

Figure 1. A modern packrat (Neotoma cinerea) surrounded by midden material in a cave in northwestern Nevada. Click to view a larger image.

Figure 2. A massive complex Pleistocene packrat midden (in the alcove in the center of the image) in a cave in eastern Nevada. Click to view a larger image. What are packrat middens and what do they tell us about past environments? Dry caves and rockshelters in the American West host a unique and valuable paleobotanical resource - plant macrofossil remains preserved in middens composed of desiccated packrat (Neotoma spp.) urine. Middens are waste piles that packrats construct out of fecal matter and urine (Figure 1). Packrats incorporate pieces of plant material, bone, and other items they habitually collect from their environment into their middens. The packrat's sticky, viscous urine acts like a cement which binds the midden material together into a solid mass. Middens constructed in dry caves and rockshelters where they are protected from moisture may be preserved for tens-of-thousands of years (Figure 2). Fossil plant remains recovered from ancient midden deposits are often perfectly preserved, can be identified to species-level, and provide excellent material for radiocarbon dating. Radiocarbon-dated fossil midden assemblages provide detailed inventories of the plants and animals that lived in the vicinity of the collection site during past time periods. A series of dated middens from neighboring sites can provide a long-term record of changing plant communities and climate for a local area.

Figure 3. Middens have been studied throughout western North America from southern Canada to central Mexico. Click to view a larger image.

Figure 4. Radiocarbon ages on midden materials range from latest Holocene to 50,000 years B.P. Click to view a larger image. Methods of Quality Control and Data Standardization This dataset aims to preserve original data as it was published by each midden analyst, therefore the quality of the data is only as good as the original published data. The use and comparison of midden data produced by multiple sources is complicated by the fact that midden analysts use many different methods to record the relative abundance of plant macrofossil taxa in middens. This dataset preserves original relative abundance data as published; however this dataset also translates all original data into a standardized presence-absence scale (2=present and common, 1=present but rare [and thus could be a contaminant of a different age], 0=absent) according to the relative abundance scheme(s) used and defined by each midden analyst.