body mass

I know I'm linking a four-year-old post about dinosaurs, but I got this SV-POW post on my feed this morning and it is very relevant to those of us who think about variation among fossil hominins: "Brachiosaurus: both bigger and smaller than you think". Let's call it upcycling.

Maybe the most interesting thing about this is that, so far as we can tell, XV2 was almost exactly the same size as the holotype individual of Sauroposeidon. So anything I or anyone else has written about Sauroposeidon being bigger, absolutely, than Brachiosaurus, is bobbins. Sauroposeidon still had a considerably longer neck, 11.5 meters to XV2′s 9.5, but the cervical skeleton weighed about the same thanks to the higher air space proportion in Sauroposeidon. In fact, if the higher ASP of Sauroposeidon applied to the rest of the vertebral column, then the holotype individual of Sauroposeidon might have weighed less than XV2!

Much was published about the body size of australopithecines before a good male skeleton was found. Attempts to estimate body mass from single skeletal elements in hominins have a large associated estimation error. Human body size estimation by regression is very different from that within other ape species, because our different locomotor patterns load the hindliimb differently.

In this light, it is always frustrating to see very many conclusions based upon the body size estimate of any single skeleton. This is an argument made most effectively by Richard Smith, who wrote a classic review paper on the errors of interpretation that can spring from neglecting the error associated with body size estimation [1]. Individuals do not evolve. They are imperfect representations of variable populations.

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