Unearthing Musankwa: International team finds new link in dinosaur evolution
Around 210 million years ago, a Musankwa sanyatiensis, a bipedal dinosaur with a long neck and sweeping tail, took its last steps in an unusually swampy region of southern Pangea. In the summer of 2018, scientists from Zimbabwe, South Africa, the UK, and the USA discovered its fossils on Spurwing Island in Lake Kariba, Zimbabwe. Among them were Paul Barrett from the Natural History Museum in London and Jonah Choiniere from the University of the Witwatersrand, Johannesburg.
“It was a beautiful, warm, sunny day,” recalls Barrett. “We were working our way around the small inlets and areas of bare rock on the [water’s] surface, keeping an eye out for elephants and crocodiles as we were going... And then just happened to come across these bones in the middle of the shoreline. The rock is almost brick red… Whereas the bones are pinkish-white. So they stand out very strongly against the background.”
Although the fossils were easy to spot, the discovery was the culmination of months of fieldwork. The local team led the exploration with their knowledge of sites and excavation challenges. Choiniere’s team added geological and palaeontological expertise, and Barrett contributed his understanding of early dinosaurs.
“There were enough of [the fossils] showing that we immediately knew what we were looking at,” said Barrett. It was the remains of a single hind leg, including fragments of thigh, shin, and ankle bones. However, only after months of careful examination at the Wits laboratory could the team be sure that the fossils belonged to a dinosaur rather than a giant crocodilian reptile. Features of the shin bone revealed narrowed the classification down to sauropodomorphs: a family of long-necked, social dinosaurs that mainly ate plants.
“Despite the limited fossil material, these bones possess unique features that distinguish them from those of other dinosaurs living at the same time,” said South African paleobiologist Kimberley’ Kimi’ Chapelle of Stony Brook University, New York.
Belonging to the subgroup Massopoda, Musankwa (meaning “boy close to marriage” in Tsonga) was named after their houseboat, which also served as their floating laboratory during the expedition. The discovery was published the Journal Acta Palaeontologica Polonica.
Musankwa sanyatiensis fossil bones in situ, after mechanical preparation, and after CT scanning. Artist reconstruction of Musankwa sanyatiensis showing position of fossil bones
Source: Barrett et al. 2024, Atashni Moopen
Two-legged ancestors of Jurassic giants
Musankwa and other Massopoda sauropodomorphs lived during the late Triassic era (200-235 million years ago) before the supercontinent Pangea began to break apart. Although the climate was warm and dry, today’s Lake Kariba was an unusually watery environment, characterised by rivers and freshwater swamps. Conifers and ferns lined the rivers, where phytosaurs – huge, crocodile-like reptiles – and other aquatic predators lurked.
Early sauropodomorphs are the ancestors of the sauropods – the giant, long-necked dinosaurs of popular culture. From Musankwa’s leg fossils, the team calculated that Musankwa itself would have weighed about 390kg, the equivalent of a small horse. (In the future, the team might be able to extract a small piece from the leg fossil, thinly slice it, and count the growth rings – similar to tree rings – to determine the animal’s age at its death.)
In this dinosaur lineage, four legs came after two. Early sauropodomorphs like Musankwa and earlier, smaller cousin Mbiresaurus raathi stood on their hindlegs. As their descendants became larger and heavier, they planted their forelegs firmly on the ground and reached their necks ever higher towards the sky. The early sauropod Ledumahadi mafube – unearthed by Choiniere and his colleagues in South Africa in 2018—appeared in the early Jurassic era (200 million years ago).
Although Ledumahadi walked on fours and rivalled later sauropods in size, its limbs remained partly bent at the joints. Later sauropod giants, such as Brontosaurus and Diplodocus, supported themselves on straight, tree-trunk legs and flourished for millions of years. The largest animal to have lived on land, Dreadnoughtus, grew up to 26 metres long – a far cry from its diminutive bipedal ancestors.
An evolutionary puzzle piece
Musankwa’s discovery adds another puzzle piece to the evolution of the Sauropodomorphs. “A lot of what we know about the early stages of dinosaur evolution comes from Southern Africa and from southern South America,” Barrett says. This discovery suggests that Zimbabwe, like South Africa and Lesotho, could offer a valuable window to the prehistoric world.
The authors note ‘striking similarities’ between the Musankwa remains and fossils of other sauropomorphs found in Argentina (Riojasaurus ) and South Africa (Eucnemesaurus). It’s possible that “there’s a little group of closely related animals that…was going backwards and forwards between South America and Southern Africa at the time,” Barret said.
The scientists are hopeful that future fossils will shed light on Musankwa and its contemporaries. For now, however, their current material is keeping them busy. “We’ve still got a lot of material in the lab that is still being cleaned…” said Barret. “It wouldn’t surprise me if we have at least one or two other new dinosaurs lurking among the material we’ve already been able to collect.”
