Femur cross section comparisons (IMAGE)
Caption
The three images are cross sections of femurs from a marsupial (the Virginia opossum, left), a placental (the eastern chipmunk, center) and a 66-million-year-old multituberculate fossil (right). The opossum femur has a thick layer of organized bone in the outermost cortex (labeled “POB” for periosteal organized bone), with little disorganized bone (labeled “DB”). In the chipmunk and multituberculate femurs, a layer of disorganized bone (“DB”) is “sandwiched” between layers of organized bone (“POB” and “EOB,” which stands for endosteal organized bone). Scale bar is 0.1 millimeters. The multituberculate specimen (UWBM 70536) is likely a member of the genus Mesodma.
Credit
Henry Fulghum/Lucas Weaver/University of Washington
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