When it comes to prehistoric animals, dinosaurs are arguably the most popular of them all, and for good reasons too.
They were the most diverse and dominant animal group on Earth for most of the Mesozoic Era.
What’s even more interesting is the fact that they are still around today.
Birds, which are one of the most diverse groups of vertebrates today, are technically dinosaurs.
The name dinosaur is a broad term to describe a large group of animals that includes several orders, families, genera, and species.
Estimates vary, but there are at least 800 valid genera of non-avian dinosaurs discovered so far, and up to 1000 species spread across these genera.
And that’s just the ones we know.
The fossil record only preserves a small percentage of prehistoric animals, meaning the dinosaurs were probably more diverse than we are currently aware.
Dinosaurs exhibited a wide range of sizes, shapes, and behaviors.
Studying their diversity and adaptations provides insights into how life forms evolve and change over time based on their environments and other ecological factors.
Dinosaurs also played a significant role in shaping Earth’s ecosystem for over 160 million years, so understanding their diversity helps us comprehend prehistoric times better.
In this article, we’ll explore the different types of dinosaurs, explaining their key features and providing examples for each group.
What Are Dinosaurs?
The term “dinosaurs” is a common name for an extinct group of reptiles that lived during the Mesozoic Era.
The name, which literally means “terrible lizard,” was coined in 1842 by anatomist Richard Owen.
Dinosaurs were the most dominant and most diverse animal group on the planet for about 160 million years.
They first evolved in the Triassic Period and were around till the end of the Cretaceous Period.
During this time, this group of reptiles evolved into a wide variety of shapes and sizes.
While some of them were herbivores, others were carnivores and omnivores.
Some were small and agile, while others were large and slow.
It is worth noting that not all prehistoric reptiles that lived during the Mesozoic Era were dinosaurs.
Regardless of their diversity, the dinosaurs were all connected by a number of key identifying features.
Some of these features include:
- Dinosaurs had straight legs that were perpendicular to their bodies. This gave them an upright stance.
- Their legs were positioned underneath their body instead of sprawling to the side like other reptiles.
- Except for the birds that took to the skies, dinosaurs lived almost entirely on land. The flying reptiles (pterosaurs) and marine reptiles (such as plesiosaurs) of the Mesozoic Era were not dinosaurs.
- Dinosaurs had a hole in their skull just between their eye socket and nostrils. They share this feature with all archosaurs (pterosaurs and crocodilians), so it’s not a perfect diagnostic feature.
- They had two holes behind their eye socket, which served as articulation points for strong jaw muscles. This allowed their jaws to open wide and clamp down with considerable force.
Categorizing Dinosaurs
When Owen coined the name “dinosauria” in the 19th Century, only a handful of dinosaurs were in the clade, known from a few incomplete specimens.
As more dinosaurs were discovered, there was a need to put each of them into greater context.
Categorizing these dinosaurs became necessary to show how they were all related to each other and their relationship with their common ancestors.
The most basic subdivision of dinosaurs is based on their anatomical peculiarities.
Most notably, the hip structure of the dinosaurs determined how they were placed within the two main groups (Saurischia and Ornithischia).
This classification also helped to differentiate them from other groups of reptiles that lived during the Mesozoic.
Over time, the major subdivisions were further classified into suborders, families, and genera based on their size, diet, and unique physical features.
For instance, the ceratopsians were known for their elaborate frills and horns, while the sauropods were popular for their massive size and long necks and tails.
Types of Dinosaurs
The world of the dinosaurs was a very diverse one.
Today, we classify them into different types based on a combination of their physical characteristics, size, habitats, and other features.
Here’s an overview of the different types of dinosaurs that existed in prehistoric times.
Saurischia and Ornithischia
The most basic way dinosaurs are subdivided is based on their hip structure.
This is an interesting but slightly controversial approach to classifying dinosaurs, but one that still stands as the primary basis for grouping them.
Historically, all dinosaurs are either classified as saurischians or ornithischians.
Their classification into either of these two groups is based on the structure of their hip bones.
Saurischians are also known as “lizard-hipped” dinosaurs because the two lower bones that form their hips (pubis and ischium) tend to point away from each other, as is the case in modern lizards.
