Historical perspective on the dinosaur family tree

Megalosaurus at Crystal Palace Park, London. From Wikimedia Commons.

In the 19th century, the famous Victorian anatomist Richard Owen diagnosed Dinosauria using three taxa: Megalosaurus, Iguanodon and Hylaeosaurus, on the basis of three main features: large size and terrestrial habits, upright posture and sacrum with five vertebrae (because the specimens were from all Late Jurassic and Cretaceous, he didn’t know that the first dinosaurs had three or fewer sacrals). These characteristics were more mammalian than reptilian. But new fossil findings from Europe and particularly North America forced to a new interpretation about those gigantic animals.

In 1887, Harry Govier Seeley summarised the works of Cope, Huxley and Marsh who already subdivided the group Dinosauria into various orders and suborders. However, he was the first to subdivide dinosaurs into Saurischians and the Ornithischians, based on the nature of their pelvic bones and joints. He wrote: The characters on which these animals should be classified are, I submit, those which pervade the several parts of the skeleton, and exhibit some diversity among the associated animal types. The pelvis is perhaps more typical of these animals than any other part of the skeleton and should be a prime element in classification. The presence or absence of the pneumatic condition of the vertebrae is an important structural difference…” Based on these features, Seeley denied the monophyly of dinosaurs.

Seeley’s (1901) diagram of the relationships of Archosauria. From Padian 2013

At the mid 20th century, the consensual views about Dinosauria were: first, the group was not monophyletic; second almost no Triassic ornithischians were recognised, so they were considered derived morphologically, which leads to the third point, the problem of the ‘‘origin of dinosaurs’’ usually was reduced to the problem of the ‘‘origin of Saurischia,’’ because theropods were regarded as the most primitive saurischians. A great influence on the views about the dinosaur origins was Alan Charig. He was Curator of Amphibians, Reptiles and Birds at the British Museum (Natural History), now the Natural History Museum, in London for almost thirty years. Charig thought that the first dinosaurs were quadrupedal, not bipedal. He based this on the kinds of animals that he and his colleagues found in the early Triassic localities of eastern and South Africa. He thought that forms such as ‘‘Mandasuchus’’ were related to dinosaurs, but that they had a posture intermediate between a sprawling and upright gait that he called ‘‘semi-improved” or ‘‘semi-erect’’.

Herrerasaurus skull. From Wikimedia Commons.

The discovery of Lagosuchus and Lagerpeton from the Middle Triassic of Argentina induced a change in the views of dinosaurs origins. Also from South America came Herrerasaurus from the Ischigualasto Formation, the basal sauropodomorphs Saturnalia, Panphagia, Chromogisaurus, and the theropods Guibasaurus and Zupaysaurus, but no ornithischians except a possible heterodontosaurid jaw fragment from Patagonia. The 70s marked the beginning of a profound shift in thinking on nearly all aspects of dinosaur evolution, biology and ecology. Robert Bakker and Peter Galton, based on John Ostrom’s vision about Dinosauria, proposed, for perhaps the first time since 1842, that Dinosauria was indeed a monophyletic group and that it should be separated (along with birds) from other reptiles as a distinct ‘‘Class”. In 1986, the palaeontologist Jacques Gauthier showed that dinosaurs form a single group, which collectively has specific diagnostic traits that set them apart from all other animals.

From Baron et al., 2017.

Phylogenetic analyses of early dinosaurs have  supported the traditional scheme. But back in March of this year, a paper, authored by Matthew Baron, David Norman and Paul Barrett, challenged this paradigm with a new phylogenetic analysis that places theropods and ornithischians together in a group called Ornithoscelida. The team analysed a wide range of dinosaurs and dinosauromorphs (74 taxa were scored for 457 characters), and they arrived at a dinosaur evolutionary tree containing one main branch that subdivides into the groupings of Ornithischia and Theropoda, and a second main branch that contains the Sauropoda and Herrerasauridae (usually positioned as either basal theropods or basal Saurischia, or outside Dinosauria but close to it). The term Ornithoscelida was coined in 1870 by Thomas Huxley for a group containing the historically recognized groupings of Compsognatha, Iguanodontidae, Megalosauridae and Scelidosauridae. The synapomorphies that support the formation of the clade Ornithoscelida includes: an anterior premaxillary foramen located on the inside of the narial fossa; a sharp longitudinal ridge on the lateral surface of the maxilla; short and deep paroccipital processes; a post-temporal foramen enclosed within the paroccipital process; a straight femur, without a sigmoidal profile; absence of a medioventral acetabular flange; a straight femur, without a sigmoidal profile; and fusion of the distal tarsals to the proximal ends of the metatarsals.

Of course, those results have great implications for the very origin of dinosaurs. Ornithischia don’t begin to diversify substantially until the Early Jurassic. By contrast, the other dinosaurian groups already existed by at least the early Late Triassic. If the impoverished Triassic record of ornithischians reflects a true absence, ornithischians might have evolved from theropods in the Late Triassic (Padian, 2017). The study also suggest that dinosaurs might have originated in the Northern Hemisphere, because most of their basal members, as well as their close relatives, are found there. Furthermore, their analyses places the origin of dinosaurs at the boundary of the Olenekian and Anisian stages (around 247 Ma), slightly earlier than has been suggested previously.

