Agrosaurus (AG-roh-SAWR-us; “field lizard”) is a genus of herbivorous dinosaur whose classification has been a subject of much scientific debate. Originally thought to have lived during the Early Jurassic period in Australia, the fossils attributed to Agrosaurus are now believed by many paleontologists to have come from England and likely belong to a different, already known dinosaur, possibly a basal sauropodomorph like Thecodontosaurus. The name was given by Harry Seeley in 1891.
Description and Classification
Agrosaurus was initially described based on very limited fossil remains, including parts of a limb bone and a claw, found in the 19th century. For many years, it was considered one of the earliest dinosaurs from Australia. However, later research in the late 20th and early 21st centuries cast serious doubt on this. Paleontologists re-examined the fossils and the rock material they were preserved in. They concluded that the fossils were much more likely to have come from the Bristol area of England, from rocks dating to the Late Triassic or Early Jurassic period, not Australia.
If the remains do indeed belong to an animal like Thecodontosaurus, then Agrosaurus would have been a relatively small, early sauropodomorph dinosaur. These dinosaurs were ancestors of the giant long-necked sauropods like Brachiosaurus. Early sauropodomorphs were generally bipedal, meaning they walked on two legs, but some might have also walked on four. They had long necks, small heads, and long tails. Due to the uncertainty and the fragmentary nature of the fossils, most scientists today consider Agrosaurus a nomen dubium, which means a “doubtful name,” or they consider it a synonym of Thecodontosaurus or a similar basal sauropodomorph.
Distinguishing Features
Because the classification of Agrosaurus is uncertain and its remains are sparse, defining its unique distinguishing features is difficult. If Agrosaurus was indeed a basal sauropodomorph similar to Thecodontosaurus, it would likely have shared features common to that group:
- Relatively small size for a dinosaur, probably around 1 to 2.5 meters (3 to 8 feet) in length.
- A lightly built body with a long neck that helped it reach vegetation.
- A small head with leaf-shaped, serrated teeth suited for shredding plant material.
- Primarily bipedal locomotion, using its two hind legs for walking and running, though it might have been able to move on all fours at times.
- A long tail that would have acted as a counterbalance.
The specific fossils once assigned to Agrosaurus are not distinct enough to separate it clearly from other known early sauropodomorphs from the same time and potential region.
Paleoenvironment and Diet
If the Agrosaurus fossils originated from the Early Jurassic (or Late Triassic) of England, as currently thought, the dinosaur would have lived in a terrestrial environment. During this time, the area was warmer than today, with distinct wet and dry seasons. The landscape likely consisted of open woodlands and floodplains, with a variety of plants such as ferns, cycads, and conifers.
As a basal sauropodomorph, Agrosaurus would have been an herbivore. Its diet would have consisted of low-growing plants. Its long neck would have allowed it to browse on vegetation that was out of reach for smaller herbivores. It would have shared its environment with other early dinosaurs, small mammals, and various reptiles.
Significance and Ongoing Research
The story of Agrosaurus is significant in paleontology not so much for the dinosaur itself, but as an example of how scientific understanding evolves. It highlights the importance of careful fossil provenancing (knowing exactly where a fossil was found) and how re-examination of old collections with modern techniques can lead to major revisions. The initial claim of it being an early Australian dinosaur was exciting, but the later correction, suggesting it was European and likely synonymous with an existing genus like Thecodontosaurus, showcases the self-correcting nature of science.
There is little ongoing research focused specifically on Agrosaurus as a distinct genus due to its doubtful status. Instead, the fossils once attributed to it are now part of the broader study of early sauropodomorph dinosaurs, particularly those from the Late Triassic and Early Jurassic of Europe, such as Thecodontosaurus. Understanding these early forms is crucial for learning about the initial diversification of dinosaurs and the evolutionary path that led to the giant sauropods. The Agrosaurus case also serves as a caution in paleontology regarding fragmentary remains and the potential for misidentification or misinterpretation of locality data.