Overview

An organism’s ecology is a key component of their evolutionary history and accurately characterizing diverse fossil ecosystems improves our understanding of the evolution of fossil clades (Benson, 2018). The Upper Jurassic Morrison Formation (Fm.) records an unusually diverse dinosaur community (Woodruff, 2019), and stable isotope geochemistry is a powerful tool to determine ecosystem structure. However, before ecological questions can be asked, one must identify the extent of diagenesis in the fossils being analyzed. We will utilize LA-ICP-MS to determine diagenetic changes in tooth material with a focus on comparing enamel and dentine. Enamel is less porous than dentine, suggesting that stable isotopes in enamel are less likely to be overprinted by diagenesis in enamel than in dentine. We will compare the elemental abundances of Jurassic dinosaur teeth with modern crocodilian teeth to inform our understanding of diagenesis. If diagenesis in the teeth is not extensive, then this investigation will be expanded to search for annual variations in elemental abundances throughout the tooth growth axis using LA-ICP-MS. Dinosaurs constantly shed and grew new teeth throughout their lives, meaning that if original elemental and isotopic abundances are preserved, they can provide information about the animal at whatever age/season it was when the tooth was lost/buried. This project and its use of LA-ICP-MS will allow us to assess diagenesis more reliably in fossil teeth to ask new and interesting questions, including understanding annual variation in dinosaur behavior.

Research Objectives and Hypotheses

Dinosaurs were the primary terrestrial group during the Mesozoic but despite the long history of studies, many questions about the ecology and biology of these animals remain (Benson, 2018). The Upper Jurassic Morrison Formation records abnormally high diversity of sauropod dinosaurs with more than 10 species in some horizons (Woodruff et al., 2019). These giants likely had space and resource requirements that make their abundance unusual, and their size would make them challenging prey for smaller contemporaneous carnivores (MacNulty et al., 2014). The overarching goal of this project is to develop a method to assess diagenesis in fossil dinosaur teeth and use that understanding to look at variation in dinosaur behavior during the growth of the tooth. No standardized method to determine diagenesis in fossil material has been developed or has not become widespread if it has. Work should be done to find the best method of assessing diagenesis in fossils, including assessment of rare earth elements (REEs) (Rogers et al., 2010) or elements which are not common in fossils (Galiova et al., 2013). This project will explore these and other methods of assessing diagenesis by comparing fossil teeth from the Jurassic (which potentially have significant diagenesis) with modern crocodile teeth (which would not have significant diagenesis).

Research significance/justification

We will use LA-ICP-MS to determine diagenetic changes in tooth material with a focus on comparing enamel and dentine, and then determine whether elemental values are reliable enough to search for annual variations in elemental abundances throughout the tooth growth axis. Previous work has been done to determine how diagenesis has affected multiple contemporaneous dinosaur bone beds (Rogers et al., 2010), but comparisons have not yet been made between modern and fossil teeth. Our results from modern and Jurassic archosaurs will increase the utility of this isotope system for dinosaur paleobiology, and together with other isotope systems, we can ask exciting new questions.

Project outcomes

These data will allow us to determine how archosaurs fractionate isotopes during tooth growth, which will allow us to account for isotope ratio variability in the location on the tooth and in the jaw. This insight will have repercussions across biology and paleontology. They will also provide greater information about how dinosaurs incorporate trace elements into their teeth throughout the year as their diets, water sources, and environmental temperatures change. Successful completion of the first part of the project would inform a protocol that allows confident sampling of archosaur teeth (i.e., identifying what factors need to be accounted for) and provide a greater understanding of how diagenesis affects different parts of the tooth. Should these teeth not have been completely overprinted by diagenesis, then successful completion of the second part of this project will allow a more in depth understanding of dinosaur biology than has previously been reported in the ICP-MS literature.

Timeline and budget

Samples have already been sourced from Dinosaur National Monument (DNM), including multiple sectioned dinosaur teeth. These tooth sections will be analyzed using an LA-ICP-MS before November 4^th. Assuming these sections can be analyzed with LA-ICP-MS under the loan agreement with DNM, that will be the method which we use. Because of the size of the teeth, we will budget 6 hours to sample the maximum number of teeth for a cost of $438. If the DNM loan agreement does not allow for use of LA-ICP-MS, we will switch to solution mode ICP-MS. Because the UT ICP-MS is $17 per solution, we budget $306 for all nine sample solutions. In total the budget for this project will be $744, and will help inform how we use LA-ICP-MS to investigate elemental values and isotopic ratios in the fossil record.