Ischigualasto, and the discovery of Herrerasaurus.

Ischigualasto National Park . From Wikimedia Commons.

Ischigualasto National Park . From Wikimedia Commons.

Ischigualasto is an arid, sculpted valley, in northwest Argentina (San Juan Province), limiting to the north with the Talampaya National Park, in La Rioja Province. Both areas belong to the same geological formation: the Ischigualasto-Villa Unión Basin, which is centered on a rift zone that accumulated thick terrestrial deposits during the Triassic.

The most accepted hypothesis gives the name “Ischigualasto” a Quechua origin, meaning “place where the moon sets”. A second hypothesis suggested that the name “Ischigualasto” has Diaguita roots and means “place of death”.

Time-stratigraphic chart for Middle–Upper Triassic rocks of the Ischigualasto basin. (Currie, 2009)

Time-stratigraphic chart for Middle–Upper Triassic rocks of the Ischigualasto
basin. (Currie, 2009)

During Mesozoic time, the southwestern margin of Pangea produced a region of extensional deformation cratonward of the proto-Andean magmatic arc, and the Ischigualasto basin is one of a series of continental-rifts that developed in the region as a result of this extension.

The Ischigualasto Formation has 300–700 m of mudstone, sandstone, conglomerate, and basalt, and consists of four lithostratigraphic members which in ascending order include the La Peña Member, the Cancha de Bochas Member, the Valle de la Luna Member, and the Quebrada de la Sal Member.

Several thin volcanic ash horizons, indicates that the deposition of the Ischigualasto Formation began at the Carnian Stage (approximately 228 mya).

Alfred Sherwood Romer (1894-1973) Credit: Courtesy of the Harvard University News Service

Alfred Sherwood Romer (1894-1973)
Credit: Courtesy of the Harvard University News Service

Adolf Stelzner in 1889 published the first data on the geology of Ischigualasto, but it was not until 1911 that Guillermo Bodenbender briefly refers to the fossils of the site. In the early 40′s, Joaquin Frenguelli, initiates a geological survey in the western margen of the basin. Later, in 1943, Angel Cabrera described fragmentary therapsid fossils.

On April, 1958, after an expedition of 6 month in Mendoza Province (south of San Juan Province) with negative results, Alfred Romer arrived to Ischigualasto for first time. He found a rhynchosaur skull the following day, and other fossil finds were reported by every crew member. On May 14, Romer wrote in his field notebook: “more and more fossils coming in daily, in blocks and packages.”

In the same year, but a few months after Romer’s expedition, the University of Tucumán sent a team led by Osvaldo Reig and Jose Bonaparte.

Skull of Herrerasaurus ischigualastensis (Sereno, 2013)

Skull of Herrerasaurus ischigualastensis discovered in 1958 by the Harvard Paleontological Expedition (Sereno, 2013)

The first skull and skeleton of Herrerasaurus were discovered by Romer in 1958 (five years before  Osvaldo Reig described it), but the fossils from Romer’s expedition, were impounded for two years at the port in Buenos Aires, and when finally arrived at Harvard they were set aside.

In 1961, the Argentinian team arrived to Valle Pintado, in the Cancha de Bochas Member of the Ischigualasto Formation, with the help of the local rancher Victorino Herrera, where they found the posterior one-half of a skeleton. That specimen was later designated as Herrerasaurus ischigualastensis.

Jose Bonaparte continued to work in the Ischigualasto Formation periodically in the late 1960s and early 1970′s.

In 1988, a joint expedition between the Universidad Nacional de San Juan, the Museo Argentino de Ciencias Naturales “Bernardino Rivadavia” in Buenos Aires and the University of Chigaco, lead by Paul Sereno and Fernando Novas discovered the first complete skeletons of Herrerasaurus ischigualastensis.

Victorino Herrera and his wife, in San Juan, 1991. From Sereno, 2013

Victorino Herrera and his wife, in San Juan, 1991. From Sereno, 2013

References.

Currie, B. S., C. E. Colombi, N. J. Tabor, T. C. Shipman, and I. P. Montanez. 2009. Stratigraphy and architecture of the Upper Triassic Ischigualasto Formation, Ischigualasto Provincial Park, San Juan, Argentina. Journal of South American Earth Sciences 27:74–87.

