Climate Change and the Evolution of Mammals.

Wyoming_Bighorn_Basin

Bighorn Basin, Wyoming (Image: University of New Hampshire, College of Engineering and Physical Sciences).

Rapid global climate change can lead to rapid evolutionary responses. The Paleocene-Eocene Thermal Maximum (PETM; 55.8 million years ago), was a short-lived (~ 200,000 years) global warming event attributed to a rapid rise in the concentration of greenhouse gases in the atmosphere. It was suggested that this warming was initiated by the melting of methane hydrates on the seafloor and permafrost at high latitudes. This event was accompanied by other large-scale changes in the climate system, for example, the patterns of atmospheric circulation, vapor transport, precipitation, intermediate and deep-sea circulation, a rise in global sea level and ocean acidification.

The PETM onset is also marked by the largest deep-sea mass extinction among calcareous benthic foraminifera (including calcareous agglutinated taxa) in the last 93 million years. Similarly, planktonic foraminifera communities at low and high latitudes show reductions in diversity, while larger foraminifera are the most common constituents of late Paleocene–early Eocene carbonate platforms.

Phenacodus

Phenacodus by Heinrich Harder (1858-1935) . From Wikimedia Commons.

During the PETM, around 5 billion tons of CO2 was released into the atmosphere per year, and temperatures increased by 5 – 8°C. The rise in temperature coincided with a dramatic decrease in the body size of marine and terrestrial organisms. Dwarfing of mammalian taxa across the Palaeocene-Eocene Thermal Maximum (PETM) was first described in the Bighorn Basin, Wyoming. The basin has a remarkably fossil-rich sedimentary record of late Palaeocene to early Eocene age.  The interval of the Paleocene–Eocene Thermal Maximum is represented by a unique mammalian fauna composed by smaller, but morphologically similar species to those found later in the Eocene. Diminutive species include the early equid Sifrhippus sandrae, the phenacodontids Ectocion parvus and Copecion davisi. Two main hypotheses have been proposed to explain the observation of smaller body sizes during the global warming event. The first hypothesis is that mammal population decreased the average body-size in response to the environmental conditions that existed during the PETM global warming event. The second hypothesis is that the observed decrease in the average body-size was the result of extrinsic forces, such as the range extension of small species into the Bighorn Basin, displacing larger species (Burger, 2012). 

Comparison of the effects of anthropogenic emissions (total of 5000 Pg C over 500 years) and PETM carbon release (3000 Pg C over 6 kyr) on the surface ocean saturation state of calcite. From Zeebe, 2013

Comparison of the effects of anthropogenic emissions (total of 5000 Pg C over 500 years) and PETM carbon release (3000 Pg C over 6 kyr) on the surface ocean saturation state of calcite. From Zeebe, 2013

New findings revealed that the remarkable decrease in mean body size across the warming event, occurred through anagenetic change and immigration. However, species selection also was strong across the PETM but, intriguingly, favoured larger-bodied species, implying some unknown mechanism(s) by which warming events affect macroevolution (Rankin et al., 2015). 

Climate change is the major threat to biodiversity. The combination of global warming and the release of large amounts of carbon to the ocean-atmosphere system during the PETM has encouraged analogies to be drawn with modern anthropogenic climate change. Reduction in nutrients, food availability and water will probably have negative implications and are interrelated with climate change and shrinking organisms.  We need to understand how and why organisms are shrinking, and what it means for biodiversity and humanity.

References:

Rankin, B., Fox, J., Barron-Ortiz, C., Chew, A., Holroyd, P., Ludtke, J., Yang, X., Theodor, J. 2015. The extended Price equation quantifies species selection on mammalian body size across the Palaeocene/Eocene Thermal Maximum. Proceedings of the Royal Society B. doi: 10.1098/rspb.2015.1097

Barnosky, A. D. 2004 Biodiversity response to climate change in the middle Pleistocene: the Porcupine Cave fauna from Colorado. Berkeley, CA: University of California Press.

Burger, B.J., Northward range extension of a diminutive-sized mammal (Ectocion parvus) and the implication of body size change during the Paleoc…, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2012), http://dx.doi.org/10.1016/j.palaeo.2012.09.008

Jablonski, D. 2008, Species selection: theory and data. Annu. Rev. Ecol. Evol. Syst. 39, 501–524.

Sheriden, J. A; Bickford, D. 2011, Shrinking body size as an ecological response to climate change. Nat. Clim.

Wright JD, Schaller MF (2013) Evidence for a rapid release of carbon at the Paleocene-Eocene thermal maximum. Proc Natl Acad Sci USA 110(40):15908–15913.

The legacy of the feud between Florentino Ameghino and P. Moreno.

Sin título

Portrait of Florentino Ameghino (1854-1911) by Luis De Servi (1863-1945).

In 1887, Florentino Ameghino, former Assistant Director of the Museo de la Plata, and Francisco P. Moreno, head of the museum, were in a middle of a bitter dispute. The discovery of the phorusrhacid birds played a big role in this story. The feud between Ameghino and Moreno is in many aspects similar to the well-known feud between E.D. Cope and O.C. Marsh, which took place in the United States at roughly the same time.

