We will take a 65 million year trip back in time and introduce the main types of dinosaurs discovered so far: terrestrial, flying, or aquatic dinosaurs, together with their names and main characteristics.
Before we dive into the fascinating world of dinosaur classification, we need to make a small stop and discuss the cornerstone of all saurian taxonomy. According to paleontology theory, dinosaurs are grouped into two main divisions depending on the differences in their pelvic morphology.
Saurischia is one of the two primary divisions of dinosaurs which have been called "lizard-hipped" because of their pelvic structure in which the hip bones point forward. The dinosaurs pertaining to this category were both large and small carnivores as well as herbivores of all sizes.
Dinosaurs which have hip bones similar to what we see in birds nowadays are classified as being a part of the Ornithischia clade. It does need clarifying, however, that birds did not evolve from bird-hip dinosaurs but lizard-hip ones, which were bipedal feathered dinosaurs.
The etymology behind the two names ("bird-hipped" vs. "lizard-hipped") is somewhat confusing, since some saurischians had bird-like hips, and ornithischians' hips were somewhat birdlike due to convergent evolution, not due to shared ancestry.
Ornithischians were herbivorous dinosaurs (they far outnumbered the Saurischians) with strong molars apt for grinding fern leaves. Ornithischians lived in herds which protected them from predator attacks.
This division of dinosaurs included four-legged giants but also smaller, bipedal species.
As part of the two big categories of dinosaurs, we will look at terrestrial specimens which are classified into different families, depending on the characteristics of each one.
Sauropods are the largest animals to ever roam the Earth and part of the Saurischia clade, also known as long neck dinosaurs because of their impressive neck length and relatively small size of their head. Some species also had a long tail which was used as a whip in case of attacks.
Sauropods were known to herd together and protect themselves of predators.
Probably one of the best-known dinosaurs due to its feature in the saga Jurassic World. This great genus of sauropod measured 23 meters in length and between 10 and 15 meters in height.
The Apatosaurus was another gargantuan long neck dinosaur which reached lengths of 25 meters although its height didn't surpass 5 meters. The main difference between the Apatosaurus and the Brachiosaurus is that the former couldn't straighten its neck and instead, kept it leveled with its tail and back.
Among the best-known sauropods, also called Brontosaurus, the Diplodocus is another dinosaur name that makes us think back to our childhood years. A strange fact about this dinosaur is that to better digest the food it ate, the giant creature also ingested stones to help grind the leaves in its stomach.
Another species of Diplodocus was discovered, Diplodocus hallorum, which may have been up to 52 meters long- compared to the Diplodocus carnegii which only measured 25-27 meters.
Theropods (meaning "beast feet") are a dinosaur suborder characterized by hollow bones and three-toed limbs. Their forelimbs evolved into short claws while their hind legs became stronger and more agile, fit for chasing their prey.
Theropods exhibit a wide range of diets, from insectivores to herbivores and carnivores. Solitary hunters, theropods would often work together in smaller groups to defeat a bigger dinosaur.
Despite his towering stature, 14 meters long and 6 meters tall, the T-Rex wasn't the biggest carnivore of them all, but it did have the most dangerous bite, due to exceptionally powerful mandibular muscles characteristic of raptor dinosaurs.
A lighter version of the T-Rex but with functional claws that it used for grabbing prey, the Allosaurus (meaning "different lizard") measured 12 meters in length and 3 in height. This theropod had a longer neck than the T-Rex and displayed a pair of horns above and in front of the eyes, which could have been used as sunshades for the eyes, mating purposes, or for combating other dinosaurs.
The largest carnivorous dinosaur to walk the Earth, the Spinosaurus (15 meters long) possessed distinctive spines on his back which were probably used for thermoregulation and display. The Spinosaurus was piscivore as indicated by its elongated jaws, conical teeth, and raised nostrils.
Contrary to what we see in Jurassic Park III, the Spinosaurus spent more time in the water than on land (some have called it a water dinosaur due to this) and it used all four legs to walk, so it rarely stood up.
Belonging to the Ornithischian clade, Thyreophora is a group of armored dinosaurs (also known as "shield bearers" ) which contains three separate subclassifications of terrestrial dinosaurs: scelidosaurus, stegosauridae, and ankylosaurus. The last two dinosaurs on this list represent subspecies that evolved from bipedal ancestors, but because of their impressive armors they were forced to adopt a quadruped stance.
The most representative dinosaurs of this order, the Stegosaurus used his spiked tail as a weapon against attackers and had an unusual feature that sets it apart among other creatures of its kind. Experts believe that the Stegosaurus had one of the tiniest dinosaur brains compared to his 3-ton stature: its small brain was only the size of a walnut.
