Description and Morphological Analysis of a Turtle Paleofauna (Cretaceous) from Suoth-Central Montana
Dickason, John W.
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Several quarries in the south-central Montana Judith River Formation (late Cretaceous in age) have yielded abundant turtle faunas. For nearly a decade, summer field parties from the University of Pennssylvanial Academy of Natural Sciences of Philadelphia (ANSP) have excavated in this area and have deposited their findings in the vertebrate paleontology collection at ANSP. The objective of this report was primarily to describe the collection of recently excavated turtle fossils at ANSP in the form of a faunal list In addition, an analysis of carapace size of trionychid (soft-shell) turtles was performed. Trionychid carapaces from ANSP were co~pared with a sample of carapaces from a similar stratigraphic level and geologic setting in Dinosaur Provincial Park (southern Alberta). It was found that the ANSP carapaces from south-central Montana were significantly greater in average width than were those from the southern Alberta sample (p=0.0018). Carapace length of Cretaceous trionychids from the study areas was also compared to a sample containing the maximum carapace lengths of the 22 extant species. This test showed that the sample of modem trionychids possesses a significantly greater average carapace length than does the sample of fossil trionychids (p=0.0026). It was concluded, after the examination of Cretaceousrrertiary temperature curves and studies regarding the effects of temperature on growth of terrestrial turtles, that the size differences between the two fossil samples compared in this study may be due to differing species distributions and / or the effect of different climatic regimes on ontogenetic growth .With honors.