Florentino Ameghino was born on September 19, 1853. He came from a family of Italian immigrants who settled in 1854 in the town of Lujan, where the extraction and exportation of fossils were a lucrative activity. Throughout his scientific career, he was seconded by his younger brother Carlos Ameghino (1865–1936).  Carlos had been employed by Moreno at the same time as his brother, as “travelling naturalist” for the Museo de La Plata. During his trips, he gathered a remarkable collection of fossil mammals, later described by Florentino. In January 1888, Florentino Ameghino resigned from his position at the Museo de La Plata, and Moreno denied him access to the paleontological collection.  From that moment, and until became head of the Museo Argentino de Ciencias Naturales in Buenos Aires in 1902, the Ameghino brothers continued with their palaeontological exploration, without any permanent official support, but they managed to get the funds to run their paleontological investigations as a private enterprise. For instance, Karl von Zittel subsidized their explorations, receiving in exchange fossils for the collection of the Munich University. Meanwhile Moreno, in order to gain priority over his rivals, published a series of brief reports about the new palaeontological discoveries made by his field researchers.

Francisco Pascacio Moreno (1852-1919). From Wikimedia Commons

Francisco Pascacio Moreno (1852-1919). From Wikimedia Commons

In 1895, the critical financial situation forced Florentino Ameghino to sell his fossil bird collection, in order to support his further work in Patagonia. The collection was purchased by the London Museum by the sum of 350 £ in 1896. When Florentino became director of the Museo Nacional de Buenos Aires in 1902 the selling of fossils ceased, and he started making claims for the return of the museum’s collections. He also proposed that the most remarkable specimens of Patagonian and Pampean fossil faunas be cast and stored in Buenos Aires and La Plata museums to be used in Argentinean schools. The same casts were sent to Museums all over the world and in exchange, Ameghino received casts of the oldest fossil mammals from Africa and the Northern Hemisphere to compare with the Patagonian faunas (Podgorny, 2005). It was a smart way to prevent the sale of the original fossils.

References:

Ameghino, F. 1895. Sobre las aves fosiles de Patagonia. Boletín del Instituto Geografico de Argentina 15:501–602.

Ameghino, F. 1891a. Mamíferos y aves fósiles Argentinos: espécies nuevas: adiciones y correciones. Revista Argentina Historia Natural, 1:240-259.

Eric Buffetaut (2013), Who discovered the Phorusrhacidae? An episode in the history of avian palaeontology, Proceedings of the 8th International Meeting of the Society of Avian Paleontology and Evolution Paleornithological Research 2013.

Moreno, F.P. 1889. Breve reseña de los progresos del Museo La Plata, durante el segundo semestre de 1888. Boletin del Museo La Plata, 3:1-44.

Podgorny, I. 2005. Bones and devices in the constitution of paleontology in Argentina at the end of the nineteenth century. Science in Context 18(2): 249-283

 

 

A brief introduction to the stratigraphy of mass extinctions.

gallery_image_11433

The permian triassic boundary at Meishan, China (Photo: Shuzhong Shen).

Extinction is the ultimate fate of all species. The fossil record indicates that more than 95% of all species that ever lived are now extinct. Over the last 3 decades, mass extinction events  have become the subject of increasingly detailed and multidisciplinary investigations. In 1982, Jack Sepkoski and David M. Raup used a simple form of time series analysis at the rank of family to distinguish between background extinction levels and mass extinctions in marine faunas, and identified five major extinction events in Earth’s history: at the end of the Ordovician period, Late Devonian, End Permian, End Triassic and the End Cretaceous. These five events are know as the Big Five. The most recently identified mass extinction occurred during the Middle Permian, about  262 million years ago, and it was first recognised in the marine realm as a turnover among foraminifera, with fusulinaceans among the principal casualties.

A central question in the understanding of mass extinctions is whether the extinction was a sudden or gradual event. This question may be addressed by examining the pattern of last occurrences of fossil species in a stratigraphic section.  Also, the geochemical history recorded in marine sediments preserves a valuable record of environmental change during mass extinctions. However, stratigraphical processes of sediment accumulation could affect the chronology of environmental change. And of course, the Signor–Lipps effect complicates the timing of extinction.

The trilobite Kainops invius, in lateral and ventral view. From Wikimedia Commons

The trilobite Kainops invius, in lateral and ventral view. From Wikimedia Commons

The last occurrences of fossil species generally predate the times of extinction. Based on principles of sequence stratigraphy, marine ecology, and evolution, numerical models of fossil occurrences in stratigraphic sections suggest that the last occurrences of fossil species are controlled by stratigraphic architecture. In some cases, stratigraphical architecture can give the illusion of a double pulse or even a triple pulse of extinction (Holland, 2015).

The Cambrian and Lower Ordovician record involve the abrupt termination of many shallow-water trilobite lineages, a reduction in the number of biofacies across the shelf, and the immigration and origination of new lineages; and in many locations, the extinction is closely associated with an unconformity. With the notable exception of the end-Cretaceous extinction, mass extinction events have similar stratigraphical expressions. In depositional dip settings, they are recorded as a single cluster of last occurrences that is closely associated with a major flooding surface, which in some cases is combined with a sequence-bounding subaerial unconformity. Where depositionally downdip sections are available, such as for the Late Ordovician and the Late Devonian, two clusters of last occurrences are present. They may suggest discrete pulses of extinction, although they are equally consistent with a more prolonged extinction. In the Late Devonian, the faunal changes occur in three separate episodes, with the Taghanic event at the end of the Givetian, the Kellwasser event at the end of Frasnian and the Hangenberg event at the end of the Famennian. Of these, the Kellwasser event is the largest. One of the characteristics of the Kellwasser event is that the extinction was more severe in shallow-water faunas, and the stratigraphical pattern of last occurrences is consistent not only with a pulse of extinction timed with the flooding surface, but also with a more protracted interval of extinction. (Holland et Patzkowsky, 2015)

References:

Holland, S. M., Patzkowsky, M. E. (2015), The stratigraphy of mass extinction. Palaeontology. doi: 10.1111/pala.12188

Bambach, R.K., Knoll, A.H. and Wang, S.C., 2004. Origination, extinction, and mass depletions of marine diversity. Paleobiology, 30, 522–542.

