tailieunhanh - Respiratory and Reproductive Paleophysiology of Dinosaurs and Early Birds

In addition to ovulation, another critical function occurs during the menstrual cycle. The woman’s body must be prepared in case fertilization occurs. Everything must be ready to nurture the developing embryo. Dur- ing the first two weeks of the cycle, estrogen causes the lining of the uterus to thicken. There is also an increase in the amount of blood that flows to this area. During the second half of the cycle, after ovulation has occurred, the follicle (now without the egg cell) develops into a yellow-colored body, the corpus luteum. The corpus luteum begins to secrete progesterone, the pregnancy hormone, which prepares the uterus for an embryo. Sperm can survive. | 141 INVITED PERSPECTIVES IN PHYSIOLOGICAL AND BIOCHEMICAL ZOOLOGY Respiratory and Reproductive Paleophysiology of Dinosaurs and Early Birds John A. Ruben1 Terry D. Jones2 Nicholas R. Geist3 1Zoology Department Oregon State University Corvallis Oregon 97331-2914 2Biology Department Stephen F. Austin State University Nacogdoches Texas 79562-3001 3Biology Department Sonoma State University Rohnert Park California 94928-3609 Accepted 1 24 03 ABSTRACT In terms of their diversity and longevity dinosaurs and birds were are surely among the most successful of terrestrial vertebrates. Unfortunately interpreting many aspects of the biology of dinosaurs and the earliest of the birds presents formidable challenges because they are known only from fossils. Nevertheless a variety of attributes of these taxa can be inferred by identification of shared anatomical structures whose presence is causally linked to specialized functions in living reptiles birds and mammals. Studies such as these demonstrate that although dinosaurs and early birds were likely to have been homeothermic the absence of nasal respiratory turbinates in these animals indicates that they were likely to have maintained reptile-like ectothermic metabolic rates during periods of rest or routine activity. Nevertheless given the metabolic capacities of some extant reptiles during periods of elevated activity early birds were probably capable of powered flight. Similarly had for example theropod dinosaurs possessed aerobic metabolic capacities and habits equivalent to those of some large modern tropical latitude lizards . Varanus they may well have maintained significant home ranges and actively pursued and killed large prey. Additionally this scenario of active although ectothermic theropod dinosaurs seems reinforced by the likely utilization of crocodilian-like diaphragm breathing in this group. Finally persistent in vivo burial of their nests and ap E-mail rubenj@. f E-mail .