This is an individual opinion on this topic. To read a number of different peoples' answer to this question click this link here. If you have your own answer, read the last paragraph of this post for details on how to get yours posted.
Craig Dylke answering the question above this time around. Though my answer seemed simple in my head, it has proven rather complex and difficult to capture in writing. This is just the introduction of a much larger essay I have been working on for 2 weeks now. I may or may not finish the rest depending on how people respond to my slightly controversial view of Palaeo-art.
My definition of Palaeo-art is:
It is any piece of work created through human effort that causes viewers to reconnect with (or more to the point re imagine) the prehistoric past.
Okay, easy enough, right? Any piece of art that invokes prehistory in people's imagination. In principle this is a simple enough premise. It is when the philosophy and semantics of this all come to bear I'm left with a rather interesting definition of Palaeo-art.
The biggest problem with my view of Palaeo-art is that it rests on 1. Prehistory and 2. more to the point people's understanding and connection with this "Prehistory" concept. None of us has ever seen it or been there before. This lack of tangibility with deep time becomes the fundamental issue in defining Palaeo-art.
From a pure knowledge point of view our understanding of prehistory comes from the scientific method. Which begs the question how important is science to Palaeo-art?
Science is an important part of the equation in Palaeo-art, but the extent of this science doesn't have to go as deep as many would hope, I suspect wish. The science is more of an artistic "flavour", and need only be added so much that the subject matter of a piece (the organisms) be recognizable as being "prehistoric" in nature. There is as much a cultural component to Palaeo-art as there is science.
These pictures are from here, here, there, and here (I do not endorse, nor have I read, the sites they are from. They simply came up in an image search of "Dinosaur" on google)
For example all the above images are instantly recognizable as both being Dinosaurs, and thus being of something "Prehistoric". However the majority of us here on this site know this isn't true, at least in reality (aka scientific terms). They are images that loosely draw on elements of real Dinosaurs, and thus conjure an association. In the realm of science they'd be torn to shreds, and look nothing like their flesh and blood name sakes would have in life.
Yet can we discount this cultural power when considering Palaeo-art? If anyone can tell you these pictures are of animals from a long time ago, how does this make these pictures any more or less valuable than scientifically accurate pieces by the likes of Gregory Paul or Charles Knight? If anything some modern scientific understandings of prehistoric animals are almost too alien for the public to accept (feathered Dinosaurs being an example that jumps to mind).
You could argue that my above prehistorically "inaccurate" pieces invoke a fantasy prehistory rather than anything resembling the real past, and thus they are not prehistoric renderings at all. However I'd be careful before making such an argument. It is a trap... for you!
I've noticed many people would like to have something about Palaeo-art being work that adheres to absolute science. This is probably what is going to differentiate my definition from many. I argue, on pretty solid grounds, you can not have a "perfect scientific restoration" of any extinct fossil creature at all, and so to define Palaeo-art as requiring such accuracy is paradoxical.
There are too many unknown variables with the creatures and times solely known from the fossil record. These unknowns must than be filled in by human imagination, which is the realm of art not science. At the same time these leaps of imagination can be completely tempered by science. However it is important to keep in mind this is not the same as having science fill in these holes!
This creativity is not just restricted to artworks, it finds its way into every step of palaeontology. Right from the time fossils are discovered, dug up, described, and finally conjured in art (painted, sculpted, etc.) there has been a lot of human creativity applied to interpreting the fossils through out these processes. This is part of what makes palaeontology so much fun, but also what makes it frustrating.
Yet I don't think we should despair in face of all this. Rather I think we should rejoice! Part of what makes Palaeo-art so much fun and so rewarding is that you can connect people with the MANY real chunks of science by filling in the unknown gaps with your own imagination. Your art becomes the closest thing we have to a time machine, and I think that is just awesome!
This concludes my general definition. It was just my thesis for a much larger essay. I go into the various genres of Palaeo-art I feel exist (Fossil Preparation, Skeletal Reassembly, Scientific Reconstructions, Pop Culture, and Abstract/Symbolism). I also address the problems with science as a pure basis for Palaeo-art. If any of these interest you, just let me know, and I'll finish them up and post them!
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