Scampering, trotting, walking tridactyl bipedal dinosaurs in Lesotho
Palaeoenvironmental snapshot of the track-bearing surface at the Lephoto dam site showing some of the trackways made by two different tridactyl bipedal trackmakers that walked near the shoreline of a shallow desiccating pond.
In Gondwana, Early Jurassic dinosaur track sites are especially concentrated in Lesotho, however, despite intensive investigations during the third quarter of the twentieth century, a limited number of vertebrate track sites of this country have been studied with rigorous ichnological1 and sedimentological methods.
In a recent paper, UCT MSc student Miengah Abrahams and Dr Emese Bordy, both from the Department of Geological Sciences at UCT, together with Dr Lara Sciscio and Dr Fabien Knoll, present a previously undescribed track site in Lesotho. Fifty-two individual tridactyl tracks were found on the Lephoto palaeosurface, which were generated by three-toed bipedal dinosaurs (tridactyl bipeds) that moved towards or away from the shoreline of a shallow pond. Two track morphologies were recognised. The first is identified as Grallator-like, an ichnotaxon common in the Lower Jurassic of both Laurasia and Gondwana that can be attributed to small and medium-size carnivorous, theropod dinosaurs. The second ichnotaxon is reminiscent of Trisauropodiscus, which, in contrast, is a rare ichnotaxon that resembles tracks of birds and is known with certainty from only a few places in the world.
Their work provides further evidence that the ichnological record of the Elliot Formation of southern Africa is in a unique position to shed light not only on Early Jurassic biostratigraphy and palaeoenvironments but also on the biodiversity and palaeobiology of early dinosaurs. They reconstructed the behaviour of the various tridactyl bipedal trackmakers in terms of locomotion speed. The gait analysis of the five trackway makers at the site range from a walking gait to a running gait. While it is established that larger theropods walked more slowly than smaller theropods, this is not directly observed at the Lephoto dam site. The largest trackmaker is more than three times the size of the smallest trackmaker but both have similar gaits and speeds.
In summary, the Lephoto tracksite preserves a snapshot into life some 200 million years ago. The area was very active with small and medium sized dinosaurs, of different species, walking, trotting and running across a 4 m2 area of saturated sand perhaps heading to a nearby water source. In addition to the vertebrate track traces, invertebrate worm-like trails are preserved throughout the surface. Pitted surface textures suggest that microbial algal mats, which were formed by micro-organisms exploiting the wet conditions, aided in preserving these shallow track impressions.
Amazing what a set of footprints in sandstones can tell about dinosaurs and the land they walked on!
1. Ichnology is a branch of geosciences that bridges sedimentology & palaeontology and studies the traces left behind by organisms in sediments. Trace fossils can provide unique insights into an animal’s behaviour.