Steve C. Wang, Aaron E. Zimmerman, Brendan S. McVeigh, Philip J. Everson, and Heidi Wong, (2012), Confidence intervals for the duration of a mass extinction, Paleobiology, 38(2), pp. 265–277.

Seth D. Burgess, Samuel Bowring, and Shu-zhong Shen, High-precision timeline for Earth’s most severe extinction, PNAS 2014, doi:10.1073/pnas.1317692111

Wignall, P. B. 2001. Sedimentology of the Triassic–Jurassic boundary beds in Pinhay Bay (Devon, SW England). Proceedings of the Geologists’ Association, 112, 349–360

Owen, Dickens and the ‘invention’ of dinosaurs.

Sir Richard Owen (1804-1892)

Sir Richard Owen (1804-1892)

On 20 February 1824, William Buckland published the first report of a large carnivore animal: the Megalosaurus. He had a piece of a lower jaw, some vertebrae, and fragments of a pelvis, a scapula and hind limbs, probably not all from the same individual. Buckland’s published description was based on specimens in the Ashmolean Museum, in the collection of Gideon Algernon Mantell of Lewes in Sussex and a sacrum donated by Henry Warburton (1784–1858). One year later, the Iguanodon entered in the books of History followed by the description of Hylaeosaurus in 1833. After examined the anatomy of these three genera, Richard Owen recognized that Iguanodon, Megalosaurus, and Hylaeosaurus share several traits that distinguished them from other ancient or living creatures, like their giant size and five fused vertebrae welded to their pelvic girdle. In April 1842, Owen created the “Dinosauria” : “The combination of such characters, some, as it were, from groups now distinct from each other, and all manifested by creatures far surpassing in size the largest of existing reptiles, will, it is presumed, be deemed sufficient ground for establishing a distinct tribe or suborder of Saurian Reptiles, for which I would propose the name of Dinosauria.“(Richard Owen, “Report on British Fossil Reptiles.” Part II. Report of the British Association for the Advancement of Science, Plymouth, England, 1842)

Megalosaurus sacrum with fused vertebrae (from Buckland 1824, pl. 42).

Megalosaurus sacrum with fused vertebrae (from Buckland 1824, pl. 42).

It was an exciting time full of discoveries and the concept of an ancient Earth became part of the public understanding. The study of the Earth was central to the economic and cultural life of the Victorian Society and Literature influenced the pervasiveness of geological thinking. Mr Venus, the taxidermist in  Dickens’s Our Mutual Friend (1864–65) was slightly based on Richard Owen. By the time when Dickens wrote this novel, Owen was the curator of the Hunterian Museum of the Royal College of Surgeons. Our Mutual Friend, also exhibits  traces of the work of Lyell, Jean-Baptiste Lamarck, and Darwin. Dickens  also published some of Owen’s work in his periodical, Household Words and All the Year Round.

Owen used his influence with Prince Albert, Queen Victoria’s husband, to propose the financing of the three-dimensional reconstruction of the first known dinosaurs: Megalosaurus, Iguanodon and Hylaeosaurus, for the closure of the first international exposition in modern European history: the Crystal Palace exhibition. About six million people visited the Great Exhibition. Megalosaurus became so popular that is mentioned in Charles Dickens’s novel Bleak House: “Implacable November weather. As much mud in the streets as if the waters had but newly retired from the face of the earth, and it would not be wonderful to meet a Megalosaurus, forty feet long or so, waddling like an elephantine lizard up Holborn Hill.”  It was the first appearance of a dinosaur in popular literature.

Reference:

Buckland, Adelene , ‘“The Poetry of Science”: Charles Dickens, Geology and Visual and Material Culture in Victorian London’, Victorian Literature and Culture, 35 (2007), 679–94 (p. 680).

Moody, R. T. J., Buffetaut, E., Naish, D.& Martill, D. M. (eds) Dinosaurs and Other Extinct Saurians: A Historical Perspective. Geological Society, London, Special Publications, 343, 335–360

RUPKE, N. A. (2009): Richard Owen. Biology without Darwin. University of Chicago Press: 344

Torrens, H. S. (2014), The Isle of Wight and its crucial role in the ‘invention’ of dinosaurs. Biological Journal of the Linnean Society, 113: 664–676. doi: 10.1111/bij.12341

 

A brief introduction to the T. rex Family Tree.

“Sue” specimen, Field Museum of Natural History, Chicago

Tyrannosaurus rex is the most iconic dinosaur of all timeIt was discovered in the Hell Creek Formation by Barnum Brown in 1902, and later described  by Henry Fairfield Osborn in 1905. Osborn actually named two large Hell Creek tyrannosaurids, T. rex and Dynamosaurus imperiosus. He later realized that Dynamosaurus imperiosus and Tyrannosaurus rex were synonymous, but Tyrannosaurus has priority, as it preceded Dynamosaurus in the description (Osborn, 1906).

