Some film histories erroneously cite this as the first animated cartoon, ignoring not only Humorous Phases of Funny Faces (1906) (probably the first true animated cartoon), but even Winsor McCay's own earlier work, Winsor McCay, the Famous Cartoonist of the N.Y. Herald and His Moving Comics (1911) and How a Mosquito Operates (1912).
The first movie featuring a dinosaur.
This film required Winsor McCay and his assistant John A. Fitzsimmons (who traced the backgrounds) to create 10,000 drawings, which they inked on rice paper and mounted on cardboard. Although later animators created techniques (such as the "slash system" and especially celluloid-over-paper) that would eliminate the need to redraw backgrounds or stable objects, McCay was working without precedents. Consequently, he chose to redraw the entire picture-- Gertie and the richly-detailed background-- for each frame.
Winsor McCay's employer, William Randolph Hearst, was displeased with McCay's success outside of the newspapers, and used his contractual power to reduce McCay's stage activities. In late 1914 William Fox offered to market the film to moving-picture theaters. McCay accepted, and extended the film to include a live-action prologue and intertitles to replace his stage patter. This is the version of the film generally seen nowadays; the original animation comprises roughly five minutes of the entire 12-minute film.
In creating the film, Winsor McCay came up with a number of techniques that would later become standard in the animation industry. He used registration marks to keep the background aligned from frame to frame, so that it did not appear to "swim", as often happened in early cartoons. He avoided some repetitious work by re-using drawings, in what would later be called cycling. He devised what he called the "McCay Split System", the first occurrence of key-frame animation. Rather than draw each frame in sequence, he would start by drawing Gertie's key poses, and then go back and fill in the frames between. McCay was also very concerned with accurate timing and motion; he timed his own breathing to determine how to animate Gertie's breathing, and included subtle details such as the ground sagging beneath Gertie's great weight.