This research project was the basis of MDN’s PhD thesis at George Mason University. Here is a brief description of the problem, method, and results of this research:
Problem
Some taxonomic groups, either through poor scientific practices, or poor scientific understanding of the group itself, end up as a “wastebasket group”: one that contains fragmentary or poorly identified specimens, or unrelated species. Wastebasket groups lose scientific meaning, and must be systematically reviewed. The Squalodontidae, a family of ancient whales, was a wastebasket which obscured its evolutionary significance.
Methods
We analysed relevant publications, specimens, taxonomic information, and occurrences of squalodontid fossils with age and lithology data. For each species within the Squalodontidae, we decided if the species was based on a specimen that was sufficiently complete to be taxonomically diagnostic.
Results
The review of the Squalodontidae revealed the following:
- In the European record of the family, consisting of 22 species in two genera, only eight species were actually based on specimens that were taxonomically diagnostic; this drastically reduced the known diversity of the family but is more accurate.
- The Squalodontidae indisputably first appear in the late Oligocene. However, in contrast with previous scientific consensus, we find that the family may not have persisted well into the middle Miocene (Serravallian) as the only unequivocal specimens of Squalodon are found in boundary-straddling units.
As a result, we have a better understanding of the diversity through time of the Squalodontidae.
Here is the abstract of the paper which was published in Papers in Paleontology by Nelson et al.:
The Squalodontidae is one of the most historic families within the Cetacea, as Squalodon was first named in 1840. Since Squalodon’s initial description, workers in the 1800s were eager to assign heterodont cetacean teeth to this family; as a result, it became a wastebasket with many species based on fragmentary remains. Taxa represented by well-preserved specimens demonstrate that the Squalodontidae possess a mixture of ancestral and derived traits: they exhibit polydonty as most modern odontocetes do, but their teeth are still differentiated into incisor, canine, and molariform types. Despite their position as a transitional form, the Squalodontidae have been neglected in the scientific literature and much of this is due to their poorly resolved taxonomy. While revisional work has been done for the North American record, the European record has remained a wastebasket. We assess here the taxonomic status of the 22 species included in two squalodontid genera recorded from Europe spanning from the Chattian to the Serravallian. Both species of Eosqualodon bear diagnostic name-bearing specimens. However, of the 20 species of Squalodon, only six bear diagnostic types and of those, one is a junior synonym. Our literature review of historic papers reveals that the other 14 species of Squalodon have nondiagnostic name-bearing types, are synonymous with other species of Squalodon, or never had a specimen associated with the name. We also call into question the assertion that the Squalodontidae persist into the Serravallian, as the youngest family-diagnostic specimens are found in Langhian-Serravallian boundary straddling units.
Works Cited:
Nelson, M.D., Lambert, O. and Uhen, M.D. (2025), Taxonomic revision of the family Squalodontidae (Cetacea, Odontoceti): emptying the wastebasket of fragmentary holotypes. Pap Palaeontol, 11: e70002. https://doi.org/10.1002/spp2.70002