Paul C. Sereno (2012) Preface, Journal of Vertebrate Paleontology, 32:sup1, 1-9, DOI: 10.1080/02724634.2013.819809

Ricardo N. Martínez , Cecilia Apaldetti , Oscar A. Alcober , Carina E. Colombi , Paul C. Sereno , Eliana Fernandez , Paula Santi Malnis , Gustavo A. Correa & Diego Abelin (2012) Vertebrate succession in the Ischigualasto Formation, Journal of Vertebrate Paleontology, 32:sup1, 10-30, DOI: 10.1080/02724634.2013.818546

 

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Agostino Scilla and the true nature and origin of fossils.

Agostino Scilla (1629-1700)

Agostino Scilla (1629-1700)

At the beginning of the sixteenth century and throughout the seventeenth century a great debate about the true nature of and the origin of fossils started in Italy, the cradle of Leonardo and Aldrovandi. There was two hypothesis in dispute: the first one postulated an inorganic origin for the fossils (directly formed within rocks) and the second, which contemplated an organic origin.

The most strong supporter for the organic origin of fossils was the italian painter Agostino Scilla. He was born in Messina on August 10, 1629. He was  a disciple of Antonio Barbalunga in Messina and Andrea Sacchi in Rome, and later became a member of the Academy of Messina ‘della Fucina.

Original frontispiece of ‘La vana speculazione disingannata dal senso by A. Scilla

Original frontispiece of ‘La vana
speculazione disingannata dal senso by A. Scilla

He published only one scientific treatise: La vana speculazione disingannata dal senso, lettera risponsiva Circa i Corpi Marini, che Petrificati si trouano in vari luoghi terrestri (The vain speculation disillusioned by the sense, response letter concerning the marine remains, which are found petrified in various terrestrial places). The aim of the work was the demonstration that fossils, which are found embedded in sediments on mountains and hills, represent the remains of lithified organisms, which at one time lived in the marine environment. The text was later translated to Latin and it was written as a response to a letter sent to him by Giovanni Francesco Buonamico, a doctor from Malta.

Scilla  applied a method of analysis that we today define, in all respects, empirical and scientific and his observations constitute the seeds for the emergence of taphonomy and paleontology in general. The central theme of Scilla’s work was the demonstration that the ‘Glossopetrae’ (shark teeth) and other petrified objects resembling living animals actually represent the remains of organisms that once lived in the sea. He thought that the correspondence of so many parts, well structured and coincident in the fossil, cannot be due to a coincidence or  a freak of nature.

Several shark teeth (Glossopetrae) (II and III in the original plate). From Scilla, 1670, plate VII.

Several shark teeth
(Glossopetrae) (II and III in the original plate). From Scilla, 1670, plate VII.

Like Aldrovandi, he thought that the natural world must first be analysed in the field by direct observation. He went to fossiliferous sites himself, especially a locality name Musorrima, near the city of Reggio Calabria.

He was also a pioneer in the field of taphonomy. For example, starting from the original shape that characterises echinoids in life, Scilla  infers that many shells had been compressed and crushed by the weight of the sediment after burial, and he pointed out that individual shells were deformed in different ways, in relation to how they were oriented in the sediment and thus in relation to the direction of the compressive force.

Illustration of sea urchins compressed and fractured in different ways. From Scilla, 1670, plate XXVI.

Illustration of sea urchins compressed and fractured in different ways. From Scilla, 1670, plate XXVI.

Scilla’s writing includes some fundamental concepts for paleontology and the geological sciences like: actualism, taphonomy, preservation through the process of internal/external moulding and basic sedimentology.

References:

Romano, Marco, Historical Biology (2013): ‘The vain speculation disillusioned by the sense’: the Italian painter Agostino Scilla (1629–1700) called ‘The Discoloured’, and the correct interpretation of fossils as ‘lithified organisms’ that once lived in the sea, Historical Biology: An International Journal of Paleobiology, DOI: 10.1080/08912963.2013.825257

To see the world in a grain of sand: Planktonic foraminifera and Evolution.

Planktonic foraminifera. (Credit: Paul Pearson, Cardiff University)

Planktonic foraminifera. (Credit: Paul Pearson, Cardiff University)

“To see the world in a grain of sand…”, this is the first line of William Blake´s poem “Auguries of Innocence” which describe a series of paradoxes about innocence, evil and corruption. But in a biological sense, this line can also describe how “a grain of sand” could gives a glimpse of how evolution works using the remains of planktonic foraminifera which resemble grains of sand to the naked eye and date back hundreds of millions of years.

Foraminifera are an important group of single celled protozoa with shells of different composition and granuloreticulose pseudopodia.  The first record of the group is from the Early Cambrian and extend to the present day. Their size range is from about 100 micrometers to almost 20 centimeters long.

