Mignon Talbot and the forgotten women of Paleontology.

 

Sin título

Mignon Talbot  (From Turner et al, 2010)

 

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

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

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

Podokesaurus holyokensis holotype (From Wikimedia Commons)

Podokesaurus holyokensis holotype (From Wikimedia Commons)

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

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

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

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

References:

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

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

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

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

 

The Poetry of the Ice Age.

Joseph Mallord William Turner Source of the Arveron in the Valley of Chamouni Savoy 1816 (Image from The Tate Gallery)

Joseph Mallord William Turner
Source of the Arveron in the Valley of Chamouni Savoy
1816 (Image from The Tate Gallery)

Glaciers occupy a privileged site between narrative and science. Percy Shelley’s “Mont Blanc: Lines Written in the Vale of Chamonix“ (1816) used the landscape as a metaphor to analyze the relationship between the human mind and the universe.

Far, far above, piercing the infinite sky,
Mont Blanc appears,— still, snowy, and serene —
Its subject mountains their unearthly forms
Pile around it, ice and rock; broad vales between
Of frozen floods, unfathomable deeps,
Blue as the overhanging heaven, that spread
And wind among the accumulated steeps.

And of course, Mer de Glace, on the slope of the mountain, is where Victor Frankenstein reunited with his Creature: “…From the side where I now stood Montenvers was exactly opposite, at the distance of a league; and above it rose Mont Blanc, in awful majesty…. The sea, or rather the vast river of ice, wound among its dependant mountains, whose aerial summits hung over its recess….” (Mary Shelley, Frankenstein, 1818)

Johann Wolfgang von Goethe,  one of the world’s greatest poets, was also a great naturalist. More important, he was the very first to believe in an ice age. Jean de Charpentier (1786- 1855)  in Essai sur les glaciers presented Goethe’s theories of glacial transport (Charpentier, 1841, p . v).

Jean Louis Agassiz in 1870 (From Wikimedia Commons)

Jean Louis Agassiz in 1870 (From Wikimedia Commons)

In 1837, Karl Friedrich Schimper, a  German botanist and geologist, wrote a poem to commemorate Galileo’s birthday, Die Eiszeit: fur Freunde gedruckt am Geburtstage Galilei.  The expression Eiszeit—“ice age”— appeared for the first time in this poem. One of its stanzas says:

Last vestige of the primal ice,
more ancient than the Alps!
Primal ice of yore, when the might of frost
buried mountain high even the South,
enveloped mountain and sea alike!

Karl Schimper was born in Mannheim, Germany, on February 15th, 1803. During the summer of 1835, he was studying mosses which were growing on erratic boulders in the alpine upland of Bavaria and came to the conclusion that ice must have been the means of transport for the boulders.

Based on the works of Schimper and de Charpentier,  Louis Agassiz (1801–1873) presented his “Discours de Neuchatel,” at the annual meeting of the Swiss Society of Natural Sciences on July 24, 1837. In this seminal work, he proposed that the Earth had been subject to a past ice age.

References:

Kate Flint, The Victorians and the Visual Imagination, Cambridge University Press, 2000.

Tobias Krüger, Discovering the Ice Ages: International Reception and Consequences for a Historical Understanding of Climate, BRILL, 2013.

A brief introduction to Dinosaur Herbivory.

 

Artist’s impression of the eastern flank of the Antarctic Peninsula during theMaastrichtian (Artist: James McKay, University of Leeds.)

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

Dinosaurs had diverse feeding mechanisms that strongly influenced their ecology and evolution. Herbivory probably evolved independently in derived silesaurids and various dinosaur groups. Although in the early Late Triassic, dinosaur herbivores were rare, by the early Middle Jurassic until the end of the Cretaceous, they became the dominant vertebrate herbivores.

Herbivory  requires numerous physiological, anatomical, and behavioral adaptations,  including cranial modifications and specialization of the gastrointestinal tract. On the contrary, plants have developed certain features to dissuade herbivores, and evolved to compensate the effects of herbivory by extending growing periods, delaying leaf senescence, and improving nutrient and water availability to surviving leaves (Barret, 2014). Notwithstanding, some plants attract herbivores to enable seed dispersal or pollination, usually by producing fleshy fruits or nectar. The sum of these factors lead to diverse mutualistic interactions between plants and vertebrate herbivores.

Possible interactions between anatomical and physiological traits in herbivorous dinosaurs. From Barret, 2014

Possible interactions between anatomical and physiological traits in herbivorous dinosaurs. From Barret, 2014

The evolution of sauropod herbivory was intimately associated with increased body size and quadrupedal locomotion. In Gondwanan faunas, titanosaurian sauropods were the principal herbivorous dinosaurs.

Several anatomical features enabled sauropods to ingest and digest massive quantities of vegetation (approximately up to 40 kg per day), much of it probably low in nutritional quality. Their long necks helped them to reach vegetation inaccessible to other herbivores, and their large bodies enabled the slower passage of plants through the gut with longer periods of gut fermentation, which allowed that enzymes chemically degrade very hard plants or large amounts of foliage, without employ other mechanical methods for breaking down food (although, is very common found sauropod skeletons with gastroliths).

Differences in body size, skull morphology, neck length, mobility, and dental features probably allowed coexisting sauropods to target different food sources and feed in distinct ways. Bonitasaura, a small sauropod from the Late Cretaceous of Argentina, may have been adapted for feeding on harder vegetation close to the ground. This is very different to the usual image of sauropods browsing high in the treetops and may have been a common feeding strategy among sauropods (Brusatte, 2012).

Triassic cycadophytes from Argentina: A) Pseudoctenis spatulata Du Toit; B) Taeniopteris Brongniart . From Cúneo et al, 2010

Triassic cycadophytes from Argentina: A) Pseudoctenis spatulata Du Toit; B) Taeniopteris Brongniart . From Cúneo et al, 2010

There were profound changes in floral composition and structure during the Mesozoic, including the rise of ferns, cycadophytes, and conifers during the Triassic and Jurassic, followed by the sharp decline of cycadophyte abundance and richness in the Early Cretaceous, and the origin and subsequent diversification of angiosperms. All these floral events have been linked to changes in dinosaur ecology, but currently the evidence for coevolutionary interactions between plants and dinosaurs is weak.

Reference:

Paul Barret, Paleobiology of Herbivorous Dinosaurs, Annu. Rev. Earth Planet. Sci. 2014. 42:207–30, DOI: 10.1146/annurev-earth-042711-105515

Brusatte SL, Benton MJ, Ruta M, Lloyd GT. 2008. The first 50 Myr of dinosaur evolution: macroevolutionary pattern and morphological disparity. Biol. Lett. 4:733–36

Langer MC, Ezcurra MD, Bittencourt JS, Novas FE. 2010. The origin and early evolution of dinosaurs. Biol. Rev. 85:55–110

Martínez RN, Sereno PC, Alcober OA, Colombi CE, Renne PR, et al. 2011. A basal dinosaur from the dawn of the dinosaur era in southwestern Pangaea. Science 311:206–10

Tiffney BH. 1992. The role of vertebrate herbivory in the evolution of land plants. Palaeobotanist 41:87–97

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.

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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.