The Rise of the Wonderchicken - By Fiona Small

It is well known that birds descended from dinosaurs, in particular from Theropods. A theory that is widely accepted by palaeontologists across the globe, due to fossil discoveries of Archaeopteryx which had teeth like the dinosaurs but also feathers and wrist bones that are shared with modern birds.

The evolutionary history of all other living tetrapods (amphibians, reptiles and mammals) is well known from the fossil record. However, the evolutionary history of birds is poorly understood and the exact time when birds diverged from dinosaurs is hard to pinpoint. This is mainly due to the fossil record of birds being sparse and lacking considerably in data. Any fossils that can help clarify the origins of modern birds are amongst the rarest and most sought-after discoveries.

What scientists do know is that there were many birds alive at the time of the dinosaurs making up a part of the archaic group Enantiornithes, which encompass toothed birds and went extinct along with the larger land animals. Scientists also know that all modern birds emerged from a group called the Neornithes, which appeared towards the end of the Cretaceous. However, bird fossils from the Cretaceous are lacking, which is what makes the discovery of the wonderchicken so important.

20 years ago, amateur fossil hunter Maarten van Dinther found what is now considered one of the most important fossil bird discoveries. He found a rock, no bigger than a deck of cards, with a few small leg fragments visible from the side. The rock was found near the Belgium Netherlands border and was dated to be 66.7 million years old. This is 700,000 years before the asteroid impact that killed all large land dinosaurs, making it the oldest known ancestor of all modern birds.

A team led by the University of Cambridge conducted a high-resolution X-ray CT scan of the rock, allowing the scientists to see what was trapped inside and produce a 3D image. What was beneath the surface came as a huge surprise but one they will never forget. A perfect skull, beautifully preserved inside the rock.

The 66.7 million-year-old fossil reveals the life of a bird that walked the Earth at the same time as the T.rex and Triceratops. The official name of this find is Asteriornis maastrichensis, after the Greek goddess of falling stars, Asteria, who transformed into a quail. Quite a fitting name with the impending asteroid impact on its way. However, it has since been dubbed the ‘wonderchicken’ because its head resembles that of a chicken. The wonderchicken has features of Anseriformes (ducks and geese) and Galliformes (such as chickens and turkeys). Scientists knew that these two clades split during the Cretaceous and that there must be an ancestor present around that time, and now they have found just what they were looking for.

The wonderchicken weighs in at around 400g, has a gently down-curved beak and long slender legs. From an analysis of the rock and the fossil itself, the scientists have concluded that the wonderchicken lived in a littoral ecology, meaning it was likely to be a shorebird, could probably fly and roamed around strings of islands in warm shallow seas, much like the climate of the present-day Bahamas. Marine sediments found in the rock confirms the conclusion that the wonderchicken was likely a shorebird.

Additionally, the beak shape indicates that it was not a picky eater, which may have been crucial to surviving post-asteroid life. It’s small body size and shoreline habitat may have been the reason the wonderchicken was able to survive when so many larger animals did not. Providing an important area of research that may lead to answers in the survival of birds after the extinction event.

To this day, the wonderchicken fossil is one of the most important bird fossil discoveries of all time This is because many bird fossils have been discovered from after the time of the dinosaurs, but very few from before. Scientists know that there were lots of birds alive and walked among the dinosaurs, but many went extinct along with them. In addition, most of the fossils already discovered have been found in the Southern Hemisphere, leading palaeontologists to suggest that modern birds originated on the supercontinent Gondwana. However, this wonderchicken discovery in the Northern Hemisphere puts a spanner in the works, shedding doubt on this theory and only future fossil discoveries will be able to tell us where modern birds originated on Earth.

The wonderchicken will lead to new insights into the evolutionary history of birds and it is a huge achievement to discover something new. It will further help scientists to understand why birds survived the asteroid impact whilst the large land dinosaurs did not.

References

1. https://www.nature.com/articles/s41586-020-2096-0

2. https://www.nationalgeographic.co.uk/science-and-technology/2020/03/wonderchicken-walked-earth-dinosaurs

3. https://www.sciencealert.com/oldest-modern-bird-fossil-holds-clues-to-how-birds-survived-when-other-dinosaurs-did-not

4. https://www.bbc.co.uk/news/science-environment-51925335

5. https://www.cam.ac.uk/stories/wonderchicken

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