Until recently, one of the biggest myths in science was that all dinosaurs have been extinct for the last 65 million years. But thanks to new fossil discoveries that filled our knowledge of bird dinosaurs, we now only know some dinosaurs became extinct after an asteroid collision with Earth – others survived and gave rise to the birds we live with today.
To find out how this development occurred, researchers in Chile conducted a strange but fascinating experiment in 2016. They manipulated the genes from ordinary chickens, causing them to develop tubular, dinosaur-like fibulae on their lower legs – one of the two long, spine-like bones you’ll find in a lower thigh.
In bird dinosaurs such as Archeopteryx, fibula was a tubular bone that reached all the way down to the ankle. Another bone, the tibia, grew to a similar length next to it.
As evolution progressed to a group of bird dinosaurs known as the Pygostylians, the fibula became shorter than the tibia and sharper and more splinter-like towards the end, and it no longer reached the ankle.
While modern bird embryos still show signs of developing long, dinosaur-like fibulae as they grow, these bones become shorter, thinner and also take the splinter-like ends of the Pygostylian bones and never reach far enough down to the bone to connect with the ankle.
Researchers, led by João Francisco Botelho of the University of Chile, decided to investigate how this transition from a long, tubular fibula in dinosaurs to a short, splinter-like fibula in birds actually occurred.
They achieved this by inhibiting the expression of a gene called IHH or Indian Hedgehog (severely), which saw their chickens continue to grow the long, dinosaur-like fibulae that arose in their embryonic form.
By doing so, the team discovered something bizarre. Regular bone development sees cell division and therefore the growth in the shaft stops long before the ends stop growing, but in modern chickens the growth of the fibula stops first at the ends.
This means that the fibulae of modern chickens are actively blocked from reaching the length of the bones of their old relatives.
Publication of their observations in the journal Development in February 2016, the researchers suggested that the early maturation of the lower end of the fibula in modern chickens is caused by a bone in the ankle, called the calcaneum.
“Unlike other animals, calcaneum in bird embryos presses against the lower end of the fibula,” the team explained in a press release at the time. “They are so dense that they have even been confused with a single element by some scientists.”
The team suggested that in ordinary chickens, interactions between the calcaneum and the end of the fibula result in signals similar to those that cause the bone shaft to stop growing, preventing the fibula from reaching anywhere near the ankle bone.
However, when the Indian Hedgehog gene was knocked off, the calcaneum strongly expresses the Parathyroid-related protein (PthrP) gene, which allows for growth at the ends of the bones. This caused their chickens to grow long fibulae attached to the ankle just as they would in Archeopteryx.
“Experimental downregulation of IHH signaling at a postmorphogenetic stage led to a shin and fibula of the same length,” the team wrote in the report. “The fibula is longer than in controls and fused with the fibular, whereas the tibia is shorter and bent.”
Unfortunately, the ‘dino chickens’ did not reach the hatching stage, but the purpose of the research was not to educate them for adulthood, but to find out the biological processes that led to the transition from dinosaur bones to modern bird bones. .
“The experiments are focused on individual features to test specific hypotheses,” explained one of the team, Alexander Vargas. “We know not only much about the evolution of birds, but also about the transition between dinosaurs and birds, which is well documented by the fossil record. This naturally leads to hypotheses about the evolution of evolution that can be explored in the laboratory.”
This was not the first time dinosaur traits have been ‘recreated’ in modern chickens. In 2015, the same team achieved growth of dinosaur-like feet on their chickens, and a separate team in the United States managed to grow a dinosaur-like ‘beak’ on its chicken embryos.
See below to see how leading scientist and renowned paleontologist Jack Horner managed to do so:
The research was published in Development.
A version of this article was first published in March 2016.