It is a form of “reverse evolution.”
Dinosaurs had it pretty good during the Jurassic and Cretaceous periods. They were the dominant species and had the lay of the land — they ruled the Earth! However, as fate would have it, the age of the dinosaurs came to a dramatic end 66 million years ago when a huge asteroid impact started them on a path towards extinction.
However, not all of them died out. For example, some ancient flying reptiles, called pterosaurs, survived and evolved to become today’s birds.
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Scientists are still unclear about the changes that occurred between pterosaurs and birds, and in order to figure out how this evolution happened, researchers in Chile have engaged in some “reverse evolution” by growing “dinosaur legs” in chicken embryos.
As discussed in their study published in the journal Evolution, the research team, led by Joâo Botelho from the University of Chile, manipulated the genes of regular chickens so they developed tubular, dinosaur-like fibulas on their lower legs. In ancient birds, the fibula reached all the way down to the ankle, and another bone, the tibia, grew to a similar length beside it.
Modern chicken embryos show signs of developing these long fibulae, but as they grow the bones become shorter, thinner and also have splinter-like ends that never grow far enough to connect with the ankle.
By inhibiting the expression of a gene called IHH or Indian Hedgehog, the chicken embryos continued to grow the long fibulae. This means that the fibulae of chickens are actively blocked from reaching the lengths of their ancient relatives. The researchers suggest that this blocking is prompted by a bone in the ankle called the calcaneum.
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“Unlike other animals, the calcaneum in bird embryos presses against the lower end of the fibula,” the team explained in a press release. “They are so close, they have even been mistaken for a single element by some researchers.”
In modern chickens, the interaction between the calcaneum and the fibula results in a signal that prompts the bone to stop growing, preventing the fibula from reaching anywhere near the ankle bone. However, when the Indian Hedgehog gene was turned off, the calcaneum expressed the gene Parathyroid-related protein (PthrP), which allowed for the growth of the bones, causing the chickens to grow long fibulae that connected with the ankle, just like their ancestors.
Unfortunately, the chickens did not make it to the hatching stage, but the team believes they are closer to determining the biological processes that led to the transition from dinosaur legs to the bird legs we know today.
But don’t worry, no one is planning on growing any dino-chickens or new dinosaurs for commercial or non-scientific purposes. Jurassic Park will remain just a movie!
Last year, the same team achieved the growth of dinosaur-like feet on chickens, which you can see in the video below.