Prior to the rise of the dinosaurs, Earth was ruled by a group of prehistoric reptiles. Among them were the Pareiasaurs, robust herbivores often referred to as the "ugliest fossil reptiles," who remain less recognized compared to their eventual successors.
What was before the dinos? Did you know there existed reptiles before the Dinosaurs? Scientists have found that the precursor of dinosaurs and pterosaurs was armored.
Scientists have identified a new species of an armored reptile that thrived during the early emergence of dinosaurs. The archosaur fossil, clad with bony plates along its spine, signifies that armor was a recurring trait in dinosaur and pterosaur evolution. This characteristic initially seen in their ancestors was later lost, only to reappear independently among specialized dinosaurs like ankylosaurs and stegosaurs. The research has been published today in the Zoological Journal of the Linnean Society.
“Dinosaur-like creatures existed globally, even before the actual dinosaurs evolved,” said the study’s leading author Sterling Nesbitt, associate professor of geosciences at Virginia Tech, and a research associate at the American Museum of Natural History’s Division of Paleontology. “Dinosaurs arrived late to the Triassic reptile gathering, appearing much later than many reptiles resembling dinosaurs.”
The Precursor of Dinosaurs
Archosaurs are reptiles divided into two prominent branches: the bird-line, encompassing pterosaurs and dinosaurs, including living dinosaurs (birds); and the crocodilian line, consisting of crocodiles, alligators, caimans, and gharials. The newly identified archosaur species, dubbed Mambachiton fiandohana, stands as the earliest member of the bird-line branch of archosaur evolution.
The fossil, approximately 235 million years old, was discovered in Madagascar in 1997 by a research team led by the Museum’s Frick Curator of Fossil Mammals, John Flynn, in association with the University of Antananarivo in Madagascar.
Importance of Southern Hemisphere Fossils
“This finding highlights the crucial role of the southern hemisphere’s fossil record in understanding the Triassic period when dinosaurs were emerging,” Flynn noted. “This period is largely unknown elsewhere in the world, which accentuates the enormous value of our 25-year-long Madagascar-U.S. research and education partnership in advancing scientific knowledge.”
Mambachiton, a four-legged, long-tailed precursor to dinosaurs and pterosaurs, is estimated to have been 4–6 feet long, weighing 25–45 pounds. Unexpectedly, the species exhibited an extensive series of bony plates, known as osteoderms, along its spine. Osteoderms are common in crocodilians but rare in bird-line archosaurs, except for specific dinosaurs like stegosaurs, ankylosaurs, and titanosaur sauropods.
Armor Evolution
Mambachiton definitively shows that the bird-line group of archosaurs was ancestrally armored. This armor was later lost in dinosaur and pterosaur evolution, only to resurface several times in the dinosaur lineage.
“The loss and re-emergence of armor sheds light on a crucial aspect of dinosaur evolution—it liberated them from some of the biomechanical body constraints of ancestral archosaurs, potentially contributing to the diversity of ecological and body forms we see in dinosaurs,” said co-author Christian Kammerer, a former Gerstner Scholar at the Museum and a research curator in paleontology at the North Carolina Museum of Natural Sciences.
Ecosystem Interaction and Trait Evolution
“Mambachiton proves that the retention of ancestral features or the development of new traits depends on interactions within the ecosystem,” pointed out project co-leader Lovasoa Ranivoharimanana of the University of Antananarivo. “A characteristic is preserved if it is essential, but it disappears when it becomes redundant.”
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