Reptiles evolved from amphibians (Anamniota), and based on certain shared morphologic features, anthracosaurs were probably the ancestors of the early reptiles. The amphibian anamniotic egg has a gelatinous coating and lacks extraembryonic membranes and is thus very susceptible to desiccation. The reptilian amniotic egg is made up of a calcareous or semicalcareous semipermeable shell surrounding the developing embryo and its extraembryonic membranes: chorion, allantois, amnion, and yolk sac. The Testudines is a well-characterized clade that is probably a part of the much larger clade, the Diapsida. The order Testudines includes 14 families, with more than 351 species of present-day turtles and tortoises. Chelonians are the only tetrapods with the pectoral girdles internal to the ribs. The majority of chelonians are aquatic or semiaquatic. The discovery in the Italian Alps of Megachirella wachtleri, the oldest known squamate fossil, reshaped the diapsid phylogeny by indicating a more gradual acquisition of features of squamates in diapsid evolution than previously thought.