end of the Ordovician period, Frasnian (Late Devonian), Permian, Triassic and Cretaceous. But the plant fossil record reveals a different pattern of major taxonomic extinctions compared with marine organisms. The first of them took place at the Carboniferous-Permian transition, which is interpreted as result of the collapse of the tropical wetlands in Euramerica. The second mass extinction corresponds to the end-Permian event.

Glossopteris sp., seed ferns, Permian - Triassic - Houston Museum of Natural Science (From Wikimedia Commons)

Glossopteris sp., seed ferns, Permian – Triassic – Houston Museum of Natural Science (From Wikimedia Commons)

At the late Carboniferous the characteristic wetland families disappeared (e.g. Flemingitaceae, Diaphorodendraceae, Tedeleaceae, Urnatopteridaceae, Alethopteridaceae, Cyclopteridaceae, Neurodontopteridaceae). The downfall of rainforests probably reflects the complexity of the environmental changes that were taking place during the late Moscovian-early Sakmarian time interval (DiMichele et al., 2006, Sahney et al., 2010). This collapse probably drove the rapid diversification of Carboniferous tetrapods (amphibians and reptiles) in Euramerica (Sahney et al., 2010).

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.

Schematic illustration comparing the three extinction events analized (From Vajda and Bercovici, 2014)

Schematic illustration comparing the three extinction events analized (From Vajda and Bercovici, 2014)

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

The end-Cretaceous biotic crisis had a significant effect on marine and terrestrial faunas, and caused localized loss of species diversity in vegetation. Patagonia shows a reduction in diversity and relative abundance in almost all plant groups from the latest Maastrichtian to the Danian, although only a few true extinctions occurred (Barreda et al, 2013). The nature of vegetational change in the south polar region suggests that terrestrial ecosystems were already responding to relatively rapid climate change prior to the K–Pg catastrophe.

Two examples of grains pollen from the Lopez de Bertodano Formation: Podocarpidites sp. (left) and Nothofagidites asperus (right)

Two examples of grains pollen: Podocarpidites sp. (left) and Nothofagidites asperus (right)

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).

References:

Cascales-Miñana, B., and C. J. Cleal, 2014, The plant fossil record reflects just two great extinction events. Terra Nova. vol. 26, no. 3, pp. 195–200. DOI: 10.1111/ter.12086

Bambach, R.K., Knoll, A.H. and Wang, S.C., 2004. Origination, extinction, and mass depletions of marine diversity. Paleobiology, 30, 522–542.

Mayhew, Peter J.; Gareth B. Jenkins, Timothy G. Benton (January 7, 2008). “A long-term association between global temperature and biodiversity, origination and extinction in the fossil record”. Proceedings of the Royal Society B: Biological Sciences 275 (1630): 47–53.

Sahney, S., Benton, M.J. & Falcon-Lang, H.J. (2010). “Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica” (PDF). Geology 38 (12): 1079–1082. doi:10.1130/G31182.1.

 

Halloween special II: Lovecraft, Paleobotany and The Shadow Out of Time.

Howard Phillips Lovecraft_in_1915_(2)

Howard Phillips Lovecraft in 1915.

Howard Phillips Lovecraft was born on August 20, 1890 in Providence, Rhode Island. He was one of the most influential writers of the twentieth century.  Despite leaving school without graduating, in his writings, evidences an extensive knowledge of archaeology, astronomy, geology, and paleontology. As an amateur astronomer, Lovecraft attended several lectures from leading astronomers and physicists of his time. He  explicitly stated in a letter to a friend that Yuggoth is in fact the then recently discovered Pluto. This was one of the key aspects in Lovecraft’s literature: to reject the old spiritual world and use the advance of science as a source of inspiration.

“The Shadow Out of Time” (1935) was H. P. Lovecraft’s last major story. It’s told from the perspective of Nathaniel Wingate Peaslee, a professor of political economy at Miskatonic University. During five years, this man suffers a bizarre form of amnesia  followed by vivid dreams of aliens cities in ancient landscapes.  Later, Peaslee discovered that a small number of people throughout history suffered the same type of amnesia. They were possessed by the Great Race, a group of cone shaped creatures who developed the technique of swapping minds with creatures of another era with the purpose of learn the secrets of the Universe.

