Dinosaur renaissance



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.

Dinosaurs and the origin of birds
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.

The relationship between dinosaurs and birds has led to considerable interest in dinosaur — particularly theropod — phylogeny, which is now far better understood.

Dinosaur monophyly
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.

Warm-bloodedness and activity levels
In a series of scientific papers, books, and popular articles in the 70s and 80s, beginning with his 1968 paper The superiority of dinosaurs, Robert Bakker argued strenuously that dinosaurs were warm-blooded and active animals, capable of sustained periods of high activity. In most of his writings Bakker framed his arguments as new evidence leading to a revival of ideas popular in the late 19th century, frequently referring to an ongoing dinosaur renaissance. He used a variety of anatomical and statistical arguments to defend his case, the methodology of which was fiercely debated among scientists.

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.

New theories on dinosaur behavior
The late 60s onwards also saw several new theories on the way dinosaurs behaved. On the basis of trackways, Bakker argued that sauropod dinosaurs moved in structured herds, with the adults surrounding the juveniles in a protective ring. However, shortly afterwards this particular interpretation was challenged by Ostrom among others, although the venerable dinosaur track expert Roland T. Bird apparently agreed with Bakker.

The first rigorous study of dinosaur nesting behaviour came in the late 70s, when palaeontologist Jack Horner showed that the duckbilled dinosaur Maiasaura cared for its young.

Changing portrayal of dinosaurs
The dinosaur renaissance changed not only scientific ideas about dinosaurs, but also their portrayal by artists. Bakker, himself a talented artist, often illustrated his ideas in a lively fashion. Indeed, Bakker's illustration of Deinonychus, made for Ostrom's 1969 description, has become one of the most recognisable and iconic of dinosaur restorations.

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.

Besides Bakker, key artists in this "new wave" were first Ely Kish, Mark Hallett, Gregory S. Paul in the 1970s, and during the 1980s Doug Henderson and John Gurche.

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.

New extinction theories, the meteor impact
Another factor contributing to the interest in dinosaurs was the acceptance and popularization of the idea, first proposed by Eugene Merle Shoemaker, that the Earth and other planets in the solar system are constantly bombarded by meteorites. This again led to the theory that the Cretaceous-Tertiary extinction event, which led to the disappearance of the dinosaurs 65 million years ago, was caused by a meteor impact, possibly the one that caused the Chicxulub Crater. This fever reached its height in 1994, when the Comet Shoemaker-Levy 9 hit Jupiter, with millions following the event live on television.

Cultural impacts
The dinosaur renaissance has been cited as the cause of renewed public interest in dinosaurs. Bakker's non-technical articles and books, particularly The Dinosaur Heresies, have contributed significantly to the popularization of dinosaur science.