Planktonic foraminifera from the Sargasso Sea in the North Atlantic Ocean. (Photograph courtesy Colomban de Vargas, EPPO/SBRoscoff.)

Planktonic foraminifera from the Sargasso Sea in the North Atlantic Ocean. (Photograph courtesy Colomban de Vargas, EPPO/SBRoscoff.)

Planktonic foraminifera are ideal subjects for testing how species evolve over time. They are a diverse extant clade that have an exceptional fossil record, due to extremely large population sizes and widespread species distributions. They also can record the climate and environmental conditions on their calcium carbonate shells.

It seems that gradual morphological trends do not strictly reflect the rate of speciation or its mode within the clade. In a paper published in 1998, Kucera & Malmgren,  showed that gradual change in the Cretaceous planktonic foraminifera Contusotruncana fornicata probably resulted in a shift in the relative proportion of high conical to low conical forms through time, yet isotopic data indicated a rapid separation of the population.

 Globigerina bulloides and Legionella inflata, two examples of planktonic foraminifera.

Globigerina bulloides and Globoconella
inflata, two examples of planktonic foramininfiera.

Using stratigraphic, phylogenetic and ecological data from the exceptional fossil record of Cenozoic macroperforate planktonic foraminifera, Dr Thomas Ezard from the  University of Southampton, explains how the fossil record contains signals of biological processes that drive genetic evolution. He used a complete phylogeny of those Cenozoic foraminifera to provide palaeontologically calibrated ages for every divergence within the clade that are independent of molecular data. Their  hypothesis is that speciation provokes a burst of rapid genetic change, giving molecular evolution a punctuational component. This rapid burst helps isolate the new species from its ancestor.

Sin título

The study shows how the fossil record contains signals of biological processes that drive genetic evolution and promotes the importance of using fossil records in conjunction with the molecular models.

References:

Ezard, T. H. G., Thomas, G. H., Purvis, A. (2013), Inclusion of a near-complete fossil record reveals speciation-related molecular evolution. Methods in Ecology and Evolution, 4: 745–753. doi: 10.1111/2041-210X.12089

The legacy of Ulisse Aldrovandi.

Ulisse Aldrovandi (1522-1605).

Ulisse Aldrovandi (1522-1605).

Ulisse Aldrovandi was born  in Bologna  to a noble family on September 11, 1522. He  studied humanities, law, mathematics, medicine and philosophy at the university of Bologna where became the first professor of natural sciences in 1561. He was arrested for heresy in 1549 and remained in custody or house arrest till he was absolved in April 1550. During this time he coined the term geology and focused on Zoology and Botany.

He is considered one of the foremost biologists of the Renaissance and in 1568 founded the Bologna City Gardens. Monstruorum Historia contains some of the most impressive illustrations of Aldrovandi’s work.

Like da Vinci and Bauhin, some of the most emblematic figures of the Renaissance, Aldrovandi was a pioneer of ichnology. He described several trace fossils in his work Musaeum Metallicum. Like most of Aldrovandi’s works it was published posthumously. The book was entitled originally De Fossilibus but it was changed by Bartolomeo Ambrosini, the book’s editor.

Gastrochaenolites, as figured in Aldrovandi’s Musaeum Metallicum and Gastrochaenolites in a coral.  From Wikimedia Commons.

Gastrochaenolites, as figured in Aldrovandi’s Musaeum Metallicum and Gastrochaenolites in a coral. From Wikimedia Commons.

In his Musaeum Metallicum Aldrovandi correctly interpreted bioerosional traces and the corresponding illustration reveals the ichnogenus Gastrochaenolites, a bioerosional trace commonly produced by bivalves. The specimen is presented as “Silicem dactylitem” and is described as a rock presenting “hollows” of varied diameter. He describes the “hollows” as “resembling the cavities in which some lithophagous bivalves seek shelter”.

a- Cosmorhaphe, described by Aldrovandi as snake-like structure. b. Detail of Cosmorhaphe.

a- Cosmorhaphe, described by Aldrovandi as snake-like structure. b. Detail of Cosmorhaphe.

He also  describes Cosmorhaphe as a natural curiosity resembling the sinuous curves of a snake. Unlike da Vinci, Aldrovandi argues for an inorganic origin of traces and believes that are  formed by fluids circulating within rocks or natural curiosities -for instance, ammonites are named Ophiomorphites or “snake-shaped stones”- , but he often compares them to existing animals.

Aldrovandi’s Musaeum Metallicum,  1648.

