Solving the mystery of Megatherium diet.

Megatherium americanum, MACN.

Around 10,000 years ago, Argentina was home of numerous species of giant Xenarthrans, giant ground sloths (relative to tree sloth) and glyptodontids (relative to tiny extant armadillo). Sloths, characteristic of the mammal fauna of the Pleistocene of South America, show a great diversity with more than 80 genera, grouped in four families: Megatheriidae, Megalonychidae, Nothrotheriidae and Mylodontidae.

For more than a century different hypotheses on the dietary preferences of giant ground sloths have been proposed. In 1860, Owen gave an extensive explanations about their possible diet and behavior. He based his conclusions on the morphology of the skull, combined with peculiarities of the rest of the skeleton, but always by analogy with living tree sloth. He wrote: “Guided by the general rule that animals having the same kind of dentition have the same kind of food, I conclude that the Megatherium must have subsisted, like the Sloths, on the foliage of tree…”. In 1926, Angel Cabrera discussed the diet of Megatherium, rejecting some theories on myrmecophagy or insectivory, and agreed with Owen’s statements about a folivorous diet.

Megatherium americanum lower right tooth series. Scale bar: 5 cm (From M.S. Bargo and S.F. Vizcaíno, 2008)

The dietary preferences of extinct mammals can usually be evaluated through their tooth morphology, but the application of stable isotopes on fossil bones has yielded very important information to solve debates about the diet of extinct large mammal groups, by comparing the carbon and nitrogen isotopic composition of their bone collagen with those of coeval herbivorous and carnivorous taxa. Another isotopic approach is to mesure the difference between the carbon isotopic abundances of the collagen and the carbonate fractions of skeletal tissues. An animal with a herbivorous diet, exhibits significantly larger differences than a carnivore. The values measured on bone collagen from Megatherium, clearly fall in the same range as the large herbivores such as the equid Hippidion, the notoungulate Toxodon and the liptoptern Macrauchenia, for which there is no doubt about their herbivorous diet. Therefore, the hypotheses of insectivory or carnivory for these extinct mammals are not supported by the isotopic data.

 

References:

Hervé Bocherens et al. Isotopic insight on paleodiet of extinct Pleistocene megafaunal Xenarthrans from Argentina, Gondwana Research (2017). DOI: 10.1016/j.gr.2017.04.003

Bargo, M.S., Vizcaíno, S.F., 2008. Paleobiology of Pleistocene ground sloths (Xenarthra, Tardigrada): biomechanics, morphogeometry and ecomorphology applied to the masticatory apparatus. Ameghiniana 45: 175-196

Darwin’s Fossil Mammals.

Portrait of Charles Darwin painted by George Richmond (1840)

Portrait of Charles Darwin painted by George Richmond (1840)

When Charles Darwin arrived to South America, he was only 22 years old. He was part of the second survey expedition of HMS Beagle. During the first two years of his voyage aboard HMS Beagle, Darwin collected a considerable number of fossil mammals from various South American localities. He sent all the specimens, to his mentor John Stevens Henslow. The samples were deposited in the Royal College of Surgeons where Richard Owen began its study. Between 1837 and 1845, Owen described eleven taxa, including: Toxodon platensis, Macrauchenia patachonica, Equus curvidens, Scelidotherium leptocephalum, Mylodon darwinii and Glossotherium sp. Previous to this expedition, the first news of “fossils” in South American were reported by early Spanish explorers, and George Cuvier, in 1796,  published the first scientific work about Megatherium americanum, based on the specimen recovered by Fray Manuel Torres from Lujan, Buenos Aires, Argentina.

Darwin recovered his first fossil at Punta Alta (Buenos Aires Province, Argentina) on September 23, 1832, and continued collecting intermittently at this locality until October 16. Later, he went to Monte Hermoso and returned to Punta Alta between August 29 – 31, 1833. Then, he moved to Guardia del Monte (Buenos Aires Province); the Rio Carcarañá (Santa Fe Province, Argentina), and the Bajada Santa Fe (Paraná, Entre Ríos Province, Argentina). After a short stay in Uruguay, Darwin returned to Argentina and collected his last specimens at Puerto San Julián (Santa Cruz Province) in 1834. During his journey between Buenos Aires and Santa Fe he wrote “We may therefore conclude that the whole area of the Pampas is one wide sepulchre for these extinct quadrupeds” (Voyage of the Beagle, Chapter VII, Oct. 1833).

