Some recent papers for dino-related physiology issues:
The ability to determine the sex of extinct dinosaurs by examining the bones they leave behind would revolutionize our understanding of their paleobiology; however, to date, definitive sexâspecific skeletal traits remain elusive or controversial. Although living dinosaurs (i.e., extant birds) exhibit a sexâspecific tissue called medullary bone that is unique to females, the confident identification of this tissue in nonâavian archosaurs has proven a challenge. Tracing the evolution of medullary bone is complicated by existing variation of medullary bone tissues in living species; hypotheses that medullary bone structure or chemistry varied during its evolution; and a lack of studies aimed at distinguishing medullary bone from other types of endosteal tissues with which it shares microstructural and developmental characteristics, such as pathological tissues. A recent study attempted to capitalize on the molecular signature of medullary bone, which, in living birds, contains specific markers such as the sulfated glycosaminoglycan keratan sulfate, to support the proposed identification of medullary bone of a nonâavian dinosaur specimen (Tyrannosaurus rex MOR 1125). Purported medullary bone samples of MOR 1125 reacted positively to histochemical analyses and the single pathological control tested (avian osteopetrosis) did not, suggesting the presence of keratan sulfate might serve to definitively discriminate these tissues for future studies. To further test these results, we sampled 20 avian bone pathologies of various etiologies (18 species), and several MB samples. Our new data universally support keratan sulfate as a reliable marker of medullary bone in birds. However, we also find that reactivity varies among pathological bone tissues, with reactivity in some pathologies indistinguishable from MB. In the current sample, some pathologies comprised of chondroid bone (often a major constituent of skeletal pathologies and developing fracture calluses in vertebrates) contain keratan sulfate. We note that beyond chemistry, chondroid bone shares many characteristics with medullary bone (fibrous matrix, numerous and large cell lacunae, potential endosteal origin, trabecular architecture) and medullary bone has even been considered by some to be a type of chondroid bone. Our results suggest that the presence of keratan sulfate is not exclusive evidence for MB, but rather must be used as one in a suite of criteria available for identifying medullary bone (and thus gravid females) in nonâavian dinosaur specimens. Future studies should investigate whether there are definite chemical or microstructural differences between medullary bone and reactive chondroid bone that can discriminate these tissues.
===
Highlights
The topography of the conducting airways in some non-avian reptiles, including alligators, iguanas, and monitor lizards, causes unidirectional airflow.
Computational fluid dynamics modeling helps reveal mechanisms underpinning patterns of airflow in the lungs
Single-cell RNA sequencing and mapping, and immuno-electron microscopy, reveal two morphologically and molecularly distinct populations of endothelial cells lining the pulmonary capillaries of mammals but not turtles or alligators.
Abstract
High rates of pulmonary gas exchange require three things: 1) that gases at the contact surface of the lung's capillaries are replenished rapidly from the environment; 2) that this surface is large and thin; 3) that the capillaries are effectively perfused with blood. In spite of this uniform requirement, lungs have evolved complex and highly diverse architectures, but we have a poor understanding of the drivers of this diversity. Here, I briefly discuss some of the diversity in gross anatomical features directing airflow in avian and non-avian reptiles. I also review new insights into the cellular anatomy of the blood-gas barrier, which in mammals is composed of specialized endothelial as well as epithelial cells.