In saurischian dinosaurs, the pubis point towards the front of their body while the ischium points towards the back.
Ornithischians, on the other hand, are called “bird-hipped” dinosaurs because the two lower bones of their hips (pubis and ischium) point backward towards the animal’s tail and in the same direction as that of modern birds.
Each of these groups is further subdivided based on other unique features.
The saurischian group includes theropods and sauropods, while ornithopods, ceratopsians, and ankylosaurs are all ornithischian dinosaurs.
Saurischians and ornithischians evolved from the same common ancestors during the Triassic Period but branched off from each other about 230 million years ago.
Saurischians likely evolved first since the earliest known ornithischian dinosaur (Pisanosaurus mertii) is dated several million years after the earliest known saurischian (Eoraptor).
This classification gets a little confusing when you add modern birds into the mix.
Although ornithischian dinosaurs are referred to as bird-hipped dinosaurs because their hips are similar to that of birds, birds themselves are more related to saurischians than to ornithischians.
The similarities between the hip structure of birds and ornithischians are merely a case of convergent evolution, with both animals developing this structure independently.
This explains why some saurischians (including birds themselves) have ornithischian-like hips.
So while the key to understanding the differences between dinosaurs is the hips, you must be careful not to get misled by the labels.
Theropods
The theropods are a diverse group of saurischian dinosaurs most famous for their carnivorous diet.
The group includes some of the most famous predator dinosaurs we know today, including the T. rex, Velociraptor, and Allosaurus.
There’s evidence that some theropods may have been omnivorous, but most were carnivores.
All theropods had hollow bones, which made them lightweight and agile.
This adaptation was necessary for an animal that survived by chasing down prey.
Their hollow bones had air sacs to fill the empty space and also helped with respiration.
This type of skeletal structure is seen in modern birds too.
This is normal since they’re considered descendants of theropod dinosaurs.
Another notable trait of theropod dinosaurs is their three-toed feet with sharp claws.
Theropods evolved during the Triassic Period.
The earliest forms, such as the Coelophysis, were small, with long slender bodies.
But the group grew into bigger sizes over the course of the Mesozoic Era, reaching their largest size during the Late Jurassic and Early Cretaceous.
The theropod group branched into different sub-lineages along the line. Some of the most notable ones include:
- Ceratosauria e.g., Carnotaurus
- Tetanurae e.g., megalosaurs & allosaurs.
- Coelurosauria e.g., tyrannosaurs, Compsognathus, ornithomimosaurs and maniraptorians.
Sauropods
Sauropods are massive herbivorous dinosaurs known for their colossal size, small head, long neck, and sturdy pillar-like legs.
The group evolved to include some of the largest animals to have ever walked the planet.
The ancestors of the sauropods (also known as prosauropods) were small, bipedal animals.
They evolved during the Late Triassic and reached their peak diversity by the Middle Jurassic Period.
Sauropods became larger and larger throughout their evolution.
They also switched from their initial bipedal posture to full quadrupeds to support their weight.
The sauropods split into two main groups during the Jurassic Period.
The first group, known as the macronarians, had boxy skulls with broad almond-shaped teeth.
The second group, the diplodocoids, is characterized by pencil-like teeth and extremely long bodies.
Some of the most notable members of this group include the Diplodocus, Apatosaurus, and Brontosaurus (some of the longest-known terrestrial animals)
Sauropods began to decline in population and diversity as the Jurassic Period closed.
By the Middle Cretaceous, most sauropod groups went extinct.
Only one group of macronarians (the titanosaurs) persisted.
They’re known for their large, stocky bodies and were among the heaviest animals to have ever lived.
Some of the largest members of this group, such as the Patagotitan, Argentinosaurus, and Puertasaurus, lived in South America.
Ornithopods
Ornithopods are a unique group of ornithischian dinosaurs named after their bird-like, three-toed feet.
Again, it is worth noting that birds descended from theropod dinosaurs and not from ornithischians like the ornithopods.
Ornithopods were small to medium-sized herbivorous dinosaurs.
