Description and Classification

Mantellisaurus was a medium-sized herbivorous dinosaur. It grew to about 7 to 9 meters (23 to 30 feet) in length and likely weighed around 1 to 2 metric tons (1.1 to 2.2 short tons). Like other iguanodontians, it had a fairly bulky body, a long, stiff tail used for balance, strong hind limbs for walking, and shorter, but still robust, forelimbs. It could walk on two legs (bipedally) to move quickly or browse from higher vegetation, but it could also walk on all fours (quadrupedally), perhaps when moving slowly or feeding on low-lying plants.

The skull of Mantellisaurus was relatively long and somewhat slender compared to its more famous relative, Iguanodon. It had a toothless beak at the front of its mouth for cropping plants, and rows of closely packed chewing teeth further back in its jaws, designed for grinding tough plant material. Its hands were notable for having a conical thumb spike, though this spike was generally smaller and less prominent than the one found on Iguanodon bernissartensis. The other fingers on its hands were capable of grasping branches and leaves.

Mantellisaurus is classified as an ornithopod dinosaur, belonging to the group Iguanodontia. Iguanodontians were a very successful group of herbivorous dinosaurs during the Cretaceous period. Mantellisaurus is considered a more lightly built and possibly more advanced (or derived) iguanodontian compared to the classic Iguanodon. It is placed within Hadrosauriformes, a group that includes the later duck-billed dinosaurs (hadrosaurs) and their closest relatives. This means Mantellisaurus shares some features with these advanced herbivores but is not a hadrosaur itself.

Distinguishing Features

Mantellisaurus can be distinguished from other iguanodontian dinosaurs, particularly Iguanodon, by several key features:

• It had a generally more slender and graceful build compared to the robust Iguanodon bernissartensis.
• Its forelimbs were proportionally longer and more slender compared to its hindlimbs than in Iguanodon.
• It possessed fewer vertebrae in its backbone, specifically in the back (dorsal) and hip (sacral) regions.
• While it had a thumb spike, it was typically less massive than that of Iguanodon bernissartensis.
• The overall shape of its pelvis and other skeletal details also differed, indicating it was a distinct animal.

Paleoenvironment and Diet

Mantellisaurus lived in Europe during the Early Cretaceous. At this time, the region was a complex landscape of floodplains, river systems, deltas, and coastal lowlands, with a generally warm and humid climate. The famous Wealden Group in southern England, where many Mantellisaurus fossils have been found, represents this type of environment, characterized by lush vegetation.

As a herbivore, Mantellisaurus would have fed on a variety of plants available in its habitat. Its diet likely included ferns, cycads, horsetails, and possibly early flowering plants. The horny beak at the front of its mouth would have been used to snip off vegetation, which was then passed to the grinding teeth at the back of its jaws. Its ability to switch between bipedal and quadrupedal stances would have allowed it to browse on plants at different heights.

Significance and Ongoing Research

The recognition of Mantellisaurus as a separate genus from Iguanodon has been significant for understanding the diversity and evolution of iguanodontian dinosaurs in Early Cretaceous Europe. For many years, fossils now attributed to Mantellisaurus were simply grouped under Iguanodon atherfieldensis. Separating them has helped paleontologists refine the family tree of these important herbivores and better understand how different species were adapted to their environments.

Ongoing research continues to explore the exact relationships of Mantellisaurus to other iguanodontians, including Iguanodon and the ancestors of the hadrosaurs. Scientists study its skeletal features to learn more about its posture, how it moved (locomotion), and how it fed. Detailed comparisons with fossils from other parts of Europe help to map its geographic distribution and any potential variations within the genus. The study of Mantellisaurus contributes to a broader understanding of the ecosystems of the Early Cretaceous and the role these medium-sized herbivores played within them.