The Cretaceous-Paleogene boundary is one of the most well-studied mass extinction events in history. However, there are still many questions left about what was occurring in terrestrial ecosystems in the 10-15 million years prior to the event. One major question is if theropod dinosaurs were declining in diversity and ecological stability prior to the event, or if they all died off suddenly. This stability is partially interpreted in this project through a geometric morphometric approach comparing Judithian and Lancian theropod teeth. Geometric morphometrics quantitatively analyzes tooth shape based on points called landmarks, that are universal across theropod teeth so variance can be measured and compared. Teeth are digitally imaged and processed with the landmarks to compute and then interpret their shapes in specialized programs. The landmarks measured are based on established standard literature of mesial and distal points of the tooth, the apex, and the mesial and distal terminal denticle. If the finalized analysis of the remaining confirms theropod dinosaurs are shown to have consistent morphological disparity through this time, this will be an indication that this group of organisms were not declining and were settled in their niches prior to the K-Pg boundary. Given that theropods were a diverse group that occupied many niches, as well as being the top carnivores that would have curbed other taxonomic populations, studying their economic stability through the window of deep time lasting from the Judithian to the Lancian immediately before the K-Pg boundary is leading to an invaluable understanding of how this environment was changing during this time.

Today there are more than 5,000 species of extant mammals that are categorized into three major clades: placentals, marsupials, and monotremes. The deep evolutionary history of marsupials is poorly known due to a fragmentary fossil record. In particular, cranial fossils of the ancient relatives of marsupials (stem marsupials) are extremely rare. The few cranial elements of these taxa that have been found are fragmentary, crushed, or missing major elements. Recently, some more complete cranial fossils of stem marsupials have been discovered at the Late Cretaceous (75 million years ago) Egg Mountain fossil locality in northwestern Montana. My research will describe the morphology of a partial skull of a stem marsupial from Egg Mountain. This delicate skull is encased in a hard siltstone, making it difficult to mechanically remove without damage to the fossil. Instead, we used micro-computed tomography (µCT) to scan the specimen block. Then I used Avizo software to virtually remove the rock and expose the details of the encased fossil. From the resulting files, I will study and describe the cranial morphology in detail. Thus far, we have identified the stem marsupial as Alphadon halleyi. With further study, I hope to (1) expand upon current knowledge regarding the morphology of Alphadon halleyi, (2) make comparisons with other stem marsupials and extant marsupials, and (3) more broadly, incorporate our findings into a phylogenic analysis of early metatherians (the clade that includes stem marsupials and marsupials) that will further elucidate the evolutionary history of marsupials.