Here artwork is incredible and demonstrates a world-class level of care for her topics. I even read (but lost the source) that when she worked with traditional media and was attempting to portray a scene or organism underwater, she would snorkel and make sketches underwater (presumably with waterproof materials!). I had come across her art several times in my internetting, but never realized that it was all mostly from one woman!
Here website and online gallery are easy to navigate and contain a treasure trove of wonderful biodiversity - alive or extinct. She also posts directions on how she paints digitally, which is neat.
Her best known work and association is with The Field Museum in Chicago, IL, an incredible museum of natural history.
The following images are samples of her work (all copyright Karen Karr and are available on her website):
PS - if you find yourself interested in illustrating natural science (I know I am!), check out the website for the Guild of Natural Science Illustrators (GNSI).