Review Essay : Industrial Organization and Socialist Development in China

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68697/2/10.1177_009770047900500204.pd

Why were extinct gigantic birds so small?

This review details the six lineages of large flightless birds that evolved in the Late Cretaceous, Tertiary and Quaternary periods of geological time. Estimates of mass for each type of bird suggest that maximal mass is no greater than 500 kg with most species attaining only 250–300 kg or less. By contrast, non-avian Archosaurs of the Mesozoic, and many mammal species of the Tertiary, attained great size with many species reaching several tonnes. Size has been limited in flightless birds because of the strength of the eggshell and in the largest species reproduction was only possible if the smaller males incubated. That reproductive characteristics limit mass in flightless birds suggests that truly gigantic non-avian theropods could not contact incubate their eggs and had to rely on environmental sources of heat energy to drive embryonic development. If fossil evidence ever arises to support proper contact incubation in a non-avian theropod then it is predicted that it will only be from a small (5250 kg) species

A Revision of Skull Morphology In Phorusrhacidae (Aves, Cariamiformes)

Phorusrhacidae, popularly known as ‘terror birds’, are the most speciose clade within the avian order Cariamiformes, with a fossil record that ranges from the Eocene to the Pleistocene. Although several species have preserved skulls, our understanding of their cranial morphology remains incomplete. Here, a comprehensive overview of the current knowledge of phorusrhacid skull anatomy is presented. The phorusrhacid skull bauplan includes salient features such as deep, triangular fossae temporales, a complex basipterygoid articulation and the loss of bending zones related to kinesis. Two skull morphotypes can be discriminated: the psilopterine and the ‘terror bird’ type. The ‘terror bird’ skull type is here considered an evolutionary specialization, indicating that among phorusrhacids, medium-size to large phorusrhacids show more rigid and stiffer skulls. Nevertheless, studies have shown that the two morphotypes may have handled prey in a similar manner, suggesting that a trophic specialization with a unique hunting technique was the key driver of the evolution of the phorusrhacid skull.Fil: Degrange, Federico Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentin