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Major Groups of Dinosaurs

Dinosaurs (leaving out the birds) developed into many distinct corporations over their roughly one hundred seventy million 12 months existence, from about 235 million years in the past to sixty six million years ago. The first actual dinosaur used to be probably a small, bipedal animal of carnivorous or omnivorous diet, comparable to Eoraptor from Argentina. The earliest real dinosaur fossils date to the early section of the Late Triassic, however it is very unlikely that we have determined the true very first dinosaurs, and the crew possibly originated in the Middle Triassic or Early Triassic.


Historically, dinosaurs have been divided into saurischians (“lizard-hipped”) and ornithischians (“bird-hipped”), primarily based on the association of their hip bones. In saurischians, the two decrease bones of the hip factor away from each other, as in lizards; and in ornithischians, the two decrease hip bones each factor backwards, as in birds. (Ironically, birds with the aid of ancestry are saurischians as a substitute than ornithischians—their evolution of proper “bird hips” came about after the saurischian–ornithischian split.)

The saurischians are divided into theropods and sauropodomorphs. Theropods are the traditional bipedal carnivorous dinosaurs, from Coelophysis to Tyrannosaurus, and additionally encompass birds. Sauropodomorphs consist of the huge quadrupedal, herbivorous long-necked, long-tailed sauropods (Brachiosaurus, Diplodocus) and their cousins the “prosauropods”. Finally, the ornithischians are tougher to outline due to the fact they consist of quite a few very special groups, however all ornithischians share a different “beak bone” (the predentary) at the tip of the decreased jaw.


Theropods started out as small hunters alongside the traces of Coelophysis, with long, narrow bodies. Some of them advanced into giant species early on, and one of these early companies sooner or later produced the abelisaurus, the important theropods of Southern Hemisphere continents in the Cretaceous. The horned Ceratosaurus is a relative of these theropods. Another lineage, the carnosaurs, had been the fundamental theropods of the Late Jurassic and Early Cretaceous.

Allosaurus. Carnosaurs grew to be an awful lot rarer in the Late Cretaceous after producing giants like Carcharodontosaurus and Giganotosaurus. The uncommon spinosaurus, additionally outstanding in the center phase of the Cretaceous, are a section of a team that break up after the ceratosaurus however earlier than the carnosaurs.


At the identical time the carnosaurs have been the foremost giant theropods, any other group, the coelurosaurs, was once diversifying as a great deal smaller theropods. Jurassic coelurosaurs are no longer recognized properly due to the fact of their small dimension and thin-walled hole bones, however we understand that they divided into countless lineages at some stage in the Jurassic that similarly cut up and rose to prominence in the course of the Cretaceous:

  • Alvarezsauridae: Small, gently constructed theropods with arms and hands decreased to single giant claws. (For reference, “small” is much less than about 10 toes long, “medium” is much less than about 20 toes long, and “large” is extra than 20 toes long.)
  • Avialae: Birds and their closest relatives.
  • Deinonychosauria: Small to medium-sized theropods with “killer claws” on the 2d toe. Early deinonychosaurs and early avialans are frequently hard to distinguish.
  • Ornithomimosauria: “Ostrich mimics”, frequently toothless and probable especially herbivorous to omnivorous, typically small to medium-sized.
  • Oviraptorosauria: Generally small to medium-sized theropods with numerous head shapes (usually toothless and frequently crested) and hands, likely filling a range of niches.
  • Therizinosauria: Something like dinosaurian sloths with lengthy tails and lengthy necks with small heads, these are thought to have been herbivores, typically medium to large.
  • Tyrannosauroidea: this team consists of the tyrannosaurids and their shut cousins, some of which lived in the American West as small predators at the same time as Allosaurus. Of course, they are most well-known for Tyrannosaurus rex.


Sauropodomorphs started as small bipedal omnivores or carnivores, however quickly shifted to herbivory and started evolving giant physique sizes. The general Plateosaurus, for example, should attain extra than 30 toes lengthy and 4 tons, properly earlier than the stop of the Triassic. These Triassic “prosauropods” already had the common sauropodomorph lengthy neck with small head, lengthy tail, and cumbersome body, however few of them may want to stroll on all 4 feet.

The first real sauropods had this ability, which must have helped later sauropods achieve such massive sizes (it’s a lot simpler to be seventy five toes lengthy and 20 lots when all of your feet are on the ground!).