What made them so unique was their dental battery, which was quite advanced for their time.
Their dentition is similar to that of modern cows or horses and was very effective for breaking down tough plant materials.
Ornithopods first evolved as small bipedal dinosaurs but grew bigger throughout the Jurassic and Cretaceous periods.
The largest ornithopods emerged during the Middle Cretaceous Period.
Some of them, like the Iguanodon, grew to lengths of over 30 feet and were quadrupedal.
But arguably, the more popular ornithopods were the hadrosaurs or duck-billed dinosaurs.
They’re known for their mouths which were modified into broad bills similar to that of ducks.
Some hadrosaurs, such as the Parasaurolophus, had long hollow crests on their heads, while some, like the Maiasaura, had solid crests or no crest at all.
Ceratopsians
Ceratopsians are probably more accurately described as parrot-beaked dinosaurs due to the extra beak bone in their upper jaw.
However, the group is more popular for its head ornaments.
The more popular ceratopsians had elaborate neck frills and prominent horns.
But some of them, especially the earliest members of this group, like the Psittacosaurus and Protoceratops, did not have horns at all.
Some notable members of this group include the famous Triceratops, Pentaceratops, and Chasmosaurus.
The oldest ceratopsians evolved about 140 million years ago at the beginning of the Cretaceous Period.
The “beak” and rows of grinding teeth in their cheeks suggest that the ceratopsians were probably herbivores.
The purpose of the elaborate frills and horns of this group of dinosaurs is still being debated, but likely uses include defense, species recognition, or mating display.
The broad ceratopsian family is further split into two subfamilies based on the size of their frills and horns.
The group with the larger trapezoidal frills and prominent brow horns is known as the chasmosaur.
Notable members of this group include the Chasmosaurus itself and the Triceratops.
The other group, the centrosaurs, are known for their larger nasal horns or bulbous bony growths.
They also had large spikes on their frills.
Styracosaurus is one of the most notable centrosaurid ceratopsians.
Stegosaurs & Ankylosaurs
Together, these two ornithischian dinosaurs are classified in the Thyreophora subgroup.
The name, which means “shield bearers,” refers to the prominent body armament of these two dinosaur groups.
The body armor of the stegosaurs and ankylosaurs was made up of bony buildups covering their skin or protruding out of their body.
Stegosaurs were among the most common ornithischians during the Jurassic Period.
They had rows of large spikes or spike-like plates running along their back.
They also had defensive tail spikes known as thagomizers.
The arrangement of these dorsal plates and tail spikes varied from one member of this group to the other.
Some of the most notable stegosaurs include the Stegosaurus, Kentrosaurus, and Miragaia.
The population of stegosaurs began to dwindle during the Early Cretaceous, and they eventually went extinct by the end of the period.
Like stegosaurs, ankylosaurs were armored as well.
They were heavily armored dinosaurs with a tank-like build that was very common during the Cretaceous Period.
Ankylosaurs had bony armor on their sides and upper surface.
Some of them also had bony tail clubs, which they probably used as defensive weapons against predators.
Pterosaurs
Pterosaurs are often referred to as flying dinosaurs.
This is a misnomer since they’re a distinct group of reptiles not directly related to dinosaurs.
Pterosaurs lived alongside the dinosaurs throughout the Mesozoic Era and were very successful and diverse too.
The earliest pterosaurs evolved during the Triassic Period about 215 million years ago.
The primitive pterosaurs were relatively small, with slim bodies and long tails.
Pterosaurs were the first group of animals (after insects) to develop the ability to fly.
And they didn’t just glide from tree to tree like some flying mammals do today.
They were quite capable of powered flight and could generate lift by flapping their wings.
Later in the Jurassic and Cretaceous, pterosaurs evolved into diverse forms and body sizes.
Some of them were as small as birds, while some, like the Quetzalcoatlus, were as big as an F-16 fighter jet.
Different groups of pterosaurs developed long, slender jaws, elaborate head crests, specialized teeth, and other unique adaptations based on their habit and habitats.
Evolution and Diversity
The Mesozoic Era is often referred to as the age of dinosaurs.