Aldrovandi’s Musaeum Metallicum,
1648.

Aldrovandi’s work represents a major step in the history of Ichnology because  includes one of the first examples of a scientific approach to trace fossils and includes some of the earliest artistic representations of invertebrate trace fossils.

References:

Baucon, A. (2010). Leonardo da Vinci, The Founding Fatheer of Ichnology,  PALAIOS, 25 (6), 361-367 DOI: 10.2110/palo.2009.p09-049r

Baucon, A. (2008). Italy, the Cradle of Ichnology: the legacy of Aldrovandi and Leonardo, Studi Trent. Sci. Nat., Acta Geol., 83 (2008): 15-29

MICROFOSSILS AND THE OCEAN HISTORY.

Forams from deep-sea. Credit: Miriam Katz, Rensselaer Polytechnic Institute. (Originally published by Micropress.)

Forams from deep-sea. Credit: Miriam Katz, Rensselaer Polytechnic Institute. (Originally published by Micropress.)

Microfossils from deep-sea are crucial elements for our understanding of past and present oceans. Their skeletons take up chemical signals from the sea water, in particular isotopes of oxygen and carbon. Over millions of years, these skeletons accumulate in the deep ocean to become a major component of biogenic deep-sea sediments.

The importance of microfossils as tool for paleoclimate reconstruction was recognized early in the history of oceanography. John Murray, naturalist of the CHALLENGER Expedition (1872-1876) found that differences in species composition of planktonic foraminifera from ocean sediments contains clues about the temperatures in which they lived.

Following this pioneering work, Schott working on sediments of the METEOR Expedition (1925-1927) introduced quantitative counting of species within the fossil assemblages on the sea floor and realized that surface water temperature changed as the climate fluctuated between glacial and interglacial conditions.

Planktonic foraminifera from the Sargasso Sea in the North Atlantic Ocean. (Photograph courtesy Colomban de Vargas, EPPO/SBRoscoff.)

Planktonic foraminifera from the Sargasso Sea in the North Atlantic Ocean. (Photograph courtesy Colomban de Vargas, EPPO/SBRoscoff.)

In 1955, Emiliani, who was then a student of Harold Urey at the University of Chicago,  published a paper entitled “Pleistocene temperatures” where introduced isotope stratigraphy to paleoceanography. He used the density of a heavy oxygen isotope in planktonic foraminifera from deep sea cores to outline oxygen isotope stages for the Quaternary, believing these would reflect surface temperature changes and the ice volume changes.  He concluded that the last glacial cycled had ended about 16,000 years ago, and found that temperature increased steadily between that time and about 6000 years ago. Many of Emiliani’s findings are still valid today, however in 1970 several improvements to Emiliani’s work were made, such as a revision of the temperature scale.

Oxygen isotope records have also been obtained from well-preserved microfossil materials in the Late Cretaceous  when bottom waters appear to have been much warmer than at present.

This concepts of paleotemperature reconstruction, as first developed for planktic foraminifera, apply to other groups of microfossils. Diatoms and radiolarians are susceptible to different set of dissolution parameters than calcareous fossils, resulting in a different distribution pattern at the sea floor and have been used for temperature estimates in the Pacific and in the Antartic Oceans, especially where calcareous fossils are less abundant. Diatom assemblage are also used in reconstructions of paleoproductivity.

Climatic modes and sea-level fluctuations indicated by calcareous nannofossils of the Oligocene deposits from the Romanian Carpathians. (Melinte, 2004)

Climatic modes and sea-level fluctuations indicated by calcareous nannofossils of the Oligocene deposits from the Romanian Carpathians. (Melinte, 2004)

The calcareous nannoplankton represents good proxy for the sea-level fluctuations. The group exhibit  a clear latitudinal distribution pattern, for instance, the presence of mixed nannofloral assemblages (taxa of low-middle latitudes together with high ones) are indicative of the sea-level rise,  while endemic assemblages characterize periods of low sea-level.

By studying cores from those ocean sediments, its possible determine the ages of the rocks, the ocean environment and some atmospheric conditions using the information  provided by the microfossils present in that core, as well as stable isotope analysis and magnetic stratigraphy.

Each layer of the core recorded the geological history of the ocean basins, changing climates, evolving biota and the events that could altered the course of Earth history.

References:

Armstrong, Howard A. and Martin D. Brasier.  Microfossils.  Blackwell Publishing, 2005.

