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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