The core question my research seeks to answer is “How can we use the fossil record to reconstruct interspecific interactions in the past, interpret biotic patterns in the present, and build predictive models for the future?” Past ecosystems and their response to disturbance offer us a case study in predicting how modern ecosystems might respond to similar disturbances arising from anthropogenic impacts. Under this framework, my current research projects focus on the following specific areas: (1) megafauna morphology, paleoecology, and biogeography; and, (2) the impact of biotic crises on ecosystem structure and function.
Megafauna Morphology, Paleoecology, and Biogeography
Mammoth and Mastodons: Taxonomic Revisions using Molar Morphology
Modern approaches to visualize fossil specimens are ideally suited for measuring variables useful for classifying species. For example, my Masters research used computed tomography (CT) to test the degree to which dental characters changed with wear in two species of mammoth. The results revealed a high degree of overlap between the two species, a finding that supported our earlier work highlighting the difficulty in distinguishing between species of mammoth in Pleistocene North America.
In collaboration with Chris Widga (East Tennessee State University) and Andrew McDonald (Western Science Center), I am submitting a proposal (NSF ADBC #15-576) to apply visualization methods to mammoth and mastodon populations throughout the United States. Our goals are to: 1) better document morphologic variation in these organisms, 2) encourage small museum and individual crowdsourcing of data, and 3) establish an online compendium of 3D models useful for K-12 and college educators as well as international researchers.
Smith and Graham, 2015 (GSA)
A chance conversation resulting from the 2017 Valley of the Mastodons workshop and conference at the Western Science Center led to an investigation into the strange molar morphology of West coast mastodons. Ultimately, my co-authors and I found statistically significant differences in morphology between this population and all other North American mastodons. These differences were consistent in space and time; thus, we named a new morphospecies - Mammut pacificus. This collaboration was an excellent example of scientific inquiry and collaboration leading to novel insights - even more remarkable, these fossils had sat largely untouched for nearly 20 years before we thought to look at them! Never underestimate the power of preserving fossil specimens for future investigations!
Dooley et al., 2019 (PeerJ)
Smith, G.J., Graham, R.W. Taxonomic implications of mammoth molar morphology as measured by computed tomography (CT) . IN PREP
Dooley, A.C., Scott, E., Green J.L., Springer, K.B., Dooley, B.S., Smith, G.J. (2019) Mammut pacificus sp. nov., a newly recognized species of mastodon from the Pleistocene of western North America. PeerJ 7:e6614. [link to open-access paper]
Smith, G.J., Graham, R.W. (2017) The effects of dental wear on impairing mammoth taxonomy: a reappraisal of the Newton Mammoth, Bradford County, Northeastern Pennsylvania. Quaternary International 443A: 40 – 51. [pdf]
Smith, G.J., Graham, R.W. (2015) Taxonomic implications of mammoth molar morphology as measured by computed tomography (CT). Geological Society of America Abstracts with Programs, 47(7): 681.
Smith, G.J., Graham, R.W. (2012) Dental wear and lamellar frequency analysis to constrain the identity of the North American mammoth species. Journal of Vertebrate Paleontology, Programs and Abstracts, 2012: 174.
Dietary Ecology of Pleistocene Proboscideans in North America
The foods eaten by an organism leave evidence of their textural and geochemical properties in mammalian tissues, which can be used to reconstruct the dietary signature of modern and extinct organisms. My early PhD research used the diets of extinct megafauna to make inferences into their interactions with other species and their environment. Over the course of this work, my research group has shown that the long-held notions of mastodons as ‘browsers’ and mammoths as ‘grazers’ do not adequately capture the dietary flexibility of these taxa. Further, the consumption of similar resources in three proboscidean groups (mammoths, mastodons, and gomphotheres) in the Pleistocene led to a competitive exclusion, wherein mammoths became a dominant megafaunal organism in North America, while gomphotheres disappeared from the continent. This work has the potential to help predict what might happen in the near future as more ecologically-similar groups are forced to share habitat, and as ever-increasing land use by humans leads to shifting and contracting biogeographic ranges. I am currently extending this work to Plio-Pleistocene sites in California, Arizona and New Mexico, and plan to better document the evolution of ecologic strategies in large mammals over this critical interval in North American history. Thus far, I have found that populations of megafauna in southern California may have been able to co-exist by specializing on disparate resources, resulting in one of the largest and most diverse assemblages of megaherbivores in late Pleistocene North America.
Smith and DeSantis, 2020 (Paleobiology)
Smith, G.J., Gibson, B.M., Gibson, M.A. (in preparation) Diet and environment of three Mammut americanum (Proboscidea, Mammutidae) from West Tennessee, United States. IN PREP
Smith, G.J., DeSantis, L.R.G., Green, J.L., Dooley, A.C. Paleoecology of the Late Pleistocene Diamond Valley Lake Local Fauna in southern California as evidenced by dental mesowear analysis and dental microwear texture analysis. Submitted.
