Spring-tooth harrows (developed in the 1860s) have curved, springy teeth designed for use in rough, stony ground and around roots.
A C.T. scan of a jaw of Homo rudolfensis, a hominid that lived about two million years ago, shows its teeth, designed for grinding tough plants, had a much thicker layer of enamel than ours.
This engages with a pinion (a gear with a small number of teeth designed to mesh with a larger wheel), whose arbor (a turning rod to which gears are attached) is attached to the second wheel that, in its turn, engages with the next pinion, and so on, down through the train to the escapement.
George Burgess, the director of the International Shark Attack File, calls them "the 'Big Three' in the shark attack world because they are large species that are capable of inflicting serious injuries to a victim, are commonly found in areas where humans enter the water, and have teeth designed to shear rather than hold".
Indeed, M. missouriensis had long, narrow teeth designed more for slicing than for crunching, and the animals were liable to lose teeth when chomping into hard substrates.
Modern African elephants have teeth designed for grazing perhaps because their ancestors sought out new dining experiences millions of years ago, according to a study in today's issue of Nature.
And yet the teeth, Arbour explains, "reminded me of piranha teeth, designed for pecking away at meat," according to CTV News.
They are notches in the teeth designed to break the chip and decrease the overall amount of material being removed by any given tooth (see the drawing above).
The dorsal side of the instrument has small cutting teeth designed to excise bone and ligament, while the ventral side is smooth to protect the neural structures.
"We cut our teeth designing things for hotels," Ms. Standefer said.
