Despite decades of digging and discovery, paleontologists still have not found fossil evidence of some of the planet’s earliest dinosaurs. Most of the specimens we have found like the T.rex all represent species that were significantly bigger and more advanced than early dinosaurs like Nyasasaurus. The earliest species of dinosaur are likely buried deep within the Earth and are incredibly difficult to reach. However, some research offers a suggestion of where to look. These bones may lie within the Amazon and other equatorial regions of South America and Africa. The findings are detailed in a study published January 23 in the journal Current Biology.
What are the oldest known dinosaurs?
Currently, the earliest known dinosaurs include Nyasasaurus, Eoraptor, Herrerasaurus, Coelophysis, and Eodromaeus. A group of fossils belonging to an unknown dinosaur in the Herrerasauridae family were described last year and date back about 231 million years. Similarly old fossils have all been unearthed in countries located south of the equator including Argentina, Brazil, and Zimbabwe, but there are likely even older specimens that have not been uncovered yet.
These early dinosaurs were also initially vastly outnumbered by their reptile cousins–a group of enormous crocodile ancestors called the pseudosuchians and pterosaurs who grew to the size of fighter jets. By comparison, Earth’s earliest dinosaurs were much smaller than their descendants. They were about the size of a dog or chicken, not 33,000 pounds like a Brontosaurus. Early dinosaurs were also bipedal and are believed to have been omnivores.
The physical differences between the earliest known fossils and those from the dinosaurs that lived much later suggest that animals had already been evolving for some time. Paleontologists believe this means that they could have evolved years earlier, pushing back the fossil record by millions of years.
“Dinosaurs are well studied but we still don’t really know where they came from,” study co-author and University College London (UCL) PhD student Joel Heath said in a statement. “The fossil record has such large gaps that it can’t be taken at face value.”
Into Laurasia
In the new study, a team of paleontologists examined the known fossils and evolutionary trees of dinosaurs and their close reptile relatives and compared them with changes to the Earth’s geography. To account for the numerous gaps in the fossil record, they treated the parts of the world where fossils have not been uncovered as missing information rather than designating them areas where no fossils exist.
Based on the results from this computer simulation, the team believes that Earth’s earliest dinosaurs likely emerged in a hot and dry equatorial region in the former supercontinent Gondwana. This massive continent began to break apart due to tectonic activity about 175 million years ago. The Amazon basin in South America and Congo basin and Sahara Desert in Africa today are what remains of Gondwana.
[ Related: 200-million-year-old dinosaur poop and vomit reveal a lost Jurassic world. ]
“So far, no dinosaur fossils have been found in the regions of Africa and South America that once formed this part of Gondwana,” said Heath. “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.”
Dinosaurs also started to outnumber other reptiles after a series of volcanic eruptions about 201 million years ago. The study suggests that after the surviving dinosaurs and reptiles that originated in low-latitude Gondwana. They spread outwards into southern Gondwana and to Laurasia–the supercontinent next to Gondwana that later split up into Europe, Asia, and North America.
According to the team, this spot is a midpoint of where the earliest known dinosaurs have been found and where many of their closest relatives have been discovered in what was north Laurasia.
Family ties
To piece together how these dinosaurs were related, the team ran their computer model of where dinosaurs originated on three potential evolutionary trees. They found a tree that included the silesaurids–cousins of dinosaurs but not dinosaurs themselves–as ancestors of a later group of ornithischian dinosaurs.
Ornithischians are one of the three main dinosaur groups that would later include Stegosaurus and Triceratops. They are absent from the fossil record of these early years of the dinosaur era. If the silesaurids are the ancestors of ornithischians, it will help fill in gaps in their evolutionary tree and pinpoint when certain traits emerged.
[ Related: Retired quarryman uncovers fossilized tyrannosaur teeth. ]
“Our results suggest early dinosaurs may have been well adapted to hot and arid environments. Out of the three main dinosaur groups, one group, sauropods, which includes the Brontosaurus and the Diplodocus, seemed to retain their preference for a warm climate, keeping to Earth’s lower latitudes,” study co-author and UCL paleobiologist Philip Mannion said in a statement.
In turn, theropods and ornithischians may have developed the ability to generate their own body heat millions of years ago. This change during the Jurassic period would have allowed them to thrive in colder regions, as many species did.
Only by digging deeper in the right area–potentially in parts of South America and Africa–will paleontologists find the earliest dinosaurs to walk the Earth.
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