South African Fossil Reveals Nyana rooiwalensis, a Giant Juvenile
Paleontologists have named Nyana rooiwalensis, a Late Triassic sauropodomorph from South Africa's Eastern Cape. The near-complete 21.3 cm skull belongs to a juvenile that was already more than four times the size of comparable young relatives, and adults may have weighed several tons.
A South African fossil reveals a new dinosaur species, Nyana rooiwalensis, that lived about 220 million years ago in the Late Triassic, according to paleontologists led by Atashni Moopen of the University of the Witwatersrand.
The find is a well-preserved, near-complete skull from a juvenile. Skulls of early sauropodomorphs, the group that later produced giant long-necked dinosaurs such as Brontosaurus, are scarce from this period.
A rare skull from the Eastern Cape
Researchers collected the skull and several other bones in 2018 on the outskirts of Qhemegha village in Eastern Cape province. The fossil came from the lower Elliot Formation, a rock layer that records a 30-million-year span from the Late Triassic into the Early Jurassic.
The skull measures 21.3 cm (8.4 inches). It includes a largely intact braincase, the palate and a hyoid, a small bone structure in the throat. Rings of bone that supported the eye survived, along with parts of the spine, limbs and a jaw.
The team says the complete skull would have been longer than that of the largest known adult Massospondylus, a well-known South African relative.
"The holotype and only specimen includes the first almost complete and articulated dinosaur skull from the South African Late Triassic and is one of only a handful of such skulls from this time in the southern continents," the researchers wrote in their paper.
Large even as a juvenile
To study the fossil, the scientists scanned it with a powerful X-ray beam at the European Synchrotron Radiation Facility. They also cut thin slices from the leg bones to read the animal's growth record.
Growth rings in bone work somewhat like tree rings. These showed at most two lines of arrested growth, and the bone's surface and structure indicated the animal was still growing actively when it died. The seams between skull bones were still open. The researchers estimate it was at least in its third year of life.
Even so, it was more than four times the size of juvenile Massospondylus and Mussaurus individuals of comparable age. That makes it one of the largest juvenile dinosaurs known from the Late Triassic.
"Extrapolation of these growth curves suggests that adult Nyana rooiwalensis may have reached multi-ton body masses," the scientists wrote. The proportions of its limb bones suggest it walked on two legs.
According to the authors, the findings support the idea that rapid growth arose early in sauropodomorph evolution, well before the true giants appeared.
Where it sits in the family tree
The team's analysis places Nyana rooiwalensis as a close relative of either Sarahsaurus, from North America, or Ngwevu, from South Africa. Depending on the analysis, it is either an early-branching member of a group called massopodans or a member of Massospondylidae.
In southern Africa, only two other Late Triassic species preserve cranial elements, Mbiresaurus and Kholumolumo, and both are represented by limited material, the authors noted.
"The placement of Nyana rooiwalensis, as the sister taxon of Sarahsaurus aurifontanalis, provides a biogeographic link between the early-diverging sauropodomorphs of southern Africa and western North America," the paleontologists wrote.
