Ceratopsidae

Ceratopsidae

Ceratopsidae is a family of ceratopsian dinosaurs that lived during the Upper Cretaceous period. Well-known members include Triceratops, Centrosaurus, and Styracosaurus. These dinosaurs were four-legged plant-eaters with special beaks and teeth for eating.

They are famous for their horns on their noses and large frills that extend from the back of their skulls. These frills and horns come in many shapes and sizes. Scientists think these features might have been used to show off to others of the same kind or to protect themselves from predators.

Ceratopsids are split into two groups: the Chasmosaurinae, which usually have long, triangle-shaped frills and horns above their eyes, and the Centrosaurinae, which often have strong horns on their noses or bony bumps, shorter frills, and special spines on the back edge of their frills. Many centrosaurines are found together in large groups, suggesting they lived in big herds. The name "ceratops" comes from Ancient Greek and means "horned face."

Paleobiology

Behavior

Fossil deposits with many ceratopsids from one species suggest these dinosaurs might have stayed together in groups. Scientists have different ideas about how they behaved. Some think these groups were like crowds of modern crocodiles or tortoises. Others believe they were large, complex herds.

Animals with special features for showing they are ready to mate, like the horns and frills of ceratopsids, often form big groups. One scientist found that some ceratopsids didn’t fully grow their special features until they were almost fully grown. This is similar to young animals today that wait to start having babies until they are older. Females did not wait as long as males to grow these features.

Some researchers think ceratopsids moved in small groups near the coast during rainy times and then moved inland when it was dry. More fossils are found inland, which might show where they went to lay eggs. Today, many animals also move seasonally. Being in groups might have helped protect them from predators, like the tyrannosaurids.

Diet

Ceratopsids had special teeth and skulls that helped them eat tough, low plants. They might have used a process in their stomachs to help break down the plants. Studies show they probably ate plants no higher than about 1 meter off the ground.

Physiology

Main article: Dinosaur physiology

Ceratopsians likely had a slower metabolism, like big animals today.

Sexual dimorphism

One scientist suggested that if ceratopsids had differences between males and females, it would show in features like horns and frills. But no clear proof of such differences has been found in ceratopsids, though it existed in a smaller relative, Protoceratops andrewsi. If there were differences, they might have been in things like colors or skin flaps that didn’t fossilize.

Evolution

Scott D. Sampson has said that ceratopsids evolved in a way that is like some groups of mammals. They grew quickly to big sizes. They had special parts for eating and many kinds of hornlike organs. The first ceratopsids, from groups like Centrosaurinae and Chasmosaurinae, lived in the early Campanian stage, but we do not have many fossils from this time. Almost all ceratopsids lived in western North America, an area called Laramidia during the Late Cretaceous. This land was separated from Appalachia by the Western Interior Seaway. Ceratopsids lived from Alaska to Mexico during this time. The only ceratopsid found outside Laramidia is Sinoceratops, from China. A tooth found in Mississippi shows that ceratopsids also lived in eastern North America near the end of the Cretaceous period.

Paleoecology

Big dinosaurs called tyrannosaurids were the main hunters of ceratopsids. Scientists found clues that show ceratopsids were sometimes eaten by these big dinosaurs.

There is proof that a Triceratops fought with a Tyrannosaurus. We can see this because a Triceratops fossil has healed bite marks from a Tyrannosaurus on its brow horn and squamosal, a bone in the neck frill. The horn was broken but grew back, showing that the Triceratops survived the fight. The famous Dueling Dinosaurs fossil shows a Triceratops buried in a fight with a Nanotyrannus from the Hell Creek formation.

Classification

Scientists described the group called Ceratopsidae in different years. In 1998, a scientist named Paul Sereno defined it as the group that includes the last shared ancestor of Pachyrhinosaurus and Triceratops, plus all its descendants. Later, in 2004, another scientist named Peter Dodson included Triceratops and Centrosaurus, along with all their descendants from their most recent shared ancestor. In 2021, the group got an official definition to make sure certain species, like Centrosaurus apertus, Ceratops montanus, Chasmosaurus belli, and Triceratops horridus, are always part of Ceratopsidae.