Complex sentence: One analogous feature is a forearm and five finger-like bones which is the same structure found in humans, birds, etc. However in the leopard seal, these fingers are covered in a web of skin, which they use to propel themselves through the water.
Split into simpler sentences: One analogous feature is a forearm and five finger-like bones, which is the same structure found in humans and birds. However, in the leopard seal, these fingers are covered in a web of skin, which they use to propel themselves through the water.