The goal of this study was to determine whether marine turtle (loggerhead) embryos communicate with one another using mechanical cues detected through the flexible egg shell. In the process, the embryos might develop faster and hatch with greater synchrony (as occurs in some freshwater turtles). To find out, we performed experiments under controlled laboratory conditions to determine how changes in the embryonic social environment affected both the rate of development and the temporal pattern of hatching when temperature, moisture, and substrate composition were controlled. We found that developmental periods were significantly shortened and hatching synchrony was increased when 1) a critical number of eggs were in contact with one another, facilitating the possibilities for embryos to communicate, and when 2) a threshold number of those eggs remained viable and completed development at about the same time. We used this information, in combination with field studies done by others, to clarify temporal relationships between hatching and emergence from the nest that occurs several days later.