A number of relatively minor changes were made to the Dolphins' helmet logo during the late 1960s and early 1970s; I have attempted to represent only the more substantial of these changes here. Note the two main versions of the logo that were used during this period: one with the dolphin's head inside the circle, and the other with it outside. There were at least some games when both of these logos were in use at the same time by different players. The size of the logo and its colors were also inconsistent during this period, the "aqua" color varying from a bluish hue to a greenish one. The logo was modernized for the 1997 season.
Here is some additional information about the two logo variations used during the Dolphins' early years, provided by site visitor Bob G.: "The team went back and forth between the "in the sun" and "out of the sun" logos between 1966 and 1969; sometimes I believe, within a season. Starting in 1970 they seemed to have settled with the "in the sun" logo, until from the final regular season game of 1973 (vs. Detroit) thru the playoffs, about half of the team (mostly lineman) started wearing the "out of the sun" version. Pictures which show both logos on the field at the same time come from this period. Please also note that this "out of the sun" logo is much smaller than the one worn in the '60s. In 1974, the Dolphins went back exclusively to the "out of the sun" logo. (One exception was running back Norm Bulaich, who played with the team around '75-'76, wore the "in the sun" logo, which drove me crazy). Sometime around 1990, perhaps due to a change in manufacturer, the dolphin in the logo (but not the sun) became slightly larger. The "in the sun" logo was brought back for "throwback" games in 1994 against the Jets and Vikings."
And here are additional comments on this matter from site visitor "Gazzoo": "The "in the sun" logo was worn in the Dolphins initial season of 1966, but only for the first three games. They then switched to the "out of sun" version for the remainder of 1966 and all of 1967 and 1968.
"Starting in 1969, the Dolphins again went to the "in the sun" version, except for the 1970 preseason, when they went logo-less. This continued until the final regular season game of 1973 against Detroit, when about half the team (mostly linemen) started wearing the "out of sun" logo. This continued for the 1973 playoffs, including Super Bowl VIII. Any pictures you come across with both logos on the field at the same time come from this four game stretch (Lions, Bengals, Raiders, Vikings). Also note that this "out of sun" logo was much smaller than the one worn in the 1960s.
"In 1974, the Dolphins went exclusively to this smaller "out of sun" logo. Sometime around 1990, perhaps due to a change in decal manufacturer, the dolphin in the logo (but not the sun) became slightly larger. The "in the sun" logo was brought back for the 1994 throwback games; but the 2003 Thanksgiving Day throwback, supposedly based on the 1973 uniforms, actually used the early 1990's version of the logo.