Archosaurs are a clade of diapsid sauropsid tetrapods, with birds and crocodilians being the only known extant representatives. Modern paleontologists define Archosauria as a crown group that includes the most recent common ancestor of living birds and crocodilians, and all of its descendants.

Dinosaurs include both avian and non-avian types, leading to questions about their classification. In essence, dinosaurs can be viewed as both reptiles and birds. The Dinosauria group, which encompasses both avian and non-avian dinosaurs along with birds, forms part of the broader reptilian family tree. Hence, it can be concluded that dinosaurs are indeed classified as reptiles.

The present scientific consensus is that birds are a group of maniraptoran theropod dinosaurs that originated during the Mesozoic era. However, due to the cogent evidence provided by comparative anatomy and phylogenetics, and the feathered dinosaur fossils from China, the idea that birds are derived dinosaurs remains widely supported among paleontologists.

A well-resolved, robustly supported consensus tree found a monophyletic Archosauria consisting of two major branches, the crocodylian-line and avian-line lineages. This supports the classification of dinosaurs within the archosaur evolutionary tree rather than as lizards.

Dinosaurs are a diverse group of reptiles that were the dominant terrestrial life form on Earth during the Mesozoic Era, about 245 million years ago. Dinosauria is the common name given to a group of reptiles that first appeared roughly 245 million years ago and thrived worldwide for nearly 180 million years. Many lines of evidence now show that one lineage evolved into birds about 155 million years ago.

The archosaurs (“ruling reptiles”) are members of a subclass that also includes the dinosaurs, the pterosaurs (flying reptiles), and several groups of extinct forms, mostly from the Triassic Period.

Dinosaurs are a group of reptiles that dominated the land for over 140 million years. Dinosaurs are archosaurs, a larger group of reptiles that first appeared about 251 million years ago, near the start of the Triassic Period.

The archosaurs are a group of reptiles that includes dinosaurs, pterosaurs, and crocodylomorphs, along with their modern descendants—birds and crocodilians. Archosaurs evolved from even more primitive reptiles and are now organized into two clades, the Crurotarsi and the Avemetatarsalia (including all dinosaurs, pterosaurs, birds, and related groups).

In a wider sense, dinosaurs belong to a group called Archosauria. Archosaurs, the 'ruling reptiles', are today represented by crocodilians and birds. Historically, dinosaurs have been divided into saurischians ('lizard-hipped') and ornithischians ('bird-hipped'), based on the arrangement of their hip bones.

Birds are reptiles, specifically theropod dinosaurs, meaning that if we compare the genomes of related reptile relations, we can get an idea of what the extinct dinosaur genomes looked like. The crown group Reptilia incorporates extinct and existing clades of reptiles, dinosaurs and birds. In particular, it encompasses the diapsid reptiles including the Lepidosauria (tuatara, lizards and snakes) and the Archosauria (extinct dinosaurs, pterosaurs, crocodilians and birds).

Among the most revolutionary insights emerging from 200 years of research on dinosaurs is that the clade Dinosauria is represented by approximately 11,000 living species of birds. Arguably the most important single insight arising from the vast body of dinosaur research is the revelation that Dinosauria includes all birds, living and extinct. The earliest crown birds would have lived alongside representatives of all three major dinosaurian subclades… until the end-Cretaceous mass extinction event left crown birds as the only surviving representatives of Dinosauria.

Recent discoveries of feathered dinosaurs have confirmed analyses of bird relationships beginning in the 1970s that placed Archaeopteryx and birds within one group of dinosaurs, the Theropoda. Cladistic analyses strongly support birds being closely related to a subgroup within the theropod dinosaurs called Coelurosauria and especially with the scansoriopterygid, dromaeosaur and troodontid coelurosaurs. Fossil coelurosaurs with feathers from China provide convincing evidence that birds are coelurosaurs, and that during the course of evolution feathers arose before flight.