Berger, W. H., Sea level in the late Quaternary: patterns of variation and implications, Int J Earth Sci (Geol Rundsch) (2008) 97:1143–1150

Ernst Stromer and the lost Dinosaurs of Egypt.

 Ernst Freiherr Stromer von Reichenbach. From Wikimedia Commons

Ernst Freiherr Stromer von Reichenbach. From Wikimedia Commons

Ernst Freiherr Stromer von Reichenbach was born in Germany on June 12, 1870. In 1893, he began to study geology and paleontology at the University of Munich and wrote his thesis about the geology of the German colonies in Africa, under the direction of Karl Alfred von Zittel.

He later became a vertebrate paleontologist at the Paläontologisches Museum in Munich and an expert on fossil fish and mammals. But I was not until 1901 that he travelled to Africa, more specifically to El Fayum, a fossiliferous location discovered by George August Schweinfurth, a German botanist. The place contains fossil mammals from the Eocene-Oligocene boundary. Supported by the Bavarian Academy of Sciences and Humanities (Bayerische Akademie der Wissenschaften), he conducted a second expedition in 1902.

Bahariya Oasis.

Bahariya Oasis.

In 1910, E. Stromer went to his  third paleontological expedition to Egypt. He arrived to Alexandria on November 7. He was initially looking for early mammals and planned visit the area of Bahariya, in the Western Desert, which has sediments from the Cretaceous era. But an expedition to the Western Desert needed the permission by the English and French colonial authorities and of course the Egyptian authorities. Although diplomatic relations with Germany were rapidly deteriorating , Stromer managed to get the permissions.

He arrived to the Bahariya Oasis on January 11, 1911. After facing some difficulties during the journey, on January 17 he began to explore the area of Gebel el Dist, and at the bottom of the Bahariya Depression, Stromer found  the remains of four immense and entirely new dinosaurs ( Aegyptosaurus, Bahariasaurus, Carcharodontosaurus and Spinosaurus aegyptiacus), along with dozens of other unique specimens.

“Illustrations of the vertebrate “sail” bones of Spinosaurus that appeared in one of Stromer’s monographs. From Wikimedia Commons.

With the help of Richard Markgraf (1856-1916), Stromer excavated in three years numerous remains of dinosaurs, snakes, turtles, marine reptiles and crocodiles. Unfortunately, due to political tensions  before and after World War I, many of this fossils were damaged after being inspected by colonial authorities and not arrived to Munich until 1922. The shipping from El Cairo was paid by the Swiss paleontologist Bernhard Peyer (1885-1963), a former student and friend of Stromer.

The most famous of all Stromer’s discoveries was the Spinosaurus. This gigantic predator is estimated to have been about 50 to 57 feet (15 to 17 m) with unusually long spines on its back that probably formed a large, sail-like structure.

This is the only photographic proof of German researcher Ernst Stromer's discovery of Spinosaurus. Image from the Washington University in St. Louis

This is the only photographic proof of German researcher Ernst Stromer’s discovery of Spinosaurus. Image from the Washington University in St. Louis

During the World War II, Stromer tried to convince Karl Beurlen -a young nazi paleontologist who was in charge of the collection- that he had to move the fossils to a safer place, but he refused to do it. Finally, on April 24, 1944, a British Royal Air Force raid bombed the museum and incinerated its collections. Of course, that was not an isolated occurrence. Between 1940 and 1944, several dinosaur fossils were destroyed in World War II battles.

Stromer was an aristocrat (“Freiherr” in his name roughly equals “baron” in English) who refused to join the Nazi, but Stromer’s defiance cost him dearly: all of his sons were sent to the German army. Two of them died in combat and one was captured and imprisoned in the Soviet Union for several years.

In 2000, a new paleontological expedition went to Bahariya and recovered the first dinosaur’s remains since the time of Stromer and Markgraf. Among the new findings is the sauropod Paralititan stromeri (named in Stromer’s honor).

References:

Sanz, José Luis,  Cazadores de Dragones, Editorial Ariel, 2007

Holmes, Thom, Last of the Dinosaurs: The Cretaceous Period, Infobase Publishing, 2008.

Pollen analysis and the science of climate change.

Example of fossil pollen grains from Eocene of Huadian , Jilin, China.

Example of fossil pollen grains from Eocene of Huadian , Jilin, China.

Pollen grains are the carriers of the male gametes or their progenitor cell, in higher plants. They also are important tools for paleoclimatic reconstruction.  They reflects the ecology of their parent plants and their habitats and provide a continuous record of their evolutionary history.

