" Eorhynchochelys isn’t the only kind of early turtle that scientists have discovered – there is another early turtle with a partial shell but no beak. Until now, it’s been unclear how they all fit into the reptile family tree. “The origin of turtles has been an unsolved problem in paleontology for many decades,” says Rieppel. “Now with Eorhynchochelys, how turtles evolved has become a lot clearer.”
The fact that Eorhynchochelys developed a beak before other early turtles but didn’t have a shell is evidence of mosaic evolution – the idea that traits can evolve independently from each other and at a different rate, and that not every ancestral species has the same combination of these traits. Modern turtles have both shells and beaks, but the path evolution took to get there wasn’t a straight line. Instead, some turtle relatives got partial shells while others got beaks, and eventually, the genetic mutations that create these traits occurred in the same animal."
Anybody have an idea how that happens via common descent only? How did the genetic information for the shells get to the ones who only had the beaks, and vice-versa? Are they saying these traits evolved independently in several strains until the strain which made it had them all?