Friday, 18 April 2014

Reconstructing the Paluxy River Dinosaur Chase Sequence.

In 1940 palaeontologist Roland Bird of the American Museum of Natural History in New York described and partially excavated a sequence of Dinosaur footprints along the Paluxy River at Glen Rose in Texas. In the intervening time this sequence has become one of the best known Dinosaur trackways in the world, most notably a chase sequence which apparently showed a Theropod Dinosaur in pursuit of a Sauropod, which for many years became a standard inclusion in popular books on Dinosaurs.

Since Bird’s excavation much of the site has been destroyed by the actions of the Paluxy River (constant flooding was a problem during Bird’s excavations). The portions excavated by Bird were split in two, with some blocks going to the American Museum of Natural History and some to the Texas Memorial Museum. Unfortunately it was discovered in 1988 that the specimens at the Texas Memorial Museum had begun to deteriorate, deterioration which has continued to date despite attempts at preservation.

In a paper published in the journal PLoS One on 2 April 2014, Peter Falkingham of the Structure and Motion Laboratory at the Department of Comparative Biomedical Sciences at the Royal Veterinary College in London and the Department of Ecology and Evolutionary Biology at Brown University, Karl Bates of the Department of Musculoskeletal Biology II at the Institute of Ageing and Chronic Disease at the University of Liverpool and James Farlow of the Department of Geosciences at Indiana-Purdue University, describe the reconstruction of a three dimensional model of the Paluxy River Dinosaur Chase Sequence, using Bird’s original photographs and maps of the site, and LiDAR laser scans of the surviving material in the American Museum of Natural History and Texas Memorial Museum.

Sixteen of Bird’s original photographs used in the photogrammetric reconstruction of the trackway. Note that the state of excavation (flooded parallel trackways, sandbags, tools etc) varies between images, causing complications for the reconstruction. Falkingham et al. (2014).

The photographic methods available to Bird in 1940 were not comparable to modern techniques, nor are the focal lengths or even models of camera used by Bird known. Nevertheless Bird appreciated the value of photography as a recording technique at a palaeontolological excavation, and took a large number of pictures, seventeen of which were used in Falkingham et al.’s reconstruction. Unfortunately these pictures were mostly taken facing towards the south, limiting the amount of three dimensional reconstruction possible from them, and in addition they are of variable quality, and contain numerous unwanted items, such as people, tools, areas of flooding and sandbags used to contain said flooding.

Bird also made numerous maps and drawings of the site, using lengths of string to obtain accurate measurements despite encroaching flooding. Comparison of these maps to the photographs suggests that they were extremely accurate, although they differed in the extent to which the tracks curved.

R.T. Bird’s maps of the Paluxy ‘chase sequence.’ (a) Bird’s Rye chart, (b) the Austin chart, and (c) the Austin and Rye charts overlaid. Note that the Austin and Rye charts diverge toward the north. Falkingham et al. (2014).

Falkingham et al. created a three dimensional model using scanned photographs plus data from the LiDAR scans of the surviving blocks. This reconstruction was compared to the maps produced by Bird, which, although apparently accurate in their spacings, differed in the curvature of the trackways. Using these methods they were able to reconstruct 45 m of trackway, concluding from the photographic evidence that the more curved interpretation of the tracks was the more accurate. The resolution of the images was improved by using height-based colouration, revealing extra Theropod tracks in the LiDAR scanned blocks that had not been detected by Bird at the time of reconstruction.

Photogrammetric reconstruction of Bird’s chase sequence. Far left, photo-textured and height mapped plan-view of the reconstructed trackway. Right, photo-textured and height mapped views, top to bottom; isometric view along trackway, close up of high fidelity southern end, close up of poor quality northern end. Falkingham et al. (2014).


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Thursday, 17 April 2014

Magnitude 3.2 Earthquake in Rutland, England.

The British Geological Survey recorded a Magnitude 3.2 Earthquake at a depth of 4 km roughly 7 km northwest of Oakham in Rutland, England, slightly after 7.05 am British Summertime (slightly after 6.05 am GMT) on Thursday 17 April 2014. This is a large quake for the area, and was felt across much of Rutland, Nottinghamshire, Lincolnshire, Northamptonshire and Leicestershire, although there are no reports of any damage or injuries.

