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HomeUncategorizedICYMI: Scientists Grew 'Dinosaur Legs' on a Chicken

ICYMI: Scientists Grew ‘Dinosaur Legs’ on a Chicken

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Until recently, one of the most widespread scientific misconceptions was that all dinosaurs had been extinct for the past 65 million years.

A chicken embryo. (Graeme Campbell/Wikimedia Commons/Public domain)

However, new fossil discoveries that have filled in the gaps in our knowledge of avian dinosaurs, we now know that only some dinosaurs became extinct as a result of an asteroid collision with Earth – others survived and gave rise to the birds we know today.

In order to understand how this evolution occurred, researchers in Chile conducted a strange but fascinating experiment in 2016. They tampered with the genes of ordinary chickens, causing them to develop tubular, dinosaur-like fibulas on their lower legs – one of two long, spine-like bones found in a drumstick.

The fibula was a tube-shaped bone that reached all the way down to the ankle in avian dinosaurs like Archaeopteryx. Along with it, another bone, the tibia, grew to a similar length.

As evolution progressed to the Pygostylians, a group of avian dinosaurs, the fibula became shorter than the tibia, 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, these bones become shorter, thinner, and take on the splinter-like ends of the Pygostylian bones as they grow, and never make it far enough down the leg to connect with the ankle.

Researchers from the University of Chile, led by Joo Francisco Botelho, decided to look into how the transition from a long, tubular fibula in dinosaurs to a short, splinter-like fibula in birds occurred.

They accomplished this by inhibiting the expression of a gene known as IHH, or Indian Hedgehog (seriously), which allowed their chickens to retain the long, dinosaur-like fibulae that originated in their embryonic form.

The team discovered something strange as a result of their efforts. Cell division and thus growth halt in the shaft long before the ends in normal bone development, but in modern chickens, the growth of the fibula halts first at the ends.

Botelho et al., Evolution, 2016

The researchers proposed in February 2016 in the journal Evolution that the early maturation of the lower end of the fibula in modern chickens is prompted by the calcaneum, a bone in the ankle.

“Unlike other animals, the 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 close, they have even been mistaken for a single element by some researchers.”

The researchers hypothesized that interactions between the calcaneum and the end of the fibula in regular chickens produce signals similar to those that cause the bone shaft to stop growing, preventing the fibula from reaching the ankle bone.

When the Indian Hedgehog gene is turned off, the calcaneum expresses the gene Parathyroid-related protein (PthrP), which allows for bone growth at the ends. This caused their chickens to develop long fibulae that connected to the ankle, just like Archaeopteryx.

“Experimental downregulation of IHH signaling at a postmorphogenetic stage led to a tibia and fibula of equal length,” the team wrote in the report. “The fibula is longer than in controls and fused to the fibulare, whereas the tibia is shorter and bent.”

Unfortunately, the ‘dino-chickens’ did not hatch, but the goal of the study was not to raise them to adulthood, but to figure out the biological processes that led to the transition from dinosaur legs to modern bird legs.

“The experiments are focused on single traits to test specific hypotheses,” one of the team, Alexander Vargas, explained. “Not only do we know a great deal about bird development, but also about the dinosaur-bird transition, which is well-documented by the fossil record. This leads naturally to hypotheses on the evolution of development, that can be explored in the lab.”

This was not the first time dinosaur characteristics were’recreated’ in modern chickens. In 2015, the same team succeeded in growing dinosaur-like feet on chicken embryos, and a separate team in the United States succeeded in growing a dinosaur-like ‘beak’ on chicken embryos.

Watch the video below to see how lead researcher and renowned paleontologist Jack Horner did it:

The research was published in Evolution. A version of this article was first published in March 2016. Minor edits were made by the author.

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