

The consensus of opinion among scholars is that Monument 19 at La Venta is the oldest-known feathered serpent in Mesoamerican art. Be sure to note that there are two quetzal birds facing a central sky band represented by crossed-bands resting on a plaque, which could have had something painting within the box. In Mayan languages the word for sky and snake are generally homophonous (can or chan). In Mixe-Zoquean (the language in transition from Olmec to Mayan), the serpent is tsan and sky tsap, which are similar enough. The man’s helmet is just like the snake’s head, so he is a priest representing the cult (religion) of the serpent. (There is an excellent drawing of this Monument in The Olmec World: Ritual and Rulership).
The drawing I’m giving you here (at the bottom) is more detailed. It was drawn by Linda Schele that she had in her guide book on one of the trips I took with her. There may have been other representation of the feathered serpent after that, but they don’t seem to show up until Teotihuacan (at A.D. 200).
The so-called “Olmec Dragon,” a combination of jaguar and serpent, is an early ancestral form of the Plumed serpent, according to Michael Coe. If it has an X on its body (referred to as crossed-bands), and it represents the center of the cosmos, or the ecliptic crossing the Milky Way.