Ornithischia Order | Ancient Beasts

There are two main orders in the dinosaur kingdom: Saurischia and Ornithischia. We’ll be dealing with the Ornithischia order in this article, breaking down every aspect so you can see the relationships within it. You’ll also notice some of the more popular dinosaurs it contains.

What are the main characteristics of Ornithischian dinosaurs, and what sets them apart from Saurischians? These are only a few of the questions that scientists have been trying to answer for a long time. We’re happy to present some of the findings. 

What is the Ornithischia order?

The name Ornithischia comes from the bird-like hips that the dinosaurs in this order had. It’s a bit of a misnomer, as they actually had ornithischian hips while birds are more closely related to the Saurischians. Be that as it may, all dinos in this order are placed here due to the same hip structure.

Some of the more common clades and groups include ornithopods, armored dinosaurs, and ceratopsians. We’ll show you the more popular dinos that were from the Ornithischia order later. For now, this should give you some idea of what the order is and consists of, for a start.

It was in 1887 when Harry Seely first determined that the dinosaur kingdom should consist of two main orders. Noting that the Ornithischia order mostly contained beak structures and bird-like hips, he placed many families and sub-groups within it. We still use this system today.

Which characteristics define Ornithischia?

If you ask any expert what the top characteristic of the Ornithischia order is, they’ll probably tell you it’s the hip structure. The technical, scientific term for it is opisthopubic, which means the pubic bone points to the back and downwards. It runs parallel with the ischium, while the ilium at the top points forward, supporting the abdomen.

While the hip bone is the defining element of Ornithischians, it’s not the only one. The lower jaw had a unpaired bone called a predentary (the color in green in the image below). With the upper jaw’s premaxilla, it formed a beak-like structure that the Saurischians didn’t have.

The premaxillary bones didn’t have any teeth. The snout tip was slightly rough at that point. Outside the eye socket, there was a slight eyebrow, called the palpebral bone. The fenestra before the eye socket was also reduced when you compare the Ornithischia order with the Saurischians.

There are two final characteristics of the Ornithischians we want to touch on before we continue. The teeth in the cheek area had a shape that looked like leaves. When looking at the pelvis, you’d find about five sacral vertebrae attached to it.

The Sub-Groups of the Ornithischia Order

Now that you have a better understanding of the basics of the Ornithischia order, we want to break it down into the sub-groups and clades. It helps to see how the various dinosaurs in this section were related in some way, if only distantly. 

While we’ll mainly focus on the main groups, there are species outside of each one that stand on their own. We’ll cover those when we deal with those species.

Genasauria

The Genasauria clade is the one that contains most of the dinosaurs in the order. These Ornithischians were mostly herbivorous in nature, preferring grass and leaves over meat. The two works ‘gena’ and ‘sauria’ literally mean cheek lizard.

That literal meaning is tied to the primary characteristic of the Genasauria dinosaurs. The Ornithischian cheek bears reference to the medial offset when it comes to the maxillary teeth. The muscular cheeks were beneficial when chewing huge amounts of leafy food. Think of a chipmunk storing nuts, but change them for foliage.

We’ll cover the two major Genasauria divisions below, but we should briefly mention the Lesothosaurus and Serendipaceratops genera. They fall directly under Genasauria and don’t have any other clade as yet.

Thyreophora

The Thyreophorans consist of a few dinosaur names you should be familiar with if you’ve seen dino movies or played dino games. Ankylosaurus and Stegosaurus are especially popular to tame in titles like ARK: Survival Evolved. Basically, the name means shield-bearer or armored dinosaur.

The time periods for the Thyreophorans were from the Early Jurassic to the Late Cretaceous, when the extinction-level event occurred. As you can tell from the name description, the top characteristic was the lined armor over the body. Other traits were the herbivorous diet and small brains relative to their massive body size. 

