Brief introduction to the Toarcian oceanic anoxic event.

Early Jurassic reconstruction (From Wikimedia Commons)

Early Jurassic reconstruction (From Wikimedia Commons)

In Earth history there have been relatively brief intervals when a very significant expansion of low-oxygen regions occurred throughout the world’s oceans. In mid-1970s the discovery of black shales at many drill sites from the Atlantic, Indian, and the Pacific Ocean led to the recognition of widespread anoxic conditions in the global ocean spanning limited stratigraphic horizons. In 1976, Schlanger and Jenkyns termed these widespread depositional black shale intervals “Oceanic Anoxic Events” (Takashima et al, 2006). This was one of the greatest achievement of the DSDP (Deep Sea Drilling Project).

The Toarcian OAE, Weissert OAE, OAE 1a, and OAE 2 are global-scale anoxic events associated with prominent positive excursions of δ13C and worldwide distribution of black shales. Two models have been proposed to explain it: the stagnant ocean model (STO model) and the expanded oxygen-minimum layer model (OMZ model). Deep-water warming may have also contributed to a decrease in oxygen solubility in the deep ocean and may have triggered the dissociation of large volumes of methane hydrate buried in sediments of the continental margins.

Time scale [Gradstein et al., 2005] illustrating the stratigraphic position and nomenclature of OAEs (From Jenkyns, 2010).

Time scale [Gradstein et al., 2005] illustrating the stratigraphic position and nomenclature of OAEs (From Jenkyns, 2010).

In the Jurassic and Cretaceous oceans, the calcareous nannoplankton was the most efficient rock-forming group, for that reason the characterization of calcareous nannofloras in OAE intervals are used to improve our understanding of the marine ecosystem and biological processes such as photosynthesis (biological pump) and biomineralisation (carbonate pump) that affect the organic and inorganic carbon cycle, as well as adsorption of atmospheric CO2 in the oceans (Erba, 2013). Calcareous nannoplankton represent a major component of oceanic phytoplankton, ranging in size  from 0.25 to 30 μm. The first records are from the Late Triassic. Their calcareous skeletons can be found in fine-grained pelagic sediments in high concentrations and the biomineralization of coccoliths is a globally significant rock-forming process.

The early Toarcian Oceanic Anoxic Event  (T-OAE; ∼183 mya) in the Jurassic Period is considered as one of the most severe of the Mesozoic era. It’s associated with a major negative carbon isotope excursion, mass extinction, marine transgression and global warming (Huang, 2014, Ullmann et al., 2014). The T-OAE has been extensively studied in the past three decades although there is no general consensus about the causes or triggering mechanisms behind this event. During the peak of the perturbation corresponding to this event, calcareous nannofossils collapsed.

 

Schizosphaerella punctulata (adapted from Clémence, 2014)

Schizosphaerella punctulata (adapted from Clémence, 2014)

Schizosphaerella is a nannofossil of uncertain biological affinities with a large globular test with two interlocking sub-hemispherical valves formed from a geometric arrangement of equidimensional crystallites with an average value of 10.5 μm in the major axis. During the Early Jurassic, suffered a major drop in abundance, and a reduction in size. The average values drastically decrease down to 8.3 μm around the interval corresponding to the T-OAE. This event is know as ‘Schizosphaerellid crisis’, ‘calcareous nannofossil crisis’ or ‘disappearance event’ (Erba 2004, Clémence, 2014). Four main hypotheses have been proposed to account for the nannoplankton biocalcification crisis through the early Toarcian: (1) a strong stratification of the water column and the development of an oxygen-minimum zone; (2) the discharge of low salinity arctic waters through the Laurasian seaway; (3) high values in atmospheric pCO2; and (4) a rapid warming (Clémence, 2014).

Results from the Paris Bassin as in other localities indicates that the increasing greenhouse conditions may have caused acidification in the oceans, hampering carbonate bio-mineralisation, and provoking a dramatical loss in the CO2 storage capacity of the oceans. The CO2 induced changes in seawater chemistry likely affected the calcification potential of both neritic and pelagic systems, as evidenced by drops of platform-derived carbonate accumulation and drastic reductions in size of the main carbonate producer Schizosphaerella.