Map showing distribution of felt reports for this event. British Geological Survey.

Earthquakes become more common as you travel north and west in Great Britain, with the west coast of Scotland being the most quake-prone part of the island and the northwest of Wales being more prone  to quakes than the rest of Wales or most of England.

The precise cause of Earthquakes in the UK can be hard to determine; the country is not close to any obvious single cause of such activity such as a plate margin, but is subject to tectonic pressures from several different sources, with most quakes probably being the result of the interplay between these forces.

Britain is being pushed to the east by the expansion of the Atlantic Ocean and to the north by the impact of Africa into Europe from the south. It is also affected by lesser areas of tectonic spreading beneath the North Sea, Rhine Valley and Bay of Biscay. Finally the country is subject to glacial rebound; until about 10 000 years ago much of the north of the country was covered by a thick layer of glacial ice (this is believed to have been thickest on the west coast of Scotland), pushing the rocks of the British lithosphere down into the underlying mantle. This ice is now gone, and the rocks are springing (slowly) back into their original position, causing the occasional Earthquake in the process. 

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. If you felt this quake, or were in the area but did not (which is also useful information) then you can report it to the British Geological Survey here.

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Asteroid 2014 FS52 passes the Earth.

Asteroid 2014 FS52 passed by the Earth at a distance of 5 867 000 km (over 15 times the average distance between the Earth and the Moon) at about 7.50 am GMT on Friday 11 April 2014. There was no danger of the asteroid hitting the Earth and had it done so it would have presented only a minor hazard. 2014 FS52 is estimated to be between 24 m and 75 m in diameter, and an object of this size would be expected to break up between 20 km and 2 km above the Earth's surface, with only fragmentary material reaching the ground, although being directly beneath an object at the upper end of this range would probably be fairly unpleasant.

The calculated orbit of 2014 FS52. JPL Small Body Database Browser

2014 FS52 was discovered on 31 March 2014 by the University of Arizona's Mt. Lemmon Survey at the Steward Observatory on Mount Lemmon in the Catalina Mountains north of Tucson. The designation 2014 FS52 implies that the asteroid was the 1318th  object (object S52) discovered in the second half  of March 2014 (period 2014 F).

2014 FS52 has a 2.85 year orbital period and an eccentric orbit that takes it from 0.83 AU from the Sun (i.e. 83% of the average distance at which the Earth orbits the Sun) to 3.19 AU from the Sun (i.e. 319% of the average distance at which the Earth orbits the Sun, and more than double the distance at which the planet Mars orbits the Sun). It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer).

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Preserved wood from an Early Eocene kimberlite pipe in northwestern Canada’s Slave Province.

Kimberlite pipes are produced by rapid volcanic intrusions carrying magma from the Earth’s mantle rapidly to the surface, often resulting in explosive phreatomagmatic eruptions (explosions caused by hot magma coming into contact with water). These pipes are considered high value economic resources due to the common occurrence of diamonds within them. Surprisingly kimberlite pipes also often contain fossil material. This can come from two separate sources; organisms can fall directly into the erupting lava and be entombed within it as it cools (such intrusions of non-volcanic material, organic or otherwise, are known as xenoliths by volcanologists), alternatively material can be preserved in volcanic craters after the eruption, as organisms are buried in fine-grained volcanic ash and clay (volcanic maar), which has high preservational potential.

In a paper published in the journal PLoS One on 19 September 2012, Alexander Wolfe of the Department of Earth and Atmospheric Sciences at the University of Alberta, Adam Csank of the Environment and Natural Resources Institute at the University of Alaska, Anchorage, Alberto Reyes of the Department of Geoscience at the University of Wisconsin, Madison, Ryan McKellar also of the Department of Earth and Atmospheric Sciences at the University of Alberta, Ralf Tappert of the Institute of Mineralogy and Petrography at the University of Innsbruck and Karlis Muehlenbachs, again of the Department of Earth and Atmospheric Sciences at the University of Alberta, describe the discovery of a number of large wood fragments from the Panda Kimberlite Pipe, a volcanic intrusion which forms part of the  Ekati diamond mining concession worked by BHP Billiton in Canada’s Great Slave Province, which has been calculated to be about 53.3 million years old (Early Eocene). The Panda Kimberlite Pipe forms part of the Lac de Gras Field, which contains about 150 such pipes, emplaced between 45 and 78 million years ago. The Panda Pipe is a simple 200 m diameter cylinder, apparently produced by a single eruption.

