Tallman Melissa, Amenta Nina, Delson Eric, Frost Stephen R, Ghosh Deboshmita, Klukkert Zachary S, Morrow Andrea, Sawyer Gary J
Department of Biomedical Sciences, Grand Valley State University, Allendale, Michigan, United States of America; New York Consortium of Evolutionary Primatology Morphometrics Group, New York Consortium of Evolutionary Primatology, New York, New York, United States of America.
Department of Computer Science, University of California Davis, Davis, California, United States of America.
PLoS One. 2014 Jul 3;9(7):e100833. doi: 10.1371/journal.pone.0100833. eCollection 2014.
Diagenetic distortion can be a major obstacle to collecting quantitative shape data on paleontological specimens, especially for three-dimensional geometric morphometric analysis. Here we utilize the recently-published algorithmic symmetrization method of fossil reconstruction and compare it to the more traditional reflection & averaging approach. In order to have an objective test of this method, five casts of a female cranium of Papio hamadryas kindae were manually deformed while the plaster hardened. These were subsequently "retrodeformed" using both algorithmic symmetrization and reflection & averaging and then compared to the original, undeformed specimen. We found that in all cases, algorithmic retrodeformation improved the shape of the deformed cranium and in four out of five cases, the algorithmically symmetrized crania were more similar in shape to the original crania than the reflected & averaged reconstructions. In three out of five cases, the difference between the algorithmically symmetrized crania and the original cranium could be contained within the magnitude of variation among individuals in a single subspecies of Papio. Instances of asymmetric distortion, such as breakage on one side, or bending in the axis of symmetry, were well handled, whereas symmetrical distortion remained uncorrected. This technique was further tested on a naturally deformed and fossilized cranium of Paradolichopithecus arvernensis. Results, based on a principal components analysis and Procrustes distances, showed that the algorithmically symmetrized Paradolichopithecus cranium was more similar to other, less-deformed crania from the same species than was the original. These results illustrate the efficacy of this method of retrodeformation by algorithmic symmetrization for the correction of asymmetrical distortion in fossils. Symmetrical distortion remains a problem for all currently developed methods of retrodeformation.
成岩变形可能是收集古生物学标本定量形状数据的主要障碍，特别是对于三维几何形态测量分析而言。在此，我们运用最近发表的化石重建算法对称化方法，并将其与更传统的反射与平均方法进行比较。为了对该方法进行客观测试，在石膏硬化时，手动对5个阿拉伯狒狒金氏亚种雌性颅骨的铸型进行了变形处理。随后分别使用算法对称化和反射与平均方法对这些变形铸型进行“逆向变形”，然后与原始的未变形标本进行比较。我们发现，在所有情况下，算法逆向变形都改善了变形颅骨的形状，并且在5个案例中有4个案例中，通过算法对称化处理的颅骨在形状上比经过反射与平均重建的颅骨更接近原始颅骨。在5个案例中有3个案例中，算法对称化处理的颅骨与原始颅骨之间的差异可控制在阿拉伯狒狒单个亚种个体间变异范围内。对于不对称变形的情况，如一侧破损或对称轴弯曲，该方法处理效果良好，而对称变形仍未得到校正。该技术还在一个自然变形且石化的阿韦龙古长臂猿颅骨上进行了进一步测试。基于主成分分析和普氏距离的结果表明，与原始颅骨相比，通过算法对称化处理的阿韦龙古长臂猿颅骨在形状上与同一物种其他变形较小的颅骨更为相似。这些结果说明了通过算法对称化进行逆向变形的方法在校正化石不对称变形方面的有效性。对称变形仍然是目前所有已开发的逆向变形方法所面临的问题。