The existence of the dinosaurs spanned the three periods of this era.
During the Mesozoic Era, dinosaurs were the most dominant animal on the terrestrial landscape both in their number and diversity.
The story of dinosaur evolution began with a devastating event roughly 250 million years ago.
The Permian–Triassic extinction event completely wiped out up to 70% of terrestrial, leaving many ecological niches vacant.
The ancestors of the dinosaurs were among the survivors of that event.
They were relatively small archosaurs considered the common ancestors of dinosaurs, pterosaurs, and crocodiles.
Dinosaurs diverged from this group between 245 and 230 million years ago.
The oldest dinosaur was probably the 245-year-old Nyassaurus.
But the fragmented nature of their fossils makes it difficult to conclusively identify them as dinosaurs.
Instead, the saurischian Eoraptor is officially recognized as the oldest dinosaur.
For many years after their initial evolution, dinosaurs remained small and relatively insignificant.
It took another extinction event during the Triassic (a smaller one this time) to eventually boost them into prominence.
The extinction killed off several other early archosaurs, allowing the dinosaurs to become the most dominant group in various ecological niches.
They evolved rapidly after that and diversified quickly during the Jurassic.
The evolution of the early herbivorous dinosaurs can be linked to the rapid radiation of the Earth’s flora during the Late Triassic and Early Jurassic periods.
Conifers and other gymnosperm plants became quite common during the Late Triassic Period, serving as an important food source for the sauropodomorph dinosaurs.
Members of this group lacked a developed dentition.
This means the digestion of the tough plant materials they consumed had to take place further down their digestive tract.
Consequently, they developed a long digestive tract and larger size to accommodate it.
Small coelophysoids and other carnivores were present during this period as well, and as the herbivores grew, the predator species became bigger too.
More theropods, including the ceratosaurians, megalosaurids, and allosaurids, emerged during the Middle to Late Jurassic Period.
Primitive sauropodomorphs also gave way to more derived sauropods and other herbivores, such as the ankylosaurs and ornithopods.
The carnivorous and herbivorous dinosaur species were soon locked in a predator-prey arms race.
The carnivores got bigger and stronger while the prey species developed sophisticated armory and other defense mechanisms.
Herbivores also developed mechanisms to process food better as the Earth’s flora continued to change.
These include cheek-like features, dental batteries, and sophisticated jaw motions for grinding food effectively.
The early dinosaurs lived together on the supercontinent Pangea.
This would eventually break up during the Cretaceous Period, allowing the distribution of dinosaurs into various land masses with new ecosystems.
This further allowed the diversification of dinosaurs as the prehistoric reptiles developed adaptations specific to their new habitats.
Major changes in Earth’s flora during the Early Jurassic further contributed to the diversification of the herbivorous dinosaurs.
Flowering plants became more common, and the emerging dinosaur groups of this period, such as the ceratopsians and hadrosaurids, developed new ways of slicing plants with their teeth and grinding them with dental batteries.
The most advanced of these were the hadrosaurids, with their stacked teeth that formed extremely efficient dental batteries.
Notable Dinosaurs from Each Group
Within the different groups of dinosaurs, some genera or species stand out among others.
Their popularity may be due to their representation in pop culture, scientific significance, individual uniqueness, or the circumstances of their discovery.
Some of the notable dinosaurs in each of the groups highlighted above include:
Tyrannosaurus rex
Popularly known as the T. rex, this dinosaur is one of the most recognizable dinosaurs.
The dinosaur was popularized by its representation as the main antagonist in the famous Jurassic Park movies.
T. rex was one of the largest land predators to have ever lived, with a massive head and powerful jaws filled with large serrated teeth.
Like many other theropod dinosaurs, the T. rex was bipedal.
The front legs of this dinosaur are particularly reduced. The purpose of this short arm is still subject to controversy.
Velociraptor
The Velociraptor is another well-known dinosaur, thanks to pop culture references.
In real life, the Velociraptor was a small, agile predator.
The most notable feature of this dinosaur is the long sickle-shaped claw on its second toes.
Velociraptor is one of the most misunderstood dinosaurs because its representation in the movies (especially in Jurassic Park) is inaccurate.