Wolfe et al. provide a detailed description of a single piece of wood, a large wood fragment which had fallen into the lava and been mummified. The wood is excellently preserved, with only the outermost millimetre having been fusinized (burned), suggesting an absence of free oxygen when it was entombed. The preserved structure of the wood allows the specimen to be assigned to a tree of the genus Metasequoia, a form of Giant Redwood now restricted to central China, but known to have been common in Alaska during the late Palaeocene and Early Eocene, and therefore not a great surprise in Slave Province.

(D) Fossil wood encrusted in olivine-rich volcaniclastic kimberlite. (E) Photograph of the specimen characterized in this study. The wood was split when removed from the ore, revealing a sliver of opaque amber (9.5 cm long by 0.5 cm wide) in the xylem. Wolfe et al. (2012).

Metasequoia requires a high level of humidity to survive, with a minimum of around 1000 mm of rainfall per year. The area where the fossil was recovered has around 280 mm of rainfall per year, suggesting that the climate was much wetter during the Early Eocene (it is possible that this 53 million year old specimen comes from a tree of the same species as the modern Chinese trees, since these are exceptionally long lived organisms). Since the tree was living close to the Paleocene-Eocene Thermal Maximum (about 55.5 million years ago), when the climate is predicted to have been substantially warmer and wetter in this region, this confirms the climatic predictions. Isotopic data obtained from both the cellulose of the wood and an amber (tree resin) inclusion within the fossil suggests that temperatures would have been around 7-12˚C warmer than at present while the tree was living, again tending to confirm the climatic predictions.

(F) RLS in transmitted light showing uniseriate and biseriate bordered pits and cross-fields. (G) TLS showing rays stacked 3–26 cells high. (H). SEM (TS) of ring boundary with earlywood (left) and latewood (right). (I) Close-up of tracheids in TS and calcite crystals within cells (arrows). J. Cross-section of ray with cross-field pits. (K and L) Close-ups of cross-field pits. (M) TLS close-up of rays. (N). Radial longitudinal section showing four contiguous rows of ray parenchyma cells with smooth end walls and no separation between the individual rows of cells. Wolfe et al. (2012).

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Fossil Tapirs from the Pleistocene of Venezuala.

Tapirs are large tropical, forest dwelling, herbivorous mammals related to Horses and Rhinoceroses. They have an unusual distribution, being found in South and Central America, as well as in Southeast Asia. The oldest known Tapirs in the fossil record lived in North America during the early Eocene, around 55.4 million years ago. These early Tapirs are thought to have been essentially similar to modern Tapirs, though they probably lacked the small fleshy trunk that Tapirs have today. 

In a paper published in the journal Acta Palaeontologica Polonica on 25 July 2011, Elizete Holanda of the Programa de Pós−Graduação em Geociências at the Universidade Federal do Rio Grande do Sul and the Setor de Paleontologia at the Museu de Cięncias Naturais at the Fundação Zoobotânica do Rio Grande do Sul, and Ascanio Rincón of the Lab. Biología de Organismos Centro de Ecología at the Instituto Venezolano de Investigaciones Científicas, describe two partial fossil Tapirs from the Pleistocene of Venezuala.

The first fossil described comes from the El Breal de Orocual tar pits near Maturin City in Monagas State in the northwest of the country. Tar pits are essentially oil deposits identical to those worked by oil drills in other parts of the world, but exposed at the surface. When oil deposits are exposed in this way the lighter fractions (crude oil is made up of a mixture of different oils, known as 'fractions' due to the process used to separate them, fractional distillation) such as petroleum evaporate off, leaving the heavier fractions, known as tar, or asphalt, behind. These form oily pools in which animals can become trapped. The El Breal de Orocual pits have previously produced 24 different Mammal taxa, and are currently thought to be Plio-Pleistocene in age.

The specimen comprises an incomplete right maxilla and mandible (upper and lower jaw bones). These are on the slender side compared to modern Tapirs, but this is a variable trait within known species and cannot for this reason be considered diagnostic. For this reason the specimen is assigned to the modern genus Tapirus, but not classified to species level. 

