Ornithopoda

Some dinosaurs were plant eaters.

These dinosaurs had feet like birds. The first ones were small. They were very fast. They ran on two legs.

Later ones grew very large. They walked on four legs. They had special teeth. These teeth were great for chewing food.

Some had long faces. People call them duck-bills. They lived a long time ago. They were very successful animals.

Ornithopods were a successful group of plant-eating dinosaurs. Their name means "bird feet." This is because they had feet like birds.

Early ornithopods were small. They were only about 1 meter long. These dinosaurs were likely very fast. They ran on two legs. They used a stiff tail to help them balance.

Later ornithopods grew much larger. Some were very heavy. The Shantungosaurus was as heavy as a medium sauropod. It could weigh up to 23 metric tons.

These big dinosaurs often walked on four legs. They were facultative quadrupeds. This means they could walk on four legs to eat plants. But they could still run on two legs.

Ornithopods had a great way to eat. They had a special chewing apparatus. This is a set of parts used for chewing. Their teeth were very good. They could even rival the teeth of a cow. The duck-billed dinosaurs were the most famous members.

Ornithopods were a very successful group of plant-eating dinosaurs. Their name comes from Greek words meaning "bird feet." This is because they had feet that looked like those of a bird.

These dinosaurs lived during the Cretaceous period. They were important because they were very good at eating plants. Many different kinds lived all over the world. They were eventually wiped out during the Cretaceous–Paleogene extinction event. This event also ended the lives of all other non-avian dinosaurs.

These dinosaurs changed a lot over a long time. Early members were small and only about 1 meter long. They likely ran very fast on two legs. They used a stiff tail to help them stay balanced.

Later members grew much larger and became facultative quadrupeds. This means they could walk on four legs but still run on two. Their spines even curved to look like modern ground-feeders like the bison. They also developed a great chewing apparatus. This set of parts for chewing was very advanced. It was even as good as the teeth of a domestic cow.

Scientists have studied these dinosaurs for a long time. In 1870, Thomas Henry Huxley listed some of them in his work. He included names like Iguanodon and Hypsilophodon. Later, in 1881, Othniel Charles Marsh created the name Ornithopoda. He was busy studying how to classify all dinosaurs. Marsh divided the group into three families. These were Camptonotidae, Iguanodontidae, and Hadrosauridae. He also named several American species himself. One of his names, Camptonotus, had to be changed in 1885. This was because a cricket already had that name.

There are many interesting facts about their bodies. Some ornithopods had thin plates along their ribs. These plates were made of cartilage. Sometimes these plates turned into bone in the fossils. We do not know exactly what these plates did.

The largest ornithopods were huge but not as big as long-necked sauropods. The Shantungosaurus was one of the biggest. It could grow up to 15 meters long. It could weigh as much as 23 metric tons. This is about the same weight as a medium-sized sauropod.

We can learn about them by looking at their teeth. Scientists look at dental microwear to see what they ate. Early ornithopods were likely browsers or frugivores. This means they ate leaves or fruit. The larger ones were bulk feeders. They ate tough plants that did not have much nutrition. They could do this because they had a long gut passage time. This allowed them to get energy from the plants.

Their success shows how well they could adapt to their world.

Ornithopoda is a large group of herbivorous dinosaurs known as ornithopods. These animals were among the most successful plant-eaters during the Cretaceous period. Their name comes from the Greek words *ornithos* and *pous*, which mean "bird feet." This name refers to their characteristic birdlike feet.

Ornithopods lived across the entire world. They eventually disappeared during the Cretaceous–Paleogene extinction event. This event also wiped out all other non-avian dinosaurs.

One of the most important features of ornithopods was their chewing apparatus. Over time, they developed a highly sophisticated way to process food. This system was the most advanced ever seen in a non-avian dinosaur. It was even comparable to the teeth and chewing abilities of modern mammals, like the domestic cow.

Because they could chew so well, they could eat many types of plants. This ability helped them become ecologically dominant in many environments.

Ornithopods changed significantly as they evolved. The earliest members were small and only about 1 meter long. These small dinosaurs were likely very fast runners. They used a stiff tail to help them balance while running on their hind legs.

As the group evolved into the subgroup Iguanodontia, they became much larger. Many became facultative quadrupeds. This means they could walk on all four legs to graze, but they could still run on two legs. Their spines even curved to resemble modern ground-feeders like the bison.

Different types of ornithopods had different diets. Scientists study dental microwear, which is the tiny wear patterns on teeth, to understand this. Early ornithopods were likely browsers or frugivores. This means they ate leaves or fruit. Larger, more derived iguanodontians were bulk feeders. They ate tough, less nutritious vegetation. They could survive on this food because they had a long gut passage time. This allowed them to extract more energy from the plants.

Some ornithopods had unusual physical traits. Certain species had thin cartilaginous plates along the outside of their ribs. In some fossils, these plates mineralized and turned into bone. Scientists do not yet know the exact function of these intercostal plates.

While ornithopods grew very large, they never reached the massive sizes of the long-necked sauropods. However, some were still enormous. The *Shantungosaurus* could reach 15 meters in length. It could weigh up to 23 metric tons. This weight is similar to a medium-sized sauropod.

Research into these dinosaurs has a long history. In 1870, Thomas Henry Huxley identified several families of dinosaurs. He included *Iguanodon* and *Hypsilophodon* in his classification. In 1881, Othniel Charles Marsh created the term Ornithopoda. He used it while investigating how to classify all dinosaurs. Marsh divided the order into three families: Camptonotidae, Iguanodontidae, and Hadrosauridae. He also named several American taxa. One of his names, *Camptonotus*, had to be changed in 1885. This was because a cricket already used that name.

Modern scientists use complex methods to classify these animals. Ornithopoda is usually ranked as a suborder within the order Ornithischia. Some researchers, like Benton in 2004, have placed it as an infraorder. The classification of the group Iguanodontia has also changed. Paul Sereno defined it in 1998, and he later amended that definition in 2005. In 2021, Iguanodontia received a formal definition under the PhyloCode. This definition identifies the smallest group containing specific species like *Iguanodon bernissartensis*.

This precise grouping helps scientists understand the exact relationships between different dinosaur lineages.