Scientists Attach Prosthetic Dinosaur Tails to Chickens

Why did the chicken with the prosthetic tail cross the road?  So that scientists can simulate the walking motion of Theropod dinosaurs in a bid to learn more about the way in which dinosaurs moved around.  That’s the rather bizarre summation from a study into non-avian, bipedal dinosaur posture and locomotion carried out by researchers at the University of Chile, working in collaboration with colleagues from the University of Chicago.

Ancestral Traits

Aves (birds) still share a number of ancestral traits of the Dinosauria and as such they can be utilised as experimental subjects to assess certain aspects of dinosaur anatomy and even inferred behaviour.  In this particular study, chickens were fitted with prosthetic tails as they grew so that scientists could assess how Theropod dinosaurs walked in comparison with their very much shorter-tailed descendants.  As birds evolved during the Mesozoic, so a number of forms gradually lost their long, reptilian tails, a tail is prominent in the fossils of Archaeopteryx (A. lithographica).  Indeed, one of the ways to tell birds apart from Maniraptoran dinosaurs in the fossil record is to count the number of likely caudal vertebrae (tail bones).

Prosthetic Dinosaur Tails

As a simple rule of thumb, if more than twenty-five tail bones are associated with the skeletal material, then chances are, you are looking at the fossilised remains of a dinosaur.  Less than twenty-five tail bones and the identification starts to lean more towards the Aves (birds).  Birds lost most of their tail as they evolved into more and more efficient fliers.  The long tail of Archaeopteryx would have made it quite a clumsy aeronaut.  Later birds, more competent fliers than Archaeopteryx for example, lost most of their tail.

Modern birds have a pygostyle, a vestigial tail that is composed of their last five caudal vertebrae fused into a plate of bone, the evolution of birds shows trends towards a lightening of the skeleton such as the loss of teeth and the gradual reduction in tail length.

The Locomotion of Theropod Dinosaurs

This then gives scientists a bit of puzzle when it comes to using birds to mimic the locomotion of theropod dinosaurs, birds don’t have a long tail and the addition of a tail alters the centre of gravity in relation to the rest of the body mass and effects the way a creature can move about.  The solution is simple, add artificial tails to your subject chickens as they grow.  With the tail the birds have to modify their gait and motion and therefore scientists can learn more about the movements of those long-tailed dinosaurs.

Extant birds today, maintain a crouched hind-limb posture and their locomotion is powered by knee flexion.  In non-avian Theropods, by contrast, scientists speculate that these dinosaurs had a more upright posture and limb movement powered by femur (thigh bone) retraction.  To test this theory, young chicks had a series of artificial tails attached to them from two days of age.  As the hatchlings grew, so bigger tails were fitted to mimic the growth of the tail in a young dinosaur.

Calculating Tail Weight

The scientists worked around a tail weight roughly equivalent to 15% of the bird’s total body mass, roughly the proportional weight of a theropod dinosaur’s tail when compared to the weight of the entire dinosaur’s body.  Velcro straps were used to keep the wooden, prosthetic tails in place and the scientists noted that by manipulating the location of the centre of mass within the chickens, the birds began to alter their locomotion and posture to accommodate the tail.

The Addition of a Tail Alters the Way In Which Chickens Walk

Watch the birdie!

Picture credit: PLoS One

Artificial Dinosaur Tails

Artificial tails provide clues to non-avian dinosaur locomotion.  In the diagram (A), above, those birds used as controls have their hind-limbs shaded grey, those chickens with a counter weight added anteriorly (hind-limbs shaded yellow) and those chickens with tails (orange hind-limbs).  Estimations of the centre of mass of the tail rig (tCOM), as well as of a control (cCOM) and of an experimental individual (eCOM), are shown.   With the tail added, the centre of mass is moved towards the rear of the bird.  (B) Diagram showing the segmental angles (f, femur; tt, tibio-tarsus; tm, tarso-metatarsus) and joint angles (k, knee; a, ankle) used in this study.

It was noted that the chickens began to recreate the limb posture and kinetic movements inferred for bipedal dinosaurs.  The more rearward located centre of gravity indicated a more vertical orientation of the thigh during standing and increased femoral displacement during walking.

Commenting on the research, lead author of this rather unusual study, Bruno Gossi (Institute of Ecology and Biodiversity, University of Chile) wrote:

“We attached more realistic artificial tails to chickens shortly after hatching and allowing proper exercise, we expected adult chickens with added tails to show a more vertical femur in standing position and increased femoral excursion during locomotion.”

Changing the Centre of Body Mass

The research team states that this study supports the hypothesis that gradual changes in the position of the centre of body mass (posterior located with tail, to anterior located without a tail), resulted in a more crouched hind-limb posture and a shift form hip-driven limb movements to the knee-driven limb movement seen in extant birds.

Having mastered  the technique of adding artificial tails to chickens thanks to Velcro, the scientists are confident that this type of research can be used to gain further, significant insights into previously unexplored aspects of bipedal theropod locomotion.

Last spring (April 2013), Everything Dinosaur reported on some research into the posture of birds carried out by scientists including a team from the Royal Veterinary College which looked at the relationship between the Aves and the Dinosauria in terms of derived posture.  So in answer to the question how did dinosaurs walk? Get yourself a chicken.

To read more about this article: Birds Have the Dinosaurs to Thank for Their Crouching Gait.

Out thanks to Constantine, for reminding us to post something up about this research.

For replicas of theropod dinosaurs and other prehistoric animals: CollectA Deluxe Prehistoric World Models.