Smith, G.J., DeSantis, L.R.G. (2020) Extinction of North American Cuvieronius (Mammalia: Proboscidea: Gomphotheriidae) driven by dietary resource competition with sympatric mammoths and mastodons. Paleobiology (Accepted; Awaiting Journal Assignment) [pdf]
Lundelius, E.L., Thies, K.J., Graham, R.W., Bell, C.J., Smith, G.J., DeSantis, L.R.G. (2019) Proboscidea from the Big Cypress Creek Fauna from the Deweyville Formation, Harris County, Texas. Quaternary International. 530-531:59-68. [pdf]
Smith, G.J., DeSantis, L.R.G. (2018) Dietary ecology of Pleistocene mammoths and mastodons in North America as inferred from dental microwear texture analysis. Palaeogeography, Palaeoclimatology, Palaeoecology. [pdf]
Green, J.L., DeSantis, L.R.G., Smith, G.J. (2017) Regional variation in the browsing diet of Pleistocene Mammut americanum (Mammalia, Proboscidea) as recorded by dental microwear textures. Palaeogeography, Palaeoclimatology, Palaeoecology 487: 59 – 70. [pdf]
Smith, G.J. (2018) Coupling paleoecological proxies to infer the dietary ecology of extinct megaherbivores. Journal of Vertebrate Paleontology, Programs and Abstracts, 2018: 147. Romer Prize Session.
Smith, G.J., DeSantis, L.R.G. (2018) Spatial and temporal variability in North American gomphothere diet as inferred from dental microwear textures. Geological Society of America Abstracts with Programs, 50(3): 4-8.
Smith, G.J., DeSantis, L.R.G. (2017) Gomphothere paleoecology in North America as inferred from stable isotope analysis. Geological Society of America Abstracts with Programs, 49(6): 91-13.
Smith, G.J., Gibson, M.A., Gibson, B.M. (2017) Seasonality and dental development of Mammut americanum from the Late Pleistocene of West Tennessee. Southeastern Association of Vertebrate Paleontology, Programs and Abstracts, 2017
Smith, G.J., DeSantis, L.R.G. (2016) Proboscidean dietary variability in North America and the Competitive Exclusion Principle. Journal of Vertebrate Paleontology, Programs and Abstracts, 2016: 226-227
Mammoth biogeographic response to hydrologic variability in the Mojave Desert
Animal migrations are a prominent feature of the modern biosphere that yield insight into processes governing community assembly. A novel way of tracking these is through the use of strontium isotopes recorded in mammalian tissues. In collaboration with Chris Widga (East Tennessee State University) and Kathleen Springer (USGS), I am currently working on establishing a map of bioavailable strontium (an 'isoscape') for the Tule Springs Local Fauna outside of Las Vegas, Nevada.
The Mojave Desert is the driest region in North America, with high variability in rainfall patterns from year to year. Thus, the region has been identified as a climate change hotspot – an area considered to be among the most sensitive to anthropogenic climate forcing. While temperatures in the Mojave Desert are likely to increase over the next century, changes in precipitation and the responses of flora and fauna are more difficult to predict. The Tule Springs fossils offer a case study in understanding how mammals responded to past changes in water availability and are thus a crucial resource for building predictive models in biotic responses to future climatic stress.
Springer et al. 2018
The Impact of Biotic Crises on Ecosystem Structure and Function
Modeling the Ecological Impacts of Extinction
My later PhD work investigated the ecological pattern of extinction in mammalian communities in North America throughout the Cenozoic. The results illustrate that phylogenetically clustered extinctions coincided with major environmental transitions, but not major extinction events – suggesting a decoupling between the taxonomic intensity and the ecological severity of extinctions in the terrestrial mammal fossil record. Further work applying this method on smaller temporal and spatial scales will work towards establishing a phylogenetic ‘signature’ for human-driven biotic crises. Our goal is to help make predictions about the ecologic structure of future mammalian communities given increased anthropogenic impacts. Additionally, I am currently working with Dr. Jonathan Gilligan to develop an agent-based model that can mimic the northern latitude transition from steppe to tundra that occurred following the late Pleistocene megafauna extinctions. This model will reveal how microscale changes in biotic and abiotic factors can lead to macroscale ecosystem changes during a major extinction interval, and should provide a tool for predicting how the extinction of modern megafauna might impact today’s endangered landscapes.
Smith and Darroch, in prep
Smith, G.J., Darroch, S.A.F. Phylogenetic Clustering of Origination and Extinction in North American Mammals through the Cenozoic. IN PREP
Smith, G.J., Darroch, S.A.F. (2019) Phylogenetic Conservatism of Biotic Crises in North American Mammals. North American Paleontological Convention, Riverside, CA, Techincal Program: 38.