 

The dinosaur family tree Credit: Max Langer

More recently, an international team of early dinosaur evolution specialists, led by Max Langer, highlighted that the lack of some important taxa (for example, the early thyreophoran Scutellosaurus, the possible theropod Daemonosaurus, and the newly described Ixalerpeton and Buriolestes) may have a substantial effect on character optimizations near the base of the dinosaur tree, and thus on the interrelationships of early dinosaurs. The study did not find strong evidence to discard the traditional Ornithischia–Saurischia division. But they reintroduced a third possibility that was articulated in the 1980s but rarely discussed since: that sauropodomorphs and ornithischians may form their own herbivorous group, separate from the ancestrally meat-eating theropods. The Phytodinosauria hypothesis was coined by Robert T. Bakker in his book The Dinosaur Heresies: “Therefore all the plant-eating dinosaurs of every sort really constitute one, single natural group branching out from one ancestor, a primitive anchisaurlike dinosaur. And a new name is required for this grand family of vegetarians. So I hereby christen them the Phytodinosauria, the “plant dinosaurs”‘

References:

Max C. Langer, Martín D. Ezcurra, Oliver W. M. Rauhut, Michael J. Benton, Fabien Knoll, Blair W. McPhee, Fernando E. Novas, Diego Pol & Stephen L. Brusatte, Untangling the dinosaur family tree, Nature 551 (2017) doi; oi:10.1038/nature24012

Baron, M. G., Norman, D. B. & Barrett, P. M. A new hypothesis of dinosaur relationships and early dinosaur evolution.  Nature 543, 501–506  (2017).  doi:10.1038/nature21700

Padian K. Dividing the dinosaurs. Nature 543, 494–495 (2017) doi:10.1038/543494a

Padian K. The problem of dinosaur origins: integrating three approaches to the rise of Dinosauria. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, Available on CJO 2013 doi:10.1017/S1755691013000431 (2013).

Seeley, H. G. On the classification of the fossil animals commonly named DinosauriaProc. R. Soc. Lond. 43165171 (1887).

Huxley, T. H. On the classification of the Dinosauria, with observations on the Dinosauria of the Trias. Quarterly Journal of the Geological Society, London 26, 32-51. (1870).

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The Winds of Winter

Gravity anomaly map of the Chicxulub impact structure (From Wikimedia Commons)

Almost thirty years ago, the discovery of anomalously high abundance of iridium and other platinum group elements in the Cretaceous/Palaeogene (K-Pg) boundary led to the hypothesis that an asteroid collided with the Earth and caused one of the most devastating events in the history of life. The impact created the 180-kilometre wide Chicxulub crater causing widespread tsunamis along the coastal zones of the surrounding oceans and released an estimated energy equivalent of 100 teratons of TNT and produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere.

Three-quarters of the plant and animal species on Earth disappeared, including non-avian dinosaurs, other vertebrates, marine reptiles and invertebrates, planktonic foraminifera and ammonites. Marine ecosystems lost about half of their species while freshwater environments shows low extinction rates, about 10% to 22% of genera.

A time-lapse animation showing severe cooling due to sulfate aerosols from the Chicxulub asteroid impact 66 million years ago (Credit: PKI)

The decrease of sunlight caused a drastic short-term global reduction in temperature (15 °C on a global average, 11 °C over the ocean, and 28 °C over land). While the surface and lower atmosphere cooled, the tropopause became much warmer, eliminate the tropical cold trap and allow water vapor mixing ratios to increase to well over 1,000 ppmv in the stratosphere. Those events accelerated the destruction of the ozone layer. During this period, UV light was able to reach the surface at highly elevated and harmful levels. This phenomenon is called “impact winter”.

Recent drilling of the peak ring of the Chicxulub impact crater has been used to create 3-D numerical simulations of the crater formation. It was estimate that the angle of impact at Chicxulub was ~60° with a downrange direction to the southwest. The new study indicates that the impact may have released around three times as much sulfur and much less carbon dioxide compared with previous calculations, suggesting that surface temperatures were likely to have been significantly reduced for several years and ocean temperatures affected for hundreds of years after the Chicxulub impact.

 

References:

Artemieva, N., Morgan, J., & Expedition 364 Science Party (2017). Quantifying the release of climate-active gases by large meteorite impacts with a case study of Chicxulub. Geophysical Research DOI: 10.1002/2017GL074879

 

Charles G. Bardeen, Rolando R. Garcia, Owen B. Toon, and Andrew J. Conley, On transient climate change at the Cretaceous−Paleogene boundary due to atmospheric soot injections, PNAS 2017 ; published ahead of print August 21, 2017 DOI: 10.1073/pnas.1708980114

Brugger J.G. Feulner, and S. Petri (2016), Baby, it’s cold outside: Climate model simulations of the effects of the asteroid impact at the end of the CretaceousGeophys. Res. Lett.43,  doi:10.1002/2016GL072241.

 

Halloween special V: Lovecraft’s paleontological Journey

H.P. Lovecraft’s love for astronomy is well known. As an amateur astronomer, Lovecraft attended several lectures from leading astronomers and physicists of his time. In 1906 he wrote a letter to the Scientific American on the subject of  finding planets in the solar system beyond Neptune. Around this time he began to write two astronomy columns for the Pawtuket Valley Gleaner and the Providence Tribune. He also wrote a treatise, A Brief Course in Astronomy – Descriptive, Practical, and Observational; for Beginners and General Readers. In several of his astronomical articles he describes meteors as  “the only celestial bodies which may be actually touched by human hands”. But Lovecraft was also obsessed with the concept of deep time, so geology and paleontology were also present in his writings.

Lovecraft’s monsters are certainly titanic, biologically impossible beings, from dimensions outside our own. He began conjuring monsters almost from the start of his career. In “The Nameless City”, published in the November 1921 issue of the amateur press journal The Wolverine, and often considered the first Cthulhu Mythos story, he describes an ancient race of reptiles that built the city: “They were of the reptile kind, with body lines suggesting sometimes the crocodile, sometimes the seal, but more often nothing of which either the naturalist or the palaeontologist ever heard.”  