For instance, instead of a scaly reptile, the real-life Velociraptor had feathers on its body.
Brachiosaurus
In the sauropod group, Brachiosaurus was one of the biggest and most popular.
It had a massive long neck and a long muscular tail.
Brachiosaurus grew to an average length of eight and 22 meters (59–72 feet) and weighed up to 46.9 tons.
The long neck of this sauropod dinosaur allowed it to reach vegetation beyond the reach of other dinosaurs.
Hadrosaurus
The Hadrosaurus is one of the most popular members of the ornithopod group.
They are also known as duck-billed dinosaurs due to their unique dental adaptation, which was effective for cropping and grinding plant materials.
Hadrosaurus also had a large, hollow crest on its skull that may have been used for vocalizations.
Triceratops
The Triceratops’ name translates as “three-horned face,” and it refers to the number of large horns that this dinosaur had.
Triceratops belongs to the ceratopsian group, which includes other frilled and horned dinosaurs.
The three horns of the Triceratops were likely used for defense and mating display.
Ankylosaurus
The entire ankylosaur group is named after the Ankylosaurus.
It was the most popular and possibly the largest member of this group.
Ankylosaurus was a heavily armored dinosaur with a tank-like build.
This dinosaur also had a bony club at the end of its tail which was used for defense against predators.
Extinction and Legacy
As the Cretaceous Period drew to a close, the population and diversity of dinosaurs began to decline.
Experts have postulated that this decline was due to changes in the Earth’s climate towards the end of the Cretaceous.
This led to the collapse of the terrestrial ecosystem and the disappearance of various dinosaur species.
A final catastrophic event eventually knocked the dinosaurs out at the end of the Cretaceous.
A massive asteroid impact 66 million years ago has been blamed for the total annihilation of the already struggling dinosaur population.
The event wiped out 75% of terrestrial life, including all non-avian dinosaurs and pterosaurs.
A group of dinosaurs did survive this devastating event.
They were the avian dinosaurs (birds).
This group evolved during the Jurassic Period and eventually gave rise to new species during the Paleogene Period.
Today, birds are one of the most diverse and widespread groups of animals on Earth, with over 10,000 species occupying a wide range of habitats.
They display incredible adaptations such as specialized beaks, complex vocalizations, and unique mating displays.
Feathers, which were present in many dinosaur groups for insulation and display, eventually evolved into mechanisms for flight in modern birds.
This ability to flap and glide helped them explore new ecological niches and increased their geographical range as well.
Fossil Discoveries and Advances in Research
Most of what we know about the physical attributes of dinosaurs and their behavior is based on fossil evidence.
Although the fossil record still has some gaps, and many of the dinosaurs found so far are still fragmentary, some significant fossil discoveries made over the years have provided insights into the anatomy, behavior, and unique ecology of different dinosaur groups.
Some of the most significant discoveries made over the years include:
The First Dinosaur Fossil Ever Described
Megalosaurus holds the title of the first dinosaur fossil to be described scientifically.
Prior to the discovery of this dinosaur in 1819, many bones that probably belonged to dinosaurs had been discovered.
Ancient humans most likely uncovered dinosaur fossils from time to time but labeled them as some sort of mythical creature or the other.
The official description of the Megalosaurus in 1824 was the first scientific acknowledgment of these creatures, and it sparked the next era of scientific inquiry into their existence.
Sue the T-Rex and Other Tyrannosaurus Fossils
The T. rex isn’t just the most well-known dinosaur to the general public but also one of the best-known dinosaurs to scientists.
Various fossils of this dinosaur, including some nearly complete specimens, have provided a detailed look at the anatomy and predatory behavior of one of the largest terrestrial predators to have ever lived.
This dinosaur stands as an iconic representation of the theropod group and their prolific predatory lifestyle.
Velociraptor and Protoceratops Fossil Pair
In the 1970s, a remarkable discovery in Mongolia depicted a Velociraptor engaged in a life-and-death struggle with a Protoceratops.
This “fighting dinosaurs” fossil offered direct evidence of predator-prey interactions in the savage world of the dinosaurs.
