Early experience discovered at the beginning of dinosaur evolution

Argentinian researchers have described a Carnian theropod with features previously only associated with later neuterpods, 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 composition, and physiological shifts during the dinosaur diversification event that followed the Carnian pluvial event. Early dinosaur diversity is difficult to resolve because few rock units preserve continuous strata across the Carnian and Norian, and several clastic sites are either restricted to Carnian time or poorly sampled.

The study, “A Carnion Theropod with Features Unexpectedly Derived During the First Dinosaur Radiation,” was published in Nature Ecology and Evolutionthe researchers integrated new fossil discoveries with stratigraphic, anatomical, histological, and phylogenetic analyzes to determine the diversity of early dinosaurs and the placement of new theropods.

Holotype PVSJ 1085 represents a single partial skeleton with cranial and postcranial remains. After determining the new genus and species, the authors formally named it Antius crurilongus.

The genus name, Antius, combines ant (“first” or “former”) and aves (“bird”), referring to its ancestral traits relative to the avian. 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. length.

The front of the face will appear long and smooth, with a relatively flat upper profile and a single row of teeth limited to the outer jaw margin. The head sat close to the body, with a smooth transition between skull and torso in a horizontal posture suitable for a small, active predator that scanned its surroundings close to the ground.

The combination of pelvic features would have given Antivaus a compact, strong hip structure that made for a muscular hindlimb and efficient stride mechanics, with bone opening to reduce weight without sacrificing strength.

Located in Escigualsto Provincial Park, Hoida de Escigualsto, San Juan Province, Argentina, Lower Cancha de Buchas Member, Isicigualsto Formation, Late Carnian, the site sits slightly above the surface of about 23 231 million years ago.

Stratigraphic patterns demonstrate a transition to semi-arid conditions with various small dinosaurs in the Cancha de Buchas Member, followed by a return to more humid conditions and a consequent record gap in dinosaur occurrence beginning around 228.91 Ma. Large-bodied dinosaurs in the Middle Norian record about 15 MYR and began to rebound with renewed abundance and diversity.

The authors conclude that early dinosaur diversity in southwestern Pangea was substantial at the onset, perhaps constrained by climate-driven turnover before later dominance, with Antevis adding a well-supported data point near the base of the Theropoda and expanding the anatomical spectrum during the Carnian.

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