I'm curious, are all museum artifacts real or replicas?

Museums are meant to educate, so if a replica does the job, its good for them. Also, many actual artifacts are too fragile to be on general display, or too valuable to risk coming into contact with untrained visitors who may accidentally damage it. If you don't like fakes, research the museum's exhibits before you visit.

As there is only one of the real thing less people could see it. In the case of bones you often can't tell the difference and the experience standing besides a dinosaur skeleton as far as an impression of size is concerned is the same, regardless whether it's a copy or the original. Once reason why museums show replicas as well as originals is also that in order to preserve the item it has to be stored under certain conditions (e.g. low light levels or low humidity) which would not go well with the actual environment in the museum. In addition museum visitors may keep touching e.g. bones repeatedly (regardless of signs) and contribute to the slow destruction of the bones. Also they wouldn't necessarily want to drill holes into the original bones and put screws into them and whatever is necessary to provide a stable upright skeleton in a life-like posture. Good replicas are actually pretty expensive, even for something like the skull of a cat you probably would have to pay several hundred dollars. Through replicas many people instead of a few can see the bones. Edit: there is a huge difference in viewing somebody riding an old bicycle (e.g. pennyfarthing) online or in real life or particularly getting to try it yourself. It doesn't matter too much whether the pennyfarthing is original or a replica. 10 minutes on a replica would teach you more than an hour online - and you would remember it better.

The calendar you referred would almost certainly be a molded copy of the original, unless collected a hundred years ago, because these days Mexico and countries to the south refuse to let their heritage out of the country. And although very large and stone, it would likely be broken or otherwise damaged in moving. Dinosaur skeletons are, by the time they are collected, stone fossils which are brittle, heavy and may be in pieces to start with. Collecting an entire skeleton is very unusual, so to display an entire skeleton may require making copies of the bones from the other side or from another skeleton in another museum. Because the fossils are so heavy, the mounted shapes may be mostly fiberglass or plaster with steel rods inside. Normally, museum personnel or the signs make it clear how much is reproduced. Skulls of humans, because the old ones are so rare, are often only fragments, but it is normally made obvious that the skull has been filled out because material of a different color is used. For example, in the image here http://www.mentalfloss.com/blogs/archives/1855, the white is the pieces of the fossil and the brown is supporting material. The article describes the skull as being "amazingly complete" even with all the holes because enough pieces exist, when fitted together, to show the size and curves of the skull. And of course, any display of the body and skin of a dinosaur is entirely a reproduction, usually in fiberglass, because while some impressions of skin on rock have been found, nothing exists as clues to color or most texture. And if you can "stand next" to an image and understand the size and scale of things, then you have a huge background of experience that was built going to museums, in spite of your poor attitude.