Fossil Toxodon on display at Bernardino Rivadavia Natural Sciences Museum.

Fossil Toxodon on display at Bernardino Rivadavia Natural Sciences Museum.

Toxodon was named by Owen based on a large skull purchased by Darwin. He paid 18 pence for it. Darwin described it as “one of the strangest animals, ever discovered…” Owen bestowed the name because its upper incisors were strongly arched (Toxodon means “arched tooth”). He also recognized Toxodon as “A gigantic extinct mammiferous animal, referable to the Order Pachydermata, but with affinities to the Rodentia, Edentata, and Herbivorous Cetacea”. Toxodonts shares a number of dental, auditory and tarsal specializations. They had  short hippopotamus-like head with broad jaws filled with bow shaped teeth and incisors, a massive skeleton with short stout legs with three functional toes. The estimated weight is over a tonne. About the different groups that appeared to be related to Toxodon, Darwin stated:“How wonderfully are the different orders, at the present time so well separated, blended together in different points of the structure of Toxodon”

A recent phylogenetic analysis indicates that Toxodon is most closely related to perissodactyls, a group that includes rhinos, tapirs, and horses.

Macrauchenia patachonica by Robert Bruce Horsfall.

Macrauchenia patachonica by Robert Bruce Horsfall.

Macrauchenia, meaning “big neck,” was named by Owen based on limb bones and vertebrae collected by Darwin in January 1834 at Puerto San Julian, in Santa Cruz Province, Argentina. The bizarre animal had a camel-like body, with sturdy legs, a long neck and a relatively small head. Owen described as “A large extinct Mammiferous Animal, referrible to the Order Pachydermata; but with affinities to the Ruminantia, and especially to the Camelidae”. Macrauchenia is now considered among the more derived native South American litopterns. Darwin also made inferences about the environment which Macrauchenia lived: “Mr. Owen… considers that they form part of an animal allied to the guanaco or llama, but fully as large as the true camel. As all the existing members of the family of Camelidae are inhabitants of the most sterile countries, so we may suppose was this extinct kind… It is impossible to reflect without the deepest astonishment, on the changed state of this continent. Formerly it must have swarmed with great monsters, like the southern parts of Africa, but now we find only the tapir, guanaco, armadillo, capybara; mere pigmies compared to antecedents races… Since their loss, no very great physical changes can have taken place in the nature of the Country. What then has exterminated so many living creatures?…We are so profoundly ignorant concerning the physiological relations, on which the life, and even health (as shown by epidemics) of any existing species depends, that we argue with still less safety about either the life or death of any extinct kind” (Voyage of the Beagle, Chapter IX, Jan. 1834).

Scelidotherium leptocephalum, Muséum national d'Histoire naturelle, Paris (From Wikimedia Commons)

Scelidotherium leptocephalum, Muséum national d’Histoire naturelle, Paris (From Wikimedia Commons)

Darwin recovered fossil remains of at least five species of giant ground sloth. In a letter sent to John Stevens Henslow in November, 1832, Darwin listed the fossils collected, among which he emphasized “… the upper jaw & head of some very large animal, with 4 square hollow molars — & the head greatly produced infront. — I at first thought it belonged either to the Megalonyx or Megatherium.” Darwin decided in favor of Megatherium based on the presence of osteoderms collected in the same formation, but Owen (1838-1840) recognized the specimens assigned by Darwin to Megatherium as glyptodonts, toxodonts, and large ground sloths (Fernicola et al., 2009; Allmon 2015). Scelidotherium, was described by Owen on the basis of the only nearly complete skeleton found by Darwin at Punta Alta (Buenos Aires Province). Darwin considered the specimen as “allied to the Rhinoceros”. Scelidotherium is distinctive by an elongated, superficially anteater-like head. Another sloth, Mylodon was named by Richard Owen on the basis of a nearly complete lower jaw with teeth, which was found by Charles Darwin at Punta Alta (Buenos Aires Province). Owen (1839b) erected Mylodon for two species, Mylodon darwini and Mylodon harlani. The former species was based on a left dentary from Punta Alta (Buenos Aires Province), whereas the second was based on a cast of a mandible from North America.

