Fossil Friday – Max’s femur

Mammut americanum (1)An oddity in the preservation of Max the mastodon is that, while the skull and pelvis were beautifully preserved, very little was recovered from the massive limb bones. The only significant piece was the distal end of the left femur, and a few months ago while working on our mastodon project we opened our exhibit case to photograph and measure this fragment.

The image above is in anterior view. The smooth curved surface at the bottom of the bone is part of the articulation for the knee joint. Below is the same fragment in posterior view:

Mammut americanum

One of the reasons we wanted to get measurements of this bone is that we’ve often stated (following Springer et al., 2009) that Max is one of the biggest mastodons known from the western United States. The femur is one of the better bones for estimating body size, because in most terrestrial animals it’s the primary weight-bearing bone, so its dimensions are often indicative of both height and weight. Ideally, we would like to have the entire femur to measure, but we take what we can get. In Max’s case we can get a good measurement of the maximum distal width, which gives us a point of comparison to other mastodons. The graph below shows how Max’s femoral width compares to mastodons from Rancho La Brea and New York:

Femur graph

The two left bars are Rancho La Brea specimens, the tall bar in the middle is Max, and the two bars on the right are respectively the Watkins Glen mastodon (an adult male) and North Java mastodon (an adult female) from New York (measurements from Hodgson et al., 2008). Max’s femur is quite wide compared to other mastodons, which was part of the reason Springer et al. suggested that Max was such a large animal.

Using these measurements, I made a sketch estimating the total size of Max’s femur and compared it to images of the same four specimens from the graph, with the caveat that proportions often don’t scale exactly linearly so this is only an approximation. In addition, since Max’s femur is the left one and the other four specimens are right femora, I’ve reversed Max’s image so they’re more directly comparable. (The Watkins Glen and North Java images are from Hodgson et al., 2008):

Mammut femur comparison

Any way you look at him, Max seems to have been a pretty big mastodon. Yet Max’s teeth are relatively small. This disparity in Max’s measurements is what started us looking at the tooth shape and size in California mastodons, and is something I’ll be exploring further next month as part of our mastodon project.

References:

Hodgson, J., W. D. Allmon, P. L. Nester, J. M. Sherpa, and J. J. Chiment, 2008. Comparative osteology of Late Pleistocene mammoth and mastodon remains from the Watkins Glen Site, Chemung County, New York. In W. D. Allmon and P. L. Nester, eds., Mastodon Paleobiology, Taphonomy, and Paleoenvironment in the Late Pleistocene of New York State: Studies on the Hyde Park, Chemung, and North Java Sites. Palaeontographica Americana 61:301-367.

Springer, K., E. Scott, C. Sagebiel, and L. K. Murray, 2009. The Diamond Valley Lake Local Fauna: Late Pleistocene vertebrates from inland Southern California. In L. B. Albright, ed., Papers on Geology, Vertebrate Paleontology, and Biostratigraphy in Honor of Michael O. Woodburne. Museum of Northern Arizona Bulletin 65:217-235.

 

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