SPECIES SPECIFIC CORRELATION NEEDED TO CALCULATE BODY MASS OF ANCIENT SMALL MAMMALS

For mammals, body mass is correlated to a host of physiological, ecological and life history traits. Trends and changes in body mass over longer time periods can help inform about how a species’ ecology has changed in relation to changes in climate and/or paleoenvironment, for example. For fossil specimens, body mass is, generally, relatively simple to calculate as it typically correlates to length measurements of skeletal features. For rodents, body mass is usually calculated using the length measurements of a particular tooth or tooth row. This relationship can then be calculated using regression equations, which show very high correlation between rodent body mass and tooth/tooth row length measurements. In a series of analyses on different small mammal species aimed at determining the effects of current global climate change on body size, we noticed that the body mass-tooth/tooth row length correlation, from modern specimens, may not be as high in all rodent species.

The rodent in question, Myodes gapperi, is a small vole that inhabits most of the northern parts of the United States, and almost all of the forests of Canada. This species is known to fluctuate in body mass over the course of a year, similar to many other small mammal species. In this study we analyzed 11 measurements on the skulls of over 700 modern skulls of Myodes gapperi specimens from NY State with the initial aim of assessing geographic differences in body mass as well as the effects of on-going global warming on body size. The examined specimens were all housed in the Vertebrate Paleontology and Mammalogy collections at the NY State Museum. The results showed that the correlation between body mass and tooth/tooth row measurements, while still significant for some measurements, was not as high as provided in previous studies, even when focusing on particular seasons. These results have implications for the use of tooth/tooth row measurements to calculate body size in rodents, and may complicate the interpretations of some previous studies. These results also show the need to assess the appropriate body mass-skeletal length correlation in a particular study species before extending the use of a correlation on fossil specimens.