Fossil mammals collected by Charles Darwin in South America during the voyage of H.M.S. Beagle (From Allmon, 2015).

Fossil mammals collected by Charles Darwin in South America during the voyage of H.M.S. Beagle (From Allmon, 2015).

Darwin also found fossil horse teeth assignable to the modern genus Equus. The two molars from Argentina were recovered from Punta Alta (Buenos Aires Province) and Bajada Santa Fe (Entre Rios Province), and represent the first fossil horses found in South America. He wrote: “Certainly it is a marvellous event in the history of animals that a native kind should have disappeared to be succeeded in after ages by the countless herds introduced with the Spanish colonist! (1839, p. 150).

By the end of the expedition, Darwin was already earned a name as a geologist and fossil collector. He narrated his experiences in his book “Journal of Researches into the Geology and Natural History of the Various Countries visited by H.M.S. Beagle, under the Command of Captain FitzRoy, R.N. from 1832 to 1836″, published in 1839 and later simply known as “The Voyage of the Beagle”. When Darwin wrote his memories in 1858, he described the expedition in one strong and powerful sentence: “the voyage of the Beagle has been by far the most important event in my life and has determined my whole career”.

 

References:

Warren D. Allmon (2015): Darwin and palaeontology: a re-evaluation of his interpretation of the fossil record, Historical Biology, DOI: 10.1080/08912963.2015.1011397

Fernicola JC, Vizcaíno SF, 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 Asocición Geológica Argentina. 64(1):147–159.

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

 

Letters from Father Tolkien.

tolkien

John Ronald Reuel Tolkien was born on January 3, 1892, in Bloemfontein, South Africa, and died on September 2, 1973, in Bournemouth, England. He grew up in the waning days of the Victorian Era, and died along with the Swinging London. He saw the horror of the war, and the memories of his experiences as an officer in World War I were sublimated in his fiction. As he wrote in the Introduction to the second edition of The Lord of the Rings: “it seems now often forgotten that to be caught by youth in 1914 was no less hideous an experience than to be involved in 1939 and the following years. By 1918 all but one of my close friends were dead”.

He started writing stories for his children as early as 1920, when he first sent to John, the eldest son, a letter purporting to be from Father Christmas. The letters were written over a period of 20 years to entertain Tolkien’s children each Christmas. He also created the envelopes, and designed his own stamps. In the letters, Tolkien documented the adventures and misadventures of Father Christmas and his helpers. There are some similarities between the early letters and The Hobbit. Even more, Laurence and Martha Krieg in the journal Mythlore suggested that Gandalf himself may have been developed from Father Christmas.

FatherChristmasLetters_1932

Cave Drawings with Goblin Graffiti from the Father Christmas Letter of 1932.

In the letter for 1932, Father Christmas rescues the North Polar Bear from the caves and finds Goblin wall paintings. It’s a wonderful piece full of mammoths, bison, and goblin scribblings. Tolkien wrote: “must be very old, because the Goblin fighters are sitting on drasils: a very queer sort of dwarf ‘dachshund’ horse creature… I believe the Red Gnomes finished them off, somewhere about Edward the Fourth’s time.” 

It has been suggested that the painting was copied from Baldwin Brown’s The Art of the Cave Dweller: A Study of the Earliest Artistic Activities of Man. In his work, Brown emphasized that the primitive hunter must naturally have become a keen observer of nature. The first cave paintings were found in 1870 in Altimira, Spain. The Lascaux Caves, near the village of Montignac, in France, contain some of the best-known Upper Paleolithic art, estimated in 17,300 years old. During the Pleistocene and the early Holocene, most of the terrestrial megafauna became extinct. It was a deep global-scale event. Europe witnessed the extinction of several large mammalian herbivores, such as steppe bison Bison priscus, woolly mammoth Mammuthus primigenius, woolly rhinoceros Coelodonta antiquitatis and giant deer Megaloceros giganteus. The patterns exhibited by the Late Quaternary megafauna extinction (LQE) indicated a close link with the geography of human evolution and expansion.