Panorama of Ross Island showing Hut Point Peninsula (foreground), Mount Erebus (left) and Mount Terror (right), Antarctica. Photo: John Bortniak, NOAA

According to his biographer S. T. Joshi, Lovecraft was fascinated by Antarctica since an early age. Much of this fascination is recognizable in his famous novel “At the Mountains of Madness”, written in 1931. The novel was rejected by Weird Tales and finally was published by Astounding Stories in a serial form in 1936. “At the Mountains of Madness” is told from the perspective of William Dyer, a geologist from Miskatonic University who flies into an unexplored region of Antarctica. He’s accompanied by Professor Lake, a biologist, Professor Pabodie, an engineer, and some graduate students. The basic plot of the novel is the discovery of the frozen remains of bizarre entities from the deep space and their even more terrifying “slaves”:  the  shoggoths. The story could be divided in two parts. The first one is particularly rich, detailed and shows an impressive scientific erudition. This is clear in the following paragraph when he describes something that Professor Lake found: “He  was strangely convinced that the marking was the print of some bulky, unknown, and radically unclassifiable organism of considerably advanced evolution, notwithstanding that the rock which bore it was of so vastly ancient a date—Cambrian if not actually pre-Cambrian— as to preclude the probable existence not only of all highly evolved life, but of any life at all above the unicellular or at most the trilobite stage. These fragments, with their odd marking, must have been 500 million to a thousand million years old”. 

Of course, one of the most fascinating parts of the novel is the description of the Elder Things: “Cannot yet assign positively to animal or vegetable kingdom, but odds now favour animal. Probably represents incredibly advanced evolution of radiata without loss of certain primitive features. Echinoderm resemblances unmistakable despite local contradictory evidences. Wing structure puzzles in view of probable marine habitat, but may have use in water navigation. Symmetry is curiously vegetable-like, suggesting vegetable’s essentially up-and-down structure rather than animal’s fore-and-aft structure. Fabulously early date of evolution, preceding even simplest Archaean protozoa hitherto known, baffles all conjecture as to origin.” According with  S.T. Joshi, Lovecraft based his description of the Elder Thing in the fossil crinoids drawn by E. Haeckel in  Kunstformen der Natur.

E. Haeckel’s Kunstformen der Natur (1904), plate 90: Cystoidea. From Wikimedia Commons

“The Shadow Out of Time” (1935) was H. P. Lovecraft’s last major story. It’s told from the perspective of Nathaniel Wingate Peaslee, a professor of political economy at Miskatonic University. During five years, this man suffers a bizarre form of amnesia  followed by vivid dreams of aliens cities in ancient landscapes.  Later, Peaslee discovered that a small number of people throughout history suffered the same type of amnesia. They were possessed by the Great Race, a group of cone shaped creatures who developed the technique of swapping minds with creatures of another era with the purpose of learn the secrets of the Universe. Peaslee describes the gardens that surround the cities of his visions with detail. There was calamites, cycads, trees of coniferous aspect, and small, colourless flowers: “The far horizon was always steamy and indistinct, but I could see that great jungles of unknown tree-ferns, calamites, lepidodendra, and sigillaria lay outside the city, their fantastic frondage waving mockingly in the shifting vapours.”

Calamites was a genus of tree-sized, spore-bearing plants that lived during the Carboniferous and Permian periods (about 360 to 250 million years ago), closely related to modern horsetails. They reached their peak diversity in the Pennsylvanian and were major constituents of the lowland equatorial swamp forest ecosystems. The Cycadales are an ancient group of seed plants that can be traced back to the Pennsylvanian. Cycads have a stem or trunk that commonly looks like a large pineapple and composed of the coalesced bases of large leaves.  Today’s cycads are found in the tropical, subtropical and warm temperate regions of both the north and south hemispheres.

Lepidodendron (fossil tree) on display at the State Museum of Pennsylvania, From Wikimedia Commons

Lepidodendron was a tree-like (‘arborescent’) tropical plant, related to the lycopsids. The name of the genus comes from the Greek lepido, scale, and dendron, tree, because of the distinctive diamond shaped pattern of the bark. The name Lepidodendron is a generic name given to several fossil that clearly come from arborescent lycophytes but are difficult to assign to one species. Fossil remains indicate that some trees attained heights in excess of 40 m and were at least 2m in diameter at the base. They were dominant components of swamp ecosystems in the Carboniferous and frequently associated with Sigillaria, another extinct genus of tree-sized lycopsids from the Carboniferous Period. The absence of extensive branching and the structure of the leaf bases are the principal feature that distinguish Sigillaria from other lycopsids (Taylor et al, 2009). Sigillariostrobus is the name assigned to the reproductive organs or cones of Sigillaria. Unlike Lepidodendron cones, which were attached attached individually near the tip of the branches, Sigillaria cones occurred in clusters attached in certain places along the upper stem.

Tunguska forest (Photograph taken by Evgeny Krinov near the Hushmo river, 1929).

“The Colour Out of Space” is a short story written by  H. P. Lovecraft in 1927.  The story is set in the fictional town of Arkham, Massachusetts, where an unnamed narrator investigates a local area known as the “blasted heath”. Ammi Pierce, a local man, relates him the tragic story of a man named Nahum Gardner and how his life crumbled when a great rock fell out of the sky onto his farm. Within the meteorite there was a coloured globule impossible to describe that infected Gardner’s family, and spread across the property, killing all living things. It’s the first of Lovecraft’s major tales that combines horror and science fiction. The key question of the story of course is the meteorite. Although “the coloured globule” inside the meteorite has mutagenic properties we cannot define their nature. But as Lovecraft stated once, the things we fear most are those that we are unable to picture.