Tapirus sp., El Breal de Orocual, Plio−Pleistocene. (A) Right maxilla in lateral (A1) and occlusal (A2) views. (B) Mandible in labial (B1) and occlusal (B2) views. Scale bars are 30 mm. Holanda & Rincón (2011).

If the Plio-Pleistocene data currently assigned to the El Breal de Orocual tar pits is correct (they were previously thought to be younger), then this specimen will represent the oldest known Tapir from South America. Tapirs are thought to have originated in North America in the Late Eocene; the oldest known fossils are North American and of early Miocene age, and Tapirs are Perissodactyls, related to Horses and Rhinoceroses that are also thought to have originated in the Eocene of North America. It has been suggested that Tapirs could have reached South America as early as the Late Miocene, but it is more likely that they arrived during the Great American Biotic Interchange, when the formation of the modern Isthmus of Panama allowed animals to migrate between North and South America from the Pliocene onwards.

The second specimen is from Zumbador Cave in eastern Falcón State, where a rich collection of Late Pleistocene bones has been found within a cave set it limestone of the Middle Miocene Capadare Formation, apparently having been carried there by the action of a river. This specimen is assigned to the modern species Tapirus terrestris, and comprises a partial skull, and incomplete left dentary (jawbone), an incomplete thoracic (back) vertebrae, an incomplete left humerus and femur (foreleg bones), a right astragalus (ankle bone) and part of the right pelvis.

 
Tapirus terrestris, Zumbador Cave, Pleistocene. (A) Incomplete skull in lateral (A1), posterior (A2), and dorsal (A3) views. (B) Left dentary in lingual view; a, height of the sagittal crest. Holanda & Rincón (2011).

Tapirus terrestris, Zumbador Cave, Pleistocene. (A) Thoracic vertebra in right lateral view. (B) Left humerus in posterior view. (C) Left radius in anterior view. (D) Incomplete right pelvis in lateral view. (E) Left femur in anterior view. (F) Right astragalus in dorsal view. Scale bars 30 mm. Holanda & Rincón (2011).

While a Late Pleistocene fossil of a modern species is not surprising, this represents the first known fossil of Tapirus terrestris. It is also outside the current range of the species, which is known from modern Venezuela, but largely south of the Orinoco.

The localities where the Venezuelan Tapir fossils were found. Holanda & Rincón (2011).

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Magnitude 1.4 Earthquake near Dumfries, southwest Scotland.

The British Geological Survey recorded a Magnitude 1.4 Earthquake at a depth of 6 km, toughly 2 km to the northwest of Dumfries in southwest Scotland, slightly before 7.30 pm British Summertime (slightly before 6.30 pm GMT) on Wednesday 16 April 2014. This is a small quake, highly unlikely to have caused any damage or injuries, though it may have been felt locally.

The approximate location of the 16 April 2014 Dumfries Earthquake. Google Maps.

Earthquakes become more common as you travel north and west in Great Britain, with the west coast of Scotland being the most quake-prone part of the island and the northwest of Wales being more prone  to quakes than the rest of Wales or most of England.

The precise cause of Earthquakes in the UK can be hard to determine; the country is not close to any obvious single cause of such activity such as a plate margin, but is subject to tectonic pressures from several different sources, with most quakes probably being the result of the interplay between these forces.

Britain is being pushed to the east by the expansion of the Atlantic Ocean and to the north by the impact of Africa into Europe from the south. It is also affected by lesser areas of tectonic spreading beneath the North Sea, Rhine Valley and Bay of Biscay. Finally the country is subject to glacial rebound; until about 10 000 years ago much of the north of the country was covered by a thick layer of glacial ice (this is believed to have been thickest on the west coast of Scotland), pushing the rocks of the British lithosphere down into the underlying mantle. This ice is now gone, and the rocks are springing (slowly) back into their original position, causing the occasional Earthquake in the process. 

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. If you felt this quake, or were in the area but did not (which is also useful information) then you can report it to the British Geological Survey here.

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Wednesday, 16 April 2014

A new species of Rhabdodontid Dinosaur from the Late Cretaceous of Hungary.

