You always wondered, right? No? Oh well, some researchers looked into it:
Florida Museum of Natural History researchers used 3D data to study skull shape in 158 species representing all living frog families. Radically shaped skulls were often covered in intricate patterns of grooves, ridges and pits formed by extra layers of bone. The research team found that this trait, known as hyperossification, has evolved more than 25 times in frogs. Species with the same feeding habits or defenses tended to develop similarly shaped and patterned skulls, even if they were separated by millions of years of evolution.Florida Museum of Natural History, “Skulls gone wild: How and why some frogs evolved extreme heads” at ScienceDaily
That’s called convergent evolution. One can’t just assume common ancestry because life forms share traits. That makes as much sense as assuming that two random people who look alike must be closely related. Also, get this:
While the study sheds new light on frog skull shape, Blackburn said we still don’t know much about the basic biology of frogs.
“Weirdly, it’s easier for us to generate beautiful images of skulls than it is to know what these frogs eat,” Blackburn said. “Natural history remains quite hard. Just because we know things exist doesn’t mean we know anything about them.”Florida Museum of Natural History, “Skulls gone wild: How and why some frogs evolved extreme heads” at ScienceDaily
We better conserve them or we’ll just be left with the skulls.
See also: Evolution appears to converge on goals—but in Darwinian terms, is that possible?