Fossils preserved for more than 60 years could shift a major marker in the history of the first dinosaurs by several million years.
The story begins in Tanzania, with bones discovered during a British expedition in 1963. Kept at London’s Natural History Museum, some had never been studied in detail. An international team has now identified a new species among them, named Dinodontosaurus isiyavamanda. The animal lived around 240 million years ago, during the Triassic.
Reconstruction of Dinodontosaurus isiyavamanda, a herbivorous dicynodont that lived in Tanzania around 240 million years ago.
Credit: Gabriel Ugueto et al. — CC BY 4.0
It was not a dinosaur. It belonged to the dicynodonts, large four-legged herbivores that lived long before the emergence of modern mammals. Their lineage is more closely related to that of mammals than to that of dinosaurs. The Tanzanian specimen notably includes a skeleton associated with a skull discovered more recently.
The biggest surprise concerns its identity. Until now, the genus Dinodontosaurus was known only from South America. Its confirmed presence in East Africa therefore helps link Tanzania’s fossil-bearing rocks to South American formations where the same genus lived.
Why does this change the history of dinosaurs? The Tanzanian rock layers in question have also yielded Nyasasaurus and Asilisaurus. These animals are at the center of discussions about the very first dinosaurs and their close relatives. The precise age of these fossils therefore plays a direct role in the chronology of their origins.
Reconstruction of Asilisaurus kongwe, a close relative of dinosaurs discovered in the Triassic layers of Tanzania, which are also being studied for dating purposes.
Credit: Smokeybjb — CC BY-SA 3.0
Until now, researchers had notably linked these rocks to formations in South Africa considered to be older. But Dinodontosaurus now establishes a connection with better-dated layers in South America. Recent radiometric measurements indicate that these may be up to 10 million years younger than the South African formations used as a reference.
In other words, the candidates for the title of the oldest dinosaurs found in Tanzania were probably not as old as previously thought.
This discovery also highlights the value of old collections. One of the researchers had already examined this skeleton in 1994 and thought it represented an unknown species. It took nearly three additional decades, a new team, and modern examination techniques to establish its identity precisely and determine its links with South American fossils.
A large part of the Tanzanian skeleton remains to be studied. The researchers plan to compare these bones with those of South American specimens and analyze how these large herbivores moved and fed. This work could also clarify how several species of dicynodonts shared the same environments during the Triassic.