Lallensack Jens N
Section Paleontology, Institute of Geosciences, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany.
PeerJ. 2019 Jun 27;7:e7203. doi: 10.7717/peerj.7203. eCollection 2019.
The objective definition of footprint margins poses a central problem in ichnology. The transition from the footprint to the surrounding sediment is often continuous, and the footprint wall complex, requiring interpolation, approximation, and a priori assumptions about trackmaker anatomy to arrive at feasible interpretations of footprint shapes. The degree of subjectivity of such interpretations is substantial, and outlines produced by separate researchers can differ greatly. As a consequence, statistical shape analysis, regardless if based on linear and angular measurements or on the shape as a whole, are neither fully repeatable nor objective. Here I present an algorithm implemented in the programming environment R that is able to generate continuous footprint outlines based on three-dimensional models-fully automatically, objectively, and repeatable. The approach, which is based on contour lines extracted from the model, traces the outline at the point where the slope of the track wall is steepest. An option for automatic landmark placement is implemented for tridactyl footprints. A case study was carried out on 13 footprints of a single trackway of a theropod trackmaker from the Lower Cretaceous of Münchehagen, Germany. Analysis of the landmark coordinates returned by the script did reproduce statistical results published in an earlier study that was based on human-made interpretative drawings, demonstrating the applicability of the present method for the objective and quantitative shape analysis of tracks. Although faint anatomical details are not always recorded and features not related to the foot anatomy may be included, the generated outlines tend to correspond with human-made interpretative drawings regarding the overall shape. While not suited as a full replacement of interpretative drawings, these generated outlines may be used as an objective basis for such interpretations.
足迹边缘的客观定义是遗迹学中的一个核心问题。从足迹到周围沉积物的过渡通常是连续的，而足迹壁复合体需要进行插值、近似处理，并对造迹者的解剖结构进行先验假设，才能对足迹形状得出可行的解释。这种解释的主观程度很高，不同研究人员绘制的轮廓可能差异很大。因此，无论基于线性和角度测量还是基于整体形状的统计形状分析，都既不完全可重复也不客观。在此，我展示一种在R编程环境中实现的算法，它能够基于三维模型完全自动、客观且可重复地生成连续的足迹轮廓。该方法基于从模型中提取的等高线，在足迹壁坡度最陡的点追踪轮廓。针对三趾足迹实现了自动地标放置选项。对来自德国明希哈根下白垩统的一个兽脚类造迹者单条足迹道的13个足迹进行了案例研究。对脚本返回的地标坐标的分析确实重现了一项早期基于人工解释性绘图的研究中发表的统计结果，证明了本方法在足迹客观和定量形状分析中的适用性。尽管微弱的解剖细节并不总是被记录下来，可能会包含与足部解剖结构无关的特征，但生成的轮廓在整体形状上往往与人工解释性绘图相符。虽然这些生成的轮廓不适合完全替代解释性绘图，但它们可以作为此类解释的客观基础。
