Early experiment at the dawn of dinosaur evolution discovered
Justin Jackson
褋ontributing writer
Gaby Clark
scientific editor
Robert Egan
associate editor
Argentinian researchers have described a Carnian theropod with features previously thought to belong only to much later neotheropods, indicating greater early dinosaur diversity than expected as well as a possible climate-related ebb and return of dinosaur abundance in northwestern Argentina.
Fossil assemblages in northwestern Argentina offer a way to examine abundance, body size structure, and faunal shifts during the dinosaur diversification event that followed the Carnian pluvial episode. Early dinosaur diversification remains hard to resolve because few rock units preserve continuous strata across the Carnian and Norian and several classic sites are either limited to Carnian time or poorly sampled.
In the study, "A Carnian theropod with unexpectedly derived features during the first dinosaur radiation," in Nature Ecology & Evolution, researchers integrated new fossil discovery with stratigraphic, anatomical, histological, and phylogenetic analyses to evaluate early dinosaur diversification and the placement of the new theropod.
Holotype PVSJ 1085 represents a single partial skeleton with cranial and postcranial remains. After determining the new genus and species, authors formally named it Anteavis crurilongus.
The genus name, Anteavis, combines ante ("before" or "preceding") and avis ("bird"), referring to its ancestral traits relative to avians. Species name, crurilongus, joins crus ("leg") and longus ("long"), describing the proportionally long lower legs, with the femur at 80% of tibial length and metatarsal III at 63% of tibial length.
The front of the face would appear elongated and streamlined, with a relatively flat upper profile and a single row of teeth confined to the outer jaw margins. The head would sit relatively close to the body, with a smooth transition between skull and torso in a horizontal posture suitable for a small, active predator scanning its surroundings close to the ground.
A combination of pelvic features would have given Anteavis a compact, strong hip structure built for muscular hind limbs and efficient stride mechanics, with bone openings that reduced weight without sacrificing strength.
Located in Ischigualasto Provincial Park, Hoyada de Ischigualasto, San Juan Province, Argentina, lower Cancha de Bochas Member of the Ischigualasto Formation, late Carnian, the site sits slightly above a level dated to approximately 231 million years ago.
Stratigraphic patterns show a shift to semi-arid conditions coincident with diverse small dinosaurs in the Cancha de Bochas Member, followed by a return to more humid conditions and an ensuing record gap in dinosaur occurrences beginning around 228.91 Ma. Records rebound about 15 Myr later in the middle Norian with larger-bodied dinosaurs and renewed abundance and diversity.
The authors conclude that early dinosaur diversification in southwestern Pangaea was considerable at onset, probably punctuated by climate-driven turnover before later dominance, with Anteavis adding a well-supported data point near the base of Theropoda and expanding the anatomical spectrum present during the Carnian.
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More information: Ricardo N. Mart铆nez et al, A Carnian theropod with unexpectedly derived features during the first dinosaur radiation, Nature Ecology & Evolution (2025).
Journal information: Nature Ecology & Evolution
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