On the left are 3 examples of narrow unmodified stones with evidence of wear on one narrow surface. These conveniently shaped stones are not local and are the simplest in the series. Using a narrow edge for grinding was not an efficient method for processing plant material and these were the only examples found. Since a mano and metate are multifunctional tools, these manos may represent tools for grinding other materials or are early . This is followed by a number of hand sized unmodified river cobbles with a generally rounded shape that show evidence of wear on a single surface. Again, no processing to create a tool is evident only a conveniently shaped rock was chosen for use.
The mono forms continue as round in shape but evidence of modification is observed around the edges where the stone was pecked producing a more rounded and useable form. These manos also often are bifacial with wear on both surfaces and vary in size allowing single hand or 2 hand use. The next change noted is an elongation of the mano. This transition, while still maintaining rounded corners, manos became longer and larger suggesting 2 handed use. Increased modification of the original stone is evident. These larger loaf shaped manos would, with a large grinding surface areas, allow more plant material to be processed and therefore appear more efficient. Interestingly one of the loaf shaped manos displays a directionality of use. The upper surface of one side is angled allowing easier handling while grinding. The next form of mano is a highly processed stone that is uniform in thickness with bifacial wear. These thin leaf like bifacial manos would require a significant amount of work to produce. Finally, fragments of elongated tubular shaped manos were found. Only 2 examples of these were found and represent the largest amount of production processing observed in mano.
The wide range of shapes and sizes suggest the idea that form follows function
was very flexible in the development of manos as grinding tools and that multiple forms were useful in grinding and may be grinding material specific. In addition, these observations conflate complexity (increased production processing) with time (less complex = older, more complex = newer) and undoubtedly multiple forms co-existed in time. The increased reliance on corn (a shift towards monoculture) as a food source as opposed to relying primarily on a variety native plant species would have driven some forms of manos toward a more efficient form, seen in the highly processed bifacial leaf and tubular manos. But at other times a simple rounded rock would do.
|Mano and mano fragments of varying complexity|