Jaws evolved from the gill arches, a series of structures in fish that support their gills. A new study, published in the journal Science Advancestoday, explores how a breathing structure came to be a biting structure. To do this, researchers based at Bristol's School of Earth Sciences collected data on the shapes of fossil jaws during their early evolution and mathematical models to characterise them. These models allowed the team to extrapolate a wide range of theoretical jaw shapes that could have been explored by the first evolving jaws. These theoretical jaws were tested for their strength -- how likely they were to break during a bite, and their speed -- how efficiently they could be opened and closed. These two functions are in a trade-off -- meaning that increasing the strength usually means decreasing the speed or vice versa.