This 10-meter tank was heavily armored and covered in bony osteoderms which protected from predator attacks. The Ankylosaurus was also endowed with a large club-like protrusion at the end of its tail.
This dinosaur was very similar to the Ankylosaurus, but it was smaller in size (6 meters long).
Ornithopods are a group of ornithischian dinosaurs, and the smallest of them were Hypsilophodontidae and Heterodontidae, which received their names due to their teeth. They were small, bipedal running grazers with large eyes, apt for surveying the surrounding areas.
From the smallest ornithopods, we witnessed the evolution of a much bigger clade of dinosaurs, the iguanodonts, which developmentally speaking, were placed between the former category and the next one.
A giant herbivore dinosaur that measured up to 10 meters, the Iguanodon could shift from bipedality to quadrupedality and used its claws for protection against attacks.
Another category of Ornithopods was Hadrosaurids or duck-billed dinosaurs such as:
Measuring 10 meters in length, the Parasaurolophus had a distinctive crest, much like the Corythosaurus that got its name because its crest has the same shape as helmets worn by Corinthian soldiers and the Lambeosaurus that also had a distinctive hatchet-shaped crest.
Cerapoda is divided into two groups: Ornithopoda ("bird-foot") and Marginocephalia ("fringed heads"). The latter group includes the Pachycephalosauria ("thick-headed lizards") and Ceratopsia ("horned faces").
Ceratopsians are easily recognized by features of the skull. On the tip of a ceratopsian's upper jaw is the rostral bone, a toothless bonemass, unique to ceratopsians, which forms a superficially parrot-like beak.
Triceratops, which means "three-horned face," was a 9-meter long ceratopsid. Other related dinosaurs are Pentaceratops, Torosaurus, or the Chasmosaurus, each with an individual bony frill and horns.
Pachycephalosauria ("thick-headed lizards"), as mentioned previously, along with Ceratopsia makes up the clade Marginocephalia. They were herbivorous bipedal dinosaurs, and genera include the Pachycephalosaurus and the Stygimoloch.
Reaching 8 meters in length and 3 in height, the Pachycephalosaurus would attack by lowering its head and charging at full speed.
The Stygimoloch was 3 meters long and only 1 meter tall. One of its most notable features was its domed skull, and unlike other dinosaurs in its family, the Stygimoloch had short, conical horns that covered its nose. The back corners of the skull bore an enormous pair of massive, backward-pointing spikes which were used for display.
Dinosaurs not only roamed the Earth but were also said to be masters of the sky. Which begs the question: "Are birds dinosaurs?"
Pterosaurs are often referred to in the popular media and by the general public as "flying dinosaurs," but this is scientifically incorrect. The term "dinosaur" is restricted to just those reptiles descended from the last common ancestor of the groups Saurischia and Ornithischia.
Pterosaurs were part of the family of hollow-boned vertebrates that evolved powered flight. Their wings were formed by a membrane of skin and muscle stretching from the ankles to a dramatically elongated fourth finger. Their diet consisted of fish although they were known to snatch prey in mid-flight.
Aside from a distinctive head crest, the Pteranodon sported a 7-meter wingspan, its beak was long and ended in a thin, sharp point, suited for fishing.
A small pterosaur, the Dimorphodon had a 2-meter wingspan, a 1-meter long body and unlike its other winged brothers and sisters, it had teeth.
One of the biggest flying reptiles that ever existed was the Ornithocheirus. Due to its impressive size: wingspan of 12 meters and a body length of almost 5 meters, this winged creature is believed never to have flown.
Similarly to the case of the "flying dinosaurs," it would be scientifically incorrect to call these marine reptiles anything but that - marine reptiles.
Plesiosaurus was a type of large aquatic reptile, distinguishable by its small head, long and slender neck, broad turtle-like body, a short tail, and two pairs of large, elongated paddles.
The most iconic dinosaur in the family, the Elasmosaurus measured up to 6 meters long. A fun fact about this dinosaur is that scientists believe it to be related to “Nessie,” the infamous Loch Ness monster.
Ichthyosaurs resembled both modern fish and dolphins, but unlike them, the ancient reptile needed to surface to breathe and gave birth to live young.
Named for its huge eyes, the Ophthalmosaurus had a smooth 6-meter long dolphin-shaped body, and its almost toothless jaw was well adapted for catching squid. It had a tail similar to that of a shark which it used to propel its body in the water.
The biggest known swimming reptile and one of the most distinctive regarding its appearance, Pilosaurs had short necks and powerful jaws with sharp, conical teeth.
Apex predator of the seas during the Jurassic Period, the Liopleurodon was a giant carnivorous aquatic reptile. It had a large head compared to the rest of its body and powerful jaws to catch prey.