ScienceDaily (Oct. 8, 2009) — A new investigation of a fossilized tracksite in southern Africa shows how early dinosaurs made on-the-fly adjustments to their movements to cope with slippery and sloping terrain. Differences in how early dinosaurs made these adjustments provide insight into the later evolution of the group.
The research, conducted by researchers at the University of Michigan, Argentina's Universidad de Buenos Aires, and the Iziko South African Museum in Cape Town, South Africa, will be published online Oct. 6 in the open-access journal PLoS ONE.
The Moyeni tracksite in Lesotho contains more than 250 footprints made by a variety of four-legged animals near the beginning of the Jurassic Period (about 200 million years ago), when the Earth's landmasses were united as Pangea. The site was first discovered and described in the 1960s and 1970s by French paleontologist Paul Ellenberger but has not since been examined in detail. In their re-analysis of the fossil tracksite, the researchers created a high-resolution map of trackway surface using a combination of traditional mapping techniques and a 3D surface scanner, which recorded millimeter-scale detail. The digital record of the site will serve as an archive and will be the source of future research, said U-M's Jeffrey Wilson, an assistant professor in the Department of Geological Sciences and an assistant curator in the Museum of Paleontology.
The researchers' re-interpretation of the geology of the tracksite indicated that the dinosaurs were walking across an ancient point bar that presented the animals with varying surface conditions. Based on the map, scans, and first-hand observations at the site, Wilson and coworkers Claudia Marsicano and Roger Smith interpreted the tracks to understand how dinosaurs adjusted to changes in terrain as they moved between a wet riverbed, a sloping bank, and a flat, upper surface of the point bar.
"Tracks and trackways bring animals to life in a way that their bones cannot, by providing a brief but vibrant record of a living, breathing animal as it moved through its environment," Wilson said. "While fossilized bones can provide a wealth of information about extinct animals' anatomy and physiology, inferences about their locomotion and behavior are necessarily indirect." Tracks, on the other hand, are a direct record of the animal's behavior.
The disadvantage, though, is that tracks preserve the impression of nothing more than the sole of the foot, rendering trackmaker identification an approximation. It is very difficult to identify species with such limited information.
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Journal reference:
Wilson JA, Marsicano CA, Smith RMH. Dynamic Locomotor Capabilities Revealed by Early Dinosaur Trackmakers from Southern Africa. PLoS ONE, 2009; 4 (10): e7331 DOI: 10.1371/journal.pone.0007331
Jeffrey A. Wilson1*, Claudia A. Marsicano2, Roger M. H. Smith3
1 Museum of Paleontology & Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan, United States of America,
2 Departamento de Ciencias Geológicas, Universidad de Buenos Aires, Buenos Aires, Argentina,
3 Department of Karoo Paleontology, Iziko South African Museum, Cape Town, South Africa
Abstract Top
Background
A new investigation of the sedimentology and ichnology of the Early Jurassic Moyeni tracksite in Lesotho, southern Africa has yielded new insights into the behavior and locomotor dynamics of early dinosaurs.
Methodology/Principal Findings
The tracksite is an ancient point bar preserving a heterogeneous substrate of varied consistency and inclination that includes a ripple-marked riverbed, a bar slope, and a stable algal-matted bar top surface. Several basal ornithischian dinosaurs and a single theropod dinosaur crossed its surface within days or perhaps weeks of one another, but responded to substrate heterogeneity differently. Whereas the theropod trackmaker accommodated sloping and slippery surfaces by gripping the substrate with its pedal claws, the basal ornithischian trackmakers adjusted to the terrain by changing between quadrupedal and bipedal stance, wide and narrow gauge limb support (abduction range = 31°), and plantigrade and digitigrade foot posture.
Conclusions/Significance
The locomotor adjustments coincide with changes in substrate consistency along the trackway and appear to reflect ‘real time’ responses to a complex terrain. It is proposed that these responses foreshadow important locomotor transformations characterizing the later evolution of the two main dinosaur lineages. Ornithischians, which shifted from bipedal to quadrupedal posture at least three times in their evolutionary history, are shown to have been capable of adopting both postures early in their evolutionary history. The substrate-gripping behavior demonstrated by the early theropod, in turn, is consistent with the hypothesized function of pedal claws in bird ancestors.
Citation: Wilson JA, Marsicano CA, Smith RMH (2009) Dynamic Locomotor Capabilities Revealed by Early Dinosaur Trackmakers from Southern Africa. PLoS ONE 4(10): e7331. doi:10.1371/journal.pone.0007331
Editor: Andrew Allen Farke, Raymond M. Alf Museum of Paleontology, United States of America
Received: April 30, 2009; Accepted: September 11, 2009; Published: October 6, 2009
Copyright: © 2009 Wilson et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This research was supported by grants from Palaeontological Scientific Trust (to RMHS), a Woodrow Wilson National Fellowship Foundation Career Enhancement Fellowship for Junior Faculty (to JAW), and support from Consejo Nacional de Investigaciones Científicas y Técnicas (to CAM). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
* E-mail: wilsonja@umich.edu
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