Walk Like a Sloth–lesson 11: the toes

Introduction to Walk Like a Sloth: lessons in ground sloth locomotion

compassGetting Oriented

Like you, and unlike tree sloths and most other ground sloths, Megalonyx had five (5) toes on each foot.  Your toes, like your fingers, have three (3) phalanges (segments) each, except your big toe and thumb which each have just two (2) phalanges. Megalonyx is the same, only the middle toe is the big toe, and has two (2) bones.  In Megalonyx the proximal phalanx (the bone closer to the body) and medial phalanx (middle bone) of the 3rd toe are fused, so completely that all traces that they started out as two separate bones have vanished. What looks like the proximal phalanx is actually the third metatarsal.

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Walk Like a Sloth–lesson 4: the claw

Introduction to Walk Like a Sloth: lessons in ground sloth locomotion

compassGetting Oriented

The claw is from the middle toe of the left foot.  It’s the largest of all of the claws.  In life the bony core would have been covered with a toenail growing out of the pocket or sheath at the wide end. The nail probably didn’t extend far beyond the tip.  Sloth claws didn’t retract like a cat’s so a long nail would get in the way of planting the foot down flat and would have abraded quickly. Half of the nail sheath is missing from the specimen (broken off after burial) but the accident reveals the impressions left by the major blood vessels feeding the nail and penetrating into the interior through foramina (holes).  The ventral tuberosity would have supported a tough pad of tissue on which the sloths walked, lifting the tip of the claw slightly off the ground. Continue reading