T-rex and its closest relatives, known as tyrannosaurids, comprise the clade Tyrannosauroidea, a relatively derived group of theropod dinosaurs, more closely related to birds than to other large theropods such as allosauroids and spinosaurids, that originated in the Middle Jurassic, approximately 165 million years ago. All tyrannosaurs were bipedal predators characterized by premaxillary teeth with a D-shaped cross section, fused nasals, extreme pneumaticity in the skull roof and lower jaws, a pronounced muscle attachment ridge on the ilium, and an elevated femoral head (Brusatte et al., 2010). For most of their evolutionary history, tyrannosauroids were mostly small-bodied animals and only reached gigantic size during the final 20 million years of the Cretaceous.

Skulls of the basal tyrannosauroids Guanlong (A), Dilong (B); Skulls of juvenile (C) and adult (D)Tyrannosaurus. (Adapted from Brusatte et. al., 2010)

Skulls of the basal tyrannosauroids Guanlong (A), Dilong (B); Skulls of juvenile (C) and adult (D)Tyrannosaurus. (Adapted from Brusatte et. al., 2010)

During the past 15 years, new discoveries from Russia, Mongolia and China helped to build the Tyranosaurs family tree. The oldest and most basal tyrannosaurs comprise a subclade, Proceratosauridae, which includes Kilesksus, Gualong, and Proceratosaurus. They were small-bodied animals no larger than a human, with elaborate cranial crests, extremely elongated external naris, a short ventral margin of the premaxilla, and depth of the antorbital fossa ventral to the antorbital fenestra is greater than the depth of the maxilla below the ventral margin of the antorbital fossa (Rauhut et al., 2010; Averianov et al., 2010).

Kileskus artistotocus, from the Middle Jurassic (167 mya), was discovered in 2010 in Western Siberia, by Alexander Averianov on the basis of an associated maxilla and premaxilla, a mandible fragment, and some possible associated postcranial elements. The cranial crest is currently unknown for Kileskus.

Pedal ungual phalanx of Kileskus aristotocus. Abbreviations: ft – flexor tubercle; lgr – lateral groove. Scale bar = 1 cm (From Averianov et. al.; 2010)

Pedal ungual phalanx of Kileskus aristotocus. Abbreviations: ft – flexor tubercle; lgr – lateral groove. Scale bar = 1 cm (From Averianov et. al.; 2010)

Guanlong wucaii, from the Late Jurassic of China, was first described in 2006. The generic name is derived from the Chinese Guan (crown) and long (dragon). The specific epithet wucaii (five colours) referred to the colours of rock of the Wucaiwan area where the fossil was found. The most striking trait of Guanlong is the complex nasal crest consisting of a highly pneumatic median crest that is about 1.5 mm thick for most of its length, and four supporting lateral laminae (Xu et al., 2006).

Proceratosaurus bradleyi, discovered in Gloucestershire, England in 1910 and described by Arthur Smith Woodward, it was originally thought to be an ancestor of Ceratosaurus. Some of the characters uniting Proceratosaurus with Guanlong are the  strongly  enlarged  nares, and a midline cranial crest or horn  on  the  nasals (Rauhut et al., 2010).

Guanlong wucaii. (Image adapted from Xu et al., 2006)

Guanlong wucaii. (Image adapted from Xu et al., 2006)

The giant, feathered tyrannosaur Yutyrannus huali, lived during the early Cretaceous period in what is now Northeastern  China. It was discovered in 2012 by Chinese palaeontologist Xing Xu. Yutyrannus weighed about 1,400 kilograms and  was at least 8 metres in length, and shares some features, particularly of the cranium, with derived tyrannosauroids, but is similar to other basal tyrannosauroids in possessing a three-fingered manus and a typical theropod pes.

Dilong paradoxus, also described by Xu, was discovered in 2004. This small tyrannosauroid shows a mosaic of characters, including a derived cranial structure resembling that of derived tyrannosauroids and a primitive postcranial skeleton similar to basal coelurosaurians. And at least one specimen was preserved with remnants of protofeathers.

Yutyrannus skeleton (From Wikimedia Commons)

Yutyrannus skeleton (From Wikimedia Commons)

Eotyrannus lengi, from the Early Cretaceous of the Isle of Wight, United Kingdom, was described in 2001. The holotype of Eotyrannus are estimated to have measured about 4 m (13 ft) long. However, as it is believed to have been juvenile, an adult specimen might have been somewhat larger.

Qianzhousaurus sinensis, was discovered in 2014 in China. Nicknamed “Pinocchio rex”, this long-snouted tyrannosaurids along with Alioramus, shows that these type of tyrannosaurids were widely distributed in Asia.

Nanuqsaurus hoglund, was a small dinosaur discovered in Alaska in 2014. The name is the combination ofnanuqthe Iñupiaq word for polar bear and the Greek ‘sauros’ (lizard). The specific name, hoglundi, honors the Texas philanthropist Forrest Hoglund.

Skull of Qianzhousaurus sinensis (Image credit: Junchang Lü et al.)

Skull of Qianzhousaurus sinensis (Image credit: Junchang Lü et al.)

