Volcaniclastic matrix: methods, problems and solutions of extraction

Over the last two decades, expeditions to the Chilean Andes have produced diverse mammal faunas and extremely well-preserved specimens. Many of these specimens are preserved in volcaniclastic matrix that is the hardest encountered by preparators at the American Museum of Natural History, and it offers unusual challenges for collection and for preparation. The nature of the matrix requires that specimens sometimes be collected in multiple pieces and with a much higher proportion of matrix than is common in specimens from more typical localities. Many times, the Chilean fossils are exposed in section and, in contrast to the matrix, the included fossils are very soft and fragile. The exposed, eroded surfaces of the specimens often cannot withstand the impact of typical tools such as airscribes and needles. Here, I describe the difficulties offered by this matrix, a protocol for dealing with those issues, and an embedding technique that allows recovery of all salient details of the specimen.