Agilisaurus: The Nimble Herbivore from the Middle Jurassic of Eastern Asia

Today, we invite you to delve into the lives of some of the most captivating creatures that once inhabited our planet. Discover the Agilisaurus, a remarkably agile dinosaur that roamed Asia during the Middle Jurassic period. The completeness of this herbivore’s fossil remains offer us a unique window into a world that existed millions of years ago.

Agilisaurus Key Facts

Agilisaurus pronunciationaj-i-li-sore-us
Meaning of nameAgile lizard
Type SpeciesAgilisaurus louderbacki
When it Lived170.3 to 157.3 MYA
PeriodMiddle Jurassic
EpochBajocian to Oxfordian
Length3.5 to 6.0 ft
Height2.0 ft
Weight0.4 tons
First Discovery1984 by George Louderback
Location of first findSichuan, China
First Described by1990 by Peng Guangzhou

Agilisaurus Origins: Taxonomy, Timeline, and Discovery

The Agilisaurus’ name is derived from the Latin “agilis” meaning ‘agile’ and the Greek “sauros” meaning ‘lizard’, is a testament to the dinosaur’s nimble nature. This creature belonged to the Ornithopoda group of dinosaurs, specifically the Genasauria family, and its type species is Agilisaurus louderbacki.

Illustration of Agilisaurus in life, showing a small bipedal dinosaur with a long tail, a spotted body, and a vibrant orange neck and head.
image by Danny Cicchetti is license under CC BY-SA 4.0

Our agile friend lived during the Middle Jurassic period, specifically the Bajocian to Oxfordian epochs. This was a time when dinosaurs were the dominant terrestrial vertebrates.

The first discovery of fossil remains was made in 1984 by American geologist George Louderback in Sichuan, China. However, it wasn’t until 1990 that Chinese paleontologist Peng Guangzhou described this dinosaur in detail.

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Fossil Evidence

The first fossil evidence was discovered during the construction of the Zigong Dinosaur Museum in 1984. This find was significant, as it was one of the most complete small ornithischian skeletons ever found. Only a few parts of its left forelimb and hind limb were missing, but these could be reconstructed from their counterparts on the right side.

Fossil of the type species Agilisaurus louderbacki displayed at the Zigong Dinosaur Museum, showing the skeletal structure embedded in rock.
image by Zhangzhugang is license under CC BY 4.0

‘The fossil skeleton is now housed in the Zigong Dinosaur Museum. The museum features many dinosaurs recovered from the famous Dashanpu Quarry outside the city of Zigong, in the Chinese province of Sichuan. The quarry preserves sediment from the Lower Shaximiao Formation. It spans from the Bathonian through Callovian stages of the Middle Jurassic Period, or from about 168 to 161 million years ago.

Agilisaurus Size and Description

Let’s take a closer look at the physical characteristics of our agile friend.

Agilisaurus was a small herbivore, about 2 meters (6.5 feet) in length. It had a beak-like structure on the ends of both upper and lower jaws to help it crop plant material. Its tibia (lower leg bone) was longer than its femur (upper leg bone), indicating that it was an extremely fast bipedal runner that used its long tail for balance. However, it may have walked on all fours when browsing for food.

Size and Weight of Type Species

The dinosaur was about 3.5 to 6 ft  long and 2 ft in height, and weighing approximately 40 kg (88 lbs). This compact size likely contributed to its agility and speed, allowing it to navigate its environment effectively.

Size comparison between a human silhouette and Agilisaurus, showing the small stature of the dinosaur relative to a human.
image by Slate Weasel is license under Public Domain

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The Dinosaur in Detail

This was a unique dinosaur with several distinguishing features. Its leaf-shaped teeth were well-adapted to their abrasive, plant-based diets. Most surprisingly, the wavy enamel of the teeth, presumably to make it more resistant to wear, was previously thought to be exclusive to the hadrosaurs. This is also the case for Changchunsaurus parvus, another herbivorous dinosaur. 

Small and agile, its tail could have helped it balance as it ran. Some paleontologists think it may have been a burrow dweller due to the lack of interwoven struts in the tail bones that would have stiffened the tail.

The skeleton discovered during the construction of the Zigong Dinosaur Museum is one of the most complete small ornithischian skeletons ever found. This notable specimen has greatly contributed to our understanding of this nimble dinosaur..

The Agilisaurus in its Natural Habitat and Environment

Agilisaurus lived in what is now eastern Asia during the Middle Jurassic period. The climate, geography, and types of vegetation present during its time are not well known, but we can infer some details based on the overall conditions of the Jurassic period.

As an herbivore, Agilisaurus would have fed on the plant life abundant in its environment. Its beak-like structure would have been ideal for cropping plant material. Its bipedal locomotion suggests it was a fast runner, possibly using this speed to evade predators.

Interesting Points about Agilisaurus

  • This was one of the most agile dinosaurs, as suggested by its lightweight skeleton and long legs.
  • It had leaf-shaped teeth with wavy enamel, a feature previously thought to be exclusive to hadrosaurs.
  • There is only one known skeleton of this dinosaur, however it is one of the most complete small ornithischian skeletons ever found.
  • Some paleontologists believe it may have been a burrow dweller due to the lack of tail-stiffening interwoven bony struts.
  • It was discovered during the construction of a dinosaur museum in China, where it is now housed.

Contemporary Dinosaurs

The Shunosaurus, a larger Chinese dinosaur, was a striking contrast to the nimble Agilisaurus. Its long neck reached out to the high branches, accessing food resources that were out of reach for much smaller Agilisaurus. Despite their differences in size, these two dinosaurs coexisted and each found their own niche in the vibrant ecosystem. Another large dinosaur of the time, the Omeisaurus, was a herbivore sauropod. Its sheer size might have been an imposing sight for the smaller Agilisaurus. However, it is likely that these creatures lived side by side with their lives unfolding in parallel.

The Mamenchisaurus, with its extraordinarily long neck, stands out among these contemporaries. This dinosaur, also considerably larger than the Agilisaurus, might have been a competitor for resources, yet it is also possible that their different diets allowed for peaceful coexistence. Finally, the Tuojiangosaurus presents a stark contrast to the agile and lightly built Agilisaurus due to its extensive heavy body armor. One can only imagine the fascinating dynamics between these two dinosaurs, one relying on speed and agility and the other on its formidable defenses.

Through their interactions and relationships, we gain a deeper understanding of this dinosaur and its place in the world, a world that was as dynamic and complex as the creatures that inhabited it.

Featured Image Credit: ArthurWeasley~commonswiki assumed (based on copyright claims), CC BY-SA 3.0, via Wikimedia Commons


The information in this article is based on various sources, drawing on scientific research, fossil evidence, and expert analysis. We aim to provide a comprehensive and accurate overview of the dinosaurs. However, please be aware that our understanding of dinosaurs and their world is constantly evolving as new discoveries are made.”

Article last fact checked: Joey Arboleda,06-09-2023