“The Colour Out of Space” was published nineteen year after the Tunguska Event. On the morning of June 30, 1908, eyewitnesses reported a large fireball crossing the sky above Tunguska in Siberia. The object entered Earth’s atmosphere traveling at a speed of about 33,500 miles per hour and released the energy equal to 185 Hiroshima bombs. The night skies glowed and the resulting seismic shockwave was registered with sensitive barometers as far away as England. In 1921, Leonid Kulik, the chief curator for the meteorite collection of the St. Petersburg museum led an expedition to Tunguska, but failed in the attempt to reach the area of the blast. Later, in 1927, a new expedition, again led by Kulik, discovered the huge area of leveled forest that marked the place of the Tunguska “meteorite” fall. At the time, Kulik mistook shallow depressions called thermokarst holes for many meteorites craters. However, he didn’t find remnants of the meteorite, and continued to explore the area until World War II. In the early 1930s, British astronomer Francis Whipple suggested that the Tunguska Event was caused by the core of a small comet, while Vladimir Vernadsky, suggested the cause was a lump of cosmic matter. (Rubtsov, 2009). More than a century later the cause of the Tunguska Event remains a mystery.

 

References:

Lovecraft, H. P, “At the Mountains of Madness”, Random House, 2005.

Lovecraft, H. P, “The Dreams in the Witch House and Other Weird Stories”, Penguin Books, 2004.

Joshi, S. T. (2001). A dreamer and a visionary: H.P. Lovecraft in his time. Liverpool University Press, 302.

LONG, J. (2003): Mountains of Madness – A Scientist’s Odyssey in Antarctica. Jospeh Henry Press, Washington: 252

N. Taylor, Edith L. Taylor, Michael Krings: “Paleobotany: The Biology and Evolution of Fossil Plants”. 2nd ed., Academic Press 2009.

Kathy Willis, Jennifer McElwain, The Evolution of Plants, Oxford University Press, 2013

 

 

Brief history of the Ocean Acidification through time: an update

Corals one of the most vulnerable creatures in the ocean. Photo Credit: Katharina Fabricius/Australian Institute of Marine Science

About one third of the carbon dioxide released by anthropogenic activity is absorbed by the oceans. Once dissolved in seawater, most of the CO2 is transported into deep waters via thermohaline circulation and the biological pump. But a smaller fraction of the CO2, forms carbonic acid and causes a decline in pH in the surface ocean. This phenomenon is called ocean acidification, and is occurring at a rate faster than at any time in the last 300 million years.

Acidification affects the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus in the ocean and interferes with a range of processes, including growth, calcification, development, reproduction and behaviour in a wide range of marine organisms like planktonic coccolithophores, foraminifera, pteropods and other molluscs,  echinoderms, corals, and coralline algae.

The pH within the ocean surface has decreased ~0.1 pH units since the industrial revolution and is predicted to decrease an additional 0.2 – 0.3 units by the end of the century. An eight-year study carried out by the Biological Impacts of Ocean Acidification group (Bioacid), with the support of the German government, has contributed to quantifying the effects of ocean acidification on marine organisms and their habitats. Among the many effects of ocean acidification on marine organisms are including: decreased rate of skeletal growth in reef-building corals, reduced ability to maintain a protective shell among free-swimming zooplankton, and reduced survival of larval marine species, including commercial fish and shellfish. Even worse, the effects of acidification can intensify the effects of global warming, in a dangerous feedback loop.

Coccolithophores exposed to differing levels of acidity. Adapted by Macmillan Publishers Ltd: Nature Publishing Group, Riebesell, U., et al., Nature 407, 2000.

The geologic record of ocean acidification provide valuable insights into potential biotic impacts and time scales of recovery.  Rapid additions of carbon dioxide during extreme events in Earth history, including the end-Permian mass extinction (252 million years ago) and the Paleocene-Eocene Thermal Maximum (PETM, 56 million years ago) may have driven surface waters to undersaturation. But, there’s  no perfect analog for our present crisis, because we are living in an “ice house” that started 34 million years ago  with the growth of ice sheets on Antarctica, and this cases corresponded to events initiated during “hot house” (greenhouse) intervals of Earth history.

The end-Permian extinction is the most severe biotic crisis in the fossil record, with as much as 95% of the marine animal species and a similarly high proportion of terrestrial plants and animals going extinct . This great crisis ocurred about 252 million years ago (Ma) during an episode of global warming. The cause or causes of the Permian extinction remain a mystery but new data indicates that the extinction had a duration of 60,000 years and may be linked to massive volcanic eruptions from the Siberian Traps. The same study found evidence that 10,000 years before the die-off, the ocean experienced a pulse of light carbon that most likely led to a spike of carbon dioxide in the atmosphere. This could have led to ocean acidification, warmer water temperatures that effectively killed marine life.

Taxonomic variation in effects of ocean acidification (From Kroeker et al. 2010)

The early Aptian Oceanic Anoxic Event (120 million years ago) was an interval of dramatic change in climate and ocean circulation. The cause of this event was the eruption of the Ontong Java Plateau in the western Pacific, wich led to a major increase in atmospheric pCO2 and ocean acidification. This event was characterized by the occurrence of organic-carbon-rich sediments on a global basis along with evidence for warming and dramatic change in nanoplankton assemblages. Several oceanic anoxic events (OAEs) are documented in Cretaceous strata in the Canadian Western Interior Sea.

The Paleocene-Eocene Thermal Maximum (PETM; 55.8 million years ago) was a short-lived (~ 200,000 years) global warming event. Temperatures increased by 5-9°C. It was marked by the largest deep-sea mass extinction among calcareous benthic foraminifera in the last 93 million years. Similarly, planktonic foraminifer communities at low and high latitudes show reductions in diversity. The PETM is also associated with dramatic changes among the calcareous plankton,characterized by the appearance of transient nanoplankton taxa of heavily calcified forms of Rhomboaster spp., Discoaster araneus, and D. anartios as well as Coccolithus bownii, a more delicate form.