The better understanding of the Mesozoic ocean-climate system and the formation of OAEs would help us to predict environmental and biotic changes in a future greenhouse world.

References:

Marie-Emilie Clémence: Pattern and timing of the Early Jurassic calcareous nannofossil crisis.  Palaeogeography, Palaeoclimatology, Palaeoecology, 2014/doi: 10.1016/j.palaeo.2014.06.022.

Elisabetta Erba, Calcareous nannofossils and Mesozoic oceanic anoxic events, Marine Micropaleontology 52 (2004) 85 – 106

Bown, P.R., Lees, J.A., Young, J.R., (2004), Calcareous nannoplankton evolution and diversity through time. In: Thierstein, H.R., Young, J.R. (Eds.), Coccolithophores From Molecular Processes to Global Impact. Springer, Amsterdan, pp. 481–508.

Jenkyns, H. C. (2010), Geochemistry of oceanic anoxic events, Geochem. Geophys. Geosyst., 11, Q03004, doi:10.1029/2009GC002788.

 

Ancient Greek theater and the past Mediterranean climate.

Theatre of Dionysos, Athens, Greece. From Wikimedia Commons

Theatre of Dionysos, Athens, Greece. From Wikimedia Commons

Ancient manuscripts, paintings and plays  provide valuable information to help modern scientists to reconstruct the climate of the past. The information recovered from these ancient sources are mainly focused on extreme events with a great impact in society like droughts or floods, and other less dramatic conditions. For instance, the analysis of the writings of scholars and historians in Iraq during the Islamic Golden Age between 816 and 1009 AD revealed an increase of cold events in the first half of the 10th century  immediately before the Medieval Warm Period. It’s also possible analyze  volcanic eruptions in the past by studying the colouration of the atmosphere in paintings that portrayed sunsets in the period 1500–1900 AD.

The analysis of the writings of Aeschylus, Sophocles, Euripides and Aristophanes during the Golden Age (5th and 4th centuries B.C) provides a valuable insight into the Mediterranean climate of the time.

A vase illustrating a Lenaia celebration. (Image from the Naples National Archaeological Museum, Italy.)

A vase illustrating a Lenaia celebration. (Image from the Naples National Archaeological Museum, Italy.)

Halcyon days occur in Greece, especially in Attica, and in southeastern Europe in the middle of winter between 15 January and 15 February, during which the halcyon birds were supposed to lay their eggs . The Halcyon days has its origins in an ancient myth. Halcyon was the daughter of Aeolus, the God of the Winds. She was married to Ceyx the King of Thessaly. After his brother died, Ceyx embarked on a voyage across the sea to consult the oracle of Apollo. He died in a storm and Halcyon threw herself into the waters to reunite with him. The gods amazed by her love and devotion, transformed Ceyx and Halcyon into kingfishers. Then, Zeus decreed that the winter sea stay calm for a period of 14 days so that the birds could keep their eggs safe in the winter.

Euripides in Medea wrote about the pleasant and harmonious climate: “Men celebrate in song how Aphrodite, filling her pail at the streams of the fair flowing Cephisus, blew down upon the land temperate and sweet breezes“.

The comedies of Aristophanes, often invoke the presence of the halcyon days. In Birds he mentioned the ‘skiadeion’, a kind of umbrella used solely to protect people from the sunlight rather than rain. Also, the drawn from the paintings on vessels showing that the clothes worn in Lenaia (an annual Athenian festival with a dramatic competition) were not designed for rainy weather.

 

 

 

Reference:

Christina Chronopoulou, A. Mavrakis, ‘Ancient Greek drama as an eyewitness of a specific meteorological phenomenon: indication of stability of the Halcyon days.’ Weather, DOI: 10.1002/wea.2145

Domínguez-Castro F, Vaquero JM, Marín M et al. 2012. How useful could Arabic documentary sources be for reconstructing past climate? Weather 67(3): 76–82. doi:10.1002/wea.83

Zerefos CS, Gerogiannis VT, Balis D, Zerefos SC, Kazantzidis A. 2007. Atmospheric effects of volc anic eruptions as seen by famous artists and depicted in their paintings. Atmos. Chem. Phys. 7: 4027–4042.

