The oldest dinosaurs may still be hidden in the Amazon and other tropical areas of South America and Africa, according to a recent study conducted by researchers from University College London (UCL).
The oldest dinosaurs may still be hidden in the Amazon and other tropical areas of South America and Africa, according to a recent study conducted by researchers from University College London (UCL).
Currently, the earliest known dinosaur fossils are about 230 million years old and have been discovered in regions like Brazil, Argentina, and Zimbabwe. However, the variations in these fossils indicate that dinosaurs were likely evolving for a longer period, suggesting their origins may date back millions of years earlier.
The research, featured in the journal Current Biology, addressed gaps in the fossil record and posited that the first dinosaurs likely appeared in a warm equatorial region of Gondwana – a supercontinent that comprised today’s Amazon, Congo basin, and Sahara Desert.
Joel Heath, the lead author and PhD student from UCL Earth Sciences and the Natural History Museum in London, stated, “Dinosaurs are well-researched, yet we lack clarity on their origins. The fossil record has significant gaps that should be approached with caution.”
“Our modeling indicates that the earliest dinosaurs may have originated in the western parts of low-latitude Gondwana, characterized by hotter and drier conditions, resembling desert and savannah landscapes more than previously believed.”
So far, no dinosaur fossils have been discovered in the African and South American regions that originally formed this segment of Gondwana. This might be due to the challenges researchers face in accessing these areas and the limited research efforts made there.
The modeling conducted for this study incorporated fossils, evolutionary trees of dinosaurs and their close relatives, as well as the geographical conditions at the time. It viewed the absence of fossils in certain locations as a lack of information rather than an outright absence.
In their early stages, dinosaurs were greatly outnumbered by other reptiles.
These included the precursors to crocodiles, known as pseudosuchians (a diverse group with some species growing up to 10 meters long), and pterosaurs, the first creatures to develop powered flight, some of which were as large as fighter jets.
In contrast, the earliest dinosaurs were significantly smaller than their later descendants, comparable in size to a chicken or a small dog rather than a Diplodocus. They primarily moved on two legs and are believed to have been omnivorous.
Dinosaurs rose to prominence after a series of volcanic eruptions wiped out many of their reptilian relatives around 201 million years ago.
The new modeling indicates that both dinosaurs and other reptiles likely emerged in low-latitude Gondwana before dispersing, eventually reaching southern Gondwana and Laurasia, the neighboring northern supercontinent that later fractured into Europe, Asia, and North America.
This theory is supported by the fact that it lies centrally between areas where the oldest dinosaurs have been found in southern Gondwana and where numerous fossils of their relatives have been located to the north in Laurasia.
Given the uncertainties regarding the relationships among the most primitive dinosaurs and their close relatives, the researchers tested their model against three different proposed evolutionary trees.
They found the strongest evidence supporting a low-latitude Gondwana origin for the dinosaurs in the model that considers silesaurids (traditionally seen as dinosaur cousins but not true dinosaurs) as the ancestors of ornithischian dinosaurs.
Ornithischians are one of the three main dinosaur classifications, which later included plant-eating dinosaurs like Stegosaurus and Triceratops. They are notably absent from the fossil records of the earliest dinosaur era, and if silesaurids are indeed their ancestors, it helps address this evolutionary gap.
Senior author Professor Philip Mannion from UCL Earth Sciences remarked, “Our findings suggest that early dinosaurs were well-equipped to thrive in hot and dry environments. Among the three major dinosaur families, sauropods, which encompass Brontosaurus and Diplodocus, appeared to prefer warm climates and remained in the Earth’s lower latitudes.”
“Evidence indicates that the other two groups, theropods and ornithischians, may have developed the capacity to regulate their body heat millions of years later during the Jurassic period, enabling them to prosper in cooler regions, including polar areas.”
Some of the earliest known dinosaurs comprise Eoraptor, Herrerasaurus, Coelophysis, and Eodromaeus.
