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A dicynodont collected in 1963 makes Tanzania's oldest dinosaur candidates younger
Dinodontosaurus turns up outside South America for the first time, in Tanzanian rocks that also hold the world's oldest dinosaur candidates, and the South American sequences it matches carry younger radiometric dates.
The Scientist · Science desk
What happened
- An international team led by the University of Bristol has named Dinodontosaurus isiyavamanda, a Tanzanian dicynodont from around 240 million years ago, in the Journal of Vertebrate Paleontology.
- The fossils came out of a British expedition in 1963 to what is now Tanzania and had sat only partly studied at the Natural History Museum in London ever since.
- Dinodontosaurus had been known only from South America, and George said the Tanzanian material is the first confirmed record of the genus outside that continent.
- The same Tanzanian deposits have produced the fossils thought to represent the world's oldest possible dinosaurs.
- New radiometric dates from South America put those early dinosaur-bearing sequences up to 10 million years younger than the South African rocks.
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Why it matters
- constraint If the genus identification on one associated skeleton and one fragmentary skull is revised, the age assignment for the Tanzanian beds moves with it, and so does the ranking of the world's oldest dinosaur candidates.
- decision Anyone writing an origins timeline now has to choose whether to keep citing the Tanzanian specimens as the earliest or to shift the anchor to the dated South American record.
- contradiction Shared genera are what placed these beds beside Middle Triassic South Africa in the first place, so the stability of the framework turns on taxonomy as much as on geochronology.
- precedent A specimen in museum care for more than six decades moved a dating framework without new fieldwork, which raises the expected return on describing what is already in the drawers.
Tanzania's Triassic beds had been correlated with rocks in South Africa, then thought to be Middle Triassic, because the two appeared to share some fossil genera [8]. The new material changes which continent Tanzania is matched to. Dinodontosaurus is now known from both Tanzania and South America, so the paper treats the two countries' sequences as equivalent in age [9]. The radiometric dates behind the revision were measured in South America, and Tanzania's age follows from the fossil match [10] [9].
Hady George, a Ph.D. student in the School of Earth Sciences at the University of Bristol and the paper's lead author [14], said the result "helps confirm that the oldest dinosaur candidates from Tanzania are probably no older than those from South America, refining the timeline of dinosaur origins" [13]. The identification rests on one associated skeleton from the old collection plus a fragmentary skull found more recently [4]. On that basis the authors argue that the Triassic rocks of Tanzania can no longer be regarded as preserving the oldest potential dinosaur fossils, and that when and where dinosaurs first evolved needs reassessing [11].
The skeleton was recognised as something new long before it was named. Nigel Larkin, a visiting research fellow in the School of Biological Sciences at the University of Reading and a co-author [16], said, "I studied this dicynodont skeleton for my MSc thesis at University College London back in 1994 and judged it to be a species new to science, but it took me nearly 30 years to start the process of writing it up for publication" [17]. That thesis came 31 years after the expedition that collected the bones [20]. Larkin said the tools had changed in the interval: "we can do so much more with micro-CT scanning to examine such specimens than we ever could have imagined in the 1990s" [18].
Mike Day, curator of non-mammalian tetrapods at the Natural History Museum, London, said the specimen has been in the museum's care for over 60 years [19]. The species name refers to the land of the Wamanda people, who inhabit the region of Tanzania where the fossils were found [6].
What to watch
- George said forthcoming projects will examine the remaining 1963 material and the biomechanics and ecology of Triassic dicynodonts, which will test whether more of the collection fits the South American correlation.
- A radiometric date measured on the Tanzanian deposits themselves would replace the fossil correlation with a direct age.
- Whether other workers accept the Dinodontosaurus identification, or find the genus in a third region, would change how far the correlation reaches.