No. Humor was/is very important in traditional Native cultures. It was sacred even. It was specifically used to highlight that humans do have a lot of weaknesses so clowns/other figures showed how people act and explained why.

As /u/brutalboonie and /u/ahalenia have pointed out, no. Author Hampton Sides, in his book Blood and Thunder, described the Navajo's "famous" sense of humor as including an "unslakable appetite for teasing and puns" and "delight in any incongruous or absurd situation." Emotion was also on public display during times of sadness: "The Arapaho relatives mourned in the self-flagellatory tradition of the tribe - pulling out hanks of hair, tearing at their own skin, perhaps cleaving a finger" (also from Blood and Thunder). As far as showing emotion with European colonists or their descendants, it would very much depend on time, place, and circumstance.

Perfect timing! The Horace Poolaw exhibit is up at NMAI George Gustav Heye—he began photographing his fellow Kiowas only a few short years after non-native Edward S. Curtis published his photogravure's in North Native American.

Anyway no. Most photos of the 19th century of anyone features unsmiling people. You can look at the movies or photographs of Native by non-natives and compare them to movies or photographs by Native peoples. For example, Cherokee comedian Will Rogers was the first Native American movie producer and was far from stoic.

It also makes a difference if the photographer dictated the subject (Curtis had a very specific vision of the "Vanishing Indian") or if the Indians themselves commissioned the photos. If you can get your hands on a copy of People of the Big Voice: Photographs of Ho-Chunk Families by Charles Van Schaick, 1879-1942, it's fantastic. These are portrait photos that Ho-Chunk families commissioned and include such gems as a family posing with their pet racoon and another of a wife and husband, in which the husband felt the need to pose with an apple stuffed in his mouth like a roast pig.

This might have been true for some tribes more than others, especially the ones who were at war with each other. Not showing emotions to your enemy is a pride/dignity thing I guess, it helped keep them fearless. Remember also, the famous "stoic" photos were taken by force most of the time by whites after they managed to capture a Native. Nobody is going to smile for their enemy. If you think they were giving the camera: I'm going to kill you in your sleep glare, it's because they probably were. Natives feel just as many emotions as everyone else. Maybe too much sometimes. Natives definitely love to laugh. They like to tease a lot.