Molecular data can also be used to examine relationships between organisms, but the inaccessibility of comparative DNA samples for extinct taxa limits the usefulness of these data. Evidence for shared characters between whales and ungulates based on protein or nucleic acid sequences involves sampling of extant taxa only. However, whale skeletal data incorporateextensive paleontological data from fossils as well as data from extant species. Scientists use fossil data to help reconstruct the hypothetical relationships among whales and other even-toed ungulate taxa. This is a valuable source of data, because like many other taxa, most of the even-toed ungulates that have existed are now extinct.

Name a character you would expect to find in fossils of early whales that would provide evidence that whales share a common ancestor with other even-toed ungulates.