Chilesaurus diegosuarezi: The Bizarre Herbivorous Dinosaur from Chile

The Chilesaurus (Chilesaurus diegosuarezi) is an extinct genus of dinosaur that lived during the Late Jurassic period, around 148-147 million years ago, in what is now Chile. This unique dinosaur is notable for its blend of features from three major dinosaur groups—theropods, ornithischians, and sauropodomorphs. Its discovery has raised intriguing questions about dinosaur evolution and has sparked debate over the traditional classification of dinosaurs.

Scientific Classification

• Domain: Eukaryota
• Kingdom: Animalia
• Phylum: Chordata
• Clade: Dinosauria
• Genus: †Chilesaurus
• Species: †Chilesaurus diegosuarezi
• Described by: Novas et al., 2015

Description of Chilesaurus

Appearance and Size

Chilesaurus measured about 3.2 meters (10.5 feet) from head to tail. The holotype, a smaller individual, measured around half this size. This dinosaur stood out due to its herbivorous adaptations, despite belonging to a group known for carnivores—theropods. The most notable feature of Chilesaurus was its spatula-shaped teeth, which pointed forward at an angle, a trait more commonly found in herbivores than carnivores.

Herbivorous Adaptations

• Teeth: Unlike typical theropods, which have sharp teeth for cutting flesh, Chilesaurus had elongated, spatula-shaped teeth adapted for a plant-based diet.
• Pelvis Structure: It had a backward-pointing pubic bone, providing space for a large gut, a common trait in herbivorous dinosaurs. This pelvic arrangement is also seen in the ornithischians.
• Limbs: Its hind legs were less adapted for running, with a broad foot and a small cnemial crest on the shinbone, indicating a shift away from the fast-paced lifestyle of many theropods.

Defensive Features

Although Chilesaurus was a plant-eater, it may have used its strong arms for defense. Its large first claw could extend outward, similar to some basal sauropodomorphs, suggesting that it could fend off predators if needed.

Discovery and Naming

Chilesaurus diegosuarezi was discovered in the Aysén Region of Chile in 2004 by Diego Suárez, a seven-year-old boy, while he and his geologist parents were searching for decorative stones. Initially, the fossils were thought to belong to several different species, but in 2015, researchers realized they all came from a single species with a unique mix of features.

In 2015, the type species Chilesaurus diegosuarezi was officially described by Fernando Emilio Novas and colleagues. The genus name, Chilesaurus, refers to the country where it was found, while the species name honors Diego Suárez, the young discoverer.

Classification and Evolutionary Debate

Original Classification

When Chilesaurus was first described, it was placed within the theropod group Tetanurae. However, its unusual blend of features, combining traits from theropods (traditionally carnivores), sauropodomorphs, and ornithischians (both plant-eating groups), led to confusion over its exact classification.

Evolutionary Debate: Theropod or Ornithischian?

In 2017, paleontologists Matthew Baron and Paul Barrett proposed that Chilesaurus was a basal ornithischian, placing it closer to theropods than to sauropodomorphs. This hypothesis supported the controversial "Ornithoscelida" theory, which redefines the traditional split between theropods and ornithischians.

However, a follow-up study by Müller et al. in 2018 argued that Chilesaurus might be better classified as a basal sauropodomorph. The debate continued as new analyses and datasets were published, each refining or challenging previous conclusions.

Recent Findings

Despite the debate, the general consensus now leans toward Chilesaurus belonging to the Theropoda group, albeit with many herbivorous adaptations. In 2024, Andrea Cau's study placed Chilesaurus as a sister taxon of Tetanurae, reinforcing its position among theropods, though its precise classification remains somewhat uncertain.

Significance in Dinosaur Evolution

The discovery of Chilesaurus has had far-reaching implications for understanding dinosaur evolution. Its peculiar mix of traits calls into question the long-held distinction between saurischians (lizard-hipped dinosaurs, including theropods and sauropods) and ornithischians (bird-hipped dinosaurs). Instead, Chilesaurus supports the idea of a more complex evolutionary relationship, potentially lending credence to the Ornithoscelida hypothesis, which groups theropods and ornithischians together.

Conclusion

Chilesaurus diegosuarezi is a fascinating example of how complex and intertwined dinosaur evolution truly is. With its bizarre combination of herbivorous and theropod traits, Chilesaurus continues to challenge traditional views of dinosaur classification and evolutionary relationships. Its discovery in Chile has shed light on the diverse and adaptive nature of dinosaurs during the Late Jurassic period.

As more fossils are uncovered and studies continue, Chilesaurus will undoubtedly play a crucial role in refining our understanding of the dinosaur family tree.