New genus and species of theropod dinosaur named Anteavis crurilongus was described by a team of paleontologists from the Universidad Nacional de San Juan, the Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, the University of Birmingham, CONICET and CIGEOBIO.
An artistic reconstruction of Anteavis crurilongus. Image credit: Jorge Blanco.
Anteavis crurilongus roamed the Earth during the Carnian epoch of the late Triassic, 231 to 226 million years ago.
This dinosaur measured approximately 1.2 m (4 feet) in length and weighed approximately 8 to 9 kg.
The ancient species was an early-diverging theropod placed outside the Neotheropoda group of dinosaurs, but it unexpectedly exhibited features previously thought to be exclusive to that group.
“It is one of the oldest and most primitive dinosaurs known to date,” said Dr. Ricardo Martínez of the National University of San Juan and his colleagues.
“Early dinosaur diversification produced a major ecological shift in terrestrial ecosystems, culminating in tetrapod assemblages dominated in abundance by dinosaurs at the Triassic/Jurassic boundary 201 million years ago.”
“Therefore, studying the initial diversification of dinosaurs is crucial to understanding the establishment of Mesozoic assemblages.”
“However, the lack of stratigraphically continuous fossil data in the few geologic units that preserve the oldest known dinosaurs (233 to 227 million years ago) obscures our understanding of this initial diversification.”
Paleontologists have unearthed the fossilized remains of Anteavis crurilongus – a partial skeleton and skull – in the Ischigualasto Formation in northwest Argentina in 2014.
“There are very few places in the world that preserve fossils this old and this well preserved,” Dr. Martinez said.
“One of them is the Santa Maria Formation in the Brazilian state of Rio Grande do Sul; the other is the Ischigualasto Formation.”
Anteavis crurilongus lived in a hot and arid savannah about two million years after the Carnian pluvial episode.
“We show that dinosaur diversity and abundance in the Ischigualasto Formation was higher than previously thought, particularly among small herbivores (<30 kg) and medium-sized predators (30 to 200 kg)," the researchers said.
“This diversification occurred at Ischigualasto during a climate shift toward semi-arid conditions, but the return of wetter conditions resulted in a gap in the dinosaur record that began about 229 million years ago.”
“Only 15 million years later, in the middle of the Norian Age, dinosaurs regained their abundance and diversity in the basin, but they are now characterized by larger species.”
“Our findings demonstrate an early diversification of dinosaurs, probably punctuated by a climate-driven turnover of fauna, at least in southwest Pangea.”
An article on the discovery was published this week in the journal Ecology and evolution of nature.
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RN Martínez and others. A Carnian theropod with unexpected features derived during the first radiation of dinosaurs. Nat Ecol Evolpublished online October 14, 2025; doi: 10.1038/s41559-025-02868-4
