Anteavis

MEANING: Before birds

PERIOD: Late Triassic

CONTINENT: South America

Anteavis is an early theropod that lived during the Late Triassic period in what is now South America.

Abstract from paper: The early diversification of dinosaurs produced a major ecological change in the terrestrial ecosystems, culminating with tetrapod assemblages dominated in abundance by dinosaurs by the Triassic/Jurassic boundary (~201 million years ago (Ma)). Therefore, studying the initial diversification of dinosaurs is crucial to understand the establishment of Mesozoic assemblages. However, the lack of stratigraphically continuous fossil data in the few geological units that preserve the oldest known dinosaurs (~233–227 Ma, Carnian age) obscures our understanding of this initial diversification. The Ischigualasto Formation in northwestern Argentina (231.4–225.9 Ma) yields a rich vertebrate assemblage and new studies resulted in an abundant and stratigraphically near-continuous fossil record, which offers new insights into the early diversification of dinosaurs. Among the discoveries, we report Anteavis crurilongus gen. et sp. nov., an early-diverging theropod, which supports the notable diversity of small- to medium-sized dinosaurs during the late Carnian. Anteavis is recovered outside Neotheropoda, but it has features previously thought to be exclusive to that group. We show that dinosaur diversity and abundance in the Ischigualasto Formation were higher than previously recognized, particularly among small herbivores (<30 kg) and medium-sized (30–200 kg) predators. This diversification occurred in Ischigualasto during a climatic shift to semi-arid conditions, but the return of more humid conditions resulted in a gap in the dinosaur record that started at 228.91 ± 0.14 Ma. Only 15 million years (Myr) later, in the middle Norian age, the dinosaur record recovered its abundance and diversity in the basin, but now it was characterized by larger-bodied species. Our findings demonstrate an early dinosaur diversification probably punctuated by a climate-driven faunal turnover in, at least, southwestern Pangaea.

Anteavis is from the Late Triassic. The Triassic is the first geologic period of the Mesozoic, spanning from the end of the Permian Period 252 million years ago to the beginning of the Jurassic 201 million years ago. Both the start and end of the Triassic were marked by major extinction events. In the aftermath of the devastating Permian-Triassic extinction, life gradually rebounded, giving rise to new groups that would shape the Mesozoic Era. The global climate during the Triassic was mostly hot and dry, with vast deserts dominating the interior of the supercontinent Pangea. Over time, as Pangea began to rift apart, the climate slowly became more humid, creating new environments and opportunities for ecological diversification.

For much of the Triassic, dinosaurs were not yet the dominant terrestrial animals. Instead, the land was populated by a variety of other reptiles, including sprawling archosaurs. Early synapsids, the lineage that would eventually lead to mammals, were also still present but declining. Vegetation was dominated by drought-tolerant plants such as seed ferns, cycads, ginkgoes, and early conifers. These hardy plants formed the base of recovering ecosystems during this volatile time.

It wasn't until the Late Triassic, around 230 million years ago, that the first true dinosaurs appeared. Early forms were small, bipedal, and lightly built, likely preying on insects and small vertebrates. While they remained minor players compared to other reptilian groups, their agility, upright stance, and efficient breathing gave them advantages that would prove crucial in the long run. As the Triassic drew to a close, another mass extinction event reshaped life on Earth once again, wiping out many of the dominant reptile groups and clearing the way for dinosaurs to rise to prominence in the Jurassic.

Anteavis is a basal theropod. Theropods are a lineage of bipedal saurischian dinosaurs that first appeared in the Late Triassic. The earliest forms were generally slender, lightly built predators with long legs, grasping hands, and serrated teeth. These basal theropods represent the first major radiation of carnivorous dinosaurs, establishing many of the anatomical traits that would define the group for the rest of the Mesozoic. Their adaptations for speed, agility, and active predation helped make them some of the most successful dinosaurs of the early Jurassic landscapes.

From these beginnings, theropods went on to diversify into a remarkable variety of forms. Later lineages produced the giant allosauroids and tyrannosaurs, as well as smaller, feathered maniraptorans including modern birds - the only theropods still alive today. While most theropods remained carnivores, some later groups evolved herbivorous or omnivorous diets, reflecting their evolutionary flexibility. Basal theropods stand at the root of this history, providing an important window into how the earliest meat-eating dinosaurs set the stage for one of the most dynamic and enduring dinosaur lineages.