DENTAL VARIATIONS AND ANOMALIES IN EXTINCT PILOSANS (MAMMALIA: XENARTHRA)

Dental anomalies are expressed in a variety of ways from variations in tooth number to changes in tooth morphology. The occurrence of such variations is well documented within extant mammals and in various extinct mammals, which has increased understanding about the evolution of teeth and has been used in establishing taxonomic speciation. Dental variations, such as anodontia and hyperdontia, have recently been recognized at a frequency of less than 3% in the two extant genera of sloths, Bradypus and Choloepus. Review of dental anomalies within extinct ground sloths reveals a greater diversity of taxa exhibiting variations away from the typical 5/4 or 4/4 dental pattern than previously documented and with some taxonomic implications. Most anomalies are of a rare frequency similar to the rate found in extant sloths, as in the single documented cases of anodontia via connation in Eremotherium and hyperdontia (supernumerary tooth) in Megalonyx. Lestobradys, recently erected from the Miocene of Uruguay, is a potential erroneous creation as the supposed M1 occurs anterior to or within the diastema space and just posterior to the caniniform, which is a where most supernumerary teeth occur in Choloepus. Mylodon and Paramylodon from the late Pleistocene both exhibit rather frequent anodontia of the upper caniniforms. The base dental formula for Mylodon was long thought to be 4/4 but recent evidence shows individuals born with a 5/4, as exhibited by a juvenile specimen and also by alveolar scaring in adult specimens at C1 location, indicating the loss is postnatal instead of prenatal. Paramylodon is unique with a high frequency of postnatal loss of the upper caniniforms (~55%), and is more anomalous with the loss occurring in either one or both sides as seen in specimens from the La Brea tar pits. Increased tendency toward a 4/4 dentition in this genus could correlate with environmental factors as the cause of loss as individuals aged, possibly from tooth damage, but the occurrence of this anomaly in other, non-La Brea populations instead suggests a potential shift to being prenatal and thus a true speciation event, had the taxon survived the Pleistocene mass extinctions.