Here are the two main Ornithischia order groups under Thyreophora were the following:

• Ankylosauria
• Stegosauria
  
  

We’ll delve into each one further when we deal with their families in other articles. There were also some species outside of these groups. These include Bienosaurus, Emausaurus, Laquintasaura, Scelidosaurus, Scutellosaurus, Tatisaurus, and Yuxisaurus.

Neornithischia

This group’s name basically means new Ornithischians. While they may not have had armor on their bodies, their lower teeth were strengthened by hard asymmetrical enamel. As they chewed their food, the teeth wouldn’t wear down evenly. It caused them to sharpen, which was helpful for breaking off tougher meals.

In 1985, Cooper classified dinosaurs under Neornithischians as being more closely related to the Parasaurolophus genus than Ankylosaurus. While there have been slight traces in the Triassic period, they mostly lived from the Early Jurassic to the Late Cretaceous. 

There are three primary Neornithischian groups in the Ornithischia order:

• Jeholosauridae
• Thescelosauridae
• Cerapoda
  
  

Names of species that existed outside these sub-groups under Neornithischia are possibly Agilisaurus, Fulgurotherium, Hexinlusaurus, Hypsilophodon, Isaberrysaura, Kulindadromeus, Nanosaurus, Phyllodon, Sanxiasaurus, and Xiaosaurus.

Before we turn to dinosaur families, we want to turn our attention to the Cerapoda sub-group. While Jeholosauridae and Thescelosauridae were relatively small, Cerapoda contains two extra clades that will become important for other parts of our site:

• Ornithopoda
• Marginocephalia
  
  

The Ornithopoda group is where the Ornithischia order gets its name. It contains popular dinosaurs you may recognize, such as the Iguanodon, Camptosaurus, and Dryosaurus. Marginocephalia is also massive, holding the Pachycephalosaurians and Ceratopsians. It should be no surprise that you’d find the Triceratops in the latter.

Families within Ornithischia

We don’t want to go into too much detail explaining each of the families within the Ornithischia order. We’re creating separate pages for all of them, which will link to this page. We want to really dig into each family with as much information as possible, showing you what separates one from the other.

Here’s a quick outline of the top Ornithischian families, which excludes a few genera in between without allocated families:

• Heterodontosauridae
• Ankylosauria
  • Ankylosauridae
  • Nodosauridae
  • Parankylosauria
  • Euankylosauria
• Stegosauria
  • Stegosauridae
  • Huayangosauridae
•  Jeholosauridae
• Thescelosauridae
• Ornithopoda
  • Iguanodontidae
  • Hadrosauroidea
  • Camptosauridae
  • Dryosauridae
  • Rhabdodontidae
• Ceratopsia
  • Ceratopsidae
  • Protoceratopsidae
  • Leptoceratopsidae
  • Chaoyangsauridae
  • Neoceratopsia
• Pachycephalosauria
  • Pachycephalosauridae
    
    

What are some dinosaur examples of ornithischians?

We’re sure you’re wondering which of the famous dinosaurs were in the Ornithischian order. While there are many popular names, we’ve selected five we’re sure you’re familiar with. Here’s a quick overview of their main characteristics, but we’ll have more detailed articles on them in time to come.

Pachyrhinosaurus

The Pachyrhinosaurus genus is one of my favorite genera. I first encountered it when I played ARK: Survival Evolved on the PlayStation, but I’d heard of it before in my youth. The name means thick-nosed lizard, but I fell in love with the frill.

They had massive cheek teeth, which were ideal for chomping on large amounts of vegetative food. As you can tell from the skull design, it’s part of the Ceratopsidae as distant cousins to the Triceratops. Scientists believe it lived during the Late Cretaceous period.

Stegosaurus

Very few dinosaur lovers don’t know the might Stegosaurus. It’s mostly known for its plated armor lined up as ridged along the back. Its name means roof-lizard, mainly for how the plates look on the backs of these ancient beasts.