Haeckel and the legacy of early radiolarian taxonomists.

Ernst Haeckel and his assistant Nicholas Miklouho-Maclay, photographed in the Canary Islands in 1866. From Wikimedia Commons.

Ernst Haeckel and his assistant Nicholas Miklouho-Maclay, photographed in the Canary Islands in 1866. From Wikimedia Commons.

In the nineteenth century, the study of radiolarians was the domain of German scientists. These early German workers laid the foundation for all future work with this group of organisms, both living and fossil.

Christian Gottfried Ehrenberg (1795–1876) made a series of special monographs from 1838 to 1875 and named the group Polycystina. He described a half-dozen species of both Spumellaria and Nassellaria. Ehrenberg’s microscopic researches also included diatoms and  fossil cyst of dinoflagellates. His book “Mikrogeologie” (1854) has many illustrations of a great number of microfossils.

Many of Ehrenberg’s early radiolarian species descriptions come from Neogene biosiliceous sediments of Italy. Despite the fact he worked before the concept of type specimens for species had become established, Ehrenberg not only documented most of his species with published figures, but preserved the original material and microscope preparations for future generations of scientists to study (Lazarus 2014).

Christian Gottfried Ehrenberg and Johannes Müller. Source: Museum für Naturkunde, Berlin and Humboldt Universität, Berlin.

Christian Gottfried Ehrenberg and Johannes Müller. Source: Museum für Naturkunde,
Berlin and Humboldt Universität, Berlin.

Johannes Müller (1801–1858), one of the most famous German biologists of his generation, published three substantial papers on radiolarians. He described a total of 69 species, including both polycystines and acantharians. As a professor on Berlin’s Medical Faculty, he  influenced a great number of students. Among them were Ernst Haeckel (1834-1919) and Rudolf Virchow (1821-1902).

Like  Ehrenberg, Müller never believed that species had evolved over time, and he died before the publication of Charles Darwin’s Origin of Species.

After Müller’s death, E. Haeckel focused on the group last studied by his friend and professor: the radiolarians. With a copy of Müller’s paper and a wealth of material available off Messina, Haeckel began the first of his major studies of nature.

il_570xN.210850396

In 1862, Haeckel made the first complete  classificatory system for the Radiolaria and produced finely detailed drawings of them in his book: “Die Radiolarien”. He dedicated this monograph to Müller. In this work, he  included polycystines, phaeodarians and acantharians.

In 1864, Haeckel sent to Darwin, two folio volumes on radiolarians. The gothic beauty of these drawings impressed Darwin. He wrote to Haeckel that “were the most magnificent works which I have ever seen, and I am proud to possess a copy from the author”.

Haeckel became the most famous champion of Darwinism in Germany and he was so popular that, previous to the First World War, more people around the world learned about the evolutionary theory through his work “Natürliche Schöpfungsgeschichte” (The History of Creation: Or the Development of the Earth and its Inhabitants by the Action of Natural Causes) than from any other source. His study of radiolarians established Haeckel as a young scientist of importance. Later, Haeckel focused his research in the more general aspects of evolution and development.

Ernst Haeckel's ''Kunstformen der Natur'' (1904), showing Radiolarians of the order Stephoidea. From Wikimedia Commons.

Ernst Haeckel’s ”Kunstformen der Natur” (1904), showing Radiolarians of the order Stephoidea. From Wikimedia Commons.

Along with many other scientists, Haeckel was asked by the managers of the Challenger Expedition soon after the ship’s return to examine and report on the expedition’s collections specifically for radiolarians, sponges and jellyfish. Haeckel’s Report on Radiolaria took him almost a decade.

