Abstract:
Foramina of bones are beginning to yield more information about metabolic rates and activity
levels of living and extinct species. This study investigates the relationship between estimated blood flow
rate to the femur and body mass among cursorial birds extending back to the Late Cretaceous. Data from
fossil foramina are compared with those of extant species, revealing similar scaling relationships for all
cursorial birds and supporting crown bird–like terrestrial locomotor activity. Because the perfusion rate
in long bones of birds is related to the metabolic cost of microfracture repair due to stresses applied during
locomotion, as it is in mammals, this study estimates absolute blood flow rates from sizes of nutrient foramina
located on the femur shafts. After differences in body mass and locomotor behaviors are accounted
for, femoral bone blood flow rates in extinct species are similar to those of extant cursorial birds. Femoral
robustness is generally greater in aquatic flightless birds than in terrestrial flightless and ground-dwelling
flighted birds, suggesting that the morphology is shaped by life-history demands. Femoral robustness also
increases in larger cursorial bird taxa, probably associated with their weight redistribution following evolutionary
loss of the tail, which purportedly constrains femur length, aligns it more horizontally, and
necessitates increased robustness in larger species.
