Description and Classification

Manidens was a relatively small dinosaur, estimated to be about 60 to 75 centimeters (approximately 2 to 2.5 feet) in length and weighing only a few kilograms. Like other ornithischians, it was an herbivore and likely moved around on its two hind legs (bipedal). It belongs to the family Heterodontosauridae, a group of early ornithischian dinosaurs known for their unique and specialized teeth. This group includes other well-known dinosaurs such as Heterodontosaurus from Early Jurassic Africa and Tianyulong from Late Jurassic China.

Heterodontosaurids are characterized by “heterodonty,” meaning they possessed different types of teeth in their jaws. Manidens shared this trait, having small, peg-like teeth at the front of its snout, followed by larger, tusk-like canine-shaped teeth (caniniforms) in both the upper and lower jaws, and a row of chisel-shaped cheek teeth designed for grinding plant material. The discovery of Manidens in South America helped show that heterodontosaurids were more widespread than previously thought, with representatives across the ancient supercontinent Gondwana.

Distinguishing Features

Manidens possessed several features that help distinguish it from other dinosaurs, particularly other heterodontosaurids:

• Its cheek teeth were triangular and relatively simple compared to those of Heterodontosaurus, but they still showed distinct wear facets, indicating that Manidens could chew its food by grinding its upper and lower teeth together.
• The wear pattern on its teeth was unusual: the upper teeth wore against the outer (buccal) side of the lower teeth, a pattern different from many other ornithischian dinosaurs.
• While it had the characteristic caniniform “tusks” of heterodontosaurids, they were proportionally smaller in Manidens compared to those seen in Heterodontosaurus.
• The skull of Manidens was relatively short and high.
• It is one of the smallest known members of the Heterodontosauridae family.

Paleoenvironment and Diet

Manidens lived in what is now Patagonia during the Early to Middle Jurassic. The environment of the Cañadón Asfalto Formation at that time was likely a warm, semi-arid landscape with distinct wet and dry seasons. Extensive river systems and lakes were present, surrounded by vegetation that included ferns, seed ferns, cycads, and conifers. Manidens would have shared this environment with other dinosaurs, including early sauropods like Patagosaurus and theropods like Piatnitzkysaurus.

As an herbivore, Manidens fed on plants. Its specialized dentition suggests it was capable of processing tough vegetation. The tusk-like caniniforms might have been used for display, defense against small predators, or possibly for nipping or digging up plants or roots. The cheek teeth were then used to slice and grind this plant material before swallowing. Its small size suggests it probably ate low-growing plants.

Significance and Ongoing Research

The discovery of Manidens is significant for several reasons. It represents one of the oldest known heterodontosaurids from South America and provides valuable information about the early evolution and diversity of ornithischian dinosaurs. Its presence in Argentina highlights the widespread distribution of heterodontosaurids across Gondwana during the Jurassic period. Studying the anatomy of Manidens, especially its unique teeth and jaw mechanics, helps paleontologists understand how early ornithischians adapted to herbivorous diets and how complex chewing systems evolved.

Ongoing research continues to explore the evolutionary relationships of Manidens within Heterodontosauridae and its place among other early ornithischians like Eocursor. Scientists are also interested in learning more about the paleoecology of the Cañadón Asfalto Formation to better understand the world Manidens inhabited. Further fossil discoveries could provide more complete skeletal material, offering more insights into its locomotion, behavior, and overall biology.