CONCLUSIONS

Taphonomic studies of modern owl pellets are common, but few investigators have directly applied these methods and conclusions to specific open-air fossil deposits. In this study, quarrying blocks of matrix followed by preparing the microvertebrate bones in a single bedding plane provided taphonomic evidence that was lost when screenwashing was used as the sole method of recovering fossils. Several lines of evidence suggest that the microvertebrate assemblage the Verde Formation at House Mountain, Arizona, MNA loc. 318, represents an accumulation of owl pellets deposited at the edge of the ancient Lake Verde on dry land or perhaps in shallow water at the lake's edge. Weathering of the pellets prior to burial probably was limited to relatively brief exposure to invertebrate activity, rainfall, or slight wave action in shallow water that was sufficient to disintegrate the pellets but not sufficient to completely dissociate some skeletal elements of individual prey animals. During or after burial, bones were crushed in place by sediment compaction with little or no additional separation of the bone fragments. When the sediments were screenwashed, fragments of crushed bones were separated or lost and thus information on the partial association of skeletal elements was lost, by contrast with the quarrying technique. Therefore, if the recovery of taphonomic data is a prime concern in working a microvertebrate locality, field recovery methods should not be limited to underwater screening only, and much more time for preparation will be necessary.