School of Life Sciences | Ask A Biologist

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Human, bird, and bat bone comparison

show/hide words to know

  • Common ancestor: a single species that gave rise to at least two other species.
  • Density: the measure of mass per unit of volume. Think of it as how solid something is. If you have two equal size objects, the one with the higher density would weigh more.
  • Mass: is used to describe how much matter is in an object. If you know the number of atoms, the density of the atoms, and what type of atoms are in an object you can calculate its mass.

Human, bird, and bat bone comparison

From the outside human arms, bird wings, and bats wings look very different. Humans are covered in skin, birds are covered in feathers, and bats are covered in hair. But on the inside there are many similarities among human, bird, and bat forearms. Did you know that humans, birds, and bats have the exact same types of bones in their forearm? These organisms share the same forearm bones because they all evolved from a common ancestor.

Human, bird, and bat forearm bones include the humerus, ulna, radius, carpals, metacarpals, and phalanges. Can you identify these bones on the diagram below?

bone comparison illustration

While these organisms all have the same basic types of bones, the bones have been modified to have different functions. Humans use their forearms to reach and pick up objects, swing a baseball bat, and play the piano. Bird and bat forearms have evolved into wings allowing them to fly. Can you find any more differences and similarities among human, bird, and bat forearms?

Download your own human, bird and bat bone coloring page.

Looking inside bones

Bones of animals are strong and mostly dense, but they don't all have the same structure. Unlike human bones, birds have a lot more empty space inside their bones. If you compare bat and human bones they look smaller and more delicate. This was thought to make them lighter so they can fly. Some recent research has shown this is not true. Even though bird bones have more empty space inside and bat bones are thinner, the bone material is actually denser than the bones of a similar size rodent. Rather than lighter weight bones making it possible for birds and bats to fly, the research shows that these bones only look like they would be lighter. Instead their increased bone density makes them strong and stiff to handle the stress of flight.

Bird and Human Bone Comparison


Reference:

Elizabeth R. Dumont. (June 10, 2010). Bone density and the lightweight skeletons of birds. Proceedings of The Royal Society B Biological Sciences, 2010. Retrieved April 18, 2015 from http://rspb.royalsocietypublishing.org/content/277/1691/2193

bat

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Be part of Ask A Biologist

by volunteering, or simply sending us feedback on the site. Scientists, teachers, writers, illustrators, and translators are all important to the program. If you are interested in helping with the website we have a Volunteer page to get the process started.