His final report was published in 1887 and summarized and subsumed all prior work on radiolarians up to that point, including, for example, many of Ehrenberg’s species and genera. But while Ehrenberg eschewed higher taxa, except for a minimally adequate number of obvious, high-level groupings, Haeckel did the opposite thing and introduced a much enlarged and substantially more complex higher-level taxonomy for the radiolaria generating numerous duplicate lower-level categories, including species, which led to an unusually large percentage of Haeckel’s named species being ignored as redundant or meaningless (Lazarus, 2014).

In 1904, Haeckel published his master work “Kunstformen der Natur” (Art Forms of Nature) and helped to popularize radiolarians among scientists and the general audience.

Radiolaria illustration from the Challenger Expedition 1873–76. From Wikimedia Commons.

Radiolaria illustration from the Challenger Expedition 1873–76. From Wikimedia Commons.

Karl Alfred Ritter von Zittel (1839-1904), was a prominent German paleontologist.  His early research was in minerals and petrography. In 1876, he published “Ueber einige fossile Radiolarien aus der norddeutschen Kreiden. Zeitschrift der deutschen geologischen Gesellschaft” where he described Mesozoic radiolarians in northern Germany. Many of the species names proposed by Zittel are still valid today.

David Rüst (1831–1916) published 10 papers on radiolarians. Although he was not the first to describe Mesozoic radiolarians, he was certainly the most prolific describing over 900 new species of fossil radiolarians from Mesozoic and even Palaeozoic rocks from Europe and North America.

 

References:

David Lazarus, The legacy of early radiolarian taxonomists, with a focus on the species published by early German workers, Journal of Micropalaeontology 2014, v.33; p3-19.

Robert J. Richards, The Tragic Sense of Life: Ernst Haeckel and the Struggle over Evolutionary Thought, (2008), University of Chicago Press.

The palynological record and the extinction events.

The main palynological provinces at the end of the Cretaceous (From Vajda and Bercovici, 2014)

The main palynological provinces at the end of the Cretaceous (From Vajda and Bercovici, 2014)

Pollen and other palynomorphs proved to be an extraordinary tool to palaeoenvironmental reconstruction. In 1921, Gunnar Erdtman, a Swedish botanist, was the first to suggest this application for fossil pollen study. Like spores, pollen grains reflects the ecology of their parent plants and their habitats and provide a continuous record of their evolutionary history. Pollen analysis involves the quantitative examination of spores and pollen at successive horizons through a core, specially in lake, marsh or delta sediments. The morphology of pollen grains is diverse. Gymnosperm pollen often is saccate (grains with two or three air sacs attached to the central body), while Angiosperm pollen shows more variation and covers a multitude of combinations of features: they could be  in groups of four (tetrads),  in pairs (dyads),  or single (monads). The individual grains can be inaperturate, or have one or more pores, or slit-like apertures or colpi (monocolpate, tricolpate).

Since the 1980s, many fossil pollen data sets were developed specifically to reconstruct past climate change.

Aquilapollenites quadricretaeus and Nothofagidites kaitangata

Aquilapollenites quadricretaeus and Nothofagidites kaitangata

 

The palynological record across the Cretaceous–Paleogene (K–Pg) boundary  is a unique global  marker that can be use as template to asses the causal mechanism behind other major extinction events in Earths history. Four major palynological provinces have been recognized based on distinctive angiosperm pollen and fern spores of restricted geographic and stratigraphic distribution. The Aquilapollenites Province had a northern circumpolar distribution that extended from Siberia, northern China, Japon and the western North America. The Normapolles Province occupied eastern North America,  Europe and western Asia. The Palmae Province occupied equatorial regions in the Late Cretacic and included SouthAmerica, Africa and India. Finally, the Notofagidites Province that extended across southern South America, Antartica, New Zeland and Australia.

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. Although, during the middle Maastrichtian, there was a short-lived warming event related to an increase in atmospheric carbon dioxide from the first Deccan eruption phase, the global climate cooled during the latest Maastrichtian and across the K–Pg boundary (Wang et al., 2014; Brusatte et al., 2014). The variations in floral composition reflect these paleoclimatic changes.

Fern spike adapted from Bercovicci

Fern spike adapted from Bercovicci

Mainly angiosperms, disappear at the boundary, as evidenced the palynofloral records of North America and New Zealand. 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.

