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The ancient fossils of the world's earliest dinosaurs may be buried in places that are almost inaccessible to study, according to new research from University College London and the Natural History Museum in the UK. The oldest known dinosaur fossils date back about 230 million years. These specimens, found in areas that were once part of Gondwana — the southern half of the late Paleozoic supercontinent Pangaea — occupy fairly distant branches of the dinosaur family tree. This suggests that they may have already been evolving and spreading across the world for millions of years.
Moreover, the discovery of dinosaurs from the same period on the northern massif of the supercontinent, Laurasia, has further changed our understanding of dinosaur history. Convinced that the true place of origin of dinosaurs has not yet been found, paleontologists suspect that their beginnings may be hidden in the most inaccessible places on Earth.
Map of Pangaea
Map of Pangaea about 250 million years ago, at the beginning of the Triassic period. (Scotese et al./Wikimedia Commons) There is a large gap between the fossil records from the southern and northern hemispheres near the equator. In places where dinosaur fossils are not found, it is easy to assume that they were not there, but this is not necessarily the case.
Ideal conditions for fossil formation
Fossils need certain conditions to form. For example, dinosaur tracks in soft soil must be filled with sand, which then compacts. For a body fossil to form, the animal's remains must be covered with mud or sediment soon enough after death to prevent the body from completely decaying. But even if a fossil is formed, it can be very difficult to find, especially in hard-to-reach regions. In a new paper led by University College London paleontologist Joel Geet, the authors note that paleontological expeditions to the Amazon and the Sahara have been infrequent and difficult.
Difficulties of research in hard-to-reach regions
Searching for fossils in the Sahara Desert or the Amazon is no easy task. (Paul Biris/Getty Images)
“Paleontological expeditions to these regions may be rare due to the harsh conditions of the Sahara and the inaccessibility of many parts of the Amazon,” the researchers write. “It is also well documented that socioeconomic factors, the legacy of colonialism, and political instability likely hindered research efforts in these regions.”
Modeling dinosaur evolution
In their study, the team modeled dinosaur evolution in reverse using known fossils, taxonomic data on dinosaurs and their reptile relatives, and geographic data from the time. Rather than considering areas without fossils as areas where dinosaurs were absent, they labeled them as areas with missing information. One likely candidate for the origin of dinosaurs is the low-latitude parts of Gondwana, including the Sahara and Amazonia. This hypothesis is supported by a model that suggests that silesaurs (relatives of dinosaurs) are ancestral to ornithischians.
The role of the Sahara and the Amazon
"No dinosaur fossils have yet been found in the regions of Africa and South America that once formed part of Gondwana," says Geeth. "However, this may be because researchers have not yet found the right rocks due to their inaccessibility and lack of research in these areas." The findings are published in the journal Current Biology.