Like spores, pollen grains possess a wall highly resistant to microbial attack. This wall comprises two layers,  the outer, highly resistant exine mostly composed by sporopollenin, a biopolymer considered “the most resistant organic material known”, and the inner intine that surrounds the cytoplasm. The morphology of pollen grains is diverse. Gymnosperms 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).

Arabis pollen has three colpi and prominent surface structure. From Wikimedia Commons

Arabis pollen has three colpi and prominent surface structure. From Wikimedia Commons

Pollen grains  could enter into the fossil record by falling directly into swamps or lakes, or being washed into them or into the rivers and seas. The ones which are not buried in reducing sediments will tend to become oxidized and be destroyed.

They are filtered by differential dispersal in the air and in the water. For instance, large miospores, pollen grains and megaspores will tend to settle out in rivers, estuaries, deltas or shallow shelf areas, whereas small miospores and pollen grains may settle out in outer shelf and oceanic conditions. The differences in pollen productivity and dispersion rates pose a significant problem for palaeoclimatic reconstruction because the relative abundances of pollen grains in a deposit cannot be directly interpreted in terms of species abundance in the study area. Another difficult is that spores and pollen may suffer several cycles of reworking and redeposition, leading to some confusion in the fossil record.

Scanning electron microscope image of different types of pollen grains. Image from Wikipedia.

Scanning electron microscope image of different types of pollen grains. Image from Wikimedia Commons

Gunnar Erdtman, a Swedish botanist, published  in 1921,  his thesis about pollen as a tool for study the Quaternary vegetation and climate change. He was the first to suggest this application for fossil pollen.

Pollen analysis involves the quantitative examination of spores and pollen at successive horizons through a core, specially in lake, marsh or delta sediments, especially in Quaternary sediments where the parent plants are well known. This provide information on regional changes in vegetation through time, and it’s also a valuable tool for archaeologists because gives clues about man’s early environment and his effect upon it.

In a recent study, applied to the Crisis in the Late Bronce Age (LBA) in Cyprus and Syria, the pollen record reveals the presence of plants adapted to drier weather, which indicates a decrease in rainfall. Researchers suggest that this drought lasted about three hundred years causing crop failures, dearth and famine, and forcing regional human migrations at the end of the LBA in the Eastern Mediterranean and southwest Asia.

References:

Armstrong, H. A., Brasier, M. D., 2005. Microfossils (2nd Ed). Blackwell, Oxford.

Traverse, A. (1988), Paleopalynology. Unwin Hyman

Kaniewski D, Van Campo E, Guiot J, Le Burel S, Otto T, et al. (2013), Environmental Roots of the Late Bronze Age Crisis. PLoS ONE 8(8): e71004.doi:10.1371/journal.pone.0071004

Ernst Haeckel, the scientist as an artist.

Ernst Haeckel, 1860. From Wikimedia Commons.

Ernst Haeckel, 1860. From Wikimedia Commons.

Ernst Haeckel was born on February 16, 1834, in Potsdam, Prussia. He grew up in Merseburg, where his father was a government official. He studied medicine to please his family, at the University of Berlin and graduated in 1857. But his real passion was biology, something he discovered while he was still a medicine student and his professor Johannes Müller, physiologist and anatomist, took him on a summer expedition to observe small sea creatures off the coast of Heligoland in the North Sea.

In 1859, when Haeckel was 25, travelled to Italy with the help of his parents. Haeckel spent some time in Napoli, exploring and discovering his talent as an artist. Then he went to Messina, where began to study radiolarians. Like Goethe and Humboldt, his science was influenced by deep his aesthetic aspirations and those little exquisite creatures, satisfied both.

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.

In 1864, young 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.

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

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

He was one of the first to state that humans evolved from apes and life evolved from non-living matter. He claimed that evidence of human evolution could be found in the Dutch East Indies (now Indonesia).  Eugene Dubois, inspired by Haeckel’s ideas, went to Indonesia and found the fossil remains of a hominid,  later reclassified as Homo erectus.

He also wrote more than twenty monographs about systematic biology and evolutionary history, among them his studies of radiolarians, medusae and sponges are the most popular. He formulated the concept of  ”ecology” and coined the terms of “protist”,  “ontogeny”, “phylum”, “phylogeny”,  “heterochrony”, and “monera”.

Ernst Haeckel’s ”Kunstformen der Natur” showing various sea anemones classified as Actiniae.  From Wikimedia Commons.

Ernst Haeckel’s ”Kunstformen der Natur” showing various sea anemones classified as Actiniae. From Wikimedia Commons.

