Going to the 'femoral head' of class to explain dinosaur evolution

Without the changes to their upper thigh bones, birds and dinosaurs wouldn't have been able to walk or run on their own.

New Yale paleontologists found an example of natural selection for increased body height in the oldest known fossils

The findings resolve a longstanding question about dinosaur evolution and offer a prime example of how new physical features can appear briefly during embryonic development and give way to older, known features in adults

This study looked at evolutionary shifts in the femoral head, where the upper femur connects to the hip, across a wide range of dinosaurs, early reptiles, and birds, and their modern-day counterparts

The way in which the femoral head developed has been figured out by scientists. Bipedal locomotion requires inward-turned femoral heads for fast and effective movement.

For years, there had been two conflicting theories about how dinosaur femoral heads developed

One theory held that the femoral head simply grew an attachment, or overhang The other theory was that the femoral head twisted inward over time

There is evidence for both the in-growth theory and the twisting theory, which were found in early dinosaurs and crocodiles

The researchers used 3D images to study the development of the femoral head in fossils and animal embryos. The researchers studied femoral head development in a variety of fossils and animal embryos

Even though the feature remained constant in adults for quite some time, the development of this major feature completely changed

This sort of hidden shift in development might be more common than we think, and it should serve to caution against the idea that features which develop differently must have evolved separate from one another

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