25 Days of Skeletal Facts: Day 1 – The Foot

If we’re talking holidays I’ve always been more of a Halloween aficionado, but this year I want to get into the wintery spirit by sharing some fun skeletal anatomy facts during December. Think Christmas meets Halloween, the classic combination made famous by Jack Skellington. We’re going to work up from the foot to the cranium, highlighting some basic anatomy and interesting archaeological/forensic/evolutionary facts about human skeletal elements. These posts will be short and sweet (mini candy cane style), and my hope is that they leave you appreciating and loving your skeleton even more than you already do. So please join me for this happy holiday season, skeletal anatomy style.

Jack Skellington and his Christmas lights in A Nightmare Before Christmas (1993)

Before we continue, you may be wondering what exactly makes me qualified to bring you skeletal fun facts this holiday season. I am a PhD candidate in biological anthropology at the University of South Carolina and I have spent countless hours not only learning anatomy, but also excavating, dissecting, and teaching. I am currently a Graduate Teaching Assistant at the U of SC School of Medicine, teaching anatomy to medical and physician assistant students. While these posts will give you some bare bones basics (pun very much intended) I will also include links in case you want to deep dive down your own anatomy rabbit hole.

The Foot

What we colloquially refer to as the foot includes tarsal (ankle) bones, metatarsals, and phalanges (toe/finger segment bones). In total that amounts to some 26 bones per foot and a grand total of 52 bones just in your feet. The ankle joint is formed by the articulation, or connection, of the talus (the second largest tarsal bone) with the end of the tibia and fibula – the two bones of your leg.

Bones of the right foot. Thieme Atlas of Anatomy

While our hand is very similar to that of our closest living ape cousins, our foot has been more heavily reengineered by evolution, specifically for our bipedal locomotion. As you see below on the left, the chimpanzee (and other apes) have a divergent big toe, which they can use for grasping and climbing – aka arboreal locomotion. Our big toe (called the hallux), however, is in line with the other toes as we lost the grasping ability in favor of exclusively walking upright. (Note that chimpanzee and other apes can and do sometimes walk bipedally but you will notice that they sort of waddle since their lower extremity has not undergone changes to produce the strides we do). Our calcaneus, the large bone of our heel, is more robust in humans, and larger in the back than it is for apes. We also developed arches in our feet that are absent in apes, allowing for even weight distribution through our legs and into our feet since they are bearing all of our body weight. The phalanges (toe bones) of humans are also relatively short and straight compared to the long and curved toes of chimpanzees, again down to differences in how each species gets around.

As paleoanthropologists (those that study human evolution) discover new fossils they can reconstruct locomotive patterns by examining the features I discussed above. Above on the right is the partial foot of Ardipithecus ramidus, known as Ardi, a member of our distant hominin family that lived approximately 4.4 million years ago. While other areas of the skeleton show that Ardi was suited to some sort of bipedal locomotion, you can see here that the big toe looks a lot more like that of Pan troglodytes (the chimp) than ours. The toes of Ardi are also longer and more curved, again like the chimp. So while Ardi may have had bipedal locomotion in their repertoire, it is clear this species was also climbing trees.

And that concludes the first installment in the series of skeletal anatomy fun facts for winter 2020 – I hope you learned something new, perhaps an interesting tidbit to share when there’s another lull in the Zoom call. Check back tomorrow for some fun with the fibula!

REFERENCES & MORE TO EXPORE

Ahead of the Curve in the Evolution of Human Feet. Glen A Lichtwark & Luke A. Kelly. Nature: News & Views article. 26 Feb 2020.

The evolution of the human foot. McNutt, Zipfel, and DeSilva. Evolutionary Anthropology. 2018

Rethinking the evolution of the human foot: insights from experimental research. Holowka & Lieberman. Journal of Experimental Biology. 2018

A New Kind of Ancestor: Ardipithecus Unveiled. White & Gibbons. SCIENCE News Focus. sciencemag.org. 2009

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