Lepidodendrom leaf cushions preserved in a Mazon Creek nodule. (Taylor et al., 2009)

Lepidodendrom leaf cushions preserved in a Mazon Creek nodule. (Image Credit: Taylor et al, 2009)

Peaslee describes the gardens that surround the cities of his visions with detail. There was calamites, cycads, trees of coniferous aspect, and small, colourless flowers.

Calamites was a genus of tree-sized, spore-bearing plants that lived during the Carboniferous and Permian periods (about 360 to 250 million years ago), closely related to modern horsetails. They reached their peak diversity in the Pennsylvanian and were major constituents of the lowland equatorial swamp forest ecosystems. The Cycadales are an ancient group of seed plants that can be traced back to the Pennsylvanian. Cycads have a stem or trunk that commonly looks like a large pineapple and composed of the coalesced bases of large leaves.  Today’s cycads are found in the tropical, subtropical and warm temperate regions of both the north and south hemispheres.

While angiosperm fossil pollen first appears in the Early Cretaceous, molecular data suggest that the first occurrence was in the early Permian (~275 Ma) to late Triassic (228-217 Ma). Recently, a new study describe six distinct pollen types that have angiosperm-like features from the Triassic of Switzerland.

sigillaria

Transverse section of Sigillaria approximata stem (Image Credit: Taylor et al, 2009)

Peaslee’s visions become more and more vivid:

The far horizon was always steamy and indistinct, but I could see that great jungles of unknown tree-ferns, calamites, lepidodendra, and sigillaria lay outside the city, their fantastic frondage waving mockingly in the shifting vapours.”

Lepidodendron was a tree-like (‘arborescent’) tropical plant, related to the lycopsids. The name of the genus comes from the Greek lepido, scale, and dendron, tree, because of the distinctive diamond shaped pattern of the bark. The name Lepidodendron is a generic name given to several fossil that clearly come from arborescent lycophytes but are difficult to assign to one species. Fossil remains indicate that some trees attained heights in excess of 40 m and were at least 2m in diameter at the base. They were dominant components of swamp ecosystems in the Carboniferous and frequently associated with Sigillaria, another extinct genus of tree-sized lycopsids from the Carboniferous Period. The absence of extensive branching and the structure of the leaf bases are the principal feature that distinguish Sigillaria from other lycopsids (Taylor et al, 2009). Sigillariostrobus is the name assigned to the reproductive organs or cones of Sigillaria. Unlike Lepidodendron cones, which were attached attached individually near the tip of the branches, Sigillaria cones occurred in clusters attached in certain places along the upper stem.

Later, on an expedition to Australia, Peaslee – accompanied by Professor William Dyer, leader of the Miskatonic Antarctic expedition of 1930-1931- discovered a manuscript written by himself eons ago when he was a captive mind of the Great Race.

References:

H. P. Lovecraft, The Dreams in the Witch House and Other Weird Stories, Penguin Books, 2004.

Joshi, S. T. (2001). A dreamer and a visionary: H.P. Lovecraft in his time. Liverpool University Press, 302.

N. Taylor, Edith L. Taylor, Michael Krings: “Paleobotany: The Biology and Evolution of Fossil Plants”. 2nd ed., Academic Press 2009.

Kathy Willis, Jennifer McElwain, The Evolution of Plants, Oxford University Press, 2013

Hochuli, P. A., and Feist-Burkhardt, S.. (2013). Angiosperm-like pollen and Afropollis from the Middle Triassic (Anisian) of the Germanic Basin (Northern Switzerland). Frontiers in Plant Science. 4. doi: 10.3389/fpls.2013.00344

Mignon Talbot and the forgotten women of Paleontology.

 

Sin título

Mignon Talbot  (From Turner et al, 2010)

 

The nineteenth century was the “golden age” of Geology, and women began to play an important role in the advance of this field of science. They collected fossils and mineral specimens, and were allowed to attend scientific lectures, but they were barred from membership in scientific societies. It was common for male scientists to have women assistants, often their own wives and daughters. A good example of that was Mary Lyell (1808–1873), daughter of the geologist Leonard Horner and the wife of eminent geologist Charles Lyell. But for most of men, the participation of women in geology and paleontology was perceived as a hobby.

