Joseph Smit was a Dutch zoological illustrator. His sketches are amazing. Just look at that little wallaby.
All of the slides from Alfred Edmund Brehm's "Brehms Tierleben" are available as well--absolutely gorgeous black-and-white sketches from the world's first major zoological encyclopedia. Check it out here.
Also fantastic resources: New Yorker Louis Agassiz Fuertes, who contributed to early Audubon and National Geographic publications; Charles R. Knight, who painted dinosaurs, woolly mammoths, and other creatures of the past; and Joris Joostensz Laerle, who holds a special place in our heart for his sketches of dodos.
4. Pick The Right Image The image you pick has to be as large as possible. When browsing Wikimedia, always click on the "full resolution" link right below the image. If it's below about 1,000 pixels wide? It'll be too small for your purposes. You can always shrink a high-resolution image, but it never looks good to expand a low-resolution image. Also, a white background is best for drawings, since the canvas itself is white. Once you find the one you want, right-click on it and save the image to your desktop.
5. Head To A Printing Site Now what we're going to do is find any of several cheap-ish online canvas printing sites. You can go even cheaper and print out a large image on standard poster or photo paper--even Staples will do that for you--but it won't really look wall-worthy. You want to value your animal picture! Canvas looks great and professional, and we've had good experiences with these sites. My personal favorite is called Easy Canvas Prints; they often have the cheapest prices, and they regularly have giant sales. Right now they're doing a 40 percent off sale for the holidays. Another good option is Canvas On Demand; they're a little bit more expensive, but their shipping turnaround tends to be a bit faster.
Any of these sites will walk you through the sizing process; you may have to do some trial-and-error to get the right size, but it's not too hard. The most important thing is to make sure your image isn't getting cut off at the sides. And these sites almost always have some kind of sale; there's no need to ever pay full price to get online printing done.
As far as size goes, some of these images are big enough to make enormous prints. Be careful to measure your space before you order, to make sure it fits. Once you're sure, order away! And enjoy your new animal art.