To better understand the biology of extinct animals, experimentation with extant animals and innovative numerical approaches have grown in recent years. This research project uses principles of soil mechanics and a neoichnological field experiment with an African elephant to derive a novel concept for calculating the mass (i.e., the weight) of an animal from its footprints. We used the elephant's footprint geometry (i.e., vertical displacements, diameter) in combination with soil mechanical analyses (i.e., soil classification, soil parameter determination in the laboratory, Finite Element Analysis (FEA) and gait analysis) for the back analysis of the elephant's weight from a single footprint. In doing so we validated the first component of a methodology for calculating the weight of extinct dinosaurs. The field experiment was conducted under known boundary conditions at the Zoological Gardens Wuppertal with a female African elephant. The weight of the elephant was measured and the walking area was prepared with sediment in advance. Then the elephant was walked across the test area, leaving a trackway behind. Footprint geometry was obtained by laser scanning. To estimate the dynamic component involved in footprint formation, the velocity the foot reaches when touching the subsoil was determined by the Digital Image Correlation (DIC) technique. Soil parameters were identified by performing experiments on the soil in the laboratory. FEA was then used for the backcalculation of the elephant's weight. With this study, we demonstrate the adaptability of using footprint geometry in combination with theoretical considerations of loading of the subsoil during a walk and soil mechanical methods for prediction of trackmakers weight.

Abstract. During their lifetime animals leave many tracks and traces behind, which can provide insights into the animals' behaviour. Single footprints of extant vertebrates are frequently found in sediments all over the world, often arranged into trackways. The study of footprints and trackways lead to interpretations about the mode of locomotion of the trackmaker. Here we show an approach to identify gaits from tracks.A series of experiments with horses was performed to determine whether gaits could be identified on the basis of fossil trackways, e.g. those left behind by sauropod dinosaurs of the Mesozoic era or Tertiary mammals, to unveil their locomotor abilities. The generally valid rules for quadrupedal locomotion were taken into consideration. Symmetrical gaits result in very similar trackways; a further differentiation can be made by application of statistics on step lengths, excursion angles and overstepping.A clear difference exists between the trot and the pace. These rapid, symmetric gaits imply high ground reaction forces (GRF) because of their long phases of aerial suspension at higher speeds. The resulting GRF seem to be too high to be sustained by the limb bones of huge graviportal animals like sauropods. Unfortunately, most of these factors are rarely available in the case of fossil tracks. Likewise, the asymmetrical, springing gaits can be excluded for sauropods because of the enormous GRF. Provided that limb length as well as trunk length can be approximated, and left and right, as well as forefoot and hindfoot imprints can be discriminated, the symmetrical gaits (walk, amble, pace, trot) used when making a trackway can be discerned.

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