Birds are the only living descendants of the long-lost dinosaurs, extinct 65 million years ago. This link was first established by the discovery of the fossil Archaeopteryx in 1861, and since then, dinosaur species have been divided into two groups depending on the orientation of their pubis. Paradoxically, though Ornitischia is the group which can be referred to as “bird-hipped” dinosaurs (further divided into Thyreophora, Ornithopoda and Marginocephalia) its counterpart Saurischia, meaning “lizard-hipped” dinosaurs, is the group from which birds come from. The reversed pubis of birds is only due to the independent evolution of similar features to achieve the same function (a process called convergent evolution). Saurischia is subdivided into Sauropodomorpha and Theropoda, the latter being known for dinosaurs such as Tyrannosaurus rex or Velociraptor.

What makes birds special?

The anatomy of birds is remarkable, enabling most of them to fly. Their skeleton is different to those of other animals, being composed of lightweight bones due to the existence of hollow spaces in their bones. These hollow bones serve another function as well, forming part of an effective respiratory system: air sacs present in bones are connected to the lungs. When we (humans) breathe, some air always remains in our lungs and so our lungs do not fully collapse in each breath. Birds, on the other hand, have a one-way system that moves the air into the lungs using only one direction. Inhalation in birds involves air entering the posterior air sacs and the lungs while the air from the previous breath moves out to the anterior sacs. Subsequently, exhalation is the movement of air from the posterior sacs and the lungs to the anterior sacs while the air in the anterior sacs goes out through the trachea. This means that unlike mammals, birds can take in oxygen even during exhalation.

Bird skeletons are also rigid due to the fusing of adjacent bones, meaning that they can support their weight while flying. For example, their collarbones have merged into one structure called the furcula, more commonly known as the wishbone. Birds also have large, flattened bones such as the keel, which allows them to support their strong musculature. Interestingly, the reproductive organs of birds only enlarge during mating season, contributing to being lightweight.

Birds have enlarged brains and are perhaps more intelligent than one might believe, in particular corvids (birds of the crow family) and parrots. Crows can recognise faces, enabling them to hold grudges and communicate with other crows. They also hold funerals for their dead, which is a surprising sign of social intelligence. Ravens can be paranoid and have been observed to hide food more frequently when their peers are around. If a raven steals another one’s food, he will be excluded from the group, and other ravens show a refusal to cooperate with him. This can be considered as a form of social ostracism. Various birds are known to be able to use tools, such as woodpecker finches to hunt prey and crows to probe for food into small spaces. The most unexpected example is the fact that the humble pigeon has been shown to count, subtract and sort numbers ordinally! Whilst every pigeon may not be a mathematical genius, this certainly suggests that birds may be a lot smarter than we think.

“Whilst every pigeon may not be a mathematical genius, this certainly suggests that birds may be a lot smarter than we think”

What we know about bird evolution: an interview with Cambridge expert Dr Field

The origin of birds is a fascinating story: they survived the end-Cretaceous mass extinction, which led to a radiation event. Multiple bird species have appeared over time, resulting in more than 10000 bird species we have today, which makes them one of the most diverse groups of vertebrates. I interviewed Dr Daniel Field, a group leader in evolutionary paleobiology at Cambridge, who is investigating the origins of avian biodiversity. He recently discovered the fossil of the oldest modern bird called Asteriornis maastrichtensis, also known as Wonderchicken.

This fossil was found in Belgium close to the border of Maastricht in the Netherlands and comes from the age of dinosaurs, at the end of the Cretaceous period. The skull of the Wonderchicken is well preserved, allowing Dr Field’s lab to gather information about what birds looked like at the time of dinosaurs. A model of Asteriornis will soon be present in the museum of Zoology at Cambridge (see picture below).

Why is it so hard to understand birds?

Dr Field explained that it is extremely difficult to infer the phylogenetic relationships between all the different bird species; because multiple species arose in a very short amount of time, it is challenging to reconstruct the timeframe. Moreover, to define the lineages between modern birds and dinosaurs we would need more fossils. Fossils are often incomplete and lack the specific information we need to distinguish species. On the other hand, when working on modern birds, we can sequence their genome, but this approach has its own issues. The genome of birds contains a different proportion of DNA bases compared to ours which makes it difficult to assemble avian genomes.

“Birds could help us in our battle to cure cancer”

Nevertheless, understanding bird genomes may be useful beyond evolutionary history. Birds could help us in our battle to cure cancer: they have lower cancer rates than expected. Peto’s paradox states that large animals have lower cancer rates than predicted because in response to the extensive cell proliferation needed to generate their large size, they tend to have regulatory features that can be protective against cancer. For example, blue whales and elephants have multiple copies of the tumour suppressor gene TP53. Alternatively, another theory is that large animals have “hypertumours”: cancer cells may be able to “betray” other cancer cells by using resources without contributing to tumour development, thereby leading to tumour death.

However, birds are an exception: they have low cancer rates despite their relatively small size. This could be because they inherited the cancer defences of their much larger ancestors, the dinosaurs. With Dr Marc Tollis, Dr E. Yagmur Erten and Dr Daniel Chavez, my research work aims to investigate the presence of cancer genes in birds to better understand their cancer evolution. Shedding light on this topic could be relevant to human cancers.

We are fascinated by birds because of their history, diversity and specific characteristics. They are incredibly intelligent and beautiful at the same time, which makes them an interesting model organism to study. Birds are modern day dinosaurs full of secrets and mysteries which could potentially help us make sense of cancer evolution. We gain many benefits from studying them.