(Singular nouns: Fr-gésier pierre/gastrolite; Ger-Magenstein; Nor-magestein-?; Rus- гастлит-?)

A. Gizzard stones.  One double-notched and three triangular points, Cahokia Mounds State Historic Site, Madison and St. Clair counties, Illinois. Collection of P.A. Bostrom. (© photo by Peter A. Bostrom)  -- See third paragraph under Remarks subheading.

DESCRIPTION:   Gizzard stones that are recognized as such are well-rounded and highly polished.  They are thought to have gained their characteristics as follows:  Pre-existing rocks, which may or may not have been rounded, but certainly were not highly polished on all surfaces, were ingested by the animals (including birds).  Within the animals' gizzards the stones  knock against each other and food ingested by the animal, thus serving to macerate the food to aid its digestion.  Thus, it may be said gizzard stones have gained their identifying characteristics by a process analogous to that whereby rough stones become rounded and polished in tumblers.
Although gizzard stones could have just about any petrographic composition, it seems that at least some birds chose only certain rock types for such use -- see the second paragraph under the Remarks subheading.  In any case, until further data are collected it seems only prudent to consider the possibility that just about any rock available within the region where the animal lives might be ingested for such use.  This means that virtually all gizzard stones are of geological rather than biochemical origin, and, in turn, that most of them are chemically and physically different from the other materials herein designated "ZooGems..."

The geological, rather than biochemical, origin of most gizzard stones also means that including compositions, descriptions and properties of gizzard stones herein is quite impracticable;  indeed, it would require inclusion of a petrographic volume.  Consequently, I suggest that anyone who does not have the requisite expertise to identify rocks correctly should get a professional petrographer to identify these rocks.  Alternatively, a first step might be to get a good petrographic textbook with identification tables -- e.g., Dietrich and Skinner (1979), the appropriate use of which could lead to correct identifications.  However, it seems only prudent to add:  1. Basing identifications on matching rocks with pictures should be avoided because it often leads to misidentifications.  [So]  2. Checking identifications with a professional petrographer is strongly advised. 

USES: Gizzard stones from the large flightless birds – e.g., the Emu and the extinct Moa of Australia and New Zealand at one time, eagerly sought by the aborigines for use as charms and ornaments, continue to be marketed rather widely.  Also, albeit in the realm of fossils, dinosaur gastroliths are marketed for collectors of such oddities for several uses, including some that are chiefly decorative.

OCCURRENCES & NOTEWORTHY LOCALITIES:  Wherever animals with gizzard stones have been slaughteredno particular noteworthy localities.
REMARKS:  The following etymology for the designation gizzard paraphrases information given in The American Heritage dictionary and by Harper (2002):  Alteration of Middle English giser, which is from Old French that probably stems from  the Vulgar Latin gic ērium, from Latin gigēria (meaning "cooked entrails of poultry") that may have had its roots in the Persian jigar (liver).   The term gastrolith stems from the Greek combining form of Greek  γαστ(ε)ρ- , belly, stomach ...;   and  the  terminal indication from Greek  λίθος, stone (in adaptations of actual or assumed compounds). (O.E.D.).

In the literature, gizzard stones have, it seems, been most frequently associated with extinct animals -- e.g., several diverse dinosaurs and moas.  Among currently living animals, gizzard stones of several birds, crocodiles (Das & Ismail, 2002)  and walruses (Morris, 2003) have received special study.  Most rocks found as gastroliths are relatively resistant both physically and chemically;  chalcedony, chert, basaltic lava, pumice, quartzite, tektites (and "andropomorphic [man-made?] glass") and vein quartz are commonly among those reported from different animals in different places.  This aspect raises the question as to whether the animals selected certain stones because of some knowledge or experience as to what stones best served their purposes or whether it merely indicates that any less resistant rocks that were ingested broke down rapidly and thus did not persist long enough to become gizzard stones.  The former possibility seems to be supported by such facts as ostriches' tending to be highly selective so far as the food they eat; "Even on the dark mudstone soils of the Karoo, ostrich somehow find rounded white quartz pebbles..."(Milton and Dean, 1995);  and records indicating that moas often traveled more than 10 miles to get the pebbles that they found to process their food best (Anon., nd#1).  So far as the latter possibility (and it may be that both processes are involved), Wings (2004) in a study of ostriches, fed them cubes of various kinds of rock and found that sandstone (friable?) crumbled quickly and limestone dissolved after just a couple days in their systems. But, the question remains: Would the ostriches have ingested such sandstone or limestone by choice? -- Oliver Wings (personal communication, December 2006) provides the following answer: "most ostriches ... swallow stones indiscriminately, the 'selection' ... occur[s] in the stomach where only hard and acid-insoluble stones survive."  Yet another line of questions arise because "Other hypotheses for the function of gastroliths, such as ballast for buoyancy, mineral supply, the maintenance of a beneficial microbial gut flora, the destruction of parasites, and the alleviation of hunger ... [have been] reviewed and discussed. It is plausible that several functions overlap in specific taxa, e.g., gastroliths in herbivorous birds serve as grinding and mixing agent but also as mineral source (e.g., limestones for calcium supply)." (Wings, 2004a).

Some highly smoothed and polished arrowheads found in Cahokia Mounds State Historic Site, Madison and St. Clair counties, Illinois are hypothesized to be gizzard stones that were smoothed while in turkeys' gizzards (Bostrom, 2003). To support his hypothesis, Bostrom notes, "I recently heard a story about a woman who worked in a plant that processed turkeys: They raised the birds ... in an area where there were ... archaeological sites. This woman, after 30 years of working there, had found 32 arrow points amongst the gizzard stones that she ... [had inspected.]  She estimated approximately 80,000 turkeys had gone through her hands. So that would come to about one polished gizzard stone arrow point for every 2,500 turkeys!" (attributed to Larry Kinsella, President, Illinois Association for Advancement of Archaeology, who verified the story to me in a telephone conversation, March 13, 2006). Kinsella also told me that small, flint micro-drills, which were used to make shell beads found within the same area, appear also to have been gizzard stones.  In addition, he noted that polished arrowheads, presumed to be from gizzards, have been found in many states.

Several craftsmen -- e.g., the Anaszi (ancestral Puebloans) of the southwestern United States -- are reported to burnish ceramic vessels to high luster by using gizzard stones as their abrading tools.  And, this stone-burnishing technique is still used by those who desire to preserve prehistoric technology (Wood, 2005).

From the sublime to the ridiculous??:  "Healers concocted an elaborate remedy for Aztec rulers who complained of tiredness, according to Robert Bye of the Botanical Garden in Mexico City. They would boil some herbs in water, add some animal blood, and top off the potion with digestive "stones" found in bird gizzards [my emphasis]. To restore energy levels, haggard rulers bathed with the resulting liquid." (Fackelmann, 1993).   AND,  because of his superstitions, the wrestler Guilio wore what he referred to as an Aspilate which was so-designated because it was from the gizzard of a cock fowl. (Anon., nd#2).

SIMULANTS:  Although I know of none, certainly some fine simulants could be made in, for example, tumblers.  Also, some rather well polished ventifacts might, upon only cursory examination, be misidentified as gizzard stones.  Two things should serve to distinguish ventifacts from gizzard stones:  1. Ventifacts typically occur in groups that number from  several score to several thousand within areas that are or have been subject to wind erosion.  [and]  2. The smooth or polished surfaces of ventifacts are typically restricted to certain surfaces -- i.e., some surfaces are smooth or polished whereas other surfaces are not.


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