Proportions of animals are a little harder to figure out because the landmarks on humans are different than on animals. I mean, we stand on two feet, they walk on all fours etc. but one thing that is consistent with animals in general is the skeleton. With that said, if you are studying any kind of animal - human or otherwise- you need to know what's going on underneath, in both bones and muscles. If you don't how to get started doing this or if you have used the internet to look up an animal (say a squirrel monkey) and can't find any on the animal's anatomy, use it's Latin name (Simia sciureus) and you will be more likely to find information more closely related to the animal's anatomy.
But, and this is important, CROSS REFERENCE your information! I have seen students bring in anatomy reference examples, drawn by other previous students, which are downright wrong. Photos are best but scientific illustrations are good as well if care was taken to scan or photograph them. If you can't find anything about your animal, look up which zoos have your animal in their collection and call or email them or their veterinarian and ask about reference material for the animal in question. Or talk to a zoo keeper, they are pretty cool and can help you in your endeavor. and they are happy to help if they can. There is always the tried and true method of GOING TO YOUR LOCAL LIBRARY to do some research (gasp). I know a lot of librarians-they are really cool and willing to help! And lots of libraries have free WiFi...and some even have coffee shops...what more do you need?
When you finally do acquire reference of the animal's anatomy, namely in profile, measure the skull from the front/tip muzzle to the back of the head where the spine meets it. Most quadrupeds have a spine that meets the skull at the back rather than below, unlike humans. Below is a photo of a polar bear, ursas maritimus, acquired from this site. Even this specimen, as beautifully as it's been articulated, isn't exactly correct as the fore paws are too far forward for it to stand naturally, but let's move on. I, like many others, LOVE polar bears; they are so large and furry and cool and furry and chunky and furry and furry. Did I mention furry? When you are just getting started drawing them, all that fur kinda gets in the way and you end up with weird bear shaped balloons because...furry. The skeleton has no fur so you can measure without distraction, woo! 'Had a student once who said, "I can't draw this cat because it's fluffy." Ahem, skeleton, duh.
Okay, okay...you're right. Not everything can be measured by the skeleton. You can also measure with a fully furred animal. Here's a photo from this site. Aw, a big furry polar bear, awwww!
Thanks for stopping by.