The current rate of the anthropogenic carbon input  is probably greater than during the PETM, causing a more severe decline in ocean pH and saturation state. Also the biotic consequences of the PETM were fairly minor, while the current rate of species extinction is already 100–1000 times higher than would be considered natural. This underlines the urgency for immediate action on global carbon emission reductions.

References:

David A. Hutchins & Feixue Fu, Microorganisms and ocean global change, Nature Microbiology 2, Article number: 17058 (2017) doi:10.1038/nmicrobiol.2017.58 

Kump, L.R., T.J. Bralower, and A. Ridgwell. 2009. Ocean acidification in deep time. Oceanography 22(4):94–107, http://dx.doi.org/10.5670/oceanog.2009.100

Parker, L. M. et al. Adult exposure to ocean acidification is maladaptive for larvae of the Sydney rock oyster Saccostrea glomerata in the presence of multiple stressors. Biology Letters 13 (2017). DOI: 10.1098/rsbl.2016.0798

Kristy J. Kroeker, Rebecca L. Kordas, Ryan N. Crim, Gerald G. Singh, Meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms, Ecology Letters (2010) 13: 1419–1434
DOI: 10.1111/j.1461-0248.2010.01518.x

 

Vegaviidae, a new clade of southern diving birds

Vegavis iaai by Gabriel Lio. / Photo: CONICET

The fossil record of Late Cretaceous–Paleogene modern birds in the Southern Hemisphere is fragmentary.  It includes Neogaeornis wetzeli from Maastrichtian beds of Chile, Polarornis gregorii and Vegavis iaai from the Maastrichtian of Antarctica, and Australornis lovei from the Paleogene of New Zealand. The phylogenetic relationships of these taxa have been variously interpreted by different authors. In a more recent analysis, Polarornis, Vegavis, Neogaeornis, and Australornis, are including in a new clade: Vegaviidae.

Vegaviids share a combination of characters related to diving adaptations, including compact and thickened cortex of hindlimb bones, femur with anteroposteriorly compressed and bowed shaft, deep and wide popliteal fossa delimited by a medial ridge, tibiotarsus showing notably proximally expanded cnemial crests, expanded fibular crest, anteroposterior compression of the tibial shaft, and a tarsometatarsus with a strong transverse compression of the shaft.

Histological sections of Vegavis iaai (MACN-PV 19.748) humerus (a), femur (b), polarized detail of humerus (c). Scale bar equals 10 mm for (a), (b) and 5 mm for (c). From Agnolín et al., 2017

The recognition of Polarornis, Vegavis, Neogaeornis, Australornis, and a wide array of isolated specimens as belonging to the new clade Vegaviidae reinforces the hypothesis that southern landmasses constituted a center for neornithine diversification, and emphasizes the role of Gondwana for the evolutionary history of Anseriformes and Neornithes.

The most informative source for anatomical comparison among Australornis, Polarornis, Vegavis as well as other southern avian is a recently published Vegavis skeleton (MACN-PV 19.748). Vegavis overlaps with Australornis in the proximal portion of the humerus, proximal part of the coracoid, scapula, and ulna; with Polarornis in the humerus, femur, and proximal end of the tibia; and with Neogaeornis in the tarsometatarsus.

Phylogeny with geographical distribution of Vegaviidae. From Agnolín et al., 2017.

The humerus is probably the most diagnostic element among anseriforms. In Vegavis and Australornis the humerus is notably narrow and medially tilted on its proximal half, and the deltopectoral crest extends for more than one third of the humeral length. The femur is well known both in Vegavis and Polarornis, and share a combination of characters absent in other Mesozoic or Paleogene birds, including strongly anteriorly bowed and anteroposteriorly compressed shaft (especially near its distal end)

Osteohistological analysis of the femur and humerus of V. iaai. shows a highly vascularized fibrolamellar matrix lacking lines of arrested growths, features widespread among modern birds. The femur has some secondary osteons, and shows several porosities, one especially large, posterior to the medullar cavity. The humerus exhibits a predominant fibrolamellar matrix, but in a portion of the anterior and medial sides of the shaft there are a few secondary osteons, some of them connected with Volkman’s canals, and near to these canals, there are a compact coarse cancellous bone (CCCB) with trabeculae. This tissue disposition and morphology suggests that Vegavis had remarkably high growth rates, a physiological adaptation that may be critical for surviving in seasonal climates at high latitudes, and  may also constitute the key adaptation that allowed vegaviids to survive the K/T mass extinction event.

 

References:

Agnolín, F.L., Egli, F.B., Chatterjee, S. et al. Sci Nat (2017) 104: 87. https://doi.org/10.1007/s00114-017-1508-y

Jordi Alexis Garcia Marsà, Federico L. Agnolín & Fernando Novas (2017): Bone microstructure of Vegavis iaai (Aves, Anseriformes) from the Upper Cretaceous of Vega Island, Antarctic Peninsula, Historical Biology, DOI: 10.1080/08912963.2017.1348503

Junornis houi and the evolution of flight

Holotype of Junornis houi. (From Liu et. al; 2017)

Birds originated from a theropod lineage more than 150 million years ago. By the Early Cretaceous, they diversified, evolving into a number of groups of varying anatomy and ecology. The Enantiornithes are the most successful clade of Mesozoic birds. In the last decades, exceptionally well preserved avian fossils han been recovered from China. The most recent, Junornis houi, from the Yixian Formation of eastern Inner Mongolia, represents a new addition to the enantiornithine diversity of the Jehol Biota

The holotype (BMNHC-PH 919; Beijing Museum of Natural History), from the Early Cretaceous (~ 126±4 mya) of Yixian Formation,  is a nearly complete and articulated skeleton contained in two slabs, and surrounded by feather impressions defining the surface of its wings and body outline. The name Jun is derived from a Chinese character meaning beautiful; and ornis is Greek for bird. The species name, houi honors Dr. Hou Lianhai.

