Chilesaurus

Chilesaurus is a genus of dinosaur that lived during the Late Jurassic Epoch. To date, the genus contains a single species, Chilesaurus diegosuarezi. All known Chilesaurus fossils come from the Toqui Formation in southern Chile. Chilesaurus was a small, herbivorous dinosaur that featured several unique traits as well as common traits shared by different dinosaur groups, including theropods, ornithischians, and sauropodomorphs. As a result, Chilesaurus represents a unique specimen in terms of the evolutionary history of dinosaurs. 

Description and Size

Chilesaurus was a bipedal dinosaur that walked on two legs. Based on examinations of incomplete fossils, Chilesaurus likely measured around 10.5 feet long from nose to tail. That said, the holotype fossil only measured around half that size. In terms of height, it likely measured around 2.8 feet at the shoulder, or a little over 3 feet tall. Given these dimensions, Chilesaurus likely measured between 200 to 300 pounds. 

Chilesaurus possessed long, spatula-shaped teeth designed to chew plant material. It had a backward-facing pubic bone, typical of “bird-hipped” dinosaurs in the order Ornithischia. Chilesaurus’s hind limbs likely were not well-adapted to running due to its broad feet and a small crest on the shinbone’s front. However, it could possibly defend itself using its strong front arms, which each possessed a large claw. 

Like other dinosaurs, Chilesaurus probably sported a covering of colorful feathers. However, these features’ color, distribution, and appearance remain unknown. 

Evolution and History

Chilesaurus belongs to the reptile clade Dinosauria. However, from there its evolutionary history gets much more complex and uncertain. That’s because Chilesaurus displays traits of several different dinosaur groups, including Theropoda, Ornithischia, and Sauropodomorpha. At first, paleontologists placed it in the theropod group Tetanurae. However, a different theory proposed in 2017 placed Chilesaurus in a basal position in Ornithischia. According to this later hypothesis, theropods and ornithischians share more in common with each other than with sauropodomorphs. This theory places both theropods and ornithischians in the clade Ornithoscelida. Regardless of where it resides, paleontologists find Chilesaurus fascinating because of the implications it poses for dinosaur evolution.  

Diet – What Did Chilesaurus Eat?

Presently, paleontologists classify Chilesaurus as a herbivore. Experts came to this decision based on several key features present in recovered fossils. First, Chilesaurus contains long, forward-facing, spatula-shaped teeth. While somewhat unique among Theropoda dinosaurs, its teeth resemble the teeth of other herbivores. Additionally, Chilesaurus sports a backward-oriented pubic bone. This orientation creates additional space for digestive organs, including a large stomach and long intestines. These features are most common in herbivores as plant material takes longer to digest than animal flesh. A carnivore does not require as much space for its gut as an herbivore. As a result, these two features point to the likelihood that Chilesaurus ate plants. However, the types of plants it ate remain unknown. 

Habitat – When and Where it Lived

To date, the only known Chilesaurus fossil came from the Aysen Region in southern Chile. Today, this area features many geological formations created by glaciers, including lakes and fjords. It contains the third largest icefields in the world, the Northern and Southern Patagonian Ice Fields. The northern half of the region contains numerous volcanoes, while the western half is mountainous with dense vegetation, and the eastern half consists of flat grasslands. 

During the time of Chilesaurus, the world’s climate was starting to change. The area around modern-day southern Chile became warmer and wetter. As an herbivore, Chilesaurus likely lived in or around woodlands, forests, or riparian areas with plenty of vegetation. However, other aspects of its habitat and preferred environment remain a mystery and require additional research. 

Threats and Predators

Due to its relatively small size, Chilesaurus likely had its fair share of predators. That said, little evidence exists that sheds light on potential predators that lived in the same area as Chilesaurus during the Late Jurassic. Only a few dinosaur fossils from the Late Jurassic have been recovered from South America. These include other herbivores such as Brachytrachelopan and Tehuelchesaurus. However, one known predator that lived near Chilesaurus around the same time was Pandoravenator. 

Discovered in Argentina, Pandoravenator lived between 160 and 150 million years ago. A close relative of tyrannosauroids, allosauroids, and maniraptorans, Pandoravenator was a medium-sized carnivore. While its size remains unknown, fossil records confirm it measured slightly larger than Chilesaurus. Although we may never know, there’s a good chance that Pandoravenator preyed on Chilesaurus over 150 million years ago. 

Discoveries and Fossils – Where It was Found

The first Chilesaurus fossils were discovered in 2004 by a seven-year-old boy named Diego Suarez. Suarez found the fossil while on a trip to the Aysen Region with his parents, geologists Rita de la Cruz and Manual Suarez. The family was searching for decorative stones in the Toqui Formation, a Tithonian-stage geological formation consisting of sandstone, volcanic tuffs, and ignimbrite. While searching in the formation. young Diego Suarez discovered a vertebrae and rib fossil that turned out to be the bones of Chilesaurus. Over the next few years, paleontologists recovered more Chilesaurus bones from the same site. These include an almost complete juvenile skeleton and the current species holotype dubbed SNGM-1935. The common name Chilesaurus honors the country of Chile, while its specific name, diegosuarezi, honors its discoverer, Diego Suarez. 

Extinction – When Did It Die Out?

Chilesaurus died out approximately 145 million years ago at the end of the Late Jurassic Epoch. In geological terms, scientists refer to this period as the Jurassic-Cretaceous Boundary or the Jurassic-Cretaceous Transition. This period is baffling to scientists for several reasons. Most major geological boundaries witnessed mass extinction events or radical transformations in planetary conditions. For example, the Cretaceous Extinction Event witnessed the extinction of nearly three-quarters of all life on Earth.

Then there’s the Jurassic-Cretaceous Boundary, which lacks a massive extinction event. While minor extinctions did occur, they did not occur at the same scale as in other period boundaries. Additionally, the Jurassic-Cretaceous Boundary lacks an official global indicator that geologists can use to differentiate the Jurassic and Cretaceous Epochs. However, this timeframe did witness long, drawn-out environmental changes. The continued breakup of the Pangea supercontinent led to sea level changes, and volcanic activity picked up markedly. The world’s climate also became much wetter during this timeframe. One or several of these factors may have led to the extinction of Chilesaurus.  

Similar Animals to Chilesaurus

• Neornithischia. Neornithischia is a sister group to Thyreophora, in the order Ornithischia. These dinosaurs possessed thick enamel on their bottom teeth, enabling them to eat tougher plants than other dinosaurs.    
• Thyreophora. Meaning “shield bearers,” Thyreophora is a group of armored dinosaurs that lived between the Early Jurassic and the Late Cretaceous epochs. Represented members included Stegosaurus, Ankylosaurus, and Scelidosaurus.  
• Pisanosaurus. Pisanosaurus was a small, herbivorous dinosauriform like Chilesaurus. based on the one discovered fossil, it likely measured around 3.3 to 4.3 feet long. It lived during the Late Triassic in northwestern Argentina.