Until recently, all tyrannosaurs fossils were limited to Asia and North America, but the latest discoveries suggest a more  cosmopolitan distribution during their early evolution.  Tyrannosaurs more derived than Eotyrannus, exhibit a purely Asian or North American distribution, which indicates an increasing Laurasian-Gondwanan provincialism during the final stages of the Age of Dinosaurs (Brusatte et al., 2010).

References:

Averianov, A., Krasnolutskii, S., Ivantsov, S. 2010. A new basal coelurosaur (Dinosauria: Theropoda) from the Middle Jurassic of Siberia. Proceedings of the Zoological Institute RAS 314, 1: 42–57.

Brusatte SL, Norell MA, Carr TD, Erickson GM, Hutchinson JR, et al. (2010) Tyrannosaur paleobiology: new research on ancient exemplar organisms. Science 329: 1481–1485. doi: 10.1126/science.1193304

Fiorillo AR, Tykoski RS (2014) A Diminutive New Tyrannosaur from the Top of the World. PLoS ONE 9(3): e91287. doi:10.1371/journal.pone.0091287

Loewen MA, Irmis RB, Sertich JJW, Currie PJ, Sampson SD (2013) Tyrant Dinosaur Evolution Tracks the Rise and Fall of Late Cretaceous Oceans. PLoS ONE 8(11): e79420. doi:10.1371/journal.pone.0079420

RAUHUT, O. W. M., MILNER, A. C. and MOORE-FAY, S. (2010), Cranial osteology and phylogenetic position of the theropod dinosaur Proceratosaurus bradleyi (Woodward, 1910) from the Middle Jurassic of England. Zoological Journal of the Linnean Society, 158: 155–195. doi: 10.1111/j.1096-3642.2009.00591.x

Xu X., Clark, J.M., Forster, C. A., Norell, M.A., Erickson, G.M., Eberth, D.A., Jia, C., and Zhao, Q. (2006). “A basal tyrannosauroid dinosaur from the Late Jurassic of China”, Nature 439 (7077): 715–718. doi:10.1038/nature04511

Marie Stopes and her legacy as paleobotanist.

Marie Stopes (1880-1958)  by George Bernard Shaw. (LSE Archives Image Record, 1921)

Marie Stopes (1880-1958) photographed by George Bernard Shaw. (LSE Archives Image Record, 1921).

George Bernard Shaw once wrote: “All progress is initiated by challenging current conceptions”. Those words describe exactly what Marie Stopes did during her entire life. Her book,  Married Love (1918), is considered one of the most influential of the 20th century. A dedicated feminist, her views on birth control and contraception drew to her the hostile attentions of conservative forces in British Society, and Stope’s ideas were attacked through an assault of her own character. But in addition to her well-known work on birth control and women’s rights, she was a prolific poet, playwright and a paleobotanist.

Marie Charlotte Carmichael Stopes was born in Edinburgh, Scotland, on October 15, 1880. Her father, Henry Stopes, a brewer, architect and amateur paleontologist and archeologist, amassed the largest private collection of fossils and ancient stone tools in Britain. Her mother, Charlotte Carmichael, wrote British Freewomen: Their Historical Privilege. The book, published in 1894, was a great influence in the early twentieth century British women’s suffrage movement. They were both members of the British Association for the Advancement of Science.

Marie Stopes (From Wikimedia Commons)

Marie Stopes (From Wikimedia Commons)

Just before her twentieth birthday, Marie enrolled at University College London where she studied botany and geology. She graduated with honours after only two years and received the Gold Medal in Botany. At UCL she was employed by Francis Wall Oliver as a postgraduate research assistant on his pteridosperm project with Dukinfield Henry Scott. Shortly after, she went to study at the University of Munich, and received a Ph.D. in palaeobotany in 1904. She was the only female student among 5.000 men. During that time, she worked on the internal anatomy of cycad seed. In August 1904, Marie got her first academic job at the Victoria University of Manchester. She became more interested in Carboniferous coal balls. These concretions of calcite, dolomite, siderite, and pyrite, occur at many localities in northern England and preserved in beautiful anatomical detail the structure of the plants that formed the coal.

In 1907, she convinced the Royal Society to fund an excursion to Japan. During her work, she found what were then the earliest known flowers and fossil insects from the Cretaceous period. In 1910, she was commissioned by the Geological Survey of Canada to determine the age of the Fern Ledges, a geological structure at Saint John, New Brunswick. She proved that the rocks were Carboniferous and not Devonian or Silurian as others had earlier argued (Falcon-Lang, 2008).

In 1957 Marie Stopes was diagnosed with cancer. She died on October 2, 1958.

References:

FALCON-LANG, H.J. & MILLER, R.F. 2007. Marie Stopes and the Fern Ledges of Saint John, New Brunswick. In Burek, C.V. (ed.) The Role of Women in the History of Geology. Special

Falcon-Lang, H.J., 2008. Marie Stopes: Passionate about Palaeobotany. Geology Today, 24: 132-136.

William Garrett, 2007,  Marie Stopes: Feminist, Eroticist, Eugenicist,  Lulu.com.

Stephanie Green (2013). The Public Lives of Charlotte and Marie Stopes. London: Pickering & Chatto.

 

Ecosystem instability in the Late Triassic and the early evolution of dinosaurs.

