The exact circumstances behind dinosaurs’ debut on this planet still aren’t fully understood, but they may have emerged earlier than originally thought. While the earliest dinosaur fossils date back to around 230 million years ago, a deep dive into dinosaurs' evolutionary history suggests that they may have actually arisen 250 million to 240 million years ago.
A study recently published in the Proceedings of the Royal Society B has determined that dinosaurs likely emerged 10 million years before their first fossils appeared. This new estimate came to light after researchers modeled the morphological evolution of dinosaurs — in other words, how dinosaurs’ physical form and structure changed over time. This revealed that dinosaurs experienced a burst of evolution early on, diversifying soon after they arrived on the scene.
Chase Brownstein, one of the study’s authors and a researcher at Yale University, says this would mean dinosaurs experienced a critical evolutionary process known as radiation.
“These evolutionary radiations are thought to be responsible for generating a huge proportion of species alive today, including most living dinosaur species — the birds! Adding early dinosaurs to the list of evolutionary radiations would be a big deal, because dinosaurs dominated the planet's terrestrial ecosystems for more than 100 million years,” Brownstein told Discover.
The Emergence of Dinosaurs
The age of Dinosauria, the group that consists of all dinosaurs, has historically been tricky to pin down. According to the new study, this is due to the high lineage diversity of dinosaurs and their wide distribution upon appearing in the fossil record between 230 million and 233 million years ago, during the early stages of the Late Triassic.
The researchers involved with the study aimed to unravel this mystery by looking at the evolution of the earliest dinosaurs. To accomplish this, they referenced nine morphological datasets to examine the evolutionary relationships between various dinosaur clades.
With this data, they came up with the estimate that dinosaurs emerged between 250 million and 240 million years ago. This aligns with existing evidence of ichnofossils, or trace fossils, which represent indirect evidence of biological activity as opposed to actual preserved remains of an organism; prior research in Poland uncovered fossilized tracks — some dating as far back as 250 million years ago — that are thought to have been created by close relatives of dinosaurs, according to a 2010 study in the Proceedings of the Royal Society B.
Read More: The First Known Dinos Grew at a Rapid and Continuous Rate
Tracking the Tempo of Dinosaur Evolution
From the datasets, the researchers also pinpointed the rate, or tempo, of early dinosaurs’ morphological evolution. They found that soon after the emergence 250 million to 240 million years ago, dinosaurs diversified into multiple lineages and went through a period of rapid evolution.
Brownstein suggests that the rapid diversification may explain why it has been so difficult to understand the relationships between the “big three” dinosaur groups: Theropoda (meat-eaters and relatives, including birds), Ornithischia (horned, duck-billed, dome-headed, and armor-plated herbivorous dinosaurs), and Sauropodomorpha (long-necked dinosaurs).
These dinosaurs may have all diverged from each other so quickly that they didn’t even form key skeletal features that would’ve otherwise provided insight into their relationship with one another.
Rates of morphological evolution, however, experienced a sharp drop in the late stages of the Triassic, potentially going into the Jurassic. Brownstein says this likely represents a “cooldown” after dinosaurs had already established a range of varied body plans.
How Mass Extinctions Create Opportunities
The researchers suggest that one of the main factors driving the bursts of evolution is mass extinction events. This may seem paradoxical at first, but mass extinctions can open up a wide range of ecological niches; this causes the rapid diversification of lineages, a process referred to as adaptive radiation, according to the University of California, Berkeley.
The emergence of dinosaurs, the researchers write in the study, may have been driven by ecological opportunities becoming available after the End Permian extinction 252 million years ago.
The subsequent diversification of dinosaurs into many lineages, Brownstein says, may have then been spurred by a 2-million-year-long torrential downpour about 233 million years ago.
“This period of increased rainfall, called the Carnian Pluvial Event, had a really big effect on the nature of the ecosystems the first dinosaurs were living in,” Brownstein told Discover. “Principally, it shrunk the desert belt at the center of Pangaea, which probably allowed dinosaurs and other animals to migrate across the supercontinent. We think this rapid diversification was probably associated with this rapid burst of morphological evolution.”
Read More: A Complete Dinosaur Timeline to Extinction: How Long Did They Roam Earth?
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- This article references information from a study published in the Proceedings of the Royal Society B: An early burst of skeletal evolution at the origin of dinosaurs
- This article references information from a study published in the Proceedings of the Royal Society B: Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic
- This article references information from the University of California, Berkeley: Triggering adaptive radiation
