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Middle Miocene Rodents from Quebrada Honda, Bolivia

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Middle Miocene Rodents from Quebrada Honda, Bolivia MIDDLE MIOCENE RODENTS FROM QUEBRADA HONDA, BOLIVIA JENNIFER M. H. CHICK Submitted in partial fulfillment of the requirements for the degree of Master of Science Thesis Adviser: Dr. Darin Croft Department of Biology CASE WESTERN RESERVE UNIVERSITY May, 2009 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the thesis/dissertation of _____________________________________________________ candidate for the ______________________degree *. (signed)_______________________________________________ (chair of the committee) ________________________________________________ ________________________________________________ ________________________________________________ ________________________________________________ ________________________________________________ (date) _______________________ *We also certify that written approval has been obtained for any proprietary material contained therein. Table of Contents List of Tables ...................................................................................................................... ii List of Figures.................................................................................................................... iii Abstract.............................................................................................................................. iv Introduction..........................................................................................................................1 Materials and Methods.........................................................................................................7 Systematic Paleontology....................................................................................................10 cf. Neoreomys huilensis Fields, 1957 ................................................................................12 Orthomyctera rigens Ameghino, 1889 ..............................................................................20 cf. Prodolichotis mendocina, Rovereto 1914 ....................................................................24 Prodolichotis sp. nov. ........................................................................................................25 Chasichimys sp. nov...........................................................................................................30 Gen. et sp. nov. ..................................................................................................................34 Prolagostomus profluens Ameghino, 1887 .......................................................................39 Prolagostomus amplus Ameghino, 1889...........................................................................43 cf. Prolagostomus divisus Ameghino, 1887 ......................................................................44 Prolagostomus sp. nov.......................................................................................................45 Discussion..........................................................................................................................47 Paleoecological Implications .............................................................................................47 Evolutionary Trends...........................................................................................................50 Appendices.........................................................................................................................54 References..........................................................................................................................59 i List of Tables Table 1. Summary of tooth measurements from Quebrada Honda Orthomyctera rigens specimens...........................................................................................................................21 2. Summary of tooth measurements from Chasichimys sp. nov. specimens ....................31 3. Summary of tooth measurements from Prolagostomus profluens specimens...............40 4. Summary of tooth measurements from Prolagostomus amplus specimens ..................43 ii List of Figures Figure 1. Miocene South American Land Mammal “Ages” (SALMAs)........................................4 2. Map of South America with Miocene localities .............................................................5 3. Occlusal structure terminology .......................................................................................9 4. Right mandible of cf. Neoreomys huilensis ...................................................................13 5. Right isolated molars from dasyproctid species ...........................................................15 6. Caviid genera from Quebrada Honda ............................................................................17 7. Right lower dentition of caviid and eocardiid species ..................................................19 8. Right upper dentition for Orthomyctera rigens and O. andina .....................................22 9. Comparison of right lower dentition for cf. Prodolichotis mendocina from Quebrada Honda (UF 236854) and P. mendocina (MLP 28-X-11-477)...........................24 10. Prodolichotis sp. nov. ..................................................................................................26 11. Comparison of lower right dentition of Prodolichotis sp. nov. and P. pridiana .........27 12. Right mandible of Chasichimys sp. nov. ....................................................................29 13. Right lower dentition of Chasichimys sp. nov. and other Chasichimys species..........33 14. Right mandible of a new adelphomyine from Quebrada Honda .................................34 15. Right lower dentition of adelphomyines .....................................................................36 16. Prolagostomus specimens from Quebrada Honda ......................................................38 17. Right upper dentition of lagostomines ........................................................................42 18. Left lower dentition of lagostomines ...........................................................................46 iii Middle Miocene Rodents from Quebrada Honda, Bolivia Abstract by JENNIFER M. H. CHICK Despite South America’s rich fossil mammal record, relatively little work has focused on middle-latitude faunas of Miocene age; most current understanding of South American mammals during the middle Miocene derives from the extremes of the continent. Quebrada Honda (Laventan SALMA) in southern Bolivia is intermediate in latitude between these two regions, partly filling this large geographic gap. New collections from Quebrada Honda in 2007 facilitated this analysis of its rodents. The most abundant of these rodents are Prolagostomus and caviids. The octodontid Chasichimys from Quebrada Honda represent the earliest and northernmost occurrences of the genus. A new genus and species of adelphomyine echimyid is also present, represented by a single specimen with trilophodont, plate-like teeth. The abundance and diversity of rodents with high-crowned teeth suggests that Quebrada Honda was an open, grassland environment with fewer forests. iv Introduction: Paleontologists have been intrigued by South America’s fossil record for the past several hundred years; this is largely due to the continent’s unique geologic history. For much of the past 65 million year, including most of the Cenozoic era, South America was an island continent, drifting in “splendid isolation” from other land masses (Simpson, 1980; MacFadden and Wolff, 1981). Consequently, fossils from this large time interval, and from the Tertiary period specifically, have yielded valuable information on South American endemism (Huchon and Douzery, 2001). Mammalian evolution on the continent is typically split into three phases or strata, each with distinct faunal compositions. The first phase of mammalian evolution in South America occurred between ~65 and 40 mya, during the Paleocene and much of the Eocene (Flynn and Wyss, 1998). During this first phase of evolution, tropical and temperate forests dominated the continent; marsupials, xenarthrans, notoungulates, and litopterns proliferated (Huchon and Douzery, 2001). During the second phase, which commenced near the Eocene-Oligocene boundary (40-21mya), platyrrhine primates and caviomorph rodents invaded the continent. This phase was also accompanied by a global cooling event and the replacement of tropical and temperate forests by grasslands (MacFadden, 2006). The third phase of South American mammalian evolution is marked by the Great Faunal Interchange. This event occurred during the Miocene-Pliocene, when the Panamanian land bridge enabled the immigration of North American taxa into South America. This intermingling of immigrant and native faunas resulted in the modern faunal assemblage we see today. 1 In addition to the continent’s interesting geologic past and high degree of endemism, South America is well-known for the quality of its fossil record (Patterson and Pascual, 1968). Although the majority of fossils are from Argentina, recent efforts have been made to increase the geological sampling of the continent (Croft, 2007). Information gathered from fossils in Argentina and Colombia, and more recently from Ecuador, Brazil, Peru, and Uruguay enabled researchers to construct a sequence of provincial “ages” (Simpson, 1940) unique to South America. These South American Land Mammal “Ages” (SALMAs) reflect changing faunal assemblages throughout the Cenozoic and allow paleontologists
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