In other species, the adults have uncoiled shells and still others have adults with moderately coiled shells that developmentally start out uncoiled. You are going to study the phylogeny of snails to test hypotheses of heterochrony. Species with heterocercal tails as adults start out with diphycercal tails, then develop heterocercal tails. Species with diphycercal tails do not show either tail shape during development. Based on the fossil record and outgroup comparison, it appears that diphycercal tails evolved first, then heterocercal tails, and finally homocercal tails.
Some species have aquatic adults and retain gills throughout life.
All have head shapes that start out with flat faces and large foreheads. Humans retain this head shape throughout life, but chimpanzees, gorillas, and orangutans develop elongated snouts and flattened foreheads as adults. Draw the appropriate phylogeny, including this outgroup, to support this hypothesis. Draw the appropriate phylogeny, including this outgroup, to support this hypothesis. It turns out that both outgroup comparison and the fossil record suggest that the ape-shaped head is the primitive condition.