Counted across the classical corpus, animal names make up the largest single group in the posture vocabulary: serpent, eagle, cow, cockerel, tortoise, crocodile, frog, fish, peacock, lion, locust, camel, bull and tree stand beside a much smaller set named for people, for qualities and for objects. The Gheranda Samhita carries most of them, and the Hatha Yoga Pradipika comparatively few.
That distribution follows from the shapes each text records. The earlier manual is a book of seats, and a seat is hard to name after an animal because animals do not sit cross legged; its names accordingly tend to be qualities, the auspicious, the liberated, the accomplished. Once a compiler admits prone, kneeling and standing forms, resemblance becomes available as a naming principle, and the animals arrive with the shapes.
None of this implies that an animal posture is a way of taking on an animal's nature. The manuals do not say so, and the atlas does not import that reading from later popular writing. The names work by likeness, and they work well: a name that carries a picture is far easier to transmit orally than a description of where each limb goes, which matters in a tradition whose technical literature is terse verse intended to be memorised. Mallinson and Singleton's Roots of Yoga presents these lists in translation and makes the pattern easy to see across the corpus as a whole.