Tag: Edward Davis

Stable Isotope Analysis of Fossil Shark Teeth from the Late Cretaceous Western Interior Seaway

Presenter: Rachel Lisle − Earth Sciences

Faculty Mentor(s): Edward Davis, Kellum Tate-Jones

Session: (In-Person) Poster Presentation

The Western Interior Seaway was a Late Cretaceous (100.5-66 mya) inland sea that, at it’s largest, stretched north to south, from the modern-day Arctic Ocean to the Gulf of Mexico. Research concerning the seaway has revealed that there was likely a significant temperature gradient present, with cooler temperate waters to the north and warmer subtropical waters to the south. Using fossilized teeth from two species of sharks collected from an Arkansas site associated with the Western Interior Seaway, I seek to use carbon and oxygen isotopes to interpret the paleoecological conditions present in the southern province of the seaway during the Late Cretaceous. I also seek to identify what conditions made it suitable for these sharks to live in this province. Using stable isotope analysis by way of laser ablation, as well as conducting a literature review on relevant sources, I have found that these sharks likely preferred the subtropical temperatures over cooler temperate waters. Mirroring this is a similar pattern in salinity, wherein these species likely preferred water with a higher salinity than the more brackish water up north. This research is essential in understanding what conditions made the seaway favorable for shark species and how extinct marine vertebrates interacted with and reacted to their environment.

Topographic and Climate Change Differentially Drive Pliocene and Pleistocene Mammalian Beta Diversity of the Great Basin and Great Plains Provinces of North America

Presenter: Amy Atwater

Mentor: Edward Davis

PM Session Oral Presentation

Panel Name: A1 Evolutionary Trajectories

Location: Alsea Room

Time: 1:15pm – 2:15pm

The Great Basin region of the western United States currently has elevated beta (between-site) diversity compared to that of the past 10 million years. We test two competing hypotheses to explain this pattern: 1) Pleistocene climatic cycling, with diversity drop- ping during warm intervals and increasing during cooler ‘Ice Age’ intervals; or 2) topographic change, where tectonic expansion created a diversity of habitats, packing drastically different environments close together. To test these hypotheses, we analyzed the beta diversity of non-flying land mammals from the Late Miocene (~8 million years ago) to Recent of the Great Basin of the United States, with the central Great Plains of the United States as a control. Using mammalian faunal lists from the FAUNMAP II database, we esti- mated richness- and evenness –based beta diversity for 4 time-slices based on mammalian biochronology. Our results show that beta diversity, in terms of both richness and evenness, is higher in the Great Basin than in the Great Plains at all intervals from the Late Miocene to the Recent except for the Holocene. The Holocene of the Great Plains revealed surprisingly high evenness beta diversity and is the subject of continued investigation. The overall results support our hypothesis that Great Basin beta diversity has primarily been driven by tectonic change, but the Great Plains Holocene results suggest that other factors, particularly climate change, have affected beta diversity.

Deciduous Teeth Show Close Relationships Between Oreodont Genera (Eucrotaphus, Merycochoerus and Promerycochoerus)

Presenter : Kendra Walters

Mentor : Edward Davis

Major : Biology

Poster 27

Oreodonts lived during the Cenozoic Era, particularly from the Eocene to Miocene Epochs. They were abundant in the past but have no modern descendants. Classifying oreodonts is a difficult task because there is disagreement on the species, genus and subfamily classifications of many individual oreodont groups. The three genera of oreodonts we examined (Promerycochoerus, Merycochoerus, and Eucrotaphus) have experienced this problem and are divided between two to three different subfamilies. Our examination of the deciduous teeth of four individuals from these three genera found great morphological similarity, indicating a closer relationship than is currently recognized. We examined two individuals of Eucrotaphus trigonocephalus, one individual of Merycochoerus sp., and one of Promerycochoerus carrikeri from the collection at the University of California Museum of Paleontology. The deciduous premolars from all three genera are tellingly similar, varying only in size, and match previous descriptions of Promerycochoerus carrikeri. Simi- larities are especially evident in the last two deciduous premolars. These similar characters contradict the current subfamily divisions, indicating a close relationship between all three genera. We propose a re-division of oreodont subfamilies that reflects this close deciduous morphology. We also recognize synonymy of Promerycochoerus and Merycochoerus, as our examination primarily found size differences between them that we do not accept as genus-level distinctions.

