Biological soil crusts<span> are communities of living organisms on the </span>soil<span> surface in arid and semi-arid ecosystems. They are found throughout the world with varying species composition and cover depending on topography, </span>soil<span> characteristics, climate, plant community, microhabitats, and disturbance regimes.</span>
<span>Joints with no movement are called immoveable or fibrous joints.They are also called synathrosis, they are only separated by a thin layer of fibrous connective tissue e.g are the sutures of the skull.
Joints that are more loosely connected are called freely moveable or synovial joints. They are also called diarthrosis.The joints are held together by an articular capsule comprised of ligaments. A synovial membrane lines the inside of the capsule and secretes synovial fluid which lubricates the joint (hence it's name).</span>
Answer:
So they are lighter and move quicker.
Explanation:
With the small wings and bodies birds have it would be hard for them to escape predators and lift their own weights if their bones were dense like humans' bones. The hollow part of the birds' bone is connected to their lungs so they have enough oxygen to fly easily. Hope this can help you! :)
