BONE MINERAL CALCIUM PERCENTAGE IN BIRDS VERSUS OTHER VERTEBRATES: WHAT XRF CAN TELL US ABOUT MODERN BONE CHEMISTRY

The veterinary literature notes that bird bones have a higher percentage of calcium than the bones of other vertebrates, which results in shattering rather than fracturing in response to trauma. However, it has not been demonstrated whether this characteristic of bird bones is due to elevated amounts of calcium within the apatite structure, or a higher ratio of bone apatite to collagen within the skeleton. If differences in original bone chemistry do exist, it is important to recognize them due to the control original bone chemistry exerts on fossilization. Different percent composition of calcium in the bone may affect the amount and type of rare earth elements (REEs) and other trace elements that are incorporated during fossilization.

In this study, I use a ThermoScientific Niton XL3t XRF Analyzer and Innov-X Delta Handheld XRF Analyzer to examine chemistry of fish, reptile, mammal, and bird bones to test whether calcium values are elevated in birds compared to other vertebrate groups. Calcium was measured in overall parts per million (ppm) and converted into overall percent composition. In addition to XRF analysis, bone ash composition values were taken from the literature for comparison of overall calcium percentage in bone ash within different non-human vertebrates. Specimens consisted of the following areas of the skeleton: skull (fish, reptile, bird, mammal), vertebrae (fish, reptile, bird, mammal), long bones (bird, mammal), and limb girdles (reptile, bird, mammal). The sample included representatives of both wild and domestic species, as well as one pathologic sample (bird).

Birds did not show elevated calcium content compared to other vertebrates in both the XRF and bone ash studies. This suggests that a higher percentage of calcium in bird bones is not responsible for their brittle behavior in response to trauma; however, further testing is necessary to test whether apatite to collagen ratios differ in birds compared to other vertebrates, or if other significant differences in bone chemistry exist between vertebrate groups.