An ungulate is conventionally a hoofed mammal. The name has also been applied broadly to extinct mammals with superficially similar anatomy, so a historical grouping by body form need not specify one exact modern evolutionary lineage. Convergent traits can make fossil relationships difficult to infer.
Ancient-protein analysis tested the relationships of two enigmatic South American forms. Collagen sequences recovered from fossils were compared with sequences from living mammals, placing the sampled extinct taxa near the odd-toed ungulate lineage rather than the alternative placements suggested by some anatomical comparisons. [ref]
Ancient proteins resolve the evolutionary history of Darwin's South American ungulates by Frido Welker and others. 2015, abstract: fossil collagen sequence recovery and phylogenetic placement of Toxodon and Macrauchenia
Molecular preservation thereby supplied evidence complementary to shape, even where recoverable ancient DNA had been lacking.