The earliest Paleocene vegetation shows an anomalous concentration of fern spores just above the level of palynological extinction. R. H. Tschudy, in 1984,  was the first to recognize this very distinctive pattern when he analyzed samples from the K/PG boundary and observed that just after the extinction event, the palynological assemblages were dominated by a high abundance of fern spores.

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)

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. 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.

Despite their difference, these three extinction events are consequences of dramatic environmental upheavals that generated comparable extinction patterns, and similar phases of vegetation recovery but at different temporal scales. First, all these events share a similar pattern of a short-term bloom of opportunistic “crisis” taxa proliferating in the devastated environment. Second, there’s a pulse in pioneer communities (spore spike). Third , a recovery in diversity including the evolution of new taxa. Furthermore, the longer the extreme environmental conditions last the greater is the extinction rate and the extinction patterns between autotrophs and heterotrophs, and between terrestrial and marine faunas become more similar (Vajda and Bercovici, 2014).

 

References:

Vivi Vajda & Antoine Bercovici (2014); The global vegetation pattern across the Cretaceous–Paleogene mass extinction interval: A template for other extinction events; Global and Planetary Change (advance online publication) Open Access DOI: 10.1016/j.gloplacha.2014.07.014, http://www.sciencedirect.com/science/article/pii/S0921818114001477

Vajda, V., Raine, J.I., 2003. Pollen and spores in marine Cretaceous/Tertiary boundary sediments at mid–Waipara River, North Canterbury, New Zealand. New Zealand Journal of Geology and Geophysics 46, 255–273

Wang, Y., Huang, C., Sun, B., Quan, C., Wu, J., Lin, Z., 2014. Paleo-CO2 variation trends and the Cretaceous greenhouse climate. Earth-Science Reviews 129, 136–147.

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. DOI 10.1016/j.palaeo.2014.04.018

Barreda VD, Cúneo NR, Wilf P, Currano ED, Scasso RA, et al. (2012) Cretaceous/Paleogene Floral Turnover in Patagonia: Drop in Diversity, Low Extinction, and a Classopollis Spike. PLoS ONE 7(12): e52455. doi: 10.1371/journal.pone.0052455

Brusatte, S. L., Butler, R. J., Barrett, P. M., Carrano, M. T., Evans, D. C., Lloyd, G. T., Mannion, P. D., Norell, M. A., Peppe, D. J., Upchurch, P., and Williamson, T. E. In press. The extinction of the dinosaurs.Biological Reviews

African paleoclimate and early hominin evolution.

Olduvai Gorge. From Wikimedia Commons

Olduvai Gorge. From Wikimedia Commons

Over the last ten million years the landscape of East Africa has been altered dramatically. It has changed from a relatively flat, homogenous region covered with tropical mixed forest, to a heterogeneous region, with mountains over 4 km high and vegetation ranging from desert to cloud forest. Long-term climate change seems to be modulated primarily  by tectonic changes. The progressive formation of the East African Rift Valley led to increased aridity and the development of numerous lake basins.

Five major transitions have influenced African climate during the early stage of human evolution: 1)  the emergence of  and expansion of C4 biomes (~8 Ma); 2) The Messinian Salinity Crisis (~ 5.3 Ma); 3)  the Intensification of Northern Hemisphere Glaciation during the Pliocene epoch between 3.6 and 2.7 million years ago;  4) the development of the Walker Circulation; 5) the Early-Middle Pleistocene Transition.

Map of East Africa with modern lake and paleolake basins (from Maslin et al., 2014)

Map of East Africa with modern lake and paleolake basins (from Maslin et al., 2014)

It has been hypothesized that both the uplift of the Tibetan Plateau about 8 Ma ago and the reduction of the Paratethys Sea intensified the seasonal Indian monsoon climate,  and that the more seasonal climate favored grasses over trees.

The isolation of the Mediterranean Sea from the Atlantic Ocean was caused by the tectonic closure of the Strait of Gibraltar. During the Messinian Salinity Crisis, the Mediterranean Sea went into a cycle of partly or nearly complete desiccation and removed nearly 6% of all dissolved salts in the oceans.

