Study: Dinosaurs and Pterosaurs Descended From Tiny Reptiles
by AMNH on
Courtesy of J. Flynn
In the popular imagination, dinosaurs are towering, thundering animals like the super predator Tyrannosaurus rex. But new research suggests that dinosaurs—and their pterosaur relatives—evolved from extremely small ancestors.
A newly described reptile species from Madagascar, named Kongonaphon kely, or “tiny bug slayer,” lived around 237 million years ago and would have stood about 4 inches (10 centimeters) tall. It’s near the root of the lineage, Ornithodira, to which both dinosaurs and pterosaurs belong.
“There’s a general perception of dinosaurs as being giants,” said Christian Kammerer, a research curator in paleontology at the North Carolina Museum of Natural Sciences and a former Gerstner Scholar at the Museum who is an author on the new study, published today in the journal Proceedings of the National Academy of Sciences. “But this new animal is very close to the divergence of dinosaurs and pterosaurs, and it’s shockingly small.”
This is a great case for why field discoveries—combined with modern technology to analyze the fossils recovered—are still so important.
The Kongonaphon fossils were discovered in 1998 by a team of researchers led by the Museum’s Frick Curator of Fossil Mammals John Flynn, who worked at The Field Museum at the time, in close collaboration with scientists and students at the University of Antananarivo and project co-leader Andre Wyss of the University of California-Santa Barbara and a Museum research associate.
“This fossil site in southwestern Madagascar from a poorly known time interval globally has produced some amazing fossils, and this tiny specimen was jumbled in among the hundreds we’ve collected from the site over the years,” Flynn said. “It took some time before we could focus on these bones, but once we did, it was clear we had something unique and worth a closer look. This is a great case for why field discoveries—combined with modern technology to analyze the fossils recovered—are still so important.”
Although few specimens from near the root of this lineage have been found, Kongonaphon isn’t the first small animal known near the root of the ornithodiran family tree. Previously, such specimens were considered “isolated exceptions to the rule,” Kammerer said.
In general, the scientific thought was that body size remained similar among the first archosaurs, the larger reptile group that includes birds, crocodilians, non-avian dinosaurs, and pterosaurs, including the earliest ornithodirans, before increasing to gigantic proportions in the dinosaur lineage.
By analyzing changes in body size throughout archosaur evolution, the researchers found evidence that it decreased sharply early in the history of the dinosaur-pterosaur lineage. This “miniaturization” event has important implications for dinosaur and pterosaur paleobiology.
For instance, wear on the teeth of Kongonaphon suggests it ate insects. Insectivory is associated with small body size, so a shift to an insect diet may have helped early ornithodirans survive by occupying a niche different from their mostly meat-eating contemporaneous relatives.
The work also suggests that fuzzy skin coverings ranging from simple filaments to feathers, known in both dinosaurs and pterosaurs, may have originated in this small-bodied common ancestor to help regulate body temperatures. That’s because heat retention in small bodies is difficult, and the mid-late Triassic was a time of climatic extremes.
“Discovery of this tiny relative of dinosaurs and pterosaurs emphasizes the importance of Madagascar’s fossil record for improving knowledge of vertebrate history during times that are poorly known in other places,” said project co-leader Lovasoa Ranivoharimanana of the University of Antananarivo in Madagascar. “Discoveries like this helps people in Madagascar and around the world better appreciate the exceptional record of ancient life preserved in the rocks of our country.”