But Haeckel was a man of contradictions. His belief in Recapitulation Theory (“ontogeny recapitulates phylogeny”) was one of his biggest mistakes. His affinity for the German Romantic movement influenced his political beliefs and Stephen Jay Gould wrote that Haeckel’s biological theories, supported by an “irrational mysticism” and racial prejudices contributed to the rise of Nazism.

Despite those faults, he made great contributions in the field of biology and his legacy as scientific illustrator is extraordinary. His master work “Kunstformen der Natur” (Art forms of Nature) influenced not only in science, but in the art, design and architecture of the early 20th century.

In 1908, Haeckel was awarded with the prestigious Darwin-Wallace Medal for his contributions in the field of science. After the death of his wife in 1915, Haeckel became mentally frail. Three years later sold his house to the Carl Zeiss foundation and it presently contains a historic library.

Ernst Haeckel died on August 9, 1919 in Germany at the age of 85.

References:

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

Brief Introduction to Patagonian theropods

Skull of Giganotosaurus, MACN (]Argentinean Museum of Natural Sciences)

Skull of Giganotosaurus, MACN (Argentinean Museum of Natural Sciences)

The Cretaceous beds of Patagonia have yielded the most comprehensive record of Cretaceous non-avian theropods  from Southern Hemisphere, which includes at least five main theropod lineages: Abelisauroidea, Carcharodontosauridae, Megaraptora, Alvarezsauridae, and Unenlagiidae. These record facilitates the understanding of the origin, evolution, and radiation of theropods from Gondwana. The first remains of dinosaurs were found near Neuquen city by an officer army in 1882 and were sent to Florentino Ameghino, the “founder father” of Argentinian paleontology.

Genyodectes holotype. From Wikimedia Commons.

Genyodectes holotype. From Wikimedia Commons.

By the end of  the 1880s, Santiago Roth collected some dinosaur remains from Chubut and  sent them to Richard Lydekker and Arthur Smith Woodward. In 1901, A. Smith Woodward described Genyodectes, based on fragmentary skull bones, including portions of both maxillas, premaxillae,  parts of the supradentaries, and some teeth. Genyodectes remained as the most completely known  theropod from South American until the 1970s. In 2004, O. Rauhut concluded that Genyodectes is more closely related to Ceratosaurus than the more derived abelisaurs.

Skull of  Carnotaurus sastrei, from MACN.

Skull of Carnotaurus sastrei, from MACN.

The  Abelisauroidea reached a great taxonomic diversity and their fossils have been recovered in Argentina, Brasil, Madagascar, India, Morocco, Lybia and France. The group has been divided in two main branches: the Noasauridae which includes the small-sized abelisauroids, and the Abelisauridae which comprises medium to large-sized animals, like the popular Carnotaurus sastrei.

The group exhibits strongly reduced forelimbs and hands, stout hindlimbs, with a proportionally robust and short femur and tibia. It has been suggested that from the Cenomanian to the Maastrichtian, most South American abelisaurids may have been isolated from other Gondwanan relatives.

The Carcharodontosauridae includes the largest land predators in the early and middle Cretaceous of Gondwana, like the popular, Giganotosaurus carolinii. The group evolved large skulls surpassing the length of the largest skull of Tyrannosaurus rex.  Another common trait is the fusion of cranial bones.

Bicentenaria Argentina. MACN

Bicentenaria Argentina. MACN

The Coelurosauria is also a diverse clade. Bicentenaria argentina is a very basal coelurosaur, medium sized with elongate and gracile hindlimb bones. Another basal coelurosaur is Aniksosaurus darwini.

Megaraptora  is a clade represented by Megaraptor, Orkoraptor and Aerosteon. It has been suggested that megaraptorans were basal coelurosaurs that shared the role of top predators with abelisauroids and carcharodontosauroids.

The Alvarezsauridae is a group of highly derived theropods. The group exhibits, among other features,   a lightly built skull bearing numerous small teeth restricted to the anterior portion of the snout, robust humerus with a proximally projected inner tubercle, a robust ulna and a hand with very robust digit I carrying a large and stout claw, and keeled sternum.

Unenlagia comahuensis by Nobu Tamura. From Wikimedia Commons

Unenlagia comahuensis by Nobu Tamura. From Wikimedia Commons

South American paravians are included within the clade Unenlagiidae: Buitreraptor gonzalezorum, Unenlagia comahuensis, Unenlagia paynemili and Austroraptor cabazai, all recovered from the Upper Cretaceous of Patagonia, Argentina.