There’s no longer really any doubt that birds are a type of dinosaur. These days, the debate is about details.

Because birds are overwhelmingly interpreted as the descendants of a group of carnivorous dinosaurs, most scientists argue that they be considered living dinosaurs. The uncertainties that led to this long controversy—both empirical and methodological—have been clarified and there is an overwhelming consensus in support of the idea that birds evolved from maniraptoran theropods. Birds, therefore, are phylogenetically nested within Theropoda and belong within Dinosauria.

Traditionally dinosaurs are classified as two or three separate, independent groups of reptiles in the Subclass Archosauria. Here we present evidence that dinosaurs are a single, monophyletic group, and that the key advancements of endothermy and high exercise metabolism are justification for removing dinosaurs from the Reptilia and placing them with birds in a new class, the Dinosauria.

To date more than 20 suspected flying dinosaur species have been reported, and there is now an overwhelming consensus that birds represent a lineage of flying dinosaurs that survived the mass dinosaur extinction at the end of the Mesozoic Era, about 66 million years ago.

Evidence in support of the theropod origin of birds comes from all available sources of paleontological evidence—largely osteology, inferences about physiology and behavior, and more recently a variety of fossilized feathers. All analyses have supported the same position for birds, within a group of higher coelurosaurian theropods which are called maniraptorans—a group that includes dromaeosaurs, or raptors. Shared derived anatomical characters in support of this hypothesis come from all parts of the skeleton, and recent fossil evidence also documents that fully modern, pennaceous feathers, and many birdlike reproductive behaviors evolved in theropod dinosaurs before the origin of birds.

The feathered dinosaurs of Liaoning clinched it: birds really did evolve from dinosaurs. In truth, birds are dinosaurs—they are one of the many subgroups that can trace their heritage back to the common ancestor of dinosaurs and therefore every bit as dinosaurian as Triceratops or Brontosaurus. You can think of it this way: birds are dinosaurs in the same way that bats are an aberrant type of mammal that can fly.

Birds evolved from earlier theropods, and thus constitute the only known living dinosaurs. Birds are considered reptiles in the modern cladistic sense of the term. Aves and a sister group, the order Crocodilia, contain the only living representatives of the reptile clade Archosauria.

Indeed, she emphasizes that birds are categorized as dinosaurs. They represent the sole lineage of dinosaurs that persisted after the mass extinction event at the end of the Cretaceous period approximately 65 million years ago. Birds today have dinosaur DNA; they have dinosaur blood in their veins.

The evolution of birds began in the Jurassic Period, with the earliest birds derived from a clade of theropod dinosaurs named Paraves. Modern phylogenies place birds in the dinosaur clade Theropoda. There is significant evidence that birds emerged within theropod dinosaurs, specifically, that birds are members of Maniraptora, a group of theropods which includes dromaeosaurs and oviraptorids, among others.

Under phylogenetic nomenclature, dinosaurs are usually defined as the group consisting of the most recent common ancestor of Triceratops and modern birds (Neornithes), and all its descendants. Birds instead belong to Saurischia, the 'lizard-hipped' dinosaurs—birds evolved from earlier dinosaurs with 'lizard hips'.

The archosaurs include the living crocodilians and birds, as well as the fossil dinosaurs, pterosaurs, and basal 'thecodontians'. The archosaurs, although formerly regarded as an independent reptilian subclass, are now placed by nearly all biologists and palaeontologists in the Diapsida.

By now, most biologists agree birds are dinosaurs—that they evolved from a group of maniraptoran theropods sometime in the Jurassic Period (around 150 million years ago). Today’s biologists tend to think birds are dinosaurs, which means that, if true, the dinosaurs did not go entirely extinct after all. This position is so well supported by current science that science communicators and educators should feel utterly confident disseminating this view.

