Dental Anomalies in the Eastern Mole (Scalopus Aquaticus)

Article excerpt

ABSTRACT.-

We found dental anomalies in 36 of 249 (14.5%) cleaned skulls of eastern moles from southern Illinois and Cincinnati, Ohio. Additional teeth (supernumeration) were observed in four individuals; one specimen had a unilateral additional upper premolar, and three specimens had additional upper or lower incisors. Connation (splitting) occurred unilaterally in I^sub 1^ and P^sub 1^ of one individual. Failure of teeth to develop (agenesis) was much more common, occurring in 31 individuals. Agenesis usually involved maxillary dentition-P^sup 1^ and/or I^sup 2^ and I^sup 3^-sometimes with the same individual having lost incisors and premolars. Agenesis of mandibular dentition (P^sub 1^) was noted in only one individual. We found no anomalies involving molars and no relationship between age of individuals and dental anomalies. Rudimentary teeth ("spicules") in the mandibular diastema occurred in 68 individuals (27.3%). There was a trend toward reduction of rudimentary teeth with increasing age, but no relationship between occurrence of anomalies and rudimentary teeth.

INTRODUCTION

The evolutionary trend in most mammalian species has been a reduction in the number of teeth from the primitive eutheiian ("placental") dental formula of 3-1-4-3/3-1-4-3 = 44 teeth. Several genera of talpids, including New World Condylura, Parascalops and Scapanus, as well as Old World Talpa, possess the primitive eutheiian dental complement. All other genera have lost teeth, although it is sometimes problematic to determine which teeth are missing. Dental anomalies - including extra teeth (supernumeration or polydonty), missing teeth (agenesis or oligodonty), connation (splitting), rotation and misalignment - have been reported from a variety of mammalian taxa (Miles and Grigson, 1990). Anomalies can be caused by genetic (developmental), physiological, environmental or nutritional factors. Agenesis almost always occurs on the anterior or posterior ends of the dental arcade - usually involving small teeth or those with simple crown patterns. The greater degree of functional plasticity in these teeth suggests a reduced contribution to individual fitness and eventual loss through evolutionary time. For individual animals, severe dental anomalies also may have an impact on longevity.

The eastern mole (Scalopus ac/uaticus) has the largest geographic range of any North American talpid and is the most common species of mole east of the Mississippi River (Yates and Schmidly, 1978). The dental formula of the eastern mole is generally considered to be: 3-1-3-3/2-0-3-3 = 36 teeth - with the American shrew mole (Neurotrichus gibbsii), the fewest number of teeth among North American talpids. The dentition of eastern moles also is of interest because of the occurrence of rudimentary dentition or "spicules" that sometimes occur in the diastema of the mandible. Ziegler (1971:63) described spicules as "extremely erratic in both their presence and degree of development." Our objective was to document the age-related occurrence of dental anomalies and spicules in a sample of eastern moles.

MATERIALS AND METHODS

All moles were collected from areas of southern Illinois (about 37.72'N, 89. 20W) and Cincinnati, Ohio (39.16'7N, 84.46W) from Oct. 2004 through May 2005. Sex, date of capture, location and standard body measurements were recorded for each specimen (see Kamm et al, 2008). Skulls were removed and cleaned using dermestid beetle larvae. Yearly age classes from juvenile (young of the year) through 5 y of age were determined from wear criteria of the last tipper molar based on Hartman (1995). Because of low sample sizes, we grouped age classes 4 and 5 for analyses. For consistency, one of us (GAF) estimated age of all specimens. Rudimentary mandibular teeth were noted, but were not considered anomalous. Secondary or postnatal tooth loss evident from existing alveoli or roots was excluded from analyses. We used chi-square analyses or G-tests for independence to test for age-related relationships with dental anomalies or spicules, whether there was a relationship between anomalies and spicules in individual moles, and for differences between the two collection areas in age structure, anomalies or spicules. …