Is a Chicken a Dinosaur?

After Charles Darwin wrote his famous work Origin of Species, the American paleontologist John Ostrom, shared conclusions based on his phylogenetic studies and the bone system of the fossilized species known as Archaeopteryx lithographica. Doing so, he demonstrated that theropod dinosaurs were more similar to birds than reptiles. Initially this idea of kinship between dinosaurs and birds had been proposed by Huxley, but was later formally reformulated by Ostrom.

Over the years, evidence accumulated in favor of this hypothesis and in 1990, it was corroborated with the incredible discovery of feathered dinosaurs in China. Regardless of the continuing debate about how birds evolved and which lineage is most closely related to them, these demonstrations forged the conclusion that current bird species are short-tailed theropod dinosaurs. This includes the domestic chicken (Gallus gallus domesticus).

Due to chickens and other birds being so closely related to dinosaurs, their classification has changed to show this. In fact, they are so phylogenetically linked that they are both considered dinosaurs. Although we may think of dinosaurs as the great scaly lizards from films like Jurassic Park, this is only one form of the animal. These extinct animals are known as dinosaurs and birds like chickens are known as non-avian dinosaurs.

Learn more about how birds and dinosaurs are grouped taxonomically with our article on how birds are classified.

Chickens descend from a group of theropod dinosaurs, likely to be those known as dromaeosaurids. Together with birds, they are called Maniraptora (sometimes known by other authors as Eumaniraptora), a clade who disappeared after a mass extinction event that caused the end of the Mesozoic Era.

Currently, birds are considered to constitute a monophyletic group, which has as a common ancestor in the famous bird genus known as Archeopteryx. This includes all current birds (Neornithes) and their descendants, including chickens. Archeopteryx had a beak with teeth, unfused wing digits and feathers on their wings and tail. They were nota great flyer, but could make short flights. Despite being a very widespread and accepted theory, not everyone agrees with it, remaining controversial to this day.

Learn about the different types of dinosaurs that existed with our related guide.

The study of the fossil record has led us to determine various characteristics of non-avian maniraptoran theropod dinosaurs. Due to being extant, we have a better ability to look at the characteristics of chickens. We compare what we know below:

Osteological characteristics

The discovery of a large number of fossils has allowed the comparison of the skeletons of each of these taxa. These records represent a very valuable connection for paleontologists. For example, some of the similarities present in the skeleton of both chickens and dinosaurs include the presence of fused clavicles that form a structure called ‘furcula’, a semilunar carpal bone (crescent shape) and a backwards pubis, among many others.

Oology

Oology is the study of eggs. From the study of fossils, we can see evidence in favor of the hypothesis that chickens and non-avian dinosaurs are closely related. Until only recently, the characteristics of the eggs of non-avian theropods were not known, since none had been found with embryonic remains. A discovery in the Gobi Desert provided the first morphological evidence of these eggs. From studying this find, scientists concluded that the general shape and structure of the shell shared common traits with the eggs of modern birds such as chickens.

Learn about a modern bird which is now unfortunately no longer with our article on why the great auk went extinct.

Behavior

Thanks to discoveries in Mongolia and the United States of rocks present during the Late Cretaceous period, the nesting behavior of some maniraptorans is known. Numerous skeletons of the extinct species Citipati osmolskae were found brooding over their eggs, with their legs bent and their arms extended around the nest. These findings confirm that non-avian maniraptorans possessed the usual behavior in which chickens hover over laid eggs for prolonged periods.

Another behavior found was that of the sleeping posture common to dinosaurs and chickens. Fossils of Sinornithoides were found with their heads tucked under their arms, a posture similar to that acquired by certain modern birds when resting.

Feathers

It was believed that feathers were an exclusive feature of avians. In China, a large number of feathered dinosaurs have been discovered that can be classified as theropod dinosaurs. Their feathers covered large parts of their bodies. In some of them, such as the species of the genus Caudipterix, they covered their forelimbs and formed a kind of fan at the end of the tail. All of these incredible discoveries have led to the conclusion that these feathered dinosaurs were capable of flight and that modern birds are not the only ones that possess these structures.

Similarly, they could have had feathers, but been flightless or only capable of limited flight. This is the case with chickens that have feathers, but spend most of their time on the ground.

Respiratory system

Some species of theropod dinosaurs had a system of air sacs similar to those of modern birds. This characteristic was believed to be unique in the bird group, but has ben shown to have already existed in large carnivorous dinosaurs.

Now we know about the links between chickens and dinosaurs, we can discover more about the diversity of these prehistoric animals with our article on whether there were ocean dinosaurs.

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