Ornithopoda

Ornithopoda is a group of herbivorous dinosaurs that lived during the Cretaceous period. These dinosaurs are called ornithopods. They were very successful and became very diverse. The earliest ornithopods were small and walked on two legs, but later ones, especially in a group called Iguanodontia, walked on four legs and grew much larger.

One big reason ornithopods were so successful was their advanced way of chewing food. Their chewing system became very complex, almost as advanced as that of modern mammals like cows. This helped them eat plants more efficiently.

The most well-known ornithopods are the hadrosaurids, often called duck-bills. They were very diverse and widespread. Sadly, like all dinosaurs that were not birds, ornithopods disappeared suddenly at the end of the Cretaceous period, in what is called the Cretaceous–Paleogene extinction event.

History of research

In 1870, a scientist named Thomas Henry Huxley grouped certain dinosaurs together, including Iguanodon, Hypsilophodon, and Hadrosaurus. Later, in 1881, another scientist named Othniel Charles Marsh introduced the term Ornithopoda to describe these dinosaurs. He placed them in one of the main groups of dinosaurs, along with Therapoda, Sauropoda, and Stegosauria. Marsh divided Ornithopoda into three families, including Iguanodontidae and Hadrosauridae, which he took from earlier work. He also created a new family called Camptonotidae for some smaller dinosaurs. Over time, some of these names changed, like Camptonotidae becoming Camptosauridae.

Description

Ornithopoda means "bird feet" because these dinosaurs had feet that looked like birds'. They did not have body armor or a horny beak, and they had a special bone in their hips that was longer than others. Some ornithopods had thin plates along their ribs, but we do not know what these plates were for.

Early ornithopods were small, about 1 metre (3 feet) long, and could run fast on two legs. Later ones got bigger and started walking on all fours more often, with curved backs like modern animals that eat grass. Even the largest ornithopods, like Shantungosaurus, were not as big as the long-necked sauropods, reaching up to 15 metres (50 feet) long.

These dinosaurs mostly ate soft plants or fruits at first, but the bigger ones later ate tougher plants because they could process food slowly in their long digestive systems.

Classification

Ornithopods were a group of plant-eating dinosaurs. At first, many small two-legged dinosaurs were called ornithopods, but many of these have been sorted into different groups since then.

Ornithopods are usually placed in a group called Suborder, within a bigger group called Ornithischia. Some scientists still use this way of organizing dinosaurs, even though others prefer different methods. One scientist suggested placing ornithopods in a smaller group called infraorder, inside another group called Cerapoda.

A part of ornithopods called Iguanodontia is often listed as an infraorder inside ornithopods. However, some scientists place ornithopods as an infraorder and do not rank Iguanodontia. Early studies showed that traditional iguanodontids were not a single group but led up to duck-billed dinosaurs, called hadrosaurs. Even though some scientists still use old group names, many "iguanodontids" are now included in a larger group called Hadrosauroidea.

In 2021, ornithopods were formally defined as the largest group that includes one specific dinosaur but not two others. This helps scientists clearly define which dinosaurs belong to this group.