The "Dinosaur renaissance was a small-scale scientific revolution started in the late 1960s, which led to renewed academic and popular interest in dinosaurs. It was sparked by new discoveries and research indicating that dinosaurs may have been active and warm-blooded animals, rather than cold-blooded and sluggish as had been the prevailing view and description during the first half of the twentieth century.
The new view of dinosaurs was championed by John Ostrom, who argued that birds evolved from coelurosaurian dinosaurs, and particularly Robert Bakker who argued passionately that dinosaurs were warm-blooded in a way similar to modern mammals and birds. Bakker frequently portrayed his ideas as a renaissance of those popular in the late nineteenth century, referring to the period in between the wars as "the dinosaur doldrums".
The dinosaur renaissance led to a profound shift in thinking on nearly all aspects of dinosaur biology, including physiology, evolution, behaviour, ecology and extinction. It has also lead to multiple depictions of dinosaurs in popular culture.
In the mid and latter parts of the nineteenth century, many scientists thought there was a close relationship between birds and dinosaurs—and that dinosaurs represented an intermediate stage between "reptiles" and birds.
It was shortly after the 1859 publication of Charles Darwin's The Origin of Species, British biologist and evolution-defender Thomas Henry Huxley proposed that birds were descendants of dinosaurs. He cited skeletal similarities, particularly among dinosaurs, the "first bird"—Archaeopteryx—and modern birds.
However, in 1926, Gerhard Heilmann wrote his influential book The Origin of Birds, in which he dismissed the dinosaur-bird link, based on the dinosaurs' supposed lack of a furcula (fused clavicles). Thereafter, the accepted hypotheses was that birds evolved from 'crocodylomorph' and 'thecodont' ancestors, rather than dinosaurs. This removed dinosaurs from playing a central role in debates about the origin of living species, and may have contributed to the decline of academic interest in dinosaur evolution.
This remained the situation until 1964, when John Ostrom discovered a small carnivorous dinosaur which he named Deinonychus antirrhopus, a theropod whose skeletal resemblance to birds seemed unmistakable. This led Ostrom to argue that Huxley had been right, and that birds had indeed evolved from dinosaurs. Although it was Deinonychus that inspired Ostrom to connect birds with dinosaurs, very similar birdlike dinosaurs, such as Velociraptor had been known for many decades, but no connection had been made. After Ostrom's discoveries, the idea that birds evolved from dinosaurs gained support among palaeontologists, and today it is almost universally accepted. Newer methods, such as cladistics, and the discovery of several feathered dinosaurs have helped confirm the relationship.
Initially, dinosaurs were thought to be a monophyletic group, comprising animals with a common ancestor not shared by other reptiles. However, Harry Seeley disagreed with this interpretation, and split the Dinosauria into two orders, the Saurischia ("lizard-hipped") and the Ornithischia ("bird-hipped"), which were seen as members of the Archosauria with no special relationship to each other. As such, the Dinosauria was no longer seen as a scientific grouping, and "dinosaur" was reduced to being a popular term, without scientific meaning. This became the standard interpretation throughout much of the twentieth century.
This changed in 1974, when Bakker and Peter Galton published a paper in Nature, arguing that not only were dinosaurs a natural monophyletic group, but that they should be raised to the status of a new class, which would also contain birds. Although initially this revival of dinosaur monophyly was controversial, the idea did gain acceptance, and since the rise of cladistic methodology, it has been nearly universally supported. The raising of the Dinosauria to class rank found less support, perhaps largely due to increasing use of phylogenetic taxonomy among vertebrate palaeontologists, in which ranks are entirely abandoned.
These debates sparked interest in new methods for ascertaining the palaeobiology of extinct animals, such as bone histology, which have been successfully applied to determining the growth-rates of many dinosaurs.
Today, it is generally thought that many or perhaps all dinosaurs had higher metabolic rates than living reptiles, but also that the situation is more complex and varied than Bakker originally proposed. For example, while smaller dinosaurs may have been true endotherms, the larger forms could have been inertial homeotherms, or many dinosaurs could have had intermediate metabolic rates.
During the 70s, restorations of dinosaurs shifted from being lizard-like, to being more mammal- and bird-like. Artists started to show dinosaurs in more active poses, and incorporating newer theories of dinosaur locomotion and behaviour.
Key artists in this "new wave" were Gregory Paul, Mark Hallet, and Doug Henderson. Gregory Paul in particular defended and expanded on Bakker's ideas on dinosaur anatomy. He expounded a rigorous and detailed approach to dinosaur restoration, in which he often criticised the errors of the traditionalist approach. He also produced a large number of restorations showing small dinosaurs with feathers, and defended the idea in a number of articles and his book Predatory Dinosaurs of the World. His view was proven largely correct in the late 90s with the discovery of several feathered dinosaurs. Paul's ideas and style have had a significant impact on dinosaur art, and likely will continue to do so for some time.
The 1993 film version of Jurassic Park was perhaps the most significant event in raising public awareness of dinosaur renaissance theories. For the first time in a major film, dinosaurs were portrayed as intelligent, agile, warm-blooded animals, rather than lumbering monsters more common to older films. Bakker, Jack Horner and Greg Paul, among others, were used as consultants.