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A variety of substructures have been identified within the tidal debris around interacting galaxies. These structures range in scale from Globular Clusters to the so-called “Tidal Dwarf Galaxies”. We review observations of such objects, with particular emphasis on what can be inferred from dynamical mass estimates. We then present the results of a dynamical analysis of structures which develop within the tidal tails of a large-N numerical simulation (N~1 million). We find that under the best conditions, “observations” of this system recover the true mass of the bound substructures to within a factor of two. Poor spatial and velocity resolution (coarser than the true half-light radii and velocity dispersions) and more inclined viewing geometries lead the dynamical masses to be over-estimated by factors of ten or more. A combination of poor resolution and edge-on viewing geometries lead to the most dramatic discrepancies, with dynamical masses over-estimated by factors of up to 1000. Furthermore, projection effects can lead to apparent concentrations of material at the ends of tidal tails that is in reality spread over very large distances, with mass scales well beyond that of any truly bound regions. Since many of the well studied tidal dwarf candidates are found within edge-on tails, we conclude that their mass and extent may have been greatly over-estimated.
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