Tooth Eruption Sequence of Eporeodon occidentalis

Presenter: Kendra Walters

Co-Presenters: Meaghan Emery

Mentor: Edward Davis

Poster: 33

Major: Geology/Biology

Oreodonts lived in North America during the Cenozoic Era and were especially abundant from the Eocene to Miocene Epochs. Despite their abundance, they have no modern descendants. The dentition of fossil oreodonts is often well preserved, including deciduous or “baby” teeth. In order to understand more about oreodont behavior and development, our research examines the tooth eruption sequence for juvenile Eporeodon occidentalis. Tooth eruption sequences differ among groups of animals and reflect their specific life history patterns, including time of weaning and overall lifespan. We created 3D models of the crania of juvenile Eporeodon occidentalis individuals using Agisoft PhotoScan, and examined these models to stitch together the eruption sequence. Interestingly, the eruption sequence showed only the permanent first premolar which means the deciduous first premolar either did not exist or fell out extremely early, possibly before birth. This is a unique feature shared with pigs which may be evidence of a close relationship, similar behaviors, or similar life histories. By comparing the tooth eruption sequences of Eporeodon occidentalis and modern species such as pigs, camels, and sheep, I was able to infer possible life history patterns of Eporeodon occidentalis from known life history patterns of the modern species. In the future, this tooth eruption sequence will be compared to that of other oreodonts to evaluate differences and similarities in behavior, phylogeny, and life histories.

Influences on U.S. Mammal Diversity over the 20th Century: Implications for Future Response to Climate Change

Presenter: Kendra Walters

Mentor: Edward Davis, Geology

Poster: 63

Majors: Geology and Biology

Biodiversity loss is recognized as a global crisis. Current research strives to quantify and predict the change in biodiversity throughout the world, focusing on a wide range of taxa. However, current predictive models of mammal diversity in the United States suffer from low precision. They are not scaled with adequate spatial or temporal resolution because richness has not been evaluated at a broad spatiotemporal scale. Our research is a high- resolution analysis of the changes in mammal diversity in the continental United States through the last 110 years.

We collected mammal occurrence data from the online database VertNet and individual museum collections, divided it into ten year increments, and used scripts in ArcGIS 10.2 to produce sampling-standardized patterns of mammal diversity in each decade. We then analyzed the geographic distribution of diversity change over the 20th century. Mammal diversity in the last century increased in two regions: one northern horizontal strip between 43° and 47° latitude and one southeast strip from Texas to North Carolina. Diversity decreased throughout the rest of the United States. Our study describes regions in the United States that are experiencing the most severe biodiversity changes which suggests that those regions should be focal areas for conservation efforts. Further directions include testing hypotheses about the role of climate and human population change to influence these patterns of mammal diversity shifts.

Paleoecology of the Enigmatic Rhinoceros Chilotherium in Central Asia

Presenter: Selina Robson

Mentors: Samantha Hopkins and Edward Davis, Geology

Poster: 56

Majors: Geology and Psychology 

We report a new occurrence of the rhinocerotid Chilotherium in the Kochkor basin in Kyrgyzstan. While some geologic reports refer to Chilotherium in Kyrgyzstan, no described material exists from the country and all published material has gone missing. Therefore, our new material is important for not only recognizing the occurrence of the genus, but also understanding the evolution, ecology, and dispersion of various fossil taxa including Chilotherium. Few studies have examined the global distribution of Chilotherium. While the taxon is not uncommon, we found that 84% of Chilotherium specimens were found in China. Thus, the Kyrgyz specimens represent an important geographic extension of the taxon, and may clarify the relationship between ecology and species diversity. Our database of Chilotherium occurrences only reports localities above 2,000m elevation. While paleoaltitudes may be different than modern altitudes, recent studies support the construction of both the Himalayan and Tien Shan ranges prior to the late Mio/Pliocene. This indicates that Chilotherium occupied an ecological niche that is different from other rhinos. Of the collected fossils from Kyrgyzstan, Chilotherium is the most abundant taxon. A species level diagnosis of Chilotherium is difficult because the taxonomy is poorly constrained. There are three valid species but close to 20 published species. By mapping occurrences globally, we hope to clarify taxonomic relationships as well as to assign the new Kyrgyz material to a species level.

