The Arlington Springs femora, critically, were also incomplete.

The femoral heads — the rounded upper ends of the thigh bones that fit into the hip socket and that carry important sex-diagnostic measurements — were apparently not present in the museum collection.

Phil Orr had measured the maximum femoral head diameter and published it in his 1968 monograph, but the physical specimen was not available for direct remeasurement by later researchers.

The result is a sex determination that has been revised twice and remains probabilistic rather than certain.