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Tiburón Island in the Gulf of California (or Sea of Cortés) of Mexico is the largest island in Mexico and part of the historic and current homeland of the INDIGENOUS Comcaac (Seri People). Seri oral history says the three stars making up Orion's belt represent mule deer, bighorn sheep, and pronghorn antelope. When Scorpius (the great hunter of the sky) shot his arrow at the stars he struck the central star, or the mule deer, and some of the blood dripped on Tiburón Island. The rest can still be seen in the sky as Betelgeuse (pronounced "beetle juice"). This explained why the island historically had mule deer but not pronghorn or bighorn sheep.               

In 1975 wildlife conservationists became concerned that bighorn sheep were in danger of being hunted to extinction on the mainland. They introduced 15 female and four male desert bighorn sheep to the island where there were no natural predators. If the experiment was successful, the Tiburón Island sheep would help increase the population and conserve this important desert species. Today there is a herd of about 500 animals on the island.

Ben Wilder, then a PhD student, came to Tiburón Island to understand its history. One of the things he was looking for was fossil packrat middens (see to the right). Instead, Wilder discovered a midden in a shallow cave that contained 1500-year-old bighorn sheep dung. Desert bighorn sheep had indeed lived on Tiburón Island in ancient times.

Why the Seri did not remember the original is still a mystery and an example of when different world views help illuminate the past.

Packrat Mittens?? No, silly person—It’s Packrat Middens!

Packrats make homes or middens in thick vegetation like prickly pear cactus. They haul treasures they find in their neighborhood to the spot they have chosen for their nest. These can include shiny things like screwdrivers, spoons, and foil along with a lot of plant debris such as seeds and leaves. Unlike their more fussy wild neighbors who prefer a clean home, packrats pee a lot in their middens. As the pee evaporates it forms a crystalline mat that preserves these items for thousands of years.

Meet A Field Expert!
Dr. Ben Wilder is the botanist who discovered that bighorn sheep had existed on Tiburón Island thousands of years ago. While looking for evolutionary history of plants, he came upon an ancient packrat midden in a shallow cave that did not look quite right. Instead of small rodent sized poop and lots of plant parts, this was a mat of large dung! So Ben brought a sample back to the University of Arizona where his mentor, Dr. Julio Betancourt thought he recognized it. Through carbon dating and DNA analysis it proved to be 1500 year old bighorn sheep dung. For scientists, middens are like care packages from the past.
December 2017