Dinosaur revolution

Like many inquisitive kids, I was fascinated with dinosaurs and knew the names of lots of them. When I was employed, I’d commonly see kids as young as 5, who could tell their parents (and me) the names of dozens of dinosaur genera. When I was about the same age as them, I was given a book on dinosaurs from the How and Why Wonder Book series. This series was turned out in large numbers on many topics, of which I had a few, but the dinosaur volume was my favourite¹. In that volume, the dinosaurs were looked upon as large, lumbering reptiles, essentially modelled on the large reptiles, such as varanid lizards and crocodiles, still in existence today. As a consequence, the large sauropods (e.g. Diplodocus, ‘Brontosaurus’ etc.), which were considered to be too large to wander about on land, were mostly shown lumbering about in lakes or swamps, so they didn’t ‘overload’ their leg bones².

While the sauropods waded around in water, the large predators such as Tyrannosaurus stood upright, dragging their tails along the ground², in the same posture as a stationary kangaroo, like the one who, a couple of days ago, was standing staring at us interlopers as we hopped out of the camper-trailer to get some breakfast.

Between then and now, much has changed in the understanding of the dinosaur world, and it has been termed the ‘dinosaur renaissance’. It all began not long after my How And Why book was published. During field work in 1964, palaeontologist John Ostrom and his team found a set of claws in the hills of Montana, one of these claws was a large talon connected to the well preserved foot bones of a new dinosaur species³. 

Ostrom considered that this talon implied a hunting style incompatible with the cold-blooded, slow reptiles that most palaeontologists thought dinosaurs were. To Ostrom, this animal, which he named Deinonychus antirrhopus in 1969, seemed like an agile carnivore built for speed³. This would have meant that Deinonychus antirrhopus had a high metabolic rate, something that reptiles do not have. This led Ostrom to compare the dinosaur not with modern reptiles, but with animals such as the ostrich and emu. He also noted similarities with the early bird Archaeopteryx lithographica³ from the famous Solnhofen Limestone deposit in Germany⁴.

Archaeopteryx lithographica shared the following features with dinosaurs such as Deinonychus antirrhopus: jawswith sharp conical teeth, three fingers with claws, a long bony tail, hyperextensible second toes, and feathers, among other skeletal similarities⁴.

Back in the mid 1800s, Charles Darwin’s ‘bulldog’, Thomas Henry Huxley had already argued, because of anatomical similarities, that birds and reptiles were descended from a common stock. With the discovery of more and more dinosaur fossils, Huxley considered that dinosaurs might have provided the link between the two groups. He also noted that unlike many reconstructions of the time, it was likely that many dinosaurs were bipedal⁵.

The discovery of Archaeopteryx in 1860 was another piece of evidence for Huxley; it appeared to be a bird as the feathers were preserved, but it was a transitional bird, with many reptilian features. However, it was a small dinosaur called Compsognathus that really impressed Huxley. It was an extremely bird-like dinosaur. Huxley said: “It is impossible to look at the conformation of this strange reptile and to doubt that it hopped or walked, in an erect or semi-erect position, after the manner of a bird”⁶.

One of Ostrom’s students, Robert Bakker, continued the dinosaur renaissance in arguing that unlike reptiles, which are cold-blooded (ectothermic), dinosaurs were warm-blooded (endothermic) like bids. It may not be as straightforward as this, with some of the larger dinosaurs possibly being ‘inertial homeotherms’ or ‘gigantotherms’. This is where very large animals are able to maintain a relatively high body temperature due to their smaller surface area/volume ratio. This allows it to gain heat from or lose heat to the environment much more slowly⁷.

Another palaeontologist, Jack Horner demonstrated that one dinosaur, Maiasaura, cared for its young. The fossil evidence shows that Maiasaura laid about 30 to 40 eggs in a nest and that hatchlings and juveniles continued to live alongside their parents for years, and presumably stayed with the herd well into adulthood⁸.

In the last couple of decades, there have been some startling discoveries in Liaoning, in north China. One of the first of these was Sinosauropteryx prima, a small, meat-eating dinosaur that lived about 125 million years ago. It was covered with delicate, hair-like feathers, which are preserved in exquisite detail⁹. Other specimens found in Liaoning include Yutyrannus, a 1,400 kg downy-feathered tyrannosaurid dinosaur described in 2012. In older beds was found Anchiornis huxleyi, a chicken-sized animal with enough preserved detail to become the first dinosaur ever described feather by feather with indications of the colours and the colour patterns of the feathers preserved¹⁰.

The rocks in which these Liaoning fossils are preserved consist of finely laminated lake sediments, characterised by exceptional preservation of soft tissues, such as body outlines, skin casts, wing membranes, scales, as well as the feathers and their preserved colour patterns¹¹.

There’s no longer really any doubt that birds are a type of dinosaur. These days, the debate is about details. The strong evidence doesn’t just come from fossilised bones and similarities found across the skeleton, but from fossilised soft tissue – especially the feathers. Many dinosaurs had distinctive bird-like feathers, while others, mentioned above, had filamentous feathers, and others had downy feathers¹².

Understanding of dinosaurs has come a long way since 1960, when the How And Why book on Dinosaurs was first published. Nowadays, we also know they aren’t extinct.

Sources

1. https://blotreport.com/2022/12/26/the-gift/
2. https://biblio.com.au/book/how-why-wonder-book-dinosaurs-darlene/d/831025361
3. https://daily.jstor.org/the-origins-of-the-dinosaur-renaissance/
4. https://en.wikipedia.org/wiki/Archaeopteryx
5. https://www.biodiversitylibrary.org/page/22247928#page/80/mode/1up
6. https://www.lindahall.org/experience/digital-exhibitions/paper-dinosaurs/13-origin-of-birds/15-huxley-dinosaurs-and-birds-1868/
7. https://en.wikipedia.org/wiki/Gigantothermy
8. https://www.thoughtco.com/things-to-know-maiasaura-1093792
9. https://australian.museum/learn/dinosaurs/fact-sheets/sinosauropteryx-prima/
10. https://www.smithsonianmag.com/science-nature/great-chinese-dino-boom-180968745/
11. https://www.sciencedirect.com/science/article/abs/pii/S0195667113000566
12. https://www.birdlife.org/news/2021/12/21/its-official-birds-are-literally-dinosaurs-heres-how-we-know/