Description and Classification

Erliansaurus was a medium-sized member of the Therizinosauria, a group of theropod dinosaurs known for their unusual features, including long necks, small heads, and very large claws on their hands. Although a complete skeleton has not been found, scientists estimate Erliansaurus was about 4 meters (13 feet) long and might have weighed around 400 kilograms (880 pounds). The known fossils include several vertebrae from the neck and back, parts of the hip (pelvis), and a nearly complete hind limb (leg and foot). Like other therizinosaurs, it likely had a bulky, pot-bellied body to help digest tough plant material. While not directly found with Erliansaurus, many of its close relatives are known to have had feathers, so it is probable Erliansaurus was feathered as well.

Erliansaurus belongs to the theropod group of dinosaurs, which also includes well-known carnivores like Tyrannosaurus rex and Velociraptor. However, therizinosaurs, including Erliansaurus, evolved to become primarily herbivores (plant-eaters). Within the therizinosaur family (Therizinosauridae), Erliansaurus is considered to be a more primitive, or basal, member. It was more advanced than early therizinosaurs like Beipiaosaurus but less specialized than later giants such as Therizinosaurus. Its classification helps paleontologists trace the evolutionary steps within this unique dinosaur lineage.

Distinguishing Features

• As a therizinosaur, Erliansaurus would have had characteristically long, scythe-like claws on its hands. Although the hands themselves have not been found for this specific genus, these claws in related species were likely used for pulling down branches or for defense.
• It likely possessed a long neck and a small skull, features common to most therizinosaurs, allowing it to reach various types of vegetation.
• Unlike most other theropods which were meat-eaters, Erliansaurus was adapted to an herbivorous diet, feeding on plants.
• It walked bipedally on two strong hind legs. The thigh bone (femur) of Erliansaurus is notable for being quite straight.
• Its feet had four main toes that all touched the ground, a feature known as being functionally tetradactyl, which helped support its weight.

Paleoenvironment and Diet

Erliansaurus lived in what is now the Erlian Basin of Inner Mongolia, China, during the Late Cretaceous period. The fossil deposits of the Iren Dabasu Formation, where Erliansaurus was found, suggest a warm and humid environment. This area was likely characterized by rivers, lakes, and floodplains, supporting abundant plant life which formed the base of the food web. Erliansaurus shared this ecosystem with other dinosaurs, such as the hadrosaur (duck-billed dinosaur) Bactrosaurus, the ornithomimosaur (ostrich-mimic dinosaur) Archaeornithomimus, and the giant oviraptorosaur Gigantoraptor erlianensis, which was discovered in the same region and lived around the same time.

As an herbivore, Erliansaurus would have fed on the diverse vegetation available in its habitat. Its long neck might have allowed it to reach leaves on taller shrubs or low-hanging branches. The presumed large claws on its hands could have been used to grasp and pull foliage towards its mouth. Its digestive system was likely large and adapted to break down tough plant matter, similar to other herbivorous dinosaurs.

Significance and Ongoing Research

The discovery of Erliansaurus is significant because it provides valuable information about the diversity and evolution of therizinosaurs. It represents an important transitional form within the Therizinosauridae family, helping scientists understand how these unusual dinosaurs developed their unique characteristics and adaptations. Its discovery in Asia also reinforces the idea that this continent was a key area for therizinosaur evolution and diversification during the Cretaceous period.

Ongoing research on therizinosaurs, including data from Erliansaurus, continues to fascinate paleontologists. Scientists are still working to understand the exact functions of their specialized features, such as their long claws and unique body shape. Further studies aim to clarify their precise relationships to other theropod groups and how they adapted to an herbivorous lifestyle, a rare trait among their mostly carnivorous relatives. Each new therizinosaur fossil, like that of Erliansaurus, helps piece together the puzzle of these peculiar and intriguing dinosaurs from the Age of Dinosaurs.