Curator Carter County Museum Ekalaka, Montana, United States
Well-studied amber deposits throughout the Cretaceous have yielded important data about Mesozoic insects. However, approaching the Cretaceous-Paleogene Boundary there is a considerable gap in sampling for insect body fossils. Any research towards Maastrichtian insect fossils is crucial in understanding insect extinction dynamics of the past and future. One such sampling gap is in the amber deposits of the Hell Creek Formation (HCF), largely overlooked because of the amber’s fragility and small specimen sizes. This study aims to explore amber deposits of HCF, develop a conservation methodology, and to help fill in this crucial lapse in the insect fossil record. Multiple HCF amber deposits in Southeastern Montana were sampled and specimens were conserved using epoxy embedding. HCF amber preserves in multiple lithologies and taphonomic modes including lower energy mudstones, lignites, and higher energy siltstones. It was found that epoxy embedding was a necessary step in conserving samples for study, prior to inclusion surveying. Optical microscopy and micro-computed tomography (micro CT) were used to study inclusions. Often arthropod inclusions have translucent limbs or are completely translucent, impeding surveying and definitive identification of taxa. Micro CT scans revealed preservational diversity in arthropod inclusions: some inclusions are preserved as endocasts with partial cuticular preservation, while others appeared to be infilled with resin showing almost no sign of cuticular preservation. This amber captures multiple orders of insects, as well as feathers, plant matter, and possibly fungal material. This diverse assemblage of deposits may have implications in understanding amber taphonomy, Late Cretaceous biodiversity, and extinction dynamics.