Deinonychus Fossils
Fossils of Deinonychus, a close relative of Velociraptor, have helped to solidify the link between dinosaurs and birds.
The discovery of this small, agile predator with evidence of feathers, hollow bones, and a sickle-shaped claw on its foot supported the idea of theropod dinosaurs as the ancestors of birds.
Maiasaura Nests
Also known as the good mother lizard, the discovery of Maiasaura provided evidence of parental care and herding behavior in hadrosaur dinosaurs.
These nests contained fossilized remains of juvenile dinosaurs, suggesting that these dinosaurs cared for their young after hatching.
Archaeopteryx
Discovered in the 1860s, Archaeopteryx is often referred to as the “first bird” due to its mix of bird-like and reptilian features.
This fossil helped bridge the gap between dinosaurs and modern birds, providing evidence for the evolution of flight and the presence of feathers in theropod dinosaurs.
Dinosaur Tracks and Trackways
Numerous fossilized footprints of various dinosaurs discovered in various locations all over the world have revealed information about dinosaur anatomy, locomotion, and social behavior.
Trackways provide clues about how dinosaurs moved and interacted with their environments and each other.
Pop Culture Influence
Long before they were officially identified as dinosaurs, ancient humans likely discovered and interacted with dinosaur fossils.
Various mythical animals, such as “dragons,” may have been inspired by the fossil remains of these incredible animals.
The official recognition of dinosaur fossils in the early 19th century sparked widespread fascination and curiosity about these incredible reptiles, kickstarting an era of scientific and public interest.
As scientific research into the evolution and diversity of dinosaurs intensified in the 20th century, these creatures began to make appearances in literature, movies, art, and various forms of entertainment materials.
The Lost World, a novel by Sir Arthur Conan Doyle, which was published in 1912, helped introduce the idea of dinosaurs to the general public.
The novel was based on the idea of isolated dinosaur populations surviving in remote areas.
The popularity of this novel inspired many subsequent stories and films.
Twentieth-century artists like Charles R. Knight and Zdeněk Burian created vivid and imaginative illustrations of dinosaurs.
Their work helped to bring these ancient creatures to life in the public’s imagination and made them more recognizable.
In 1993, the first Jurassic Park movie directed by Steven Spielberg was released.
The movie, which was based on a popular novel of the same title, showcased dinosaurs with cutting-edge visual effects, making them more relatable to the general public.
This marked a turning point in cinematic depictions of dinosaurs and public knowledge of the diversity that existed in the prehistoric world of dinosaurs.
The “Jurassic Park” franchise, as well as other dinosaur-themed films and TV shows, have kept the excitement alive, making people even more intrigued with these incredible creatures.
Dinosaurs are also popular subjects in children’s books, cartoons, educational programs, video games, and toys.
All of these contribute to public fascination and general knowledge of these prehistoric creatures.
Conclusion
Despite going extinct over 66 million years ago, dinosaurs remain some of the most fascinating creatures to have ever lived.
Their existence spanned the entire Mesozoic Era, during which they evolved into different forms and sizes.
These fascinating creatures are generally classified as Saurischia and Ornithischia based on their hip bone structure.
These two broad groups are further divided into various suborders, genera, and species based on their anatomy, ecological role, diet, and other attributes.
Learning about these different types of dinosaurs is crucial for understanding Earth’s past, the evolution of the dinosaurs, and the intricate interactions between these dinosaur groups that shaped the ancient ecosystems where they lived.
Sources
- https://www.nhm.ac.uk/discover/what-are-dinosaurs.html
- https://en.wikipedia.org/wiki/Dinosaur
- https://www.britannica.com/animal/dinosaur/
- https://opengeology.org/historicalgeology/case-studies/dinosaur-classification/#Ankylosaurs
- https://www.nps.gov/subjects/fossils/major-groups-of-dinosaurs.htm
- https://ucmp.berkeley.edu/diapsids/dinomm.html#
- https://ucmp.berkeley.edu/diapsids/saurischia/saurischia.html
- https://www.smithsonianmag.com/science-nature/dinosaur-division-is-all-in-the-hips-20477310/
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