Biogeography of Arikareean mammalian communities

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As part of my dissertation, I am interested in studying the biogeographic relationships between Arikareean deposits in the northern United States (Oregon, Montana, Nebraska, Wyoming, and South Dakota). As part of a statistics class at the University of Washington, I have started investigating taxonomic similarities across Arikareean faunas using (in part) ordination methods.

These initial results are published in an in-house journal:

Calede, J. 2012. Biogeography and endemism in Arikareean faunas (North America, 30-18.8 Ma). Electronic Journal of Applied Multivariate Statistics 4:12–22.

You can read the abstract below:

The rich and geographically widespread Arikareean fossil record (North America, 30 to 18.8 Ma) provides a unique opportunity to test hypothesis of geographic clusters and gradients in faunal composition. I use multivariate statistics (cluster analysis and ordinations) to test the hypotheses that early modern mammalian faunas of the Arikareean were significantly different across biogeographic regions, were arranged along geographic gradients and that this apparent biogeographic pattern cannot be accounted for by the incomplete nature of the fossil record. The results show that there is support for a biogeographic structure of Arikareean communities with some possibly endemic assemblages (Cabbage Patch Beds of western Montana, Delaho Formation of southwestern Texas). The fossil assemblages reflect a strong longitudinal gradient. No evidence for a latitudinal gradient is found. Neither age nor sampling seem to influence the observed pattern which instead is correlated with depositional environment. This suggests that much of the observed faunal differences across assemblages and regions can be explained by habitats constraining local and regional faunas. Further study exploring the functional diversity of these assemblages will further investigate the controls on community assembly during the late Oligocene-earlyMiocene.

Cabbage Patch Beds

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The Cabbage Patch beds of western Montana  span roughly 6.5 million years from about 29. 5 to 23 million years ago crossing the boundary between the Oligocene and the Miocene. This series of fossil-bearing horizons is located in Powell, Granite, Silver Bow, and Deer Lodge counties (Montana). The Cabbage Patch beds house a rich vertebrate (mostly mammals) and invertebrate (mostly land and freshwater snails) fauna as well as floral remains (mostly in the form of phytoliths). These beds have mostly been studied by Dr. Donald Rasmussen in the 1960s and 1970s.

I am continuing Dr. Rasmussen’s work with the goal of comparing the fauna from Cabbage Patch to faunas of the same age located in Oregon (John Day Formation) and Nebraska (Arikaree Group). I am collecting additional fossils and geological data from the field and  further analyzing the fossils collected by Dr. Rasmussen housed at the University of Montana and the University of Kansas (mostly).

The goals of my dissertation are to better understand:

Collaborators at the University of Washington and the University of Michigan are investigating these deposits using isotopes and phytoliths to better understand the environment at the time in Montana. You can read more about their research here.

Microwear in burrowing rodents

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The study of microwear features on the enamel surface of mammalian teeth is widely used to reconstruct paleodiets of extinct mammals. Few of these prior studies have focused on rodents and those that did often focused on a single taxon or a few related taxa. We focused on mylagaulids and geomyids, two groups of extinct subterranean rodents present in the Great Basin during the Miocene. Knowledge of their diet will allow further investigation of the paleoecology of this peculiar family of fossil rodents.

The results of this research were presented at the annual meeting of the Society of Vertebrate Paleontology in Pittsburgh (2010) and are part of my M.S. thesis at the University of Oregon.

Collaborator: Samantha Hopkins

Leptarctus oregonensis and Oregon leptarctines

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Leptarctines are enigmatic, yet common, mustelids in the North American and Asian fossil record. No consensus has yet been reached about their paleoecology. Differing interpretations of dental and cranial features and a lack of available postcranial elements have left the diet and locomotor habits of this subfamily uncertain. Initial interpretations of their ecology include coati-like omnivory, badger-like carnivory, kinkajou-like frugivory, and koala-like herbivory. The comparison to a koala-like diet implied a strongly arboreal lifestyle for leptarctines. Most recently, the cranial and dental morphology have been interpreted as evidence for a crushing omnivorous diet.
We have been studying a partial skeleton of a late early Hemphillian (7.5 – 6.7 Ma) leptarctine from the Rome fauna of Malheur County, Oregon as well as a nearly complete skull of Leptarctus oregonensis, a small Leptarctus from the Mascall Formation of central Oregon (early Barstovian, 15.9 – 14.8 Ma) with the goal of improving our understanding of the Leptarctine paleoecology.

Preliminary results have been presented by Winifred Kehl at the Geological Society of America annual meeting in Portland (2009) and the Oregon Academy of Sciences annual meeting in Portland (2010).

Collaborators: Winifred Kehl, Edward Davis, Samantha Hopkins

Mole diversity in eastern Oregon during the Miocene

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The taxonomy and morphology of the Miocene moles of eastern Oregon is well understood, but their paleoecology has not been fully resolved. It has been observed that through the Miocene, Oregon talpids decreased in diversity (number of genera and minimum number of individuals) while shifting ecologically. We explored the hypothesis of a link between faunal and environmental change using both published (MIOMAP) and museum data on talpid diversity for the northern Great Basin from the early Barstovian (~16 Ma) through the late late Hemphillian (~5 Ma). We analyzed faunal data for changes in relative abundance, evenness, rarefied number of species, and variations in habitat use.

The results of this research were presented at the annual meeting of the Society of Vertebrate Paleontology in Bristol (2009).

Collaborator: Edward Davis

Antelope astragali

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The Hemphillian (~8Ma) Thousand Creek Fauna of northwestern Nevada contains three species of closely related antilocaprids in two genera, Ilingoceros alexandrae, Ilingoceros schizoceras, and Sphenophalos nevadanus. These species were diagnosed on the basis of their distinct horn morphology, but the little work done comparing their dental or postcranial morphology showed no clear separation between the species, leading to a hypothesis that the two Ilingoceros were age classes and that Ilingoceros and Sphenophalos represented sexual morphs within one species. We used multivariate morphometric comparison of eight linear dimensions of >200 antilocaprid astragali from Thousand Creek to find out if there is enough variation to support the presence of more than one species.

Preliminary results have been presented by Dr. Edward Davis at the annual meeting of the Society of Vertebrate Paleontology in Austin (2007). The results of this research project are published in Palaeontologia Electronica.

Davis, E. B., and Calede, J.2012. Multivariate analysis of Hemphillian (Late Miocene) and recent antilocaprid astragali indicates little divergence between Ilingoceros and Sphenophalos in the Thousand Creek Formation, Nevada. Paleontologia Electronica 15.1.1A.
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Collaborator: Edward Davis

Morphology and Ontogeny of Alphagaulus pristinus

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My undergraduate research project at the University of Oregon (during an exchange program) focused on understanding changes in morphology during ontogeny in the poorly known Alphagaulus pristinus described in 1903 by Douglass on the basis of a single isolated partial jaw.

The results of this research were presented at the SVP annual meeting in 2008 and are published in the Journal of Vertebrate Paleontology.

Calede, J., and Hopkins, S.S.B. 2012. New material of Alphagaulus pristinus (Mammalia: Rodentia: Mylagaulidae) from the Deep River Formation (Montana, USA): implications for ecology, ontogeny, and phylogeny. Journal of Vertebrate Paleontology 32:151–165.
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Collaborator: Samantha Hopkins