Anchisaurus (AN-kee-SAWR-us; “Near Lizard”) is a genus of early sauropodomorph dinosaur that lived during the Early Jurassic period, about 200 to 190 million years ago. Its fossils have primarily been found in the Connecticut River Valley of North America. The name, given by paleontologist Othniel Charles Marsh in 1885, reflects his view that it was closer to the ancestral forms of dinosaurs.
Description and Classification
Anchisaurus was a relatively small dinosaur for its group, reaching lengths of about 2 to 2.5 meters (6.5 to 8 feet) and weighing an estimated 27 kilograms (60 pounds). It had a slender body, a long neck supporting a small head, and a long tail which likely helped with balance. Its hands were notable for possessing a large claw on the first digit, or thumb. While early interpretations sometimes mistakenly identified it as a meat-eater, Anchisaurus is now understood to be an herbivore.
Anchisaurus is classified as a basal (early or primitive) sauropodomorph. This group, Sauropodomorpha, is famous for including the giant, long-necked dinosaurs like Brachiosaurus and Apatosaurus, which appeared later in the Mesozoic Era. Anchisaurus therefore represents an early stage in the evolution of these massive plant-eaters. It is related to other early sauropodomorphs such as Plateosaurus from Europe and Massospondylus from Africa. Scientists believe Anchisaurus could walk on its hind legs (bipedally) but may have also moved on all fours (facultatively quadrupedal), especially when feeding or moving slowly.
Distinguishing Features
- A relatively small and slender body compared to later sauropods.
- A long neck and a proportionately small skull.
- The ability to walk on two legs, though it may have also moved on four.
- A large, sharp claw on the “thumb” of each hand, possibly used for defense or to grasp branches while feeding.
- Teeth adapted for shredding plant material rather than tearing flesh.
Paleoenvironment and Diet
Anchisaurus lived in what is now eastern North America during the Early Jurassic epoch. During this time, the supercontinent Pangaea was beginning to rift apart. The environment where its fossils are found, such as the Portland Formation in Connecticut and Massachusetts, suggests a landscape of river valleys, floodplains, and lakes with a humid, seasonal climate. Vegetation likely included ferns, cycads, conifers, and ginkgoes.
As an herbivore, Anchisaurus fed on the available plants. Its small, leaf-shaped, and serrated teeth were well-suited for stripping leaves and other soft plant matter. Its long neck would have allowed it to browse on vegetation at various heights, from low-growing plants to higher branches. Like many other herbivorous dinosaurs, especially sauropodomorphs, Anchisaurus might have swallowed small stones, known as gastroliths, to help grind up tough plant food in its digestive system, though direct fossil evidence of this in Anchisaurus is not definitively confirmed.
Significance and Ongoing Research
Anchisaurus is a significant dinosaur because it is one of the earliest sauropodomorphs known from North America and provides valuable insights into the early evolution, diversity, and geographic distribution of this important dinosaur group. Its discovery and study were part of the “Bone Wars,” a period of intense fossil hunting and scientific rivalry in the late 19th century, particularly involving Othniel Charles Marsh and Edward Drinker Cope. Studying Anchisaurus helps paleontologists understand the anatomical features and adaptations that led to the later emergence of the giant sauropods.
Ongoing research on Anchisaurus focuses on refining its exact evolutionary relationships with other early sauropodomorphs through cladistic analysis of its skeletal features. The validity of species once assigned to Anchisaurus, and the relationship between Anchisaurus and similar dinosaurs like Ammosaurus, continue to be subjects of study. Detailed examination of its limb bones also helps researchers understand more about its posture and how it moved.