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The Oligocene rodent Ischyromys of the Great Plains: replacement mistaken for anagenesis

Published online by Cambridge University Press:  20 May 2016

Timothy H. Heaton
Timothy H. Heaton*
Affiliation:
Department of Earth Sciences, University of South Dakota, Vermillion 57069
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Abstract

Ischyromys, the most abundant early Oligocene rodent from the Great Plains, has been considered by some workers to represent a single gradually evolving lineage comprising three or more chronospecies. Statistical investigation of large samples suggest instead that two closely related species coexisted, and the shift in mean size that was thought to represent anagenesis actually represents replacement. In Nebraska and eastern Wyoming both I. parvidens (small) and I. typus (large) were rare but of equal abundance in the Chadronian, I. parvidens was more prevalent in the early Orellan, and I. typus was more prevalent in the middle and late Orellan. In northeastern Colorado, northern South Dakota, and North Dakota I. typus is the only species of Ischyromys found in Orellan deposits, thus showing that the two species had differing geographic ranges.

The mean size of I. typus does increase up section at all localities, but this change is minor and not deserving of chronospecies recognition. Much of this change occurred in the latest Orellan and earliest Whitneyan as I. typus approached extinction, and it was accomplished mostly by loss of small individuals rather than a shift of the entire distribution. Rate of evolutionary change in Ischyromys is found to be inversely correlated with population size, and no new species arose during the Orellan when Ischyromys was most abundant.

Type
Research Article
Information
Journal of Paleontology , Volume 67 , Issue 2 , March 1993 , pp. 297 - 308
Copyright
Copyright © The Paleontological Society 

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References

Barbour, E. H., and Stout, T. M. 1939. The White River Oligocene rodent Diplolophus . Bulletin of the University of Nebraska State Museum, 2:29–36.Google Scholar
Black, C. C. 1965. Fossil mammals from Montana, Part 2. Rodents from the Early Oligocene Pipestone Springs local fauna. Annals of Carnegie Museum, 38:1–48.CrossRefGoogle Scholar
Black, C. C. 1968. The Oligocene rodent Ischyromys and discussion of the family Ischyromyidae. Annals of Carnegie Museum, 38:1–48.CrossRefGoogle Scholar
Eldredge, N., and Gould, S. J. 1972. Punctuated equilibria: an alternative to phyletic gradualism, p. 82–115. In Schopf, T. J. M. (ed.), Models in Paleobiology. Freeman, Cooper and Company, San Francisco.Google Scholar
Emry, R. J., Bjork, P. R., and Russell, L. S. 1987. The Chadronian, Orellan, and Whitneyan land mammal ages, p. 119–152. In Woodburne, M. O. (ed.), Cenozoic Mammals of North America: Geochronology and Biostratigraphy. University of California Press, Berkeley.Google Scholar
Flynn, J. J. 1977. Morphological variation in the Oligocene Ischyromyidae (Rodentia) from Flagstaff Rim, Wyoming. Unpubl. , Yale University, New Haven, Connecticut, 46 p.Google Scholar
Galbreath, E. C. 1953. A contribution to the Tertiary geology and paleontology of northeastern Colorado. University of Kansas Paleontological Contributions: Vertebrata, 4:1–120.Google Scholar
Gingerich, P. D. 1983. Rates of evolution: effects of time and temporal scaling. Science, 222:159–161.CrossRefGoogle ScholarPubMed
Haldane, J. B. S. 1949. Suggestions as to quantitative measurement of rates of evolution. Evolution, 3:51–56.CrossRefGoogle ScholarPubMed
Heaton, T. H. 1988. Patterns of evolution in Ischyromys and Titanotheriomys (Rodentia: Ischyromyidae) from Oligocene deposits of western North America. Unpubl. , Harvard University, Cambridge, Massachusetts, 165 p.Google Scholar
Howe, J. A. 1956. The Oligocene rodent Ischyromys in relationship to the paleosols of the Brule Formation. Unpubl. , University of Nebraska, Lincoln, 89 p.Google Scholar
Howe, J. A. 1966. The Oligocene rodent Ischyromys in Nebraska. Journal of Paleontology, 40:1200–1210.Google Scholar
Lillegraven, J. 1970. Stratigraphy, structure, and vertebrate fossils of the Oligocene Brule Formation, Slim Buttes, Northwestern South Dakota. Geological Society of America Bulletin, 81:831–850.CrossRefGoogle Scholar
Prothero, D. R. 1982a. Medial Oligocene magnetostratigraphy and mammalian biostratigraphy: testing the isochroneity of mammalian biostratigraphic events. Unpubl. Ph.D. dissertation, Columbia University, New York, 284 p.Google Scholar
Prothero, D. R. 1982b. How isochronous are mammalian biostratigraphic events? Third North American Paleontological Convention Proceedings, 2:405–409.Google Scholar
Schultz, C. B., and Stout, T. M. 1955. Classification of Oligocene sediments in Nebraska. Bulletin of the University of Nebraska State Museum, 4:17–52.Google Scholar
Skinner, M. F. 1951. The Oligocene of western North Dakota, p. 51–58. In Society of Vertebrate Paleontology Fifth Field Conference Guide Book. Rapid City, South Dakota.Google Scholar
Sokal, R. R., and Rohlf, F. J. 1981. Biometry, 2nd ed. W. H. Freeman and Company, San Francisco, 859 p.Google Scholar
Stout, T. M. 1937. A stratigraphic study of the Oligocene rodents in the Nebraska State Museum. Unpubl. , University of Nebraska, Lincoln, 138 p.Google Scholar
Swisher, C. C. III, and Prothero, D. R. 1990. Single-crystal 40Ar/39Ar dating of the Eocene–Oligocene transition in North America. Science, 259:760–762.CrossRefGoogle Scholar
Ward, J. H. Jr. 1963. Hierarchical grouping to optimize an objective function. Journal of the American Statistics Association, 58:236–244.CrossRefGoogle Scholar
Wilkinson, L. 1988. systat: The System for Statistics. systat Inc., Evanston, Illinois, 822 p.Google Scholar
Wood, A. E. 1937. The mammalian fauna of the White River Oligocene, part II: Rodentia. Transactions of the American Philosophical Society, N.S., 28:155–269.Google Scholar
Wood, A. E. 1976. The Oligocene rodents Ischyromys and Titanotheriomys and the content of the family Ischyromyidae, p. 244–277. In Churcher, C. S. (ed.), Athlon: Essays on Paleontology in Honor of Loris Shano Russell. Royal Ontario Museum Life Science Miscellaneous Publication, University of Toronto Press, Toronto.Google Scholar
Wood, A. E. 1980. The Oligocene rodents of North America. Transactions of the American Philosophical Society, 70:1–68.CrossRefGoogle Scholar