A new study led by researchers at University College London suggests that the earliest dinosaurs may have originated in ancient Gondwana regions, including areas that are now part of Africa and South America. The findings, published in the journal Current Biology, propose that the remains of the first dinosaurs might lie undiscovered in the Amazon basin, the Congo Basin, and the Sahara Desert due to inaccessibility and a lack of research efforts, according to Discover Magazine.
"Dinosaurs are well studied, but we still don't really know where they came from. The fossil record has gaps so large that it can't be taken at face value," said Joel Heath, the lead author and PhD student at UCL Earth Sciences and the Natural History Museum in London, according to Popular Science.
The research team examined known fossils and evolutionary trees of dinosaurs and their close reptile relatives to piece together their relationships. They accounted for gaps in the fossil record by treating areas with no fossils as missing information, rather than areas where no fossils exist, Newsweek reported.
"Although previous studies have focused on southern South America and southern Africa as areas of origin for dinosaurs, based on where their fossils first appeared, we suggest that gaps in the fossil record—particularly in regions that today include the Sahara Desert and the Amazon rainforest—may have the potential to reveal where the first dinosaurs lived," Heath stated.
Currently, the oldest known dinosaur fossils date back about 230 million years and have been found in southern regions, including Brazil, Argentina, and Zimbabwe. Species such as Eoraptor and Herrerasaurus from Argentina are among the earliest known dinosaurs, according to Discover Magazine.
The earliest dinosaurs were much smaller than their descendants, around the size of a chicken or a dog, unlike later species like Brontosaurus, which weighed 33,000 pounds. The first dinosaurs walked on two legs and are thought to have been omnivores.
"Our model suggests that the first dinosaurs may have originated in Gondwana, a western low-latitude area. It was a warmer and drier environment than previously thought, made up of desert and savanna regions," Heath added, as cited by Science Daily.
The team found the strongest support for a low-latitude Gondwanan origin of dinosaurs in the model that counted silesaurids, traditionally regarded as cousins of dinosaurs but not dinosaurs themselves, as ancestors of ornithischian dinosaurs. Ornithischians are mysteriously absent from the fossil record of the early years of the dinosaur era, which is puzzling given that they later included herbivores like Stegosaurus and Triceratops.
Despite the potential significance of these regions, no dinosaur fossils have been found in the areas of Africa and South America that once formed this part of Gondwana. This absence is likely due to a combination of inaccessibility and a lack of research efforts in these areas.
Paleontologists suspect that dinosaurs evolved somewhere else and expanded to the locations where we first find them. Suitable rocks in the Amazon are usually buried under lush vegetation, and the climate of the Amazon Basin and Sahara Desert deters exploration for fossils, according to IFLScience.
"The results suggest that the first dinosaurs adapted to warm and arid environments. Of the three main groups of dinosaurs, the sauropods, which include Brontosaurus and Diplodocus, preferred a warm climate, remaining at lower latitudes of the primordial Earth," noted Philip Mannion, a researcher at UCL Earth Sciences.
"The evidence suggests that the other two groups, the theropods and the ornithischians, may have developed the ability to generate their own body heat some millions of years later, in the Jurassic period, which allowed them to thrive in cooler regions, including the poles," Mannion added,
To learn more about dinosaur origins, the research team built computer models to work backward in time from the oldest known dinosaurs to the origin of the group. They ran their model on three proposed evolutionary trees, including gaps in the fossil record and possible geographic barriers.
"There are lots of areas in the globe that are quite neglected," Heath said. "The definitive test of our models will be if primitive dinosaur remains are found in the Amazon, the Sahara Desert, and other ancient low-latitude parts of Gondwana," he stated, according to 20 Minutos.