Modern birds descended from a group of two-legged dinosaurs known as theropods, whose members include the towering Tyrannosaurus rex and the smaller velociraptors. Over millions of years, these theropods decreased in body size and evolved features such as feathers and wings, eventually giving rise to birds. This evolutionary path places birds within theropod dinosaurs, not within modern lizards, which are part of a separate reptile group.

The finding that birds are descendants of certain dinosaurs has been a scientific consensus for over 20 years. Only a very few experts still question it. In this review, we explain why birds' ancestry from Mesozoic dinosaurs is a scientifically well-established fact.

In a word: Yes. "Birds are living dinosaurs, just as we are mammals," said Julia Clarke, a paleontologist studying the evolution of flight and a professor with the Department of Geological Sciences at the University of Texas at Austin. "All of the species of birds we have today are descendants of one lineage of dinosaur: the theropod dinosaurs."

Decades of major new discoveries and studies have convinced researchers that there’s a direct link between modern bird species and theropod dinosaurs. New work on old specimens, and the discoveries of dinosaur and early bird species in the field, supported the idea that dinosaurs were the direct ancestors of birds. In current scientific usage, birds are considered part of the theropod dinosaur group, rather than separate from dinosaurs or classified together with lizards.

In the 1970s, paleontologists noticed that Archaeopteryx shared unique features with small carnivorous dinosaurs called theropods. Based on their shared features, scientists reasoned that perhaps the theropods were the ancestors of birds. The birds are simply a twig on the dinosaurs’ branch of the tree of life. This evogram illustrates birds nested within theropod dinosaurs, not grouped with lizards (squamates), which occupy a different branch of the reptile tree.

Dinosaurs included the lizard-hipped saurischians and bird-hipped ornithischians. This reflects historical subgroup names and does not mean dinosaurs are actually classified as lizards or birds.

A new study just published in the Proceedings of the National Academy of Sciences provides yet more evidence that birds did not descend from ground-dwelling theropod dinosaurs, experts say, and continues to challenge decades of accepted theories about the evolution of flight. Ruben said, the weight of the evidence is now suggesting that not only did birds not descend from dinosaurs, but that some species now believed to be dinosaurs may have descended from birds. "Almost 20 years of research at OSU… are actually much more consistent with a different premise – that birds may have had an ancient common ancestor with dinosaurs, but they evolved separately on their own path."

Even though the idea was hard to swallow at first, paleontologist Donald Prothero says that 99 percent of relevant professionals now accept that modern birds are descended from dinosaurs, which were previously long thought to have gone completely extinct at the end of the Mesozoic era. The article frames "Birds Are Not Dinosaurs" as a case study in science denial, contrasting the overwhelming professional consensus with fringe opposition.

Birds are classified as theropod dinosaurs based on extensive anatomical and genetic evidence. Birds share over 100 skeletal features with theropod dinosaurs that are not found in other animal groups, including hollow, pneumatic bones, wishbones, and three-toed feet. Cladistic analyses consistently find that birds nest phylogenetically within theropod dinosaurs, while genetic and protein studies place birds as the sister group to a clade containing theropods like Velociraptor and Tyrannosaurus, rather than with modern lizards.

Instead, the Carolina evolutionary biologist regards them among the inaccurate reasons why other scientists erroneously claim that birds evolved from dinosaurs. The book’s 23 short essays also support the "Neoflightless Hypothesis" that so-called feathered dinosaurs are instead "hidden birds" such as four-winged microraptors and flightless forms such as ostrich-like species that superficially resemble dinosaurs. This work represents a minority viewpoint that rejects the standard birds-from-dinosaurs model.

Longisquama, a primitive Triassic archosaur with long feather-like scales and postulated arboreal habits, indicates that structures of this type have developed more than once in the archosauromorphs, which means they are weak evidence for a bird link to theropods. This paper reconsidered the theropod-bird link by pointing out that feather-like structures may have evolved convergently in different archosaurs. However, it did not overturn the broader anatomical and phylogenetic evidence that places birds within theropod dinosaurs, and modern consensus still supports a theropod origin for birds.