United States Fish and Wildlife Service list of threatened and endangered arthropods species may be treated as endangered or threatened if it resembles in appearance a species which has been listed and enforcement personnel would have difficulty distinguishing between the listed and the unlisted species; if the effect of this difficulty is an additional threat to the listed species; and if such treatment of the unlisted species would improve protection for the listed species. United States Fish and Wildlife Service list of threatened and endangered arthropods List of threatened and endangered arthropods, including insects, arachnids, and crustaceans under the United States Endangered Species Act as of October 2013. Key to Listing Status
Bird feet and legs The legs are attached to a strong assembly consisting of the pelvic girdle extensively fused with the uniform spinal bone (also specific to birds) called the "synsacrum", built from some of the fused bones. Birds are generally digitigrade animals (toe-walkers), which affects the structure of their leg skeleton. They use only their hindlimbs to walk (bipedalism). Their forelimbs evolved to become wings. Most bones of the avian foot (excluding toes) are fused together or with other bones, having changed their function over time. Some lower bones of the foot are fused to form the tarsometatarsus – a third segment of