The Late Triassic Petrified Forest Member of the Chinle Formation (Photo from AASG)

The Late Triassic Petrified Forest Member of the Chinle Formation (Photo from AASG)

Dinosaurs likely originated in the Middle Triassic and the first unequivocal dinosaur fossils are known from the late Carnian, but much about the geological and temporal backdrop of early dinosaur history remains poorly understood. A key question is why early dinosaurs were rare and species-poor at low paleolatitudes throughout the Late Triassic Period, for at least 30 million years after their origin.

The oldest well-dated identified dinosaurs are from the late Carnian (approx. 230 Ma) of the lower Ischigualasto Formation in northwestern Argentina. Similarly, the Santa Maria and Caturrita formations in southern Brazil preserve basal dinosauromorphs, basal saurischians, and early sauropodomorphs. In North America, the oldest dated occurrences of vertebrate assemblages with dinosaurs are from the Chinle Formation, but are less abundant and species rich compared to those from South America. The fact that those assemblages were at moderately high paleolatitudes during the Late Triassic, and the North American assemblages were near the paleoequator supports the hypotheses for a diachronous rise of dinosaurs across paleolatitudes (Irmis et al., 2011).

A reconstructed scene from the Late Triassic (Norian) of central Pangea. (Credit: image from Brusatte, S. L. 2008)

A reconstructed scene from the Late Triassic (Norian) of central Pangea. (Image from Brusatte, S. L. 2008, Dinosaurs, Quercus Publishing, London).

The Late Triassic is marked by a return to the “hothouse” condition of the Early Triassic, with two greenhouse crisis that may also have played a role in mass extinctions and long-term evolutionary trends (Retallack, 2013). The paleoclimate was a very arid with intense evaporation rate. Although there was at least one time of significant increase in rainfall known as the “Carnian Pluvial Event”, possibly related to the rifting of Pangea. Now, a multiproxy study  suggests  that fluctuating aridity in tropical and subtropical Pangea could explain why Triassic dinosaur faunas at low latitudes are restricted to small, slower growing carnivorous forms, whereas large-bodied herbivores, including sauropodomorph dinosaurs, are absent at low paleolatitudes during the Late Triassic “hothouse.” The palynomorphs recovered from sediments of the Chinle Formation indicate a major change from a seed fern-dominated (Alisporites) assemblage with accessory gymnosperms to one dominated by conifers and seed ferns in the lower portion of the Petrified Forest Member. In addition, the extensive charcoal record in the Petrified Forest Member provides evidence of paleo-environmental variability and aridity. 

 

References:

Jessica H. Whiteside, Sofie Lindström, Randall B. Irmis, Ian J. Glasspool, Morgan F. Schaller, Maria Dunlavey, Sterling J. Nesbitt, Nathan D. Smith, and Alan H. Turner. 2015. Extreme ecosystem instability suppressed tropical dinosaur dominance for 30 million years. PNAS: doi:10.1073/pnas.1505252112

Brusatte, S. L., Nesbitt, S. J., Irmis, R. B., Butler, R. J., Benton, M. J., and Norell, M. A. 2010. The origin and early radiation of dinosaurs. Earth-Science Reviews, 101, 68-100

Holz, M., Mesozoic paleogeography and paleoclimates – a discussion of the diverse greenhouse and hothouse conditions of an alien world, Journal of South American Earth Sciences (2015), doi: 10.1016/j.jsames.2015.01.001

Nesbitt,  S. J., Irmis,  R. B, Parker,  W. G. (2007) A critical re-evaluation of the Late Triassic di-nosaur taxa of North America. J Syst Palaeontology 5(2):209243

Sellwood, B.W. & Valdes, P.J. 2006. Mesozoic climates: General circulation models and the rock Record. Sedimentary Geology 190:269–287.

 

The real Jurassic World.

Global paleogeographic reconstruction of the Earth in the late Jurassic period 150 Ma. From Wikimedia Commons

Global paleogeographic reconstruction of the Earth in the late Jurassic period 150 Ma. Credit: Dr Ron Blakey

The transition from Triassic to Early Jurassic is marked by a major biotic crisis in the marine and terrestrial realms. In the oceans, this event eliminated conodonts and nearly annihilated corals, ammonites, brachiopods and bivalves. In land, most mammal-like reptiles and large amphibians disappeared, as well as early dinosaur groups. During the Jurassic (201-145 mya) the breakup of the supercontinent Pangaea continued and accelerated with the opening of the North Atlantic by the rifting of Africa and North America, giving rise to the supercontinents of Laurasia and Gondwana. The sea level rise flooded continental areas around Pangaea, forming huge epicontinental seas, especially in northern Africa and eastern Laurasia (modern China). The world was predominantly warm with at least four times the present level of atmospheric CO2. The period is also characterized by the explosive adaptive radiation of dinosaurs and the diversification of the cycads.

The Early Jurassic climate was characterized by a global warming, with average summer temperatures that exceeded  35°C in low-latitude regions of western Pangaea where eolian sandstones testify to the presence of vast deserts (Holz, 2015). The early Toarcian Oceanic Anoxic Event  (T-OAE; ∼183 mya) 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 consensus about the causes or triggering mechanisms behind this event.

Painting of a late Jurassic Scene on one of the large island in the Lower Saxony basin in northern Germany (From Wikimedia Commons)

Painting of a late Jurassic Scene on one of the large island in the Lower Saxony basin in northern Germany (From Wikimedia Commons)

After the extinction of many carnivorous crurotarsan lineages (phytosaurs, ornithosuchids, rauisuchians) at the Triassic–Jurassic boundary, theropod dinosaurs increased their diversity and exhibit a greater range of morphological disparity. Sauropodomorphs also achieved a worldwide distribution and become more graviportal and increased their body size. The presence of early armored dinosaurs (thyreophorans) in North America, Asia, and Europe, but their absent from the southern African record, suggests some degree of provinciality in early ornithischian faunas (Brusatte et al., 2010).

