Tag: Samantha Hopkins

Lagomorph Paleoecology of the Middle Cenozoic in Eastern Asia

Presenter: Amelia Lawson – Environmental Science

Faculty Mentor(s): Amanda Peng, Samantha Hopkins

Session: (In-Person) Poster Presentation

Lagomorphs are small plant eating mammals that are split into two extant families: the Ochotonidae which is comprised of pikas, and Leporidae which is made of rabbits and hares. The earliest lagomorph occurrence is 55 million years ago in Asia, which is widely recognized as the origin of lagomorphs. Through the Cenozoic, lagomorphs diversified and migrated to every continent except Australia and Antarctica. During the Cenozoic, Asia transitioned from a humid and warm environment to an arid and cool climate. These changes as well as geographic alterations in Asia dramatically effected lagomorphs at the time which can be viewed by analyzing the fossil record. Along with changes in climate, inferences can be made about lagomorph niche and habitat by comparing extinct and extant species data. The purpose of this study was to gain a deeper understanding of the effects of geography, particularly the Mongolian Plateau, on lagomorphs in Asia. In this study, I analyzed fossils from 8 localities in East Asia from the Eocene to the Miocene using the Paleobiology Database and past publications to access the environmental effects on lagomorph diversity and size in East Asia through time. This study provided further incite into the formation of the Mongolian Plateau, which is relatively sparce in information on the time of its uprise. As a result, this study suggests that the rise of the Mongolian Plateau and Hangay Mountains had dramatic impacts on Lagomorphs throughout the Cenozoic.

A Review of the Camels From the Juntura Formation of Eastern Oregon

Presenter(s): Eleanor Froehlich — Earth Sciences

Faculty Mentor(s): Samantha Hopkins

Session: (In-Person) Poster Presentation

The Juntura Formation, collected by Dr. J. Arnold Shotwell in the 1950’s and described in 1963, is found in a set of localities in Eastern Oregon near the unincorporated community of Juntura. These localities are Clarendonian in age and date to approximately 10-13 million years. As this is the only known Clarendonian site in Oregon, and one of the few Clarendonian age faunas in western North America, all information is vital to our understanding of this period. Shotwell described two camels from Juntura, Procamelus cf. grandis and Megatylopus cf. gigas. However, following the research of Brianna McHorse on the postcranial remains found at Juntura, this has been reexamined. This was done through the study of dental remains including nine lower jaws. These lower jaws have confirmed the presence of both Procamelus and Megatylopus, but in proportions dissimilar to those proposed by Shotwell.

Climate Change and Preservation Bias in the Pliocene Ringold Formation

Presenter: Christina Wilson, Geology

Poster: D-5

Mentor: Samantha Hopkins, Geology

Before oscillations of glacial and interglacial cycles began, the climate within the Pliocene epoch, (5.3 – 2.6 Ma) was relatively temperate –similar to more conservative projections for the next 100 years of our current climate. Therefore, this time period provides an excellent basis for predicting how present fauna may respond to climate change. This study compares sites with different geologic ages but similar locations to examine faunal changes over time. This will show how different factors, including climate, impact the ecosystem. I researched the Ringold Formation, located in South-Central Washington, which is early Blancan in age (4.75-1.80 Ma) and within the Pliocene epoch. I picked fossils from screened sediment, identified different types of fossil, and classified those most amenable to identification. One of the main components of the collection is Mimomys teeth. Classification of 419 teeth shows that the morals are not in the same proportions as in living Mimomys, suggesting preservation bias and highlighting the importance of sampling all members of an ecosystem. Rabbit and squirrel teeth were also classified. These were fewer in number, so conclusions could not be drawn as clearly. Further identification and cataloguing of species will enable a fuller picture of the environment preserved and continue to shed light on the changing fauna through time.

Biostratigraphy of Miocene Camelids in the Juntura Formation

Presenter: Brianna McHorse, Biology

Poster: C-1

Mentor: Samantha Hopkins, Geology

Paleoecological research relies largely on the accuracy with which fossil specimens can be identified. Species-level identifications provide the most precise data for measuring diversity and communities through changing environments, space, and time. While cranial (skull) fossils allow a researcher to quickly identify specimens to the species level because of the density of characters (teeth, foramina, sutures, etc.), postcranial elements tend to be less diagnostic. However, postcranial material is favorably preserved in the fossil record. Previous studies have shown that the dimensions of camelid metapodials (cannon bones) tend to cluster in a species- specific way, as well as provide some indication of the presence or absence of a pacing gait. This study carries out measurements on Miocene camel metapodials from the Black Butte site in the Juntura Formation to identify each specimen more precisely, suggest the presence or absence of pacing, and examine whether sexual dimorphism was likely. A more precise understanding of the Juntura camel paleoecology will help to place them in ecological context relative to the other animals with which they lived. Preliminary results suggest that the two different camels present in this fauna had similar but distinct patterns of locomotion.