Fossil Eulipotyphla from Oregon’s Middle Miocene: New Occurrences and Biogeographic Patterns

Presenter: Danielle Oberg

Mentors: Samantha Hopkins and Edward Davis, Geology

Poster: 48

Major: Geology 

Insectivores (euliptophylans) are not well understood in the Miocene of Oregon. Recent discoveries from a new locality, Cave Basin, in the John Day Formation suggest a greater diversity of insectivores than was previously known. Early Miocene records are extremely poor and lack small mammals entirely. However, the Middle and Late Miocene explode with new families never seen before in southern Oregon. The Middle Miocene has the greatest insectivore diversity with occurrences of ancient shrews (heterosoricidae), red-toothed shrews (soricidae), true moles (talpidae), and hedgehogs (erinaceidae) clustering around the Oregon-California border in southeastern Oregon. Fourteen Middle Miocene localities have red-toothed shrews and true moles, while hedgehogs and ancient shrews are found in two localities. Diversity rapidly decreases for ancient shrews and hedgehogs throughout the Late Miocene and into the Clarendonian, but remains relatively constant for true moles and red-toothed shrews. Red-toothed shrew Late Miocene localities are further south and less clustered than Middle Miocene ones. True mole localities have a greater spread across eastern Oregon, ranging from the Oregon-Washington state line to the southern corner of Oregon. These new discoveries in the Oregon Miocene are a significant addition to the understanding of the Oregon fossil record. Furthermore, these insectivores reveal new insight into the paleoecology of the Miocene, changes in diversity over time, and evolution of insectivores that are still found in Oregon today.

The Ups and Downs of the Mammal World: How Mammal Diversity Has Changed in the United States throughout the 20th Century

Presenter: Kendra Walters

Faculty Mentor: Edward Davis, Samantha Hopkins

Presentation Type: Oral

Primary Research Area: Science

Major: Geology, Biology

Funding Source: Presidential Undergraduate Research Scholar, Undergraduate Research Opportunity Program, $5,000

Biodiversity loss is recognized as a global crisis. Current research strives to create models that predict regions that are at high risk for a significant drop in biodiversity levels. These models must be scaled by analyses of historic changes in biodiversity. However, no study has yet to analyze the changes in mammal richness in the United States at a high enough spatial and temporal resolution to produce a predictive model of mammal diversity. Our research is a high-resolution analysis of the changes in mammal richness in the contiguous United States from 1906 to 1995. We collected mammal occurrence data from the online database VertNet and BISON and individual museum collections, divided it into ten year increments, and used scripts in R to produce sampling-standardized patterns of mammal richness for each decade. We then analyzed the geographic distribution of change in richness over the 20th century. From our results, we were able to determine which regions experienced a significant rise in diversity levels and which experienced a significant drop. We also identified regions where sampling intensities remain too low to conclusively determine how mammal diversity has changed. Regions experiencing the most severe biodiversity changes, as well as those without adequate data, should be focal areas for continued research in conservation efforts.

Use of the Sciuridae as a Paleoenvironmental Indicator Taxa

Presenter: Eva Biedron

Faculty Mentor: Samantha S. B. Hopkins, Edward B. Davis

Presentation Type: Oral

Primary Research Area: Science

Major: Geological Sciences, Biology

Relationships between mammal species and their preferred habitats are often used to reconstruct past ecology in fossil ecosystems. Ungulate herbivores, whose teeth reflect their diet, are one of the most common terrestrial mammal groups used in habitat reconstruction. However, small mammals, like squirrels, may sample over a narrower geographic range and offer a more sensitive signal. If squirrels and ungulates show the same paleoecological signal in the fossil record, squirrels could be used as a new habitat indicator taxa.

We hypothesized open-habitat squirrel taxa would be found in assemblages dominated by grazing ungulates and closed-habitat sciurid taxa would be found in assemblages dominated by browsing ungulates. We compiled a dataset of 25 Oregon fossil localities (aged mid-Miocene to Recent), including specimen data and ecology, using the MioMap and Fossilworks Paleobiology database. We calculated the chord distance between each unique pair of sites to understand the differences in dominant squirrel and ungulate ecologies.

We found the chord distance values of squirrels form three distinct clusters while ungulate chord distance values do not cluster, indicating differences between sciurids and ungulates as habitat indicators. The differences between these large and small mammals in home range size may yield different information about a heterogeneous landscape. If so, these results suggest sciurids and ungulates are both useful as paleoecological indicators, but at different spatial scales.