The Intensification of  Northern Hemisphere Glaciation (iNHG), the third regional climate event,  was characterised by periodic advances and retreats of ice sheets on a hemispherical scale and was the culmination of long-term high latitude cooling, which began with the Late Miocene.

Diatomites of the genera Stephanodiscus and Aulacoseira. (From Kingston et al., 2007)

Diatomites of the genera Stephanodiscus and Aulacoseira. (From Kingston et al., 2007)

The Early-Middle Pleistocene Transition, represents a major global climatic reorganization that profoundly affected ocean and atmospheric circulation, ice sheets and the distribution and evolution of biota.

The diatomite deposits from Pliocene lakes in the Baringo Basin suggest that the lakes appear rapidly, remain part of the landscape for thousands of years, then disappear in a highly variable and erratic way. Two dominant genera of diatoms present in East African lakes and Pliocene-Recent deposits helps to understand the dynamic of these humidity/aridity cycles: Aulacoseira predominates under cool windy conditions, while Stephanodiscus predominates under warmer, less windy conditions. The segregation of Aulacoseira and Stephanodiscus into subtle layers on a scale of < 100 mm and the presence of micro-laminae on a scale of one hundred to a few hundred microns suggest cyclic variation in a time frame of one to a few years (Kingston et al., 2007).

Early human evolutionary theories and climate change. From Maslin et al. 2014

Early human evolutionary theories and climate change. From Maslin et al. 2014

The major events in hominin evolution have occurred in East Africa. Several theories have been developed to explain the interaction between African paleoclimate and early hominid evolution. The savannah hypothesis suggested that hominins were forced to descend from the trees and adapted to life on the savannah facilitated by walking erect on two feet. This idea was already outlined by Lamarck in his Philosophie zoologique (1809], where he describes in details how an early ancestor of primeval human abandons an arboreal life to adapt itself to open plains.

More recent, the pulsed climate variability hypothesis  highlights the role of short periods of extreme climate variability specific to East Africa in driving hominin evolution and subsequent dispersal events (Maslin and Trauth, 2009). These periods of ‘pulsed climate variability’ are characterized by the appearance and disappearance of large, deep lakes in the East African Rift Valley. Paleoclimatic information derived from benthic foraminifera, regional aeolian dust flux data and the East African lake record indicates that hominin speciation events and changes in brain size seem to be statistically linked to the occurrence of ephemeral deep-water lakes (Shultz and Maslin, 2013).

References:

Maslin M.A., C. Brierley, A. Milner, S. Shultz, M. Trauth, K. Wilson “East African climate pulses and early human evolution” Quaternary Science Reviews (2014).

Maslin M.A., ‘Cascading uncertainty in Climate Change models and its implications for policy’ Geographical Journal 179, 264-271 (2013)

Ashley, G., Bunn, H., Delaney, J., Barboni, D., Domínguez-Rodrigo, M., Mabulla, A., Gurtov, A., Baluyot, R., Beverly, E., Baquedano, E., 2014. Paleoclimatic and paleoenvironmental framework of FLK North archaeological site, Olduvai Gorge, Tanzania. Quat. Int. 322e323, 54-65.

Shultz S, Maslin M (2013) Early Human Speciation, Brain Expansion and Dispersal Influenced by African Climate Pulses. PLoS ONE 8(10): e76750. DOI: 10.1371/journal.pone.0076750

John D. Kingston et al., Astronomically forced climate change in the Kenyan Rift Valley 2.7- 2.55 Ma: implications for the evolution of early hominin ecosystems, J Hum Evol (2007), doi:10.1016/j.jhevol.2006.12.007

Brief introduction to Paleobiology of South American titanosaurs.

 

Argentinosaurus huinculensis reconstruction at Museo Municipal Carmen Funes, Plaza Huincul, Neuquén, Argentina. PLoS ONE. From Wikimedia Commons.

Argentinosaurus huinculensis reconstruction at Museo Municipal Carmen Funes, Plaza Huincul, Neuquén, Argentina. PLoS ONE. From Wikimedia Commons.