By the Mid-Jurassic, Gondwana started to break up in different blocks: Antarctica, Madagascar, India, and Australia in the east, and Africa and South America in the west, with relatively warm sea-surface conditions (26–30◦C) from Mid-Jurassic (∼160Ma) to the Early Cretaceous (∼115Ma) in the Southern Ocean.  There was a drastic climatic decline during the Late Callovian. This decline in temperature lasted about 2.6My and is know as the “Callovian Ice Age”. It has been interpreted in terms of an inverse greenhouse effect, triggered by drawdown of CO2 consequent upon excess carbón burial (Dromart et al, 2003).  The Puchezh-Katunki impact crater in Russia is prior to the Callovian extinction event and is not considered as a factor for this biotic extinction event.

During the Late Jurassic, North America completed its separation from Gondwana, and Gondwana was split into a northern and southern continent by the rift system opening the proto-Indian Ocean. The geological and geochemical record suggest that low-latitude environments were arid and tropical ever-wet conditions were absent. Maximum plant diversity was concentrated at midlatitudes, whith forests dominated by a mixture of conifers, cycadophytes, pteridosperms, ferns, and sphenophytes.

References:

Brusatte, S. L., Nesbitt, S. J., Irmis, R. B., Butler, R. J., Benton, M. J., and Norell, M. A. 2010. The origin and early radiation of dinosaurs. Earth-Science Reviews, 101, 68-100

Holz, M., Mesozoic paleogeography and paleoclimates – a discussion of the diverse greenhouse and hothouse conditions of an alien world, Journal of South American Earth Sciences (2015), doi: 10.1016/j.jsames.2015.01.001

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

Sellwood, B.W. & Valdes, P.J. 2006. Mesozoic climates: General circulation models and the rock Record. Sedimentary Geology 190:269–287.

Corwin Sullivan et al. 2014. The vertebrates of the Jurassic Daohugou Biota of northeastern China. Journal of Vertebrate Paleontology, vol. 34, no. 2; doi: 10.1080/02724634.2013.787316

A Permian lagerstätte from Antarctica.

 

Vertebraria solid-stele and polyarch roots colonised by fungal spores (From Slater et al., 2014)

Vertebraria solid-stele and polyarch roots colonised by fungal spores (From Slater et al., 2014)

A lagerstätte (German for ‘storage place’) is a site exhibiting an extraordinary preservation of life forms from a particular era. The term was originally coined by Adolf Seilacher in 1970. One of the most notable  is Burgess Shale in the Canadian Rockies of British Columbia. The site, discovered by Charles Walcott in 1909, highlight one of the most critical events in evolution: the Cambrian Explosion (540 million to 525 million years ago). The factors that can create such fossil bonanzas are: rapid burial (obrution), stagnation (eutrophic anoxia), fecal pollution (septic anoxia), bacterial sealing (microbial death masks), brine pickling (salinization), mineral infiltration (permineralization and nodule formation by authigenic cementation), incomplete combustion (charcoalification), desiccation (mummification) and freezing. The preservation of decay-resistant lignin of wood and cuticle of plant leaves  is widespread, but exceptional preservation also extends to tissues.

The Toploje Member chert of the Prince Charles Mountains preserves the permineralised remains of a terrestrial ecosystem before the biotic decline that began in the Capitanian and continued through the Lopingian until the Permo-Triassic transition (Slater et al., 2014). During the late Palaeozoic and early Mesozoic, Antarctica occupied a central position within Gondwana and played a key role in floristic interchange between the various peripheral regions of the supercontinent.

permian

Singhisporites hystrix, a megaspore with ornamented surface.

The fossil micro-organism assemblage includes a broad range of fungal hyphae and reproductive structures. The macrofloral diversity in the silicified peats is relatively low and dominated by the constituent dispersed organs of arborescent glossopterid and cordaitalean gymnosperms.  The fossil palynological assemblage includes a broad range of dispersed bisaccate, monosaccate, monosulcate and polyplicate pollen. The roots (Vertebraria), stems (Australoxylon) and leaves (Glossopteris) of the arborescent glossopterid exhibited feeding traces caused by arthropods, but the identification is  difficult since plant and arthropod cuticles look similar in thin section. Tetrapods are currently unknown from Permian strata of the Prince Charles Mountains as either body fossils or ichnofossils (McLoughlin et al., 1997, Slater et al., 2014).

Times of exceptional fossil preservation are coincident with mass extinctions, oceanic anoxic events, carbon isotope anomalies, spikes of high atmospheric CO2, and transient warm-wet paleoclimates in arid lands (Retallack 2011). The current greenhouse crisis delivers several factors that can promote exceptional fossil preservation, such as eutrophic and septic anoxia, microbial sealing, and permineralization.

References:

Benton, M.J., Newell, A.J., (2013), Impacts of global warming on Permo-Triassic terrestrial ecosystems. Gondwana Research.

Rees, P.M., (2002). Land plant diversity and the end-Permian mass extinction. Geology 30, 827–830.