Tolkien also anticipated some of the tenets of modern environmentalism in the imagined world of Middle-earth and the races with which it is peopled.

References:

The Father Christmas Letters. By J.R.R. Tolkien; Allen and Unwin (1976).

THE ART OF THE CAVE DWELLER: a study of the earliest Artistic Activities of Man. By G. Baldwin Brown. John Murray. 1928. pp. xix, 280. 18s.

 

 

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

 

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 Late Quaternary megafauna extinction: the human factor

Mamut_lanudo_cropped

Mammuthus primigenius, Royal British Columbia Museum. From Wikipedia Commons

During the Pleistocene and the early Holocene,  most of the terrestrial megafauna became extinct. It was a deep global-scale event. Multiple explanatory hypotheses have been proposed for this event: climatic change, over hunting, habitat alteration, the introduction of a new disease and an extra-terrestrial impact.

There’s no evidence to support the last two hypothesis, but the patterns exhibited by the Late Quaternary megafauna extinction (LQE) indicated a close link with the geography of human evolution and expansion. This relation and the extinction magnitude is particularly strong in Australia and the Americas. South America exhibits high extinction levels, forming a strong contrast to sub-Saharan Africa where the extinction level was minimal in spite of similar glacial–Holocene climate changes (Sandom et al, 2014).

Fossil Toxodon on display at Bernardino Rivadavia Natural Sciences Museum.

Fossil Toxodon on display at Bernardino Rivadavia Natural Sciences Museum.

Although most Australian extinctions occurred prior to the LQE, it has been argued that modern humans caused the Australian megafauna extinctions either via fire-driven vegetation changes  or hunting.

In North America,  early observation confirms that extinctions could be severe even in relatively climatically stable regions where the vegetation changed little.

Eurasia shows a more complicated story, where human palaeobiogeography alone accounts for 64%  of the variation in extinction, while some data pointed the climate change as the main cause in the decline of late Pleistocene megafaunal.

The case of Africa fits well to the extinction pattern expected from hominin palaeobiogeography.  Also, the current low diversity in large mammals in many continental areas could be considered as an anthropogenic phenomenon, not a natural one, with important implications for nature management (Sandom et al, 2014)

Jean-Baptiste Lamarck(1744- 1829) and  Jacques Boucher de Crèvecœur de Perthes (1788 - 1868) (From Wikimedia Commons)

Jean-Baptiste Lamarck(1744- 1829) and Jacques Boucher de Crèvecœur de Perthes (1788 – 1868) (From Wikimedia Commons)

In the nineteenth century, french naturalist Jean-Baptiste Lamarck  suggested that humans had caused past extinctions, but Lyell rejected his ideas because he believed the extinctions occurred before humans were present. But after visiting stratigraphic excavations in the Somme River valley conducted by  Boucher de Perthes, Lyell wrote, “That the human race goes back to the time of the mammoth and rhinoceros (Siberian) and not a few other extinct mammals is perfectly clear.…”

Other authors like Alfred Russell Wallace and Louis Agassiz argued for mass glaciation as the cause of past extinctions.

Today, the debate remains although the new evidence indicate that human impacts were essential to precipitate the event.