Mary Anning (1799-1847), was a special case. She was the most famous woman paleontologist of her time, and found the first specimens of what would later be recognized as Ichthyosaurus, the first complete Plesiosaurus, the first pterosaur skeleton outside Germany and suggested that the “Bezoar stones” were fossilized feces. Scientists like William Buckland or Henry de la Beche owe their achievements to Mary’s work. William Buckland himself, persuaded the British Association for the Advancement of Science and the British government to award her an annuity of £25, in return for her many contributions to the science of geology.

Thanks to the pioneer work of these women,the twenty century saw the slow but firm advance of women from the periphery of science towards the center of it. Unfortunately, most of these early female scientists were forgotten and none of them reached the fame of their most illustrious predecessor, Miss Mary Anning.

Podokesaurus holyokensis holotype (From Wikimedia Commons)

Podokesaurus holyokensis holotype (From Wikimedia Commons)

Mignon Talbot was born in Iowa, on August 16, 1869. She studied geology at Ohio State University. In 1904 she received a Ph.D. from Yale and then joined at Mount Holyoke College, where she became Professor of Geology and Geography until her retirement in 1935. During her years at the faculty, she amassed a large collection of invertebrates fossil, but published few technical papers. In 1910, she became the first woman to find and describe a dinosaur: Podokesaurus holyokensis (swift-footed saurian). In 1911, she published a scientific description of the fossil. She wrote: “In a bowlder of Triassic sandstone which the glacier carried two or three miles, possibly, and deposited not far from the site of Mount Holyoke College, the writer recently found an excellently preserved skeleton of a small dinosaur the length of whose body is about 18 cm. The bowlder was split along the plane in which the fossil lies and part of the bones are in o half and part in the other. These bones are hollow and the whole  framework is very light and delicate“.  At the time, she was mentored in her investigation by Richard Swan Lull, who suggested that this dinosaur was insectivorous (although, Talbot identified it as a herbivore at a meeting of the Paleontological Society in December 1910). Unfortunately, in 1916, a fire destroyed the science hall and the only specimen of Podokesaurus holyokensis. She died on July 18, 1950.

Tilly Edinger (Photo,Museum of Comparative Zoology, Harvard University, Cambridge, MA)

Tilly Edinger (Photo,Museum of Comparative Zoology, Harvard University, Cambridge, MA)

Johanna Gabrielle Ottilie  “Tilly” Edinger was born on November 13, 1897 in Frankfurt, Germany. She was the youngest daughter of the eminent neurologist Ludwig Edinger and Dora Goldschmidt. She studied at Universities of Heidelberg, Frankfurt, and Munich. In 1921, she received her Ph. D at the University of Frankfurt. When she was preparing her doctoral dissertation about the palate of the Mesozoic marine reptile Nothosaurus, Edinger encountered a skull with a natural brain cast. Her early research was mostly descriptive and she was influenced by the work of Louis Dollo and Friedrich von Huene. In 1929,  she published Die fossilen Gehirne (Fossil Brains), the book that established Edinger’s membership in the German and international paleontological communities. She briefly worked at British Museum of Natural History after the events that followed the infamous “Kristallnacht” (Night of the Broken Glass). In 1940, with the support of Alfred S. Romer, she moved to Massachusetts to take a position at the Harvard Museum of Comparative Zoology. Shortly after, she was the first and only woman who attend the founding meeting of the Society of Vertebrate Paleontology (SVP). By the early 1950s, she was not only the major contributor to the field of paleoneurology but also the mentor to a younger generation that was following in her footsteps. She died on 27 May 1967 in Cambridge, Massachusetts.

References:

Susan Turner, Cynthia V. Burek and Richard T. J. Moody, Forgotten women in an extinct saurian (man’s) world, Geological Society, London, Special Publications 2010, v. 343, p. 111-153

Buchholtz, Emily A.; Seyfarth, Ernst-August (August 2001), “The Study of “Fossil Brains”: Tilly Edinger (1897–1967) and the Beginnings of Paleoneurology”, Bioscience 51 (8)

Kass-Simon, Gabrielle; Farnes, Patricia; Nash, Deborah, eds. (1999). Women of science : righting the record. Bloomington, Indiana: Indiana Univ. Press.

Talbot, M., 1911, Podokesaurus holyokensis, a new dinosaur of the Connecticut Valley: American Journal of Science, v. 31, p. 469-479