Palaeontology: Climate belts shaped early dinosaur distribution

A new collection of Triassic dinosaur fossils from Zimbabwe suggests that the earliest dinosaurs were confined to a temperate region in the far south of the ancient supercontinent of Pangaea. The findings, reported in Nature, enhance our knowledge of the origin and early evolution of dinosaurs across Pangaea.

Previous research has suggested that a hothouse climate, strong seasonality and high atmospheric CO2 concentrations created strong arid and humid climate belts arranged east–west across Pangaea. These different climate regions may have influenced the distribution of early dinosaurs across the supercontinent during this period, as there were few geographical barriers or continental boundaries to affect animal dispersal. However, understanding the distribution of dinosaurs across the supercontinent during the Late Triassic has been challenging, as sparse sampling has obscured their earliest history.

Christopher Griffin and colleagues discovered a new fossil assemblage from Zimbabwe, dating to the earliest part of the Late Triassic (Carnian Stage, around 230 million years ago). This collection of fossils contains Africa’s oldest known dinosaurs, including a nearly complete skeleton of a new group of sauropodomorph, a type of long-necked herbivorous dinosaur, named Mbiresaurus raathi. They found that the south-central African assemblage resembled those of dinosaur assemblages from South America, including Brazil and Argentina, and India, suggesting that similar vertebrates were widespread across this latitude band. The distribution of these dinosaurs was found to correlate with climatic barriers, and the authors suggest that dinosaur dispersal to the rest of the supercontinent was delayed until these barriers relaxed.

The authors suggest that climatic controls influenced the initial composition of terrestrial dinosaurs and other major groups ⁠— such as mammals, turtles, amphibians and reptiles ⁠— many of which persist to this day.