Abstract:This report models pulmonary airflow in the savannah monitor (Varanus exanthematicus) using computational fluid dynamics simulations, which are based on computed tomography data. Simulations were validated by visualizing the flow of aerosolized lipids in excised lungs with good but not perfect agreement. The lung of this lizard has numerous successive bronchi branching off a long intrapulmonary bronchus, which are interconnected by intercameral perforations. Unidirectional flow has been documented in the later… Show more
“…; (e) Saguinus sp., (with a diagrammatic illustration of a standardized primate bronchial tree); (f) Iguana iguana (modified from Cieri et al, 2014); (g) Varanus exanthematicus (modified from Schachner et al, 2014); (h) Chelydra serpentina (modified from Schachner et al, 2017); (i) Alligator mississipiensis; and, (j) Struthio camelus. Images not to scale however, the recent discovery of unidirectional airflow patterns in the lungs of numerous species of crocodilians (Farmer, 2010(Farmer, , 2015bFarmer & Sanders, 2010;Schachner et al, 2013), a monitor lizard (Cieri & Farmer, 2019;Schachner et al, 2014), and the green iguana (Cieri et al, 2014), suggest that the origin of unidirectional airflow predates the evolution of avian flight, and is likely independent from the evolution of birds and endothermy (