Date of this Version
ElShafie, S. J. 2014. Body size and species richness changes in Glyptosaurinae (Squamata: Anguidae) through climatic transitions of the North American Cenozoic. Masters Thesis. University of Nebraska-Lincoln. Department of Earth and Atmospheric Sciences.
Poikilothermic vertebrates offer excellent climate proxies based on relationships between environment and measurable variables such as body size and species richness. Relationships of these variables in lizards to environmental transitions over long time scales are poorly understood. Here I show that patterns of body size and species richness in a lizard clade, Glyptosaurinae (Squamata: Anguidae), correspond to known histories of paleotemperatures through the Cenozoic of North America. Glyptosaurines have the richest fossil record among North American Cenozoic lizards and exhibit a wide range of skull sizes. In order to estimate body size for glyptosaurines and other fossil anguids, I collected skull and snout-vent length measurements of extant anguimorph lizards from museum collections, and used these data to model body size from skull length. I used my glyptosaurine body size estimates to calculate mean annual paleotemperatures (MAPT) for the interior of North America through the Paleogene. I also obtained anguid species richness data at NALMA temporal resolution from museum collections and literature. I compared these data to known Paleogene climate histories for the interior of North America using published MAPT proxies derived from terrestrial paleofloras and mammalian fossils.
I found that maximum body size was comparable among the largest glyptosaurines from the early Eocene and the late Eocene, indicating paleotemperatures of about 19 – 20ºC during both intervals. Other terrestrial proxies indicated declines in continental MAPT of about 3 – 8ºC in the middle to late Eocene. This could indicate that overall temperature decreases remained above critical minimum temperatures for efficient metabolism in large lizards, or that some glyptosaurines behaviorally maintained body temperatures above cooler ambient levels in the late Eocene. Minimum MAPTs calculated using glyptosaurine body size estimates showed significant correlation with published continental MAPT proxies from other terrestrial indicators. I also found that glyptosaurine species richness peaked in the Wasatchian, followed by a decline through the remainder of the Paleogene; these patterns coarsely coincide with increases and decreases in continental MAPT.
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