Retallack, G., (2011), Exceptional fossil preservation during CO2 greenhouse crises?, Palaeogeography, Palaeoclimatology, Palaeoecology 307: 59–74.

Slater, B.J., et al., (2014), A high-latitude Gondwanan lagerstätte: The Permian permineralised peat biota of the Prince Charles Mountains, Antarctica, Gondwana Research. http://dx.doi.org/10.1016/j.gr.2014.01.004

Seilacher, A., (1970) “Begriff und Bedeutung der Fossil-Lagerstätten: Neues Jahrbuch fur Geologie und Paläontologie“. Monatshefte (in German) 1970: 34–39.

Alcide d’Orbigny and the beginning of foraminiferal studies.

Alcide_Dessalines_d'Orbigny_1802

Alcide Dessalines d’Orbigny , 1802. From Wikimedia Commons

During the eighteenth and nineteenth centuries, Paris was a busy place for science. In 1794 the Reign of Terror ended with the establishment of a new government that was more supportive of the sciences. The old Royal Botanical Garden and the affiliated Royal Museum were reorganized as the Muséum national d’histoire naturelle. The new institution fostered many brilliant scientists, including Cuvier, Lamarck, and St. Hilaire. Among those remarkable men was Alcide Dessalines d’Orbigny, considered the founder of micropaleontology and biostratigraphy. He worked in natural history, geology, paleontology, anthropology, linguistics, taxonomy and systematics.

Alcide d’Orbigny was born in Couëron (Charente-Maritime) on September 6th, 1802. In his early youth, he developed a life interest in the study of a group of microscopic animals that he named ‘Foraminifera’ and established the basis of a new science, micropaleontology. He started at an early age working with his father, a doctor, who introduced him to the study of microscopic shells they collected from La Rochelle, a major port on the coast of France. However, Bartolomeo Beccari, was the first to study these tiny shells that could only be observed under the microscope. Beccari analysed in detail the outer and inner structure of the shell, recognising the concamerations and the coiled structure, and attributed these organisms to microscopic ‘Corni di Ammone’, continuing with the enduring confusion between ammonites 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’.

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’.

On November 7, 1825, d’Orbigny presented to the Académie des Sciences, the results of his observations in a work entitled ‘Tableau méthodique de la classe des Céphalopodes’. It’s clear that d’Orbigny also considered this group of  microscopic shells as belonging to the Cephalopods. But he was the first to divide the Cephalopods into two zoological orders:  the ‘Siphonifères‘ with intercameral siphon and ‘Foraminifères’ characterized by openings (or foramina) located in the septa separating two consecutive chambers. To illustrate his work, d’Orbigny prepared 73 plates of drawings and made models of 100 of his foraminiferal species that he sculpted in a very fine limestone.

There is a long gap between the publication of his pioneering work and his other works dedicated to foraminifera because of his long journey to South America documented in the nine volumes of his ‘Voyage dans l’Amérique Méridionale’ (1835–1847). In 1835, Félix Dujardin discovered that foraminiferans were not cephalopods, but single-celled organisms. This important discovery led d’Orbigny to exclude the foraminifera from the Cephalopods. In a work published in 1839, he traced the history of foraminiferal studies and considered them as a class for the first time, dividing the history of their study in four periods culminating with the revelation of their unicellular nature.

Operculina, showing the details of d’Orbigny’s drawings intended for the Tableau.

Operculina, showing the details of d’Orbigny’s drawings intended for the Tableau.

In the volume dedicated to the recent foraminifera collected in South America he pointed out the influence of currents, temperature and depth on their distribution patterns. In Mémoire sur les foraminifères de la craie blanche du bassin de Paris published in 1840, d’Orbigny demonstrated that foraminifera could be used for classifying geological strata.

D’Orbigny‘s legacy was extraordinary with thousands of species described, the occurrences of fossils documented chiefly in France, as well as his outstanding Le Voyage dans l’Amérique méridionale published between 1835-1847, and covering the biology, ethnology, anthropology, paleontology, and other aspects of Chile, Peru, Argentina, Uruguay, and especially Bolivia.

In 1853, Napoleon III created the Chair of Paleontology in the Muséum national d’Histoire naturelle in his honour. After his death on June 30, 1857, the collection of d’Orbigny, which includes more than 14,000 species and over 100,000 specimens not counting innumerable foraminifera stored in assorted glass bottles, was auctioned by his family. The collection was bought by the Muséum National d’Histoire Naturelle, in 1858 and registered in the catalogue of the Paleontology Laboratory of this institution.

 

References:

d’Orbigny, A. 1826. Tableau méthodique de la classe des Céphalopodes. Annals des Sciences Naturelles, 1st Series, 7: 245-314.
Dujardin, F. 1835a. Observations sur les Rhizopodes et les Infusoires, Comptes Rendus, de l’Académie des Sciences, 1: 338-340.

Heron-Allen, E. (1917) Alcide d’Orbigny, his life and his work. Journal of the Royal Microscopic Society, ser. 2, 37, 1–105, 433–4.

Seguenza G. 1862. Notizie succinte intorno alla costituzione geologica dei terreni terziarii del distretto di Messina. Messina: Dalla Stamperia di Tommaso Capra. 84 pp.

Vénec-Peyré, M-T, 2004, Beyond frontiers and time: the scientific and cultural heritage of Alcide d’Orbigny (1802–1857), Marine Micropaleontology 50, 149 – 159.