References:

Sandom C, Faurby S, Sandel B, Svenning J-C. 2014 Global late Quaternary megafauna extinctions linked to humans, not climate change. Proc. R. Soc. B 281: 20133254. http://dx.doi.org/10.1098/rspb.2013.3254

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, 4527– 4531. (doi:10.1073/pnas. 1113875109)

Grayson DK. 1984. Nineteenth-century explanations of Pleistocene extinctions: a review and analysis. See Martin & Klein 1984, pp. 5–39

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

The sixth mass extinction: the human impact on biodiversity

800px-Ice_age_fauna_of_northern_Spain_-_Mauricio_Antón

Woolly mammoths in a late Pleistocene landscape in northern Spain (Author: Mauricio Antón) From Wikipedia Commons

At the beginning of the nineteenth century George Cuvier, the great French anatomist and paleontologist,  suggested that periodic “revolutions”, or catastrophes had befallen the Earth and wiped out a number of species, but under the influence of Lyell’s uniformitarianism, Cuvier’s ideas were rejected as “poor science”. One century after Cuvier definition of catastrophism, Chamberlain proposed that faunal major changes through time were under the control of epeirogenic movement of the continents and ocean basins. Despite Chamberlain’s article, the modern study of mass extinction did not begin until the middle of the twentieth century with a series of papers focused on the Permian extinction. One of the most popular of that time was “Revolutions in the history of life” written by Norman Newell in 1967.

Mass extinctions had shaped the global diversity of our planet several times during the geological ages. They are major patterns in macroevolution. Andrew Knoll defines them as perturbations of the biosphere which seem instantaneous when it is observed through the geological record.

The ‘‘Big Five’’ extinction events as identified by Raup and Sepkoski (1982)

The ‘‘Big Five’’ extinction events as identified by Raup and Sepkoski (1982)

In 1982, Jack Sepkoski and David M. Raup identified five mass extinctions. The first took place at the end of the Ordovician period, about 450 million years ago.  Now, according to the current rates of extinction, we are in the midst of  the so called “Sixth Mass Extinction”.

Mass extinctions are probably due to a set of different possible causes like basaltic super-eruptions, impacts of asteroids, global climate changes, or continental drift. But now, a group of scientists like Edward O. Wilson and Niles Eldredge identified post-industrial humans as the driving force behind the current and on-going mass extinction (Braje, 2013).

The human arrival was a “key component” in the extinction of the megafauna during the late Quaternary. In North America, approximately 34 genera (72%) of large mammals went extinct between 13,000 and 10,500 years ago, including mammoths, mastodons, giant ground sloths, horses, tapirs, camels, bears, saber-tooth cats, and a variety of other animals. South America lost an even larger number and percentage, with 50 megafauna genera (83%) becoming extinct at about the same time.

 

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.

Other extinctions on island ecosystems around the world are result from direct human hunting, anthropogenic burning and landscape clearing, and the translocation of new plants and animals. One of the most famous and well-documented of these 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  landbirds across Oceania suffered a similar fate beginning about 3500 years ago.

The anthropogenic effects increasingly took precedence over natural climate change as the driving forces behind plant and animal extinctions with the advent of agriculture and the domestication of animals.

The Panamanian golden frog (Atelopus zeteki). Credit: Brian Gratwicke. From Wikimedia Commons

The Panamanian golden frog (Atelopus zeteki). Credit: Brian Gratwicke. From Wikimedia Commons

Amphibians offer an important signal to the health of biodiversity; when they are stressed and struggling, biodiversity may be under pressure.   Today, they are the world’s most endangered class of animal, while corals have had a dramatic increase in risk of extinction in recent years. 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.

The acceleration of extinctions over the past 50,000 years, in which humans have played an increasingly important role, has left a number of hard questions about how the Anthropocene should be defined and whether or not extinctions should contribute to this definition (Erlandson, 2013)

 

References:

T.J., Erlandson, J.M., Human acceleration of animal and plant extinctions: A Late Pleistocene, Holocene, and Anthropocene continuum. Anthropocene (2013)

A.D. Barnosky, N. Matzke, S. Tomiya, G.O.U. Wogan, B. Swartz, T.B. Quental, C. Marshall, J.L. McGuire, E.L. Lindsey, K.C. Maguire, B. Mersey, E.A. Ferrer, Has the earth’s sixth mass extinction already arrived?, Nature, 471 (2011), pp. 51–57.

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.

D.A. Burney, L.P. Burney, L.R. Godfrey, W.L. Jungers, S.M. Goodman, H.T. Wright, A.J.T. Jull, A chronology for late prehistoric Madagascar, J. Hum. Evol., 47 (2004), pp. 25–63