Titanosaurus were a diverse group of sauropod dinosaurs represented by more than 30 genera, which included all descendants of the more recent common ancestor of Andesaurus  and Saltasaurus (Wilson and Upchurch, 2003). They were important terrestrial herbivores during the Jurassic and the Cretaceous periods. The group exhibits a worldwide distribution and  some of them, were the largest animals to ever walk the Earth: Argentinosaurus, Futalognkosaurus, and Puertasaurus surpassed lengths of 30m and masses of 70 tons.

The discoveries in Patagonia of embryos, eggs (Chiappe et al., 1998, 2001; Salgado et al., 2005; García et al., 2010) and exceptionally articulated specimens show the importance of the South American record for understanding the phylogeny and paleobiology of titanosaurs.

Paleoenvironmental reconstruction of the egg-bearing lower section of the Anacleto Formation at Auca Mahuevo and Los Barreales localities. From Garrido 2010

Paleoenvironmental reconstruction of the egg-bearing lower section of the Anacleto Formation at Auca Mahuevo and Los Barreales localities. From Garrido 2010

The hundreds of eggs containing embryos found in the outcrops of the Anacleto Formation at Auca Mahuevo and Los Barreales corroborated the hypothesis that sauropods were oviparous. The eggs were relatively small (10–25 cm of diameter) and were found  in excavated nests. The embryos from Auca Mahuevo present an ‘egg-tooth’-like structure which is more frequent in altricial birds (García, 2007a, 2008). If we assume that titanosaurs followed a sequence of ontogenetic stages similar to modern birds, these embryos would correspond with the stage 36-37, within the 42 prenatal stages established for birds.

The titanosaur embryos discovered in Auca Mahuevo are exclusively represented by cranial material. Comparing the skull of adults titanosaurs with the embryos from Auca Mahuevo, it seem evident that the Patagonian dinosaurs experienced a deep ontogenetic modification in this part of the skeleton.

Ontogenetic variation in titanosaurian skull morphology. From García et al, 2014.

Ontogenetic variation in titanosaurian skull morphology: aof, antorbital fenestra; en, external nares; f, frontal; j, jugal; l, lacrimal; mx, maxilla; o, orbit; paof, preantorbital fenestra; pmx, premaxilla; qj, quadratojugal; vn, ventral notch. From García et al, 2014.

The rostral portion of the embryonic skull never surpasses 50% of the total skull length while adult sauropods possess a relatively elongated skull. The premaxillae of  the embryos have extremely short nasal processes contrary to those of adult titanosaurs. It’s possible that the remodeling of the premaxillae in the ontogeny has implicated the elongation of the nasal process as well, which in turn would be related to the ontogenetic retraction of the external nares (García et al, 2014). The type of teeth is basically similar in the embryos and those of the few known adult titanosaur skulls, which may be indicative of the same basic diet.

The brain morphology shows a tendency to the reduction of the midbrain and the olfactory tract and bulbs. Titanosaurs also exhibit a reduction of the anterior semicircular canal of the inner ear and a robustness of the labyrinth in comparison with other sauropods.

Shoulder and pelvic girdle architecture of titanosaurs suggests a broader posture than that other sauropods, which is related to a shift in the specific muscular attachments that would counteract the wide posture of the limbs (García et al, 2014).

The ichnological record offers valuable information about different strategies of titanosaur locomotion and behavior. Most of the trackways are parallel and show the same direction of travel which is indication that titanosaurs moved in social groups.

References:

GARCÍA, Rodolfo A. et al. PALEOBIOLOGY OF TITANOSAURS: REPRODUCTION, DEVELOPMENT, HISTOLOGY, PNEUMATICITY, LOCOMOTION AND NEUROANATOMY FROM THE SOUTH AMERICAN FOSSIL RECORD, doi:10.5710/AMGH.16.07.2014.829. Ameghiniana, [S.l.], jul. 2014. ISSN 1851-8044

Sellers WI, Margetts L, Coria RA, Manning PL (2013) March of the Titans: The Locomotor Capabilities of Sauropod Dinosaurs. PLoS ONE 8(10): e78733. doi:10.1371/journal.pone.0078733

The early history of ammonite studies in Italy.