Deposition Bias in the Late Miocene McKay Reservoir

Presenter: Kelsey Stilson, Geology

Poster: C-7

Mentor: Samantha Hopkins, Geology

Fossils found in association have the potential to tell us about the ecology of a specific time and place in geologic history, suggest 9something about the changing prehistoric world, and give clues about the effects of present-day anthropogenic climate and habitat change. However, this is no simple process of counting up the number of bones found. A community is rarely, if ever, fossilized in the same proportions as it lived. This study suggests ways to measure the preservation bias in a system and extrapolate the composition of original fauna. My site is McKay Reservoir in north-central Oregon, where fossils were deposited by fluvial transport in the late Miocene (5.5 million years ago). Current approaches to depositional bias in such systems use the shape and evidence of postmortem damage to the bones in an assemblage to estimate the degree of sorting due to river flow. Voorhies diagrams, which use bone type (e.g. radius or metapodial) to determine the degree of sorting, indicate the McKay bones were transported at high velocity and were deposited relatively close to where they entered the water. Another method suggests that the bones were not exposed to air for long (little to no weathering) and rolled a medium distance along the stream bed (moderate abrasion). These results show that the bones came from nearby, perhaps as little as a mile from the site of desiccation to the site of final burial, and would therefore be relatively accurate indicators of ancient local species distribution.

The Evolution of Rhino Arthritis in the Cenozoic

Presenter: Kelsey Stilson

Mentor: Samantha Hopkins

PM Session Oral Presentation

Panel Name: A1 Evolutionary Trajectories

Location: Alsea Room

Time: 11:00am – 12:00pm

Arthritis is one of the most common skeletal pathologies, occurring in one-sixth of humans. Rhinocerotids provide a natural system for understanding the evolutionary underpinnings of arthritis. The severity and prevalence of arthritis in Rhinocerotidae increased substantially from 50 million years ago to the present. All five living species of rhinoceros develop arthritis before they reach maturity. Fossil rhinoceros relatives from 50 million years ago (Ma) show a dramatically different pattern of arthritic development. What changed from 50 Ma to today? Rhinos became graviportal, evolving from Hyrachyus, which was about the size and shape of a large dog, to the one-ton, stout-limbed animals of today. Despite this order of magnitude increase in size, rhinos also consistently display cursoriality (the habit of running) through time. These competing factors of increasing size and cursoriality provide a possible driver for the prevalence of arthritis. This study traces the history of arthritic development in the rhino lineage, finding that the distribution of arthritis is related to increasing body size, but that there are also clearly evolutionary effects determining its prevalence. This study is especially important because it examines an apparent pathology that persisted and even worsened despite millions of years of evolution that should have selected against it.

Conformation and Performance in Event Horses

Presenter: Brianna McHorse

Mentor: Samantha Hopkins

AM Session Oral Presentation

Panel Name: M5 Messaging and Performance

Location: Rogue Room

Time: 11:00am – 12:00pm

For thousands of years, conformation-the external physical shape of the body’s parts-has been considered a reliable indicator of a horse’s athletic ability. Despite the influence of conformation assessments on equine breeding and trade, few studies have used analytical methods to establish quantitative relationships between conformation and performance. Existing work suggests a significant relationship between judgments of quality and several conformational variables, especially shoulder and pelvis angle, which influence the reach and timing of the horse’s stride. I investigate the conformation-performance correlation in eventing, an equestrian discipline that tests the horse’s ability to complete three phases: dressage, cross-country, and stadium-jumping. Using statistical comparisons of performance records with geometric relationships between skeletal landmarks on the horse’s body, this study ultimately aims to quantify “ideal” conformation for an eventer. Preliminary results based on photographs suggest a significant relationship between con- formational variables and competition scores, especially in the dressage phase. Traits that may drive performance include back length and shoulder, hip, and pelvis angle. Future work using physical location of the skeletal landmarks may provide clearer resolution of ideal traits at each level of competition. Ultimately, this line of research may lead to a set of quantitative guidelines to be used when selecting event horses to purchase or breed.

