How Big Is a Giant? The Importance of Method in Estimating Body Size of Extinct Mammals

Ecological and evolutionary significance of sizes of giant extinct kangaroos

“…Cranial metrics may be determined and/or tightly constrained by feeding requirements, and dental dimensions are particularly problematic for macropodids, in which molars erupt continually and are successively shed. In contrast, load-bearing long bones (such as the femur or humerus) exhibit similar scaling relationships across unrelated taxa and over a wide range of body sizes and are considered more appropriate for body mass extrapolations (Anderson et al 1985;Anyonge 1993;Reynolds 2002). Predictions based on mid-shaft circumferences of load-bearing long bones are particularly powerful (Anderson et al 1985;Wroe et al 2004), and because kangaroos are bipedal, femoral dimensions are especially appropriate.…”

The largest among the smallest: the body mass of the giant rodent Josephoartigasia monesi

“…This relation is then applied to extinct species to estimate their body mass. This procedure is in principle very straightforward, but it has a number of limitations (Smith 1980(Smith , 1996Schmidt-Nielsen 1984;Damuth & MacFadden 1990;Egi 2001;Reynolds 2002). In particular, I have identified four main issues that place doubt on the body mass estimate of R&B (2008): the reference dataset; the choice of the character; the statistical analysis; and the presentation of the data.…”

“…This is especially true for fossil species that fall well outside the range of the reference group. This problem of extrapolation is regarded as one of the largest sources of error and is known to cause overestimation of body mass (Schmidt-Nielsen 1984;Damuth & MacFadden 1990;Reynolds 2002). A wider selection of taxa may offset potential bias.…”

“…The largest values were obtained from some length measurements of the skull, including the total length, the diastema length and the basicranial length. Large values (from 715 to 1929 kg) are also obtained from the skull length using the various models (the beaver model excluded) presented by Reynolds (2002). Despite the fact that all the upper dentition is preserved, R&B (2008) did not include molar measurements in their analysis.…”

Giant Beaver, <em>Castoroides ohioensis</em>, Remains in Canada and an Overlooked Report from Ontario

“…Adults reached a length of nearly 2.5 m, the size of a Black Bear (Ursus americanus), and may have weighed as much as 200 kg (compared to a 1 m-long modern Beaver weighing about 30 kg) (Kurtén and Anderson 1980). However, Reynolds (2002), treating statistically a comprehensive sample, estimates Giant Beavers had a body mass of only 60 to 100 kg while assuming a length of 1.5 m [this ignores the nearly 2.5 m length of the skeleton displayed in Chicago's Field Museum of Natural History and the 2.2 m length for the Earlham College skeleton, which represents an immature individual (Barbour 1931, Figure 109)]. Using a regression she established for all rodents, Hopkins (2008) calculated a mass of 67 kg for Castoroides, which corresponds to Reynolds' estimate.…”