While the latter is a peculiar calidrid, the sharp-tailed sandpiper is much more similar to other Calidris/Erolia species such as the pectoral sandpiper. On the one hand, its larger size and long-legged stance, and the breast pattern which gradually fades away on the belly as in the ruff instead of having a fairly sharp border as in the Calidris/Erolia stints indicate that placement in Philomachus may be correct. Still, it is just as possible that – given the fairly common instances of hybridization in calidrines – mitochondrial DNA data has given a false picture of this species' true affinities. The curlew sandpiper, which is a proposed parent of the hybrid called "Cooper's sandpiper" ("Calidris" × cooperi) together with the sharp-tailed sandpiper, is another unusual calidrid that is hard to place systematically.