Sin título

Ammonites figured by Aldrovandi on his Musaeum Metallicum.

Since antiquity, ammonites has been associated with myths, legends, religion and even necromancy. You can find reference to these fossils in the works of Emilio Salgari, Sir Walter Scott, Friedrich Schiller and Johann Wolfgang von Goethe.

From the sixteenth to the late eighteenth centuries, the study of ammonites in Italy was crucial in the debate about the real nature of fossil remains. Leonardo describes the ammonites of the Veronese mountains in the code Hammer (formerly Codex Leicester), folio 9, where he identified these fossils as lithified remains of organisms.

Ulisse Aldrovandi describes several specimens of ammonites in his Musaeum Metallicum.  Aldrovandi supported the idea of the inorganic origin of fossils, although he often compared them with existing animals. He recognized some resemblance between ammonites and snakes so he used the term ‘Ophiomorphites’ (or snake-shaped stone).

Ammonites illustration of the Metallotheca Vaticana of Michele Mercati.

Ammonites illustration of the Metallotheca Vaticana of Michele Mercati. Two examples of the ammonites described: Calliphylloceras and Phylloceras

In 1574, Michele Mercati organises the famous Metallotheca Vaticana, where describes several ammonites. But he fully embraces the inorganic interpretation of fossils, a real setback with respect to the pioneering hypothesis previously formulated by Leonardo da Vinci. Mercati treats the fossils with he generic term ‘Lapides idiomorphoi’ (stones equipped with proper shape).

In the seventeenth century, the Italian painter Agostino Scilla  compiled an enormous body of evidence, well reasoned and convincing, in favour of the organic nature of fossils found on hills and mountains (Romano, 2014). . However, there is no mention of ammonites is his work. Paolo Silvio Boccone (1633–1704) a Sicilian naturalist and botanist, also supported of the organic nature of fossils. In ‘Recherches et Observations Naturelles’ (1674), he wrote that ammonites – at that time called ‘Corne d’Ammone’ or ‘Corne de Belier’-  represent models (internal) while the original shells of organisms must have  been ‘calcined’ or ‘pulverised’.

Cover of De conchis minus notis and foraminifera of Rimini’s seaside figured by Bianchi (1739, Table I) and attributed by the author to microscopic specimens of ‘Cornu Ammonis’.

Cover of De conchis minus notis and foraminifera of Rimini’s seaside figured by Bianchi (1739, Table I) and attributed by the author to microscopic specimens of ‘Cornu Ammonis’.

In the first half of the eighteenth century, Bartolomeo Beccari began to study tiny shells that could only be observed under the microscope and classified these organisms as microscopic ‘Corni di Ammone’, continuing with the enduring confusion between cephalopods and foraminifera that started in 1565 when Conrad Gesner described the nummulites collected in the surroundings of Paris. Also Giovanni Bianchi (known by the pseudonym Jaco Planco) in his work De conchis minus notis (1739) describes numerous microforaminifera that are found in abundance on the shoreline of Rimini and assigns them the name ‘Corni di Ammone’. This confusion between cephalopods and foraminifera persisted until the French naturalist Alcide d’Orbigny, after 6 years of analysis, arrived to the correct conclusion that these microscopic organisms are a distinct order to which he gave the name of Foraminifera.

References:

Marco Romano, From petrified snakes, through giant ‘foraminifers’, to extinct cephalopods: the early history of ammonite studies in the Italian peninsula, Historical Biology 2014, http://dx.doi.org/10.1080/08912963.2013.879866

Vai, G.B. and Cavazza,W. (Eds) 2003. Four Centuries of the Word Geology, pp. 1–315. Ulisse Aldrovandi 1603 in Bologna. Minerva Edizioni; Bologna.

The Megaraptor mystery.

 

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

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 3 cm. From Porfiri et al. 2014.

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

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.

Mary Somerville, Queen of Science.

 

(From Wikimedia Commons)

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.”

Sin título2

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.