The first organizations of sauropods tended to have almond-shaped enamel and boxy heads, and some had tremendously lengthy necks. Sauropods break up into two major agencies in the course of the Jurassic. One group, the macronarians, stored the broader teeth, at least for a while. Famous Jurassic macronutrients consist of Brachiosaurus and Camarasaurus.

The different group, the diplodocids, advanced pencil-like teeth and long, low bodies. Famous diplodocids encompass Apatosaurus, Brontosaurus, and Diplodocus.

Sauropods appear to have been decreased going into the Early Cretaceous. Most organizations went extinct by using the center of the Cretaceous, to be changed by using a crew of macronarians regarded as the titanosaurs.

The titanosaurs developed stocky large bodies and pencil-like teeth, and most species had one or greater bony lumps perhaps for mineral storage. Titanosaurs unfold to all of the continents earlier than the stop of the Cretaceous. It looks like something came about in North America, though, due to the fact sauropod fossils are lacking for most of the Late Cretaceous till the look of the titanosaur Alamosaurus in the southwestern United States close to the stop of the duration (see Big Bend National Park).


The beginnings of the 1/3 and ultimate foremost team of dinosaurs, the ornithischians, are poorly known. Some scientists suppose that a Triassic team regarded as Silesauridae (quadrupedal beaked animals) are certainly early ornithischians alternatively of dinosaur cousins, however this is controversial. The ornithischians cut up into numerous very wonderful organizations throughout the Jurassic.

Most of these grew to become distinguished all through the Cretaceous. Most ornithischians can be positioned in one of 5 groups: Ankylosauria (armored dinosaurs), Ceratopsia (horned dinosaurs), Ornithopoda, Pachycephalosauria (bone-headed dinosaurs), and Stegosauria (plated dinosaurs).

  • Ankylosaurus had squat quadrupeds with portions of bony armor (osteoderms) masking their top surfaces and sections of their sides. Some of these osteoderms had been enlarged into plates or spikes. One subgroup of ankylosaurs, the ankylosaurids, had ponytail clubs.


  • Ceratopsians are recognised as horned dinosaurs, however many early varieties did not now have horns (such as Psittacosaurus and Protoceratops). All ceratopsians had a greater beak bone (the rostral) at the the front of the higher jaw, though, giving them parrot-like beaks. Ceratopsians flourished in the Late Cretaceous, evolving into sizable animals such as Triceratops with extensive bony frills, lengthy forehead horns, and effective shearing jaws.


  • Ornithopods commenced as small bipedal herbivorous dinosaurs, however some soon commenced to develop a great deal larger, such as Camptosaurus. By the center of the Cretaceous, the biggest ornithopods, such as Iguanodon, had been extra than 30 toes lengthy and switched between two legs and 4 legs. During the Late Cretaceous one department developed into the hadrosaurs, the well-known “duck-billed dinosaurs”. Hadrosaurs sincerely weren’t very comparable to geese besides for some having huge bills; they have been land animals and had effective preparations of lots of stacked teeth. Many had complicated crests.


  • Pachycephalosaurus are the least regarded of the 5 groups. (In fact, we’ve in no way observed a pachycephalosaur's hand.) They appear to have been small to medium-sized herbivorous bipeds, and are pleasantly recognized from the Late Cretaceous of Asia and North America. They are most well-known for their thickened skulls, regularly exaggerated into a dome shape, now and again with bony nodes and spikes.


  • Stegosaurus had been amongst the first ornithischians to unfold widely, spreading at some point of the Jurassic. Stegosaurus is known for its giant bony plates, however most stegosaurus had spikes or spike-like plates as a substitute than massive plates alongside their backs. Stegosaurus additionally had pairs of spikes at the ends of their tails. Stegosaurus diminished in the Cretaceous and showed up to have long gone extinct earlier than the cease of the period.



We have a frequent image of the closest family to dinosaurs. The closest most important team to dinosaurs seems to be the flying pterosaurs. In a wider sense, dinosaurs belong to a crew referred to as Archosauria. Archosaurs, the “ruling reptiles'', are these days represented via crocodilians and birds.

Therefore, when paleontologists prefer to assume about components of dinosaurs that didn’t fossilize, like conduct and smooth tissues, they can reflect on consideration on birds, which are residing dinosaurs, and crocodilians, which are their next-closest relatives. The only hassle is that many dinosaurs in all likelihood had existence and anatomies that have been nothing like both current crocodiles or birds, however these comparisons can at least slim down the possibilities.