The Rhabdodontids are a group of Iguanadontid Ornithischian Dinosaurs known only from the Late Cretaceous of southern Europe. To date three genera have been described; the first being Rhabdodon from France and Spain, which has given its name to the group.  Mochlodon suessi was originally used to describe a small tooth from Austria thought to belong to a juvenile; this genus is now generally considered to be invalid, though a number of other fragmentary specimens from Austria have been referred to the species as Rhabdodon suessi. Finally a number of specimens from the Haţeg Basin of Romania have been referred to the genus Zalmoxes; these Romanian specimens are exceptionally small, and are thought to represent an example of island dwarfism, a phenomenon observed in other Dinosaurs from Haţeg.

In a paper published in the journal PLoS One on 21 September 2012, Attila Ősi and Edina Prondvai of the Lendület Dinosaur Research Group at Eötvös Loránd University, Richard Butler of the GeoBio-Center, Ludwig-Maximilians-Universität München and David Weishampel from the Center for Functional Anatomy and Evolution at Johns Hopkins University describe a new Rhabdodontid Dinosaur from the Late Cretaceous Csehbánya Formation at the Iharkút continental vertebrate-bearing site of western Hungary.

The new material is assigned to the genus Mochlodon; it is more extensive than the Austrian material, and though still fragmentary, is evidently similar enough to be placed in the same genus, and distinct enough from the French and Spanish material to merit being placed in a separate genus, leading Ősi et al. to conclude that the genus Mochlodon should be resurrected and treated as valid. However the Hungarian material is distinct enough from the Austrian material that Ősi et al. place it in a new species, Mochlodon vorosi, after Attila Vörös, the founder of the Paleontological Research Group of the Hungarian Academy of Sciences.

The material assigned to Mochlodon suessi includes, beside the original tooth, a right dentary (jawbone), as well as another tooth and a number of fragmentary limb bones. Mochlodon vorosi is described principally from another dentary. The dentary of Mochlodon suessi has a depression beneath the coronoid process that was thought to be a developmental feature in an immature Dinosaur, however this feature is more developed in Mochlodon vorosi, which, although also small, is apparently a mature animal. From this Ősi et al. conclude that the depression is a valid diagnostic feature for the genus, and that Mochlodons, despite being continent dwellers, were considerably smaller than Zalmoxes, reaching around 150-200 cm in length, and therefore raising questions about the island dwarf interpretation of Zalmoxes.

Cranial remains of Mochlodon vorosi  from the Upper Cretaceous Csehbánya Formation, Iharkút, western Hungary. (A) Right quadrate in cranial, (B) caudal, (C) lateral, (D) medial, (E) distal views; (F) left dentale in lateral, (G) medial, (H) occlusal views; (I) left postorbital in dorsal, (J) ventral, (K) lateral views. Anatomical abbreviations: anf, articular surface for angular; cof, articular surface for coronoid; cop, coronoid process; ded, dorsal edg of the dentary; dep, depression; fo, foramen; gr, groove; jpr, jugal process; ltfm, margin of lateral temporal fenestra; orm, orbital rim; ptp, pterygoid process; qco, quadrate condyles; qh, quadrate head; qjs, articular surface for quadratojugal; sqpr, squamosal process; sqs, articular surface for squamosal; stfm, margin of supratemporal fenestra; surf, articular surface for surangular; sy, symphysis; to, tooth; 10th, 10th alveolus. Ősi et al. (2012).

In addition to the first dentary from which the diagnosis was made, a further four complete dentaries (two left and two right) as well as six fragmentary specimens are referred to Mochlodon vorosi, confirming that the initial specimen was not atypical. In addition a left postorbital, two right quadrates, 38 loose teeth, four isolated vertebrae, a compressed sacrum, three coracoids, a fragmentary scapula, a fragmentary and an intact humerus, an ulna, two femora, a fragmentary femur, one complete and two fragmentary tibias and two phalanges are referred to the species. While these are scattered bones from numerous individuals, they do serve to re-affirm Ősi et al.’s estimate of the size of Mochlodon vorosi.

Comparison of histology-based adult body sizes of Mochlodon, Zalmoxes and Rhabdodon represented by the silhouettes of the animals. Ősi et al. (2012).

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