). ` However, the terms used here are something more than convenient labels: they are intended to dispel the ambiguities that pervade existing terminology.PLoS ONE | www.plosone.orgAlthough it is tempting to describe a transmitted relief as a subdued or muted version of the footprint, the two structures are fundamentally different. The footprint is impressed directly by the track-maker into a surface exposed to the air or covered by water, whereas a transmitted relief has no contact with the track-maker and is formed beneath a blanket of sediment. In fact, the trackmaker has projected an indication of its existence and its activity (initially a trace and potentially a trace-fossil) into sediment that was deposited and buried before the animal arrived on the scene and conceivably before the track-maker ever existed. Transmitted reliefs are intrusive elements projected into sedimentary deposits of the past, the very antithesis of derived fossils, whereas the footprint (sensu stricto) must be contemporary with the animal that made it. Likewise the natural cast is fundamentally different in nature from the corresponding reliefs transmitted into the substrate. The natural cast is formed after the track-maker has impressed its footprint and departed from the scene, whereas the transmitted reliefs are formed at nearly the same instant as the footprint and are composed of sedimentary material that was already in situ.Substrates Actidione site Deformed by Cretaceous DinosaursFigure 19. Hierarchy of transmitted reliefs: the basic elements. Two sauropod footprints, each underlain by its own stack of transmitted reliefs, are enclosed in a single RR6 site larger basin of transmitted reliefs. Scale is 1 foot (c. 31 cm), but tilted and foreshortened. This specimen encapsulates the basis of hierarchical pattern – two stacks of transmitted reliefs nested into a single larger basin of transmitted reliefs. doi:10.1371/journal.pone.0036208.gUnfortunately those distinctions are not acknowledged in the prevailing terminology, which is dominated by the term track. Aside from occasional reference to overtracks (e.g. by Marty [46]), ichnological literature currently maintains that tracks exist in two forms – (1) true or direct tracks, and (2) undertracks or indirect tracks (with several synonyms). It seems to be agreed universally that the objects in the second category (whatever you might choose to call them) are not true tracks, and they would not normally be accepted as an adequate basis for defining ichnotaxa. Consequently their status is unclear: they seem to be regarded as tracks of some sort, though they are excluded from the classification of `true’ tracks.Figure 20. Hierarchy of transmitted reliefs: a saddle-shaped basin. A,B, two views of single saddle-shaped basin of deformation containing residual stacks of transmitted reliefs from two sauropod footprints. The two photographs were taken on different occasions and in the interim a storm removed some of the obscuring beach sand. doi:10.1371/journal.pone.0036208.gTheir status may be clarified by considering their origin. What has been transmitted into the substrate beneath a footprint (sensu stricto) is not a footprint or a track of any kind: it is the force of the foot’s impact. And the transmitted force has interacted with existing sub-surface structures (laminations) to replicate some physical characteristics of the footprint (size, shape and topographic relief), though only approximately and to a limited degree. Even so,.). ` However, the terms used here are something more than convenient labels: they are intended to dispel the ambiguities that pervade existing terminology.PLoS ONE | www.plosone.orgAlthough it is tempting to describe a transmitted relief as a subdued or muted version of the footprint, the two structures are fundamentally different. The footprint is impressed directly by the track-maker into a surface exposed to the air or covered by water, whereas a transmitted relief has no contact with the track-maker and is formed beneath a blanket of sediment. In fact, the trackmaker has projected an indication of its existence and its activity (initially a trace and potentially a trace-fossil) into sediment that was deposited and buried before the animal arrived on the scene and conceivably before the track-maker ever existed. Transmitted reliefs are intrusive elements projected into sedimentary deposits of the past, the very antithesis of derived fossils, whereas the footprint (sensu stricto) must be contemporary with the animal that made it. Likewise the natural cast is fundamentally different in nature from the corresponding reliefs transmitted into the substrate. The natural cast is formed after the track-maker has impressed its footprint and departed from the scene, whereas the transmitted reliefs are formed at nearly the same instant as the footprint and are composed of sedimentary material that was already in situ.Substrates Deformed by Cretaceous DinosaursFigure 19. Hierarchy of transmitted reliefs: the basic elements. Two sauropod footprints, each underlain by its own stack of transmitted reliefs, are enclosed in a single larger basin of transmitted reliefs. Scale is 1 foot (c. 31 cm), but tilted and foreshortened. This specimen encapsulates the basis of hierarchical pattern – two stacks of transmitted reliefs nested into a single larger basin of transmitted reliefs. doi:10.1371/journal.pone.0036208.gUnfortunately those distinctions are not acknowledged in the prevailing terminology, which is dominated by the term track. Aside from occasional reference to overtracks (e.g. by Marty [46]), ichnological literature currently maintains that tracks exist in two forms – (1) true or direct tracks, and (2) undertracks or indirect tracks (with several synonyms). It seems to be agreed universally that the objects in the second category (whatever you might choose to call them) are not true tracks, and they would not normally be accepted as an adequate basis for defining ichnotaxa. Consequently their status is unclear: they seem to be regarded as tracks of some sort, though they are excluded from the classification of `true’ tracks.Figure 20. Hierarchy of transmitted reliefs: a saddle-shaped basin. A,B, two views of single saddle-shaped basin of deformation containing residual stacks of transmitted reliefs from two sauropod footprints. The two photographs were taken on different occasions and in the interim a storm removed some of the obscuring beach sand. doi:10.1371/journal.pone.0036208.gTheir status may be clarified by considering their origin. What has been transmitted into the substrate beneath a footprint (sensu stricto) is not a footprint or a track of any kind: it is the force of the foot’s impact. And the transmitted force has interacted with existing sub-surface structures (laminations) to replicate some physical characteristics of the footprint (size, shape and topographic relief), though only approximately and to a limited degree. Even so,.