THE “STONY BOOKS” – THREE-DIMENSIONAL FOOTPRINTS FROM EARLY JURASSIC STRATA OF THE CONNECTICUT VALLEY

One of the curiosities of the Hitchcock Ichnological Collection (Amherst College, Amherst, MA) is the collection of specimens, catalog numerator 27, which Hitchcock placed into the ‘Stony Library'. The ‘books' of this library were each formed by splitting a thick footprint-bearing slab along laminae, forming the leaves of each book; these were then bound together with iron hinges, making books whose pages turn. The largest books contain 6 pages. Additional multi-leaved specimens exist which were not bound into books (e.g., some specimens catalogued under numerators 31 and 34).

These multi-leaved specimens have considerable scientific value in addition to their aesthetic qualities. The ichnotaxa on the slabs were originally included in Hitchcock's group ‘Leptodactyli' – footprints with slender tapering toes, and often with metatarsal impressions; it is not possible to say much about the pedal osteology of the trackmaker other than the number and relative lengths of the digits. The Leptodactyli occur typically in fine-grained sediments that were probably very wet, and not bound by microbes (as exemplified by the Wethersfield Cove (CT) locality), but similar morphologies are also seen in some sandstones around Turners Falls (MA). The Wethersfield locality demonstrates that the animal's foot sank deeply into the laminated mud; when the foot withdrew, the mud flowed back into the depression created by the foot. Now lithified, the footprint-bearing slab can be split along these laminae, preserving the penetrative footprint on multiple layers, commonly over a vertical distance of 30 mm or more. In several instances it can be clearly seen that the foot sank slightly sideways as it emplaced, rather than perpendicular to the surface. Generally, the divarication between digits decreases downwards. This has important implications for trackmaker identification - pachydactylous tridactyl prints with wide divarication are generally identified as Anomoepus, attributed to ornithischians, whereas those with narrower divarication are generally identified as Grallator, attributed to theropods. Divarication as a means of differentiating theropods and ornithischians is inapplicable to the Leptodactyli, as a single print can appear to be anomoepodid on higher surfaces but morphs into a grallatorid aspect downwards.