It seems that at least once a year, news of the “largest dinosaur ever found” makes headlines. That’s because almost all the contenders for the biggest saurian are so fragmentary that settling on an uncontested victor is almost impossible, not to mention that new discoveries are being made all the time. There hasn’t been as much of a debate about fossil mammals. For over a century, Paraceratherium – a 26-foot-long, 15 ton, hornless rhino – has been cited as the biggest of the big beasts. But, according to a new paper by Asier Larramendi, ancient elephants are in close competition for the title of the largest mammals to ever walk the Earth.
Such contests rely on how they’re measured, of course. Part of what makes Paraceratherium seem so large is its elongated neck. In terms of tonnage, however, Felisa Smith and colleagues pointed out that the largest prehistoric proboscideans – such as the anchor-tusked Deinotherium – were likely heavier. (It’s similar with sauropods – does Supersaurus hold the title of Biggest Dinosaur because of it was a bit longer, or does Argentinosaurus because it weighed more?) Giants are made by how you measure them. In this case, Larramendi drew from photos, measurements, and reconstructions of fossil and living elephants to come up with estimates of body mass and shoulder height.
Starting with the bones, Larramendi created virtual restorations of 24 different elephant species. The point, aside from trying to correct errors in articulation that are sometimes made when these animals are mounted in museums, was to restore the elephants as accurately as possible in order to estimate their volume and, from that, their body mass. Some researchers use a different methodology for these sorts of estimates – focused on estimating how body shape changes with size – but Larramendi prefers the volumetric method.
Larramendi selected elephants from various times in their 60 million year record. The very early Eritherium azzouzorum, for example, may have weighed 11-13 pounds and been a little more than half a foot high at the shoulder. From such a small start, elephants eventually attained truly enormous sizes. Larramendi calculates the largest Deinotherium weighed 13 tons and stood over 13 feet high at the shoulder. Others were bigger still. The mastodon Mammut borsoni, Larramendi calculates, would have weighed over 15 tons and been almost 13 and a half feet tall at the shoulder, and, based on some scrappy material, Larramendi estimates that the elephant Palaeoloxodon namadicus would have reached 24 tons and an imposing 16 feet at the shoulder.
Part of a femur isn’t much to rest a title on, but, if Larramendi is correct, the largest Palaeoloxodon would have been nearly a foot taller and over 5 tons heavier than the biggest known Paraceratherium. But even sticking to more complete skeletons, Larramendi’s estimates suggest that ancient elephants could get as large as, if not a bit larger than, the previous record holder.
Calling this competition doesn’t interest me, though. Whether a rhino or elephant was the largest land mammal of all time isn’t especially important. What’s curious is that there isn’t a clear winner between the two lineages. (There can’t be until better skeletal material gives us more precise dimensions for these giants.) Just as with the largest dinosaurs, the most superlative mammals of all time seem to cluster around a similar body size. This, as I believe the SV-POW!sketeers have pointed out, might tell us something about the upper limits of body size in these groups. The next step is to see if we can parse out what these limits were and how they altered the shape of life for millions of years, and what those constraints might mean for the future of evolution.
Larramendi, A. 2015. Shoulder height, body mass, and shape of proboscideans. Acta Palaeontologica Polonica. doi: 10.4202/app.00136.2014