Part 1: Skeletal Dimensions and Body Mass


        On the following pages are skeletal data from living canids (Table 1) and felids (Table 2). The data is based on published data (data from B. van Valkenburgh. 1990. Skeletal and dental predictors of body mass in carnivores. In: J. Damuth and B. J. MacFadden (eds.), Body size in mammalian paleobiology: estimation and biological implications. Cambridge University Press, Cambridge, UK, pp. 181-205), and where ever possible includes both a female and a male of each species. The data includes measurements of (Figure 1):

1) body mass (BM), measured in kg;

2) head-body length (HBL), the distance from the tip of the snout to the base of the tail, measured in mm;

3) skull length (SL), the distance from the tip of the premaxilla to the occipital condyle, measured in mm;

4) occipital-orbital length (OOL), the distance from the anterior edge of the orbit to the occipital condyle, measured in mm;

5) M1 length (ML), the maximum anterior-posterior distance of the lower carnassial (M1) measured in mm.

The data in the tables has been log-transformed to facilitate analysis. This data will be used to establish separate canid and felid regressions on the relationships between body mass and each of the skeletal characters.

        Construct a spreadsheet for analyzing this data. Determine regression equations for body mass and each of the other skeletal measurements. Plot the canid and felid data separately. Since there are eight different graphs to be displayed, you may want to name and store each one on a separate worksheet.

Extinct Carnivora
        We will be examining casts of four carnivore skulls from the Pleistocene of North America. The first is the dire wolf (Canis dirus), an extinct relative of the extant gray wolf (Canis lupus). The remaining three species are all felids; the American lion (Panthera atrox) and both juvenile and adult sabertooth tigers (Smilodon fatalis). For each specimen you should measure three features:

1) skull length (SL) the distance from the tip of the premaxilla to the occipital condyle,

2) occipital-orbital length (OOL) the distance from the anterior edge of the orbit to the occipital condyle, and

3) M1 length (ML) the maximum anterior-posterior distance of the lower carnassial (M1).

Since skulls may occasionally become deformed during fossilization, independent measurements of OOL and ML should be made on each side of each skull. Using the SL, OOL and ML regression equations generated from extant canids and felids, estimate the body mass for each extinct carnivore. For simplicity use the mean values of OOL and ML for each skull.

        A critical question to be addressed with these estimates is their degree of similarity. If all of the estimates for a single skull are similar, then this suggests that body proportions for the extinct and extant species are similar. However, if there is a marked difference between estimates for a single skull, this indicates that scaling of body parts in the extinct species is different than that of living species. This, in turn, suggests an adaptational modification of body scaling for a different life style.
 

Questions

Is there evidence of such decoupled scaling in your data?

What inferences could be drawn from any decoupled scalings?

Which skeletal measurement would you expect to produce the best estimate of body mass?

Do your results support this expectation?