Variation Through Tooth Wear Obscures the Differential Diagnoses of the Fossil Beavers Dipoides stirtoni and Dipoides smithi

Presenter : Savannah Olroyd

Mentor : Sam Hopkins

Major : Biology

Poster 30

Diagnostic features that show variation can be problematic when their variation interferes with clear distinction between species. Fossil identification can be further confounded when highly variable supposedly diagnostic dental characters change with tooth wear. The fossil beavers Dipoides stirtoni and Dipoides smithi are distinguished from one another by the presence or absence of striations on the fourth premolars. D. stirtoni has a parastria running down the cheek side of the upper P4 and a parastriid on the tongue side of the lower p4 in all wear stages. D. smithi lacks the parastria and only occasionally has a parastriid in later wear stages.

We have reviewed this diagnosis by examining over 200 cheek teeth of both species. No well-worn upper P4s of D. smithi have a para- stria, but the parastria is present in the earlier wear stages of all upper cheek teeth. Approximately 25% of the lower p4s of D. smithi studied have a parastriid in later wear stages, and one D. stirtoni lower p4 had no parastriid. We investigated other dental characters to see if other features were diagnostic to these species. The two are indistinguishable in tooth size, molar shape, and wear stages. The cur- rent diagnosis makes confident identification of new specimens difficult unless the specimen includes a well-worn upper P4. Complex series of tooth wear can produce a large amount of apparent dental variation in mammals with high-crowned teeth. Caution should be taken when using dental characters to assign diagnoses to such taxa.

Hidden Information in the Fossil Record: Using Discriminant Analysis on Isolated Postcrania

Presenter: Brianna McHorse (Biology)

Mentor: Samantha Hopkins

Oral Presentation

Panel B: “Vertebrate Expression” Walnut Room

Concurrent Session 3: 1:45-3:00pm

Facilitator: Chris Moe

Postcrania (non-skull or teeth bones) are often preserved in the fossil record but, unless found with teeth or skulls, are rarely identified beyond the family level. As a result, they offer a potentially untapped resource for studies of extinct diversity. Discriminant statistical analyses of linear measurements on these postcranial bones show remarkably high identification success rates for many mammal types, including antilocaprids (pronghorn), camelids (camels and llamas), and equids (horses). The approach we use is ideal, as it captures more subtle bone-shape variation than examining scatterplots of measurements but is more straightforward than three-dimensional morphometric methods. Further, applying Bayesian methods to the established discriminant analysis can allow integration of multiple skeletal elements, e.g., phalanges (fingers), astragali (ankles), and metapodials (hand and foot bones). We test this new method on a known, artificially created assemblage of modern cervid (deer), camelid, and antilocaprid postcranial bones. In a mixed training set of four bone types, we achieved identification success rates ranging from 87.5% to 100%. Our method is simple but has the potential to quickly and significantly improve knowledge of the hoofed mammal ecology at several postcrania-rich fossil sites. We focus on hoofed mammals, but the method should transfer well to other mammalian groups, shedding light on hidden diversity and improving any studies that rely on identification.

Mandible Morphology and Habitat in the Extant Tribes Marmotini and Sciurini (Rodentia:Sciuridae)

Presenter: Eva Biedron

Mentor: Samantha Hopkins

Poster: 4

Major: Geology/Biology

Morphological convergence among rodents living in similar habitats is common and well recorded. While upper incisor angle has been studied in connection with diet, lower incisor angle has been relatively neglected, despite textbook assertions that it correlates to habitat. Due to the difference in diets and jaw use between the terrestrial tribe Marmotini and the arboreal tribe Sciurini, it is expected that the tribes will display different mandible morphology, specifically lower incisor angle and diastema depth. The inclination of the lower incisor was quantified by measuring its angle relative to the occlusal surface of the lower molars with the mandible in lateral view. Diastema depth was measured as a vertical line along the anterior edge of the mental foramina, again viewing the mandible laterally. Preliminary data supports a relationship between smaller lower incisor angles and arboreality (t22 = 2.652, p = 0.015), but does not support diastema depth (t12 = 0.375, p = 0.714) as a predictor of arboreality. Changing habitats during the early Oligocene could have prompted the radial evolution of sciurids; by understanding how modern squirrels’ morphology is related to the habitat they live in, paleontologists will be able to better reconstruct a fossil squirrel’s paleoenvironment by using measurements of commonly preserved cranial elements as a proxy for actual habitat data.