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Virtual dinosaur stomping grounds

Photonics Spectra
Dec 2008
Caren Les, caren.les@laurin.com

Many among us, from children on up, are fascinated by dinosaurs and long to know more about them. Photonic instrumentation has been used to help document the remains of these creatures and to determine the activities they engaged in when they roamed the Earth.

An open quarry in the southeast Pyrenees, north of Barcelona, Spain, bears more than 3500 individual dinosaur tracks and 40 trackways (more than two footfalls made by the same animal) that will eventually be lost to weathering and erosion. Paleontologists have recorded significant deterioration of the track surfaces since their exposure in the 1980s by mining. They believe that the surface was trodden by titanosaurid sauropods and that there is also a theropod (predatory dinosaur) trackway to the south of the site.

Dinosaur_Fumanya6.jpgThe herbivorous sauropod dinosaurs with their small skulls and extended necks and tails were found to have roamed all of our planet’s landmasses except Antarctica and were thought to exist for 100 million years or so, from the Lower Jurassic to the Upper Cretaceous geological periods. Less is known about the carnivorous theropod, of which fewer fossil remains have been found at this site, but thousands are known from elsewhere in the world – from the tiny Compsognathus to the huge Tyrannosaurus rex.

The fragile track surfaces of the Fumanya sites have been tilted to a near-vertical position by an Alpine mountain-building event, which also has caused fracturing and veining, resulting in distortion of the original trackways. The steep incline of the site has made it difficult for researchers to study and document the tracks and has further contributed to the erosion. Toe impressions and claw marks were still visible in 2005 but have started to deteriorate in the past few years.

Led by Phillip L. Manning, senior lecturer in paleontology and research fellow at the University of Manchester in the UK, a team used light detection, range (lidar) imaging and digital photogrammetry to remotely collect 3-D spatial data on the track sites for quantitative documentation. They constructed high-resolution digital outcrop models of the track sites, which could well serve as a long-lasting virtual 3-D record of the ephemeral prints. The team’s goal was to assess lidar imaging and digital photography as tools for preserving geological heritage sites. Their work is described in the Journal of the Geological Society, London, Vol. 165, 2008.

Dinosaur_Fumanya2.jpg
Researchers have used lidar and photogrammetry to collect 3-D spatial data on dinosaur tracks at the Fumanya site between the Figols and Vallcebre villages in Spain. Courtesy of Phillip L. Manning.


Previous methods of studying the Fumanya South site have involved climbing, rope grids, photogrammetry and surveillance through binoculars to produce a qualitative record of the site – not considered adequate for comprehensively archiving the site.

The field instrumentation used in the current methodology included a portable Riegl LMS-Z420i 3-D laser scanner; a laptop and software for acquiring, viewing and processing 3-D data; a digital camera mounted on the scanner and a Trimble Pro XR differential global positioning system. Multiple scan stations provided more detailed 3-D shape information.

The researchers concluded that their new method has a number of advantages. Data collection is rapid and efficient, requiring minimal operator supervision, and the long range of the scanner allows remote surveillance of areas that are extremely fragile or that previously were difficult to access.

In terms of geoconservation – the preservation of a geological heritage site – the researchers found that the digital outcrop models have advantages over traditional documentation. The models create an effective visualization tool, especially when viewed in a 3-D environment. The fossils retain their true orientation within an outcrop, and the global positioning information places the model within a global reference framework.

Among the primary uses of this virtual, comprehensive means of preservation is desktop study and exploration: Researchers worldwide will be able to participate in the site study, and enthusiasts will be able to take virtual tours – all while leaving the site undisturbed. It is possible that the technique will be used to document many such sites, enabling comparative studies.

The researchers acknowledge that the process is expensive and that direct field observation of a site would still be necessary to obtain certain types of information.

According to Manning, the most exciting element of the technique is the accurate 3-D recording of data. Track analysis has been very “hit or miss” in the past, with each track varying according to the “eye” of the beholder. This method removes the vagaries of recording 3-D structures with 2-D methods such as drawing or photography, he said.

Manning added that he and his colleagues continue to analyze the vast amounts of data collected and that they are about to embark on further field investigations with Angel Galobart at the Institut Català de Paleontologia in Sabadell, Spain. Working closely with Galobart and his team, they hope to extend their work to all the major track sites on the Iberian Peninsula.

Manning also noted that his group is using lidar to map the site of a rare find – fossil remains of a dinosaur with preserved soft tissues – for the Washington-based National Geographic Society’s “dinosaur mummy” project.


GLOSSARY
exposure
In optics, the total radiant energy incident on a surface-per-unit area. It is equal to the integral over time of the radiant flux density. Also known as radiant exposure.
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