Photograph and interpretative drawing of the forelimb of Junornis houi (From Liu et. al; 2017)

Junornis exhibits the following combination of characters: rounded craniolateral corner of sternum; distinct trough excavating ventral surface of mediocranial portion of sternum; triangular process at base of sternal lateral trabecula; sternal lateral trabecula broad and laterally deflected; sternal intermediate trabecula nearly level with mid-shaft of lateral trabecula; sternal xiphoid process level with lateral trabeculae; costal processes of last two penultimate synsacral vertebrae three times wider than same process of last synsacral vertebra; and very broad pelvis. Non-pennaceous, contour feathers cover much of the skeleton except the wings and feet.

Based on the well-preserved skeleton and exquisite plumage of Junornis, it was possible  make some estimation of its flight capacity. The body and wings of this bird were similar to those of modern passeriforms such as Alauda arvensis and to other small-sized birds that fly using intermittent bounds. The low aspect ratio (AR = 5.5) wings of BMNHC-PH 919 suggest that it may have been adapted to rapid take-offs, given that modern birds with proportionally short, broad wings tend to maximize thrust during slow flight. The low wing loading (WL = 0.18 g/cm2) of this fossil indicates that this bird would have been able to generate a large magnitude of lift at low speeds because for a given speed and angle of attack, birds with greater wing area (and therefore lower WL) generate more lift than those with small wing areas. This value also suggest that this bird would have been highly maneuverable and able to perform tight turns.

References:

Liu D, Chiappe LM, Serrano F, Habib M, Zhang Y, Meng Q (2017) Flight aerodynamics in enantiornithines: Information from a new Chinese Early Cretaceous bird. PLoS ONE12(10): e0184637. https://doi.org/10.1371/journal.pone.0184637

Forgotten women of Paleontology: Margaret Benson

Margaret Jane Benson. Portrait in the Archives of Royal Holloway, University of London (RHC PH/282/13) From Fraser & Cleal, 2007

It is a truth universally acknowledged, that women has always work harder than men to gain some recognition. It was true in the 16th, and it’s true now. In “A Room of One’s Own”, Virginia Woolf explores the conflicts that a gifted woman must have felt during the Renaissance through the fictional character of Judith Shakespeare, the sister of William Shakespeare, and cites as obstacles the indifference of most of the world, the profusion of distractions, and the heaping up of various forms of discouragement. But not only in the Elizabethan times. In the Victorian times there was the common assumption that the female brain was too fragile to cope with mathematics, or science in general. In a letter from March 1860, Thomas Henry Huxley wrote to great geologist Charles Lyell FRS: “Five-sixths of women will stop in the doll stage of evolution, to be the stronghold of parsonism, the drag on civilisation, the degradation of every important pursuit in which they mix themselves – intrigues in politics and friponnes in science.”

Margaret Crosfield on a Geologists’ Association fieldtrip to Leith Hill with Professor Lapworth (From Burek and Malpas, 2007).

Women have played  various and extensive roles in the history of geology. Unfortunately, their contribution has not been widely recognised by the public or academic researchers. In the 18th and 19th centuries women’s access to science was limited, and science was usually a ‘hobby’ for intelligent wealthy women. Early female scientists were often born into influential families, like Grace Milne, the eldest child of Louis Falconer and sister of the eminent botanist and palaeontologist, Hugh Falconer; or Mary Lyell, the daughter of the geologist Leonard Horner. They collected fossils and mineral specimens, and were allowed to attend scientific lectures, but they were barred from membership in scientific societies. But by the first half of the 20th century, a third of British palaeobotanists working on Carboniferous plants were women. The most notable were  Margaret Benson, Emily Dix, and Marie Stopes.

Newnham began as a house for five students in Regent Street in Cambridge in 1871

Margaret Benson was born on the 20th October 1859 in London. Between 1878 and 1879, she studied at Newnham College Cambridge. After obtaining her BSc at University College London (UCL) in 1891, she started research on plant embryology.  In 1893, Benson was appointed head of the new Department of Botany at Royal Holloway College, the first woman in the United Kingdom to hold such a senior position in the field of botany. Her palaeobotanical research centred on the anatomy of reproductive structures, especially of Carboniferous pteridosperms and lycophytes. In 1904, she was among the first group of women to be elected as Fellows of the Linnean Society, and in 1912 she was appointed Professor of Botany at the University of London. Her major study on lycophyte fructifications was on the cones of the Sigillaria plant. She also speculated on the relationship between the Palaeozoic arborescent lycophytes and the Recent Isoetes, with the Triassic Pleuromeia as a possible intermediate form. She worked with ferns and cordaites and described a new species, Cordaites felicis. Benson’s work is characterized by careful description. One of her most important theoretical works concerns the phylogenetic significance of the sporangiophore in lycophytes, sphenophytes and ferns. After her retirement in 1922, she was encouraged by D. H. Scott to write up some of her earlier unpublished work on the root anatomy of the early Carboniferous pteridosperm Heterangium. She even continued with fieldwork when she was in her 70s. There is an unpublished manuscript in which she described a new fertile Rhacopteris that she collected from Teilia Quarry in North Wales in 1933. She died on 20th June 1936 at Highgate, Middlesex.

References:

H. E. Fraser and C. J. Cleal, The contribution of British women to Carboniferous palaeobotany during the first half of the 20th century, Geological Society, London, Special Publications, 281, 51-82, 1 January 2007, https://doi.org/10.1144/SP281.4

C. V. Burek (2007). The role of women in geological higher education – Bedford College, London (Catherine Raisin) and Newnham College, Cambridge, UK, Geological Society, London, Special Publications, eds Burek C. V., Higgs B. 281, pp 9–38

 

A brief history of the Spinosaurus.

