Dinosaurs dominated Mesozoic terrestrial ecosystems for approximately 160 million years, but their biogeographic origin remains poorly understood. The earliest unequivocal dinosaur fossils appear in southern South America and Africa 230 million years, leading most authors to propose southwestern Gondwana as the likely center of their origin. However, the high diversity of these earliest assemblages suggests a more ancient evolutionary history. New research led by University College London shows that dinosaurs — and, potentially, their archosaurian relatives as a wider group — likely radiated in the low-latitude region of Gondwana.
Nyasasaurus could be the earliest known dinosaur, or else a close relative of early dinosaurs. Image credit: Mark Witton / The Trustees of the Natural History Museum, London.
“Currently, the oldest known dinosaur fossils date back about 230 million years and were unearthed further south in places including Brazil, Argentina and Zimbabwe,” said University College London Ph.D. student Joel Heath and colleagues.
“But the differences between these fossils suggest dinosaurs had already been evolving for some time, pointing to an origin millions of years earlier.”
The authors found that the earliest dinosaurs likely emerged in a hot equatorial region in what was then the supercontinent Gondwana, an area of land that encompasses the Amazon, Congo basin, and Sahara Desert today.
“Dinosaurs are well studied but we still don’t really know where they came from. The fossil record has such large gaps that it can’t be taken at face value,” Heath said.
“Our modeling suggests that the earliest dinosaurs might have originated in western, low-latitude Gondwana.”
“This is a hotter and drier environment than previously thought, made up of desert- and savannah-like areas.”
“So far, no dinosaur fossils have been found in the regions of Africa and South America that once formed this part of Gondwana.”
“However, this might be because researchers haven’t stumbled across the right rocks yet, due to a mix of inaccessibility and a relative lack of research efforts in these areas.”
The study drew on fossils and evolutionary trees of dinosaurs and their close reptile relatives, as well as the geography of the period.
It accounted for gaps in the fossil record by treating areas of the globe where no fossils had been found as missing information rather than areas where no fossils exist.
Initially, early dinosaurs were vastly outnumbered by their reptile cousins. These included the ancestors of crocodiles, the pseudosuchians, and pterosaurs.
By contrast, the earliest dinosaurs were much smaller than their descendants — more the size of a chicken or dog than a Diplodocus.
They walked on two legs (were bipedal) and most are thought to have been omnivores.
Dinosaurs became dominant after volcanic eruptions wiped out many of their reptile relatives 201 million years ago.
The new modeling results suggested that dinosaurs as well as other reptiles may have originated in low-latitude Gondwana, before radiating outwards, spreading to southern Gondwana and to Laurasia, the adjacent northern supercontinent that later split into Europe, Asia and North America.
Support for this origin comes from the fact it is a midpoint between where the earliest dinosaurs have been found in southern Gondwana and where the fossils of many of their close relatives have been discovered to the north in Laurasia.
As there is uncertainty about how the most ancient dinosaurs were related to one another and to their close relatives, the researchers ran their model on three proposed evolutionary trees.
They found strongest support for a low-latitude Gondwanan origin of the dinosaurs in the model that counted silesaurids, traditionally regarded as cousins of dinosaurs but not dinosaurs themselves, as ancestors of ornithischian dinosaurs.
Ornithischians, one of the three main dinosaur groups that later included plant-eaters Stegosaurus and Triceratops, are mysteriously absent from the fossil record of these early years of the dinosaur era.
If silesaurids are the ancestors of ornithischians, this helps to fill in this gap in the evolutionary tree.
“Our results suggest early dinosaurs may have been well adapted to hot and arid environments,” said University College London’s Professor Philip Mannion.
“Out of the three main dinosaur groups, one group, sauropods, which includes Brontosaurus and Diplodocus, seemed to retain their preference for a warm climate, keeping to Earth’s lower latitudes.”
“Evidence suggests the other two groups, theropods and ornithischians, may have developed the ability to generate their own body heat some millions of years later in the Jurassic period, allowing them to thrive in colder regions, including the poles.”
The study was published in the journal Current Biology.
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Joel A. Heath et al. Accounting for sampling heterogeneity suggests a low paleolatitude origin for dinosaurs. Current Biology, published online January 23, 2025; doi: 10.1016/j.cub.2024.12.053