The fossil record shows that the macroevolutionary patterns observed in Gondwana at the Late Cretaceous differ from the records from Laurasia, but both show a common  macroevolutionary pattern during post-Coniacian times.

References:

Novas, F.E., et al., Evolution of the carnivorous dinosaurs during the Cretaceous: The evidence from Patagonia, Cretaceous Research (2013), http://dx.doi.org/10.1016/j.cretres.2013.04.001

The impact winter model

The Chicxulub asteroid impact (Image credit: NASA)

The Chicxulub asteroid impact (Image credit: NASA)

The Chicxulub asteroid impact was the final straw that pushed Earth past the tipping point.  The K-Pg extinction that followed the impact was one of the five great Phanerozoic  mass extinctions. The impact released an estimated energy equivalent of 100 teratons of TNT and produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere. The dramatic decrease of sunlight that reached the Earth surface caused a drastic short-term global reduction in temperature. This phenomenon is called “impact winter”.

Cold and darkness lasted for a period of months to years.  Photosynthesis stopped and the food chain collapsed. Three-quarters of the plant and animal species on Earth disappeared. Marine ecosystems lost about half of their species, and freshwater environments shows low extinction rates, about 10% to 22% of genera.

This difference in extinction rates between marine and freshwater ecosystems could be explained by differential effects of an impact winter on marine and freshwater biota and the difference in the use for detrital foods.

Arkhangelskiella cymbiformis and Globotruncana linneiana (d’Orbigny, 1839).

Arkhangelskiella cymbiformis and Globotruncana linneiana (d’Orbigny, 1839).

Three factors can be associated with the impact winter in marine and fresh water enviroments. First, starvation caused by the stop of photosynthesis. Second, the loss of dissolved oxygen. Third, the low temperatures. The flux of organic detritus to the sea floor also declined abruptly and remained low for about 3 Myr after the impact.

Marine extinction rates were greater among pelagic than benthic organisms. Calcareous nanoplankton (primarily the coccolithophores) and planktonic foraminifera had the highest extinction rates among the marine plankton, possibly because they commonly lack cysts or resting stages.  About 70% of planktonic foraminifera became extinct at the K/Pg boundary. The food webs supported by plankton were severely affected. For instance, ammonites were plankton feeder and they, like mosasaurs, plesiosaurs and pliosaurs that fed on them, became extinct at the  K-Pg boundary.

Mosasaurus hoffmani, Late cretaceous of Europe by Nobu Tamura. From Wikimedia Commons.

Mosasaurus hoffmani, Late cretaceous of Europe by Nobu Tamura. From Wikimedia Commons.

In case of freshwater communities, they were adapted to rapidly changing environments. For instance, starvation can be offset by dormancy, which is much more common among freshwater than marine organisms. Dormancy could have lowered extinction rates in inland waters compared to marine waters.

Because the late Cretaceous climate was warm, a major challenge for aquatic organisms, especially in inland waters, may have been the persistence of low temperatures. Inland waters had an advantage for preventing extinction caused by prolonged cold:  the presence of thermal refugia in the drainage networks of inland waters derived not only from  geothermal waters, but also from groundwater.

The abundance of refugia combined with greater adaptation to stressful conditions may explain lower extinction frequencies in freshwaters than in marine waters. Even when mortality within all taxa may have been equal to or even greater in freshwaters than in marine waters, the factors that protect some survivors against extinction  are more evident in the freshwater environment.

Jeletzkytes spedeni, a fossil ammonite from USA. From Wikimedia Commons.

Jeletzkytes spedeni, a fossil ammonite from USA. From Wikimedia Commons.

It seems clear that the terrestrial and marine extinction were separated in time by a matter of months to years.  These extinctions had two different mechanisms: an impact winter in the marine environment and a heat pulse and subsequent fires in the terrestrial environment, although an impact winter would also affect the terrestrial environment. A more comprehensive analysis also shows three separate spatial domains (terrestrial, marine, and freshwater), which provide us a more understandable picture of the K-Pg extinction.

References:

Douglas S. Robertson, William M. Lewis, Peter M. Sheehan and Owen B. Toon, K-Pg extinction patterns in marine and freshwater environments: The impact winter model, Journal of Geophysical Research: Biogeosciences, JUL 2013, DOI: 10.1002/jgrg.20086.

Schulte, P., et al. (2010), The Chicxulub asteroid impact and mass extinction at the Cretaceous-Paleogene boundary, Science, 327, 1214–1218, doi:10.1126/science.1177265