Search

Paenemarmota Hibbard and Schultz, 1948 includes 3 species of giant ground squirrels within Marmotini (Rodentia, Sciuridae) from the Late Miocene and Pliocene of central and western North America. We developed skeletal and dental models for estimating body mass across modern species of Marmotini and apply these models to Paenemarmota. The most reliable models for estimating body mass of modern species (on the basis of length and width of femur, lengths of p4 and P4) generally yielded lower estimates of body mass for Paenemarmota than less reliable models (on the basis of lengths of m1, m2, M1, and M2). Models that were most reliable across modem species yielded 2 nonoverlapping estimates for P. barbouri Hibbard and Schultz, 1948: 9.5-9.8 kg on the basis of femur dimensions, and 14.4-16.2 kg on the basis of lengths of premolars. On the basis of lengths of premolars, P. me.xicana (Wilson 1949) closely resembled P. barbouri in estimated mass (14.4-15.7 kg), but P. sawrockensis (Hibbard 1964) was smaller (10.0-12.4 kg). These large ground squirrels probably differed in mass-dependent biological attributes from all modern marmotines. [ABSTRACT FROM AUTHOR]

We investigated the evolutionary history of a group of silky pocket mice (Heteromyidae: Perognathinae: Perognathus flavus species group) composed of the species P. flavus and P. merriami to determine patterns and postulate causes of geographical diversification across arid grasslands and intermontane basins in western North America. The region represents a topographically complex landscape with a Neogene history of dramatic geological and climatic transformations. Phylogenetic and dating analyses of mitochondrial DNA support an initial split among 4 major lineages during the late Miocene, and this hypothesis receives further support from analysis of a portion of the nuclear interphotoreceptor retinoid-binding protein (IRBP) gene. Two of these lineages have a restricted geographic distribution in the Chihuahuan Desert, and 2 have distributions ranging across large portions of the Chihuahuan Desert, Colorado Plateau, Great Plains, and Tamaulipan Plain. Within the 2 widespread lineages further geographical diversification likely was concentrated in the Pliocene, which coincided with the origin of several hypothesized geographic barriers. These results are consistent with models of allopatric divergence driven by pre-Pleistocene geological and climatic events, particularly the late-Miocene expansion of interior grasslands and Miocene-Pliocene evolution of Basin and Range geomorphology. Therefore, the biogeographic structure displayed in the flavus species group may be predictive for a range of sympatric taxa. [ABSTRACT FROM AUTHOR]

Carnivores are ecologically diverse mammals. Dietary adaptations vary from strict herbivory to pure carnivory. These adaptations have evolved independently several times within families, so evolution within the order is iterative. I used 2 databases to examine whether ecological adaptations have an effect on longevity or spatial distributions of fossil carnivores. Miocene hypercarnivorous species had, on average, the widest spatial distributions. Their temporal distributions were not significantly longer than those of other carnivores. Body size also had a significant interaction with maximum spatial distribution. Largebodied carnivores, regardless of feeding adaptations, had larger geographical ranges, but did not have greater longevity. However, when all the data were pooled, temporal distribution had a significant correlation with spatial distribution. The position of hypercarnivores at the top of the food chain and their specialized adaptations for meat eating probably increased their extinction risk to the same level of more narrowly distributed, less specialized carnivores. [ABSTRACT FROM AUTHOR]