So how does one distinguish caiman from crocodile. Well, where we were, with spectacled caiman and orinoco crocodiles the difference in size between adults is obvious. This doesn't help you though if you are dealing with small animals or are somewhere with big caiman sp. like the black caiman (Melanosuchus niger). Generally caiman have very different heads to south american crocs. Take this spectacled caiman - see how the eyes are perched up on top of the head?
This isn't always as pronounced as this but it does tend to be noticably different to this.....
That's the same angle on the orinoco croc. Note the flat head. I suspect this evolved to allow the crocodile to approach bigger prey at the waters edge as stealthily as possible. Spectacled caiman tend towards more aquatic prey and are more generalist as I understand it.
Telling Spectacled caiman from any other species tends to be easy for the simple reason that the diagnostic feature is handily located so that it tends to be visible at all times. In the picture below you can clearly see a ridge or line between the eyes. This is supposed to look like the bridge of a pair of specs hence the name.