One of the photographs donate by W. Stromer. Image from the Washington University in St. Louis

Despite its low fossil record, Spinosaurus is one of the most famous dinosaur of all time. This gigantic theropod possessed highly derived cranial and vertebral features sufficiently distinct for it to be designated as the nominal genus of the clade Spinosauridae. 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. Stromer and Markgraf recovered the right and left dentaries and splenials from the lower jaw; a straight piece of the left maxilla that was described but not drawn; 20 teeth; 2 cervical vertebrae; 7 dorsal (trunk) vertebrae; 3 sacral vertebrae; 1 caudal vertebra; 4 thoracic ribs; and gastralia. This gigantic predator is estimated to have been about 14 m, with unusually long spines on its back that probably formed a large, sail-like structure.

1) Photograph of the right mandibular ramus of the holotype of Spinosaurus aegyptiacus Stromer, 1915 (BSP 1912 VIII 19), in lateral view. 2) Reproduction of Stromer’s (1915, pl. I, fig. 12a) illustration of the right mandibular ramus.

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. During the World War II, E. 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 Beurlen refused to do it. Unfortunately, on April 24, 1944, a British Royal Air Force raid bombed the museum and incinerated its collections. Only two photographs of the holotype of Spinosaurus aegyptiacus were recovered in in the archives of the Paläontologische Museum in June 2000, after they were donated to the museum by Ernst Stromer’s son, Wolfgang Stromer, in 1995. These photographs provide additional insight into the anatomy of the holotype specimen of Spinosaurus aegyptiacus.

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

In his original monograph, Stromer emphasized the peculiar character of the teeth of this unusual theropod. Because of their morphological convergence with those of crocodilians and other fish-eating reptiles, isolated spinosaurid teeth have frequently been misinterpreted. It appears that Baryonyx-like teeth were collected by Gideon Mantell in Sussex around 1820. Georges Cuvier was the first to publish an illustration of the four teeth from Tilgate Forest. These teeth, however, were generally considered as belonging to crocodilians, and when Richard Owen erected the taxon Suchosaurus cultridens to designate them he placed it among the crocodiles. Even when Owen realized that these teeth were peculiar in many respects and hinted at possible affinities with dinosaurs, he persistently classified Suchosaurus as a crocodilian, an interpretation that was accepted by most subsequent authors.

Although Stromer’s original description of Spinosaurus aegyptiacus was published in 1915, a more complete detailed picture of its anatomy, evolution, and biogeography only begun to emerge in recent decades.

 

References:

HONE, D. W. E. and HOLTZ, T. R. (2017), A Century of Spinosaurs – A Review and Revision of the Spinosauridae with Comments on Their Ecology. Acta Geologica Sinica, 91: 1120–1132. doi: 10.1111/1755-6724.13328

Smith, et al. “NEW INFORMATION REGARDING THE HOLOTYPE OF SPINOSAURUS AEGYPTIACUS STROMER, 1915.” J. Paleont., 80(2), 2006, pp. 400–406

New tetrapod assemblage from the Chañares Formation

Skeletal anatomy of the erpetosuchid pseudosuchian Tarjadia ruthae. From Ezcurra et al., 2017

In the aftermath of the Permo-Triassic mass extinction (~252 Ma), several typical Palaeozoic synapsids and parareptiles were replaced by stem and crown archosaurs (archosauromorphs) and eucynodonts, and the Late Triassic fossil record of South America has been crucial to shed light on their evolutionary histories.

The Chañares Formation is part of the Ischigualasto-Villa Unión Basin, and represents one of the most continuous continental Triassic succesions in South America. Located in Talampaya National Park (La Rioja Province), the Chañares Formation is characterized at its base by a sandstone–siltstone fluvial facies with distinct lower and upper levels. The lower levels are composed of light olive grey fine-grained sandstones with abundant small brown carbonate concretions. The upper levels include fine-grained sandstones and siltstones that yielded a rich tetrapod assemblage composed of kannemeyeriiform dicynodonts, traversodontid and probainognathian cynodonts, proterochampsid stem-archosaurs, stem-crocodylians, and dinosaur precursors.

Volcanism played an important role in the generation and preservation of the Chañares Formation’s exceptional tetrapod fossil record. Recent radioisotopic datings temporally constrained most of the lower half of this unit to the earliest Carnian (236–231 Ma), showing that this assemblage preceded the oldest members of typical Late Triassic archosaur clades that are found in the Ischigualasto Formation. The new assemblage is called here as the Tarjadia Assemblage Zone, while the upper, historically known assemblage is called the Massetognathus–Chanaresuchus Assemblage Zone. This new assemblage sheds light on the link between the Early–Middle Triassic tetrapod assemblages of Africa (for example, Karoo, Ruhuhu and Otiwarongo basins) and those from the Middle–Late Triassic of South America.

The Chañares Formation (© 2012 Idean)

Tarjadia ruthae is characterized by a dorsoventrally thick skull roof ornamented by deep pits and grooves of random arrangement; Y-shaped tuberosity on the dorsal surface of the anterior end of the parietals; marginal dentition with serrations; spine table of the presacral and anterior caudal vertebrae with a transversely concave dorsal surface; a femur with a poorly developed fourth trochanter and a hook-shaped tibial condyle; and thick dorsal osteoderms with a coarse pitted ornamentation. The abundance of the erpetosuchid Tarjadia in the lowermost levels of the Chañares Formation indicates that this pseudosuchian was an important secondary consumer in its ecosystem

The Tarjadia and Massetognathus–Chanaresuchusassemblage zones currently do not share species or low level taxa, indicating a profound faunal replacement involving both primary and secondary consumers. Therefore, the rise of dinosaurs and other archosauromorph clades that diversified worldwide in the Late Triassic was preceded by a phase of relatively rapid changing ecosystems in southwestern Pangaea, including two (Tarjadia and Massetognathus–Chanaresuchus assemblage zones) profound faunal replacements in a time span shorter than 6 Myr (around 236–231 Ma).

