Friday, 17 March 2017

Lake Kariba dinosaur expedition: Part 3, finale

On reaching island 126/127 we began our search for the original Vulcanodon site. A thick lava flow forms the top of the cliffs, capping a series of bright orange and red mudstones and sandstones that comprise the Lower Jurassic Forest Sandstone Formation. Some of these layers were swarming with the burrows of animals that had lived in the sediment, suggesting that at times this ancient environment was a little wetter than generally thought. The island is small, so we were able to narrow down our search fairly quickly. Although we're confident that we did find the area that yielded Vulcanodon, were weren't lucky enough to find any other material on this occasion. The vertical cliffs didn't offer many opportunities to prospect for fossils and we were left wondering how the original team, lead by Prof. Michael Bond in the 1960s, had accomplished the back-breaking work of getting the huge bones out of the site. The foreshore was more promising, however, and were lucky enough to find isolated fossil bones in several places, all of which were attributable to more primitive sauropodomorph dinosaurs than Vulcanodon, which were probably from a more Massospondylus-like animal. While at the site we took the opportunity to learn more about its geology, measuring detailed sections and noting the lithology and structures present. This turned out to be a valuable exercise as it helped to form a basis for correlating the Vulcanodon site with other dinosaur-bearing sites around the lake shore and it also offered us some new clues on the geological age of Vulcanodon and on some of the other sites nearby, which will be the subject of a paper that the team is currently writing.

Cervical vertebra of a Massospondylus-like dinosaur found close to the Vulcanodon type locality on island 126/127 (photo: Pia Viglietti)
The nearby islands had very similar geology and we prospected several of these hoping to find new material. All were marked by the same characteristic dark basaltic lava flows and orange-red Forest Sandstone sediments and some showed evidence of major faults. These faults created some confusion when we were trying to work out where we were in each section, but after visiting lots of sites we began to work out how all of these features were related. We found bone on most of the islands, but they were usually small, isolated pieces, rather than associated or complete specimens. Nevertheless, in those cases where we could identify the bones, they were all of sauropodomorph dinosaurs and we identified many new potential sites that we hope to revisit in the future.

After several days of prospecting the islands around 126/127, we decided to move to sites closer to Kariba town. Our captain moved Musankwa eastward to moor off of Musango Island, where Steve Edwards runs his safari camp. Steve has been prospecting the area for many years and has amassed an important collection of material. Some of these specimens, including more evidence of sauropodomorph dinosaurs, come from the Forest Sandstone, but the majority of them come from an older unit that is probably of Late Triassic age, called the Tashinga Formation. The Tashinga Formation also consists of mudstones and sandstones, but parts of it were deposited under much wetter conditions than the Forest Sandstone. This is shown by the abundance of fossil wood on Musango Island and the nearby shore - fragments of wood are scattered everywhere in the soil and some spots has masses of large tree trunks that showed the region had been densely wooded at this time. In addition, other fossils also suggest the presence of water bodies (at least on a seasonal basis) as shown by finds of numerous large lungfish tooth plates.

Some huge Late Triassic tree trunks with palaeontologists for scale (photo: Lucy Broderick)
Among Steve's collection, and among the fossils we spotted while walking, we found some sauropodomorphs , but the remains of lungfish and other reptiles were much more common. Some of these fossils represent an interesting reptile that is the first of its kind to be reported from this area of Africa and the team is currently working on a description of these specimens. Over the next few days we walked though some of the areas around the island so that we could also study the geology, with the aim of trying to pin down a narrower age estimate and to work out how the different fossil-bearing units of the area were related to each other.

 The team poring over some of Steve Edward's fossils while at Musango Safari Camp (photo: Pia Viglietti)
After long hot days of walking through the bush, usually with at least one eye peeled for nearby elephants or hippos, our evenings around Musango were spent trying to supplement dinner with the excellent fish that could be caught in the lake (with varying amounts of success), as well as spotting some of the abundant bird life. While at Musango we also witnessed brutal tropical thunderstorms, which would come rolling in during the early hours of the morning while we were asleep. As many of us slept on deck (where it was nice and cool), we'd often be awoken by the crack of thunder, some amazing celestial pyrotechnics, and the drip of cold rain onto our faces through the mosquito nets as it found a way through the canopy.

A rare example of fishing success, with a triumphant Pia showing off her skills (photo: Lucy Broderick)
Following several pleasant and productive days at Musango, the final part of the trip involved another move to the east, closer yet to Kariba town, and a stay moored off of Spurwing Island, where we walked the shorelines looking for more places that might yield fossils. Again, assisted by the local rangers, we were lucky to find sites that yielded large sauropodomorph bones. Although none of these were particularly complete, they were of high quality, well preserved and some were partially articulated, suggesting that exploratory excavations in these areas might reveal interesting new material.

Steve Edwards checking out some of the sauropodomorph bones on Spurwing Island (photo: Lucy Broderick)
By the end of our trip we'd prospected a transect over 50 km in length and had visited numerous outcrops of both Late Triassic and Early Jurassic age. Our specimens have been deposited in the National Museum in Bulawayo and the information we've obtained on new sites, many of which were previously unknown, and on the geology of the area, is currently being compiled for publication. Our trip back down the lake was marked by more interesting weather, notably an amazing waterspout that we watched cross the lake surface followed by a torrential downpour that dampened our spirits somewhat as we unloaded Musankwa back in harbour. Nevertheless, the amazing scenery of Lake Kariba, its stunning natural beauty, and the new material we'd seen all combined to make this an exceptional and productive trip. The team is already planning to return to some of the more promising locations in the hope of finding some really spectacular material in future.

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