Paleontologists have found over 80 fossil sets belonging to the Stegosaurus genus. The quadrupeds were herbivores with massive spikes on the tail used for defense. As for the plates, it’s believed that they were used to control body temperature and as a display measure. Compared to the rest of its body, it had a tiny brain and head.

The Stegosaurs appeared during the Late Jurassic period. Based on the fossils found around their remains, it seems they lived among popular dinosaurs such as Diplodocus, Apatosaurus, Brachiosaurus, Allosaurus, and Ceratosaurus. Chances are that the meat-eaters on that list feasted on them.

Ankylosaurus

The Ankylosaurus genus is my son’s favorite. It has a bony head and a tail that looks like Thor’s hammer, Mjollnir. The name has two meanings: fused lizard is the generic one and great belly is the specific one. If you’ve seen images of the dinosaur, you’ll know that both titles are apt.

Unlike the Stegosaurus, it had osteoderms over its back, which is the name of the body armor plates. It had horns on its head on the back facing backward, which were used in defense if a huge carnivore attacked from above. Unfortunately, it only lived in the Late Cretaceous before the dinosaur kingdom came to an end.

Triceratops

The Triceratops is my daughter’s favorite Ornithischian. Thanks to taming these Ancient Beasts on ARK: Survival Evolved, we refer to it as Trikey whenever we see an image of one. The name refers to the three horns on the skull, literally meaning “three-horned face.”

Many scientists believe it’s closely related to Torosaurus, which some say is simply a mature Triceratops. It existed during the Late Cretaceous period in the Maastrichtian stage. It’s believed that the Trikey may have been one of the last genera to appear before the extinction-level event.

Iguanodon

Thumbs up, how many of you know Iguanodon? This dinosaur first caught my attention when I was seven years old, reading my dino mags that appeared once a month. While some teeth were first discovered in 1882, it’s the thumbs that have held our interest for so long.

Interesting fact, the scientists first believed the thumb spikes were nose horns. The Iguanodon lived from the Late Jurassic to the Early Cretaceous, enjoying existence for several ages. The name stands for “Iguana-tooth.” They say the thumb spike was used for defense and breaking off some tough food from trees.

Dryosaurus

I didn’t think much of the Dryosaurus until I played Jurassic World Evolution 2. This small dinosaur has some stunning qualities, and the name means “tree lizard.” The reason for this title is due to the forest habitat it enjoyed living in. Paleontologists say that it’s closely related to the Iguanodonts, if not part of them.

The Dryosaurs lived during the Late Jurassic period, but it’s unknown if they extended into the Cretaceous. They had long necks with stiff tails, with short arms holding five fingers on each hand. The horned beak had cheeked teeth, which is one of the reasons it falls under the Ornithischia order.

How does Ornithischia fit into the 7 major dinosaur groups?

You may not know this, but dinosaurs are also placed in seven major dinosaur groups outside of this scientific classification mentioned above. They’re so named because they have the largest populations of dinos in which most of the families and species are placed.

The seven major dinosaur groups are:

• Theropods
• Sauropods
• Stegosaurs

• Ankylosaurs

• Ornithopods

• Ceratopsians
• Pachycephalosaurs
  
  

As you can see from the highlighted names, the Ornithischia order makes up five out of the seven major groups. That doesn’t mean there are more Ornithischians than Saurischians. It’s just that there are more groups that play significant roles from dinosaur times.

Final Thoughts on the Ornithischia Order

The Ornithischia has plenty of fascinating details, especially when you explore the different sub-orders and groups within it. We’re sure you recognized many dinosaur names in this article, so you can see why it’s so essential to understand ancient beasts from prehistoric times.

Be sure to also check out our page on the Saurischian order. There are more groups and families to explore, which make up all the other dinosaurs we haven’t mentioned as yet. If you’re looking for Tyrannosaurus Rex or the Carnotaur, you’ll want to head there.