References:

Martín D. Ezcurra, Lucas E. Fiorelli, Agustín G. Martinelli, Sebastián Rocher, M. Belén von Baczko, Miguel Ezpeleta, Jeremías R. A. Taborda, E. Martín Hechenleitner, M. Jimena Trotteyn & Julia B. Desojo; Deep faunistic turnovers preceded the rise of dinosaurs in southwestern Pangaea, Nature Ecology & Evolution (2017) doi:10.1038/s41559-017-0305-5

Benton, M. J., Tverdokhlebov, V. P. & Surkov, M. V. Ecosystem remodelling among vertebrates at the Permian–Triassic boundary in Russia. Nature 432, 97–100 (2004).

A Brief Introduction to the Osteology of Viavenator exxoni

Viavenator exxoni, Museo Municipal Argentino Urquiza

The Abelisauridae is the best-known carnivorous dinosaur group from Gondwana. Their fossil remains have been recovered in Argentina, Brazil, Morocco, Niger, Libya, Madagascar, India, and France. These theropods exhibit spectacular cranial ornamentation in the form of horns and spikes and strongly reduced forelimbs and hands. The group was erected by Jose Bonaparte with the description of  Abelisaurus comahuensis, and includes: Carnotaurus sastrei, Aucasaurus garridoi, Ekrixinatosaurus novasi, Skorpiovenator bustingorryi, Eoabelisaurus and Viavenator exxoni

The holotype of Viavenator exxoni (MAU-Pv-LI-530) was found in the outcrops of the Bajo de la Carpa Formation (Santonian, Upper Cretaceous), northwestern Patagonia, Argentina. Viavenator series of autapomorphies are: transversely compressed parietal depressions on both sides of the supraoccipital crest; ventral edges of the paraoccipital processes located above the level of the dorsal edge of the occipital condyle; basioccipital-opisthotic complex about two and a half times the width and almost twice the height of the occipital condyle, in posterior view; well-developed crest below the occipital condyle; deeply excavated and sub-circular basisphenoidal recess; basipterygoid processes horizontally placed with respect to the cranial roof and located slightly dorsally to the basal tubera; mid and posterior cervical centra with slightly convex lateral and ventral surfaces; presence of an interspinous accessory articular system in middle and posterior dorsal vertebrae; presence of a pair of pneumatic foramina within the prespinal fossa in anterior caudal vertebrae; distal end of the scapular blade posteriorly curved.

Figure 1. Rendering of the type braincase of Viavenator exxoni (MAU-Pv-LI-530) in dorsal (A,B), and right lateral (C,D) view. Adapted from Carabajal y Filippi, 2017.

Viavenator presents highly-derived postcranial characters, and a relatively plesiomorphic skull in comparison with Carnotaurus and Aucasaurus. Cranial elements of this specimen include the complete neurocranium: frontals, parietals, sphenethmoids, orbitosphenoids, laterosphenoids, prootics, opisthotics, supraoccipital, exoccipitals, basioccipital, parasphenoids and basisphenoids. The plesiomorphic traits of the skull of Viavenator are mainly related with the anatomy of frontals, wich lack osseous prominences such as domes or horns. The dorsal surface of the frontals exhibits an ornamentation that consists of pits and sinuous furrows and ridges, although it is not well-preserved. The  exoccipitals form the lateral and possibly the laterodorsal margins of the foramen magnum, as apparently occurs in Carnotaurus. 

Vertebrae of Viavenator exxoni. Scale bar: 5 cm. From Filippi et al., 2017),

The postcranial skeleton of Viavenator is represented by eight cervical vertebrae (the atlas; seven dorsal vertebrate, four of them articulated; twelve caudal vertebrae); ribs; gastralias; one chevron; scapulocoracoid; ischium foot; and fibulae. The atlas is similar to that of Carnotaurus, though less robust and anteroposteriorly shorter; and there  are not observed prezygapophyseal facets in the neurapophyses, so it is inferred that the proatlas was absent, as also occurs in Carnotaurus and Majungasaurus. The shape of the epipophyses of the cervical region, which are
characterized by anterior and posterior projections, is shared by Viavenator and Carnotaurus, but it is not present in pre-Santonian forms such as Ilokelesia and Skorpiovenator. The derived vertebral characters of Viavenator are linked with an increase in the structural rigidity of the vertebral column, and with an increase in the cursorial abilities of these abelisaurids. This combination of plesiomorphic and derived traits suggests that Viavenator is a transitional form.

 

References:

Filippi, L.S., Méndez, A.H., Gianechini, F.A., Juárez Valieri, Rubé.D., Garrido, A.C., Osteology of Viavenator exxoni (Abelisauridae; Furileusauria) from the Bajo de la Carpa Formation, NW Patagonia, Argentina, Cretaceous Research (2017), doi: 10.1016/j.cretres.2017.07.019.

Leonardo S. Filippi, Ariel H. Méndez, Rubén D. Juárez Valieri and Alberto C. Garrido (2016). «A new brachyrostran with hypertrophied axial structures reveals an unexpected radiation of latest Cretaceous abelisaurids». Cretaceous Research 61: 209-219. doi:10.1016/j.cretres.2015.12.018

Paulina-Carabajal, A., Filippi, L., Neuroanatomy of the abelisaurid theropod Viavenator: The most complete reconstruction of a cranial endocast and inner ear for a South American representative of the clade, Cretaceous Research (2017), doi: 10.1016/j.cretres.2017.06.013