The Ha Nohana palaeosurface in southern Lesotho preserves tridactyl and tetradactyl tracks and trackways
attributable to Early Jurassic bipedal, theropod-like dinosaurs. Complementary sedimentological and ichnological
observations along the palaeosurface and in the strata below and above it allow detailed interpretations
of climatically driven changes in this southern Gondwana palaeoecosystem. Sedimentological evidence suggests
trackmaking under a semi-arid climate with heavy storms and episodic flash flooding that induced ephemeral,
unconfined sheetwashes. The palaeosurface is overlain by rhythmically bedded, organic-matter rich mudstones
that formed in a deep, stratified lake indicative of a longer and wetter period in the history of the site. The unique
morphological details of the Ha Nohana tracks help refine the properties of the substrate during track making, the
ichnotaxonomic affinities of the footprints and the interpretation of the foot movement relative to the substrate.
Two footprint morphotypes, ~ 300 m apart, are defined on the palaeosurface. Tracks of morphotype I are tridactyl,
shallow, contain digital pad impressions and were impressed on a firm, sand rippled substrate that underwent desiccation.
Conversely, tracks of morphotype II are tetradactyl, deep, and have an elongated posterior region. These
tracks are preserved on the surface of a massive sandstone and are associated with soft sediment collapse structures
related to the animal’s foot sinking into the water-saturated, malleable sediment layer. Morphotype II tracks show
that as the animal waded across the substrate, the liquefied sediment lost its cohesive strength and could only
partially support the weight of the animal. In so doing, the animal’s foot sunk deep enough into the sediment such
that the impression of the metatarsal and digit I (hallux) are now visible. Thus, the palaeosurface was walked on by
small-to-medium sized theropods that traversed over ripple marks in firmer moist sand, as well as a larger theropod
that tottered through water-logged sand.
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