The Megaraptor mystery.

 

A. Cranial reconstruction of Megaraptor namunhuaiquii. B. skull of Dilong paradoxus. Scale bars equal 2 cm. From Porfiri et al. 2014.

The Cretaceous beds of Patagonia posses the most comprehensive record of  non-avian theropods  from Southern Hemisphere. Megaraptora  is a clade represented by Megaraptor, Orkoraptor and Aerosteon, and characterized by the formidable development of their manual claws on digits I and II and the transversely compressed and ventrally sharp ungual of the first manual digit (Novas et al, 2013).

For years, Megaraptor has been alternatively interpreted as belonging to different theropod lineages: as basal coelurosaurians (Novas,1998), basal tetanurans (Calvo et al.,2004; Smith et al., 2008), and allosauroids closely related with carcharodontosaurids (Smith et al., 2007; Benson et al., 2010; Carrano et al., 2012).

The main reason for so many different interpretations is the incomplete nature of most available megaraptorid skeletons and the little information about their cranial anatomy. But the partially preserved skeleton of a juvenile specimen of Megaraptor namunhuaiquii allows to make for the first time a reconstruction of the skull and body of megaraptorids.

Right maxilla of Megaraptor namunhuaiquii in medial view. Scale bar equal 3 cm. From Porfiri et al. 2014.

The data gathered from the specimen indicates that Megaraptorids had an elongated skull, with a gracile snout bearing small teeth, a gracile S-shaped neck, and a very wide and deep thorax, with gastralia similar in size to dorsal ribs. The pectoral girdle supported elongate and robust forelimbs, with large and sharp unguals on digits I and II, and the hindlimbs were gracile and slender.

Based on that information, the researchers found that Megaraptor and related taxa  are nested within Coelurosauria and Tyrannosauroidea.  They  found 14 synapomorphies between megaraptorans and  tyrannosauroids like several foramina on the premaxillary body, extremely long and straight prenarial process of the premaxilla, incisiviform premaxillary teeth with a D-shaped cross-section, and supratemporal fossae separated by a sharp sagittal median crest on frontals.

The study also shows that tyrannosaurs followed two distinct trajectories in the northern and southern continents. While in megaraptorids the forelimbs became powerful and with large-clawed hands (Calvo et al., 2004), in tyrannosaurids the overall trend was towards forelimb reduction (Brusatte et al., 2010b). However, both evolutionary trends present a common pattern which is the reduction of the third manual digit (Porfiri et al. 2014)

 

References:

Porfiri, J. D., Novas, F. E., Calvo, J. O., Agnolín, F. L., Ezcurra, M. D. & Cerda, I. A. 2014. Juvenile specimen of Megaraptor (Dinosauria, Theropoda) sheds light about tyrannosauroid radiation. Cretaceous Research 51: 35-55.

Benson, R.B.J., Carrano, M.T., Brusatte, S.L., 2010. A new clade of archaic large-bodied predatory dinosaurs (Theropoda: Allosauroidea) that survived to the latest Mesozoic. Naturwissenschaften 97, 71-78.

Novas, F.E., 2009. The Age of Dinosaurs in South America. Indiana University Press, Bloomington, pp. 1-536

Novas, F.E., 1998. Megaraptor namunhuaiquii gen. et. sp. nov., a large-clawed, Late Cretaceous Theropod from Argentina. Journal of Vertebrate Paleontology 18, 4-9.

The Late Quaternary megafauna extinction: the human factor

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.

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)

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.

Mary Somerville, Queen of Science.

 

Mary Somerville (1780- 1872) (From Wikimedia Commons)

Mary Somerville, née Mary Fairfax, was born on December 26, 1780,  in Jedburgh Scotland. She has been called  “Queen of Nineteenth Century Science.”  She was also the first English geographer. Her book “Physical Geography” (1848) was the first textbook on the subject in English and her most popular work. It was published three years after the first volume of Alexander von Humboldt’s “Cosmos”.

She had virtually no formal education but she had a very inquisitive mind. Her interest in mathematics was encouraged by her uncle, Dr. William Somerville, who later became her father in law.

In 1807, she was forced to married to Captain Samuel Greig and went to live to London. Her husband died three years later and Mary returned to Scotland and began to study astronomy and mathematics.  In 1811 she won a prize for her solution to a problem in the  journal “The Mathematical Repository.”

She married to her cousin William Somerville in 1812. He was an army doctor and unlike her first husband encouraged her to continuing writing and studying science.  The couple moved to London where they  became members of the scholarly and literary society of the time.

She was a friend of John Herschel, Charles Lyell, Alexander von Humboldt, William Buckland, Lord Henry Brougham,  and Roderick  and Charlotte Murchison. In her autobiography, Mary Somerville wrote about Charlotte: “Mrs Murchison was an amiable accomplished woman, drew prettily and what was rare at the time she had studied science, especially geology and it was chiefly owing to her example that her husband turned his mind to those pursuits in which he afterwards obtained such distinction.”

Self-portrait by Mary Somerville, Somerville College, University of Oxford

She presented a paper entitled “The Magnetic Properties of the Violet Rays of the Solar Spectrum” to the Royal Society in 1826.

In 1827, Lord Brougham asked her to translate La Place’s “Traité de Mécanique céleste” for the Society for the Diffusion of Useful Knowledge. She not only translated but she added explanations and illustrations to the text. The book was a success and became a text for young mathematicians at Trinity College.

In 1833, she and Caroline Herschel were elected honorary members of the Royal Astronomical Society, the first time women had won that recognition.  Her second book, “The Connection of the Physical Sciences” was published in 1834.

At the age of sixty eight she published “Physical Geography”. The book was dedicated to her mentor John Herschel. In the first page of “Physical Geography” she explains her aim in her scientific writings by quoting Francis Bacon: “No natural phenomenon can be adequately studied in itself alone, but to be understood must be considered as it stands connected with all of nature”.

In “Physical Geography”, she included geology and the distribution of animal and vegetable life. She also sought to understand the various transformation processes involved.

She signed a petition presented to the University of London in 1862 praying that women might be allowed to sit for degree examinations, but the petition was rejected.

In 1869 she was awarded with the first gold medal of the Royal Geographical Society and published her last scientific book: Molecular and Microscopic Science. She died three years later, on November 28 in Naples, Italy.

Mary Somerville was an outstanding scientist and her scientific writings contributed to popularize science, one of the most important cultural projects of Victorian Britain.

 

 

References:

Kathryn A. Neeley, Mary Somerville: Science, Illumination, and the Female Mind, Cambridge University Press, 2001

BUREK, C. V. & HIGGS, B. (eds) The Role of Women in the History of Geology. Geological Society, London, Special Publications, 281, 1–8. DOI: 10.1144/SP281.1.

Buckland, Adelene: Novel Science : Fiction and the Invention of Nineteenth-Century Geology, University of Chicago Press, 2013.

Marie Sanderson and Mary Somerville, Mary Somerville: Her Work in Physical, Geography, Geographical Review Vol. 64, No. 3 (July 1974), pp. 410-420.

Palynological reconstruction of the Antarctic Cretaceous-Paleocene climate.

Artist’s impression of the eastern flank of the Antarctic Peninsula during the Maastrichtian (From Bowman et al, 2014, Artist: James McKay, University of Leeds.)

Past fluctuations in global temperatures are crucial to understand Earth’s climatic evolution. During the Late Cretaceous the global climate change has been associated with episodes of outgassing from major volcanic events, orbital cyclicity and tectonism before ending with the cataclysm caused by a large bolide impact at Chicxulub, on the Yucatán Peninsula, Mexico.
The Antarctic Peninsula is an area of specific interest to modern and past climatic studies, as it seems particularly sensitive to change (Kemp et al., 2014). Most of the studies are focused on Seymour Island which has one of the most expanded Cretaceous–Paleogene successions known. The K-Pg boundary occurs in the uppermost part of the López de Bertodano Formation, where it is marked by a minor iridium anomaly.

The terrestrial palynomorph record at the López de Bertodano Formation was divided into six phases. The first one contains an assemblage dominated by Nothofagidites spp. and Podocarpidites spp., with aquatic fern spores (Azolla spp., Grapnelispora sp.) and rare freshwater algal spores, suggesting a cool and relatively humid period.

 

Two examples of grains pollen from the Lopez de Bertodano Formation: Podocarpidites sp. (left) and Nothofagidites asperus (right). From Bowman et al, 2014.

In the phase two the increased abundance of Phyllocladidites mawsonii implies a gradual increase in humidity. During phase three, bryophytes began to increase. The phase four is characterised by relatively high abundances of Podocarpidites spp. and relatively low levels of Nothofagidites spp.
The phase 5 is characterised by a rapidly changing sequence of abundance peaks of different taxa, which may indicate a successional turnover in forest composition. The phase six suggests a return to a cool climatic conditions with high abundances of Araucariacites australis and Nothofagidites at the top of the section. It seems that Araucariaceae were capable of surviving long periods of adverse climatic conditions during the Early Pleistocene, but most modern araucarians have subtropical to mesothermal climatic preferences.

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. The composition of the terrestrial palynoflora indicates that the Maastrichtian climate fluctuated from cool, humid conditions, through a rapid warming about 2 million years prior to the K–Pg event – which is consistent with the evidence from the marine palynomorph record –  followed by cooling conditions in the earliest Danian.

 

Two examples of spores from the Lopez de Bertodano Formation: Grapnelispora sp. (left) and Azolla sp.(right). From Bowman et al, 2014.

 

Reference:

Vanessa C. Bowman, Jane E. Francis, Rosemary A. Askinb, James B. Riding, Graeme T. Swindles, Latest Cretaceous–earliest Paleogene vegetation and climate change at the high southern latitudes: palynological evidence fromSeymour Island, Antarctic Peninsula, Palaeogeography, Palaeoclimatology, Palaeoecology, 408. 26-47. 10.1016/j.palaeo.2014.04.018
David B. Kemp, Stuart A. Robinson, J. Alistair Crame, Jane E. Francis, Jon Ineson, Rowan J. Whittle, Vanessa Bowman, and Charlotte O’Brien, A cool temperate climate on the Antarctic Peninsula through the latest Cretaceous to early Paleogene, Geology (2014) doi: 10.1130/G35512.1

 

Lessons from the past: Climate change and the Classic Maya collapse.

 

Temple I on The Great Plaza and North Acropolis seen from Temple II in Tikal, Guatemala. From Wikimedia Commons

The earth’s climate has already reached a tipping point. Glaciers  from the Greenland and Antarctic Ice Sheets are fading away, dumping 260 billion metric tons of water into the ocean every year. The ocean acidification is occurring at a rate faster than at any time in the last 300 million years, and  the patterns of rainfall and drought are changing and undermining food security which have major implications for human health, welfare and social infrastructure. These atmospheric changes follow an upward trend in anthropogenically induced CO2 and CH4.

The first scientists that explored the relationship between carbon dioxide concentrations in the atmosphere and global warming were Svante Arrhenius and Thomas Chamberlain at the end of the nineteenth century. Now, the current rate of increase of CO₂ emissions has no precedent in the geological record and there is no perfect analogue from the past for the temporal evolution of future climate. However, we still can learn from historical and archeological records how societies had responded in the past to the unintended consequences of human action on the environment.

Rainfall record for the Maya region (Kennett et al., 2012)

Human activity took precedence over natural climate change as the driving force behind plant and animal extinctions with the advent of agriculture and the domestication of animals. There are several cases in the past where anthropogenic environmental change has caused the collapse of economic, social and political systems. A good example of that is the collapse of Classic Maya political centers between AD 750 and 1000.

Paleoecological records indicate that the transition to agriculture was a fundamental turning point in the environmental history of Mesoamerica. Tropical forest were reduced by agricultural expansion associated with growing human populations. Also soil loss associated with deforestation and erosion was one of the most consequential environmental impacts associated with population expansion in the Maya lowlands (Kennett, 2013). This environmental crisis ended with the collapse of the Classic Maya society.

Today the most politically unstable countries are also places where environmental degradation affected food production and water supply. Other human societies have succumbed to climate change – like the Akkadians –  while others have survived by changing their behavior in response to environmental change. We have opportunity to protect the future of our own society by learning from the mistakes of our ancestors. International cooperation is one of the keys.  As Trevor Manuel, a South African government minister and co-chair of the Global Ocean Commission stated: “Governments must respond as urgently as they do to national security threats – in the long run, the impacts are just as important”.

 

References:

Kennett, D.J., Beach, T.P., Archeological and environmental lessons for the Anthropocene from the Classic Maya collapse. Anthropocene (2014), http://dx.doi.org/10.1016/j.ancene.2013.12.002

M. Morlighem, E. Rignot, J Mouginot, H. Seroussi, and E. Larour. Deeply incised submarine glacial valleys beneath the Greenland Ice Sheet. Nat. Geosci., 2014

Malcolm McMillan, Andrew Shepherd, Aud Sundal, Kate Briggs, Alan Muir, Andrew Ridout, Anna Hogg, Duncan Wingham. Increased ice losses from Antarctica detected by CryoSat-2. Geophysical Research Letters, 2014; DOI: 10.1002/2014GL060111

D. J. Lunt, H. Elderfield, R. Pancost, A. Ridgwell, G. L. Foster, A. Haywood, J. Kiehl, N. Sagoo, C. Shields, E. J. Stone, and P. Valdes, Introduction: Warm climates of the past: a lesson for the future? (2013), Phil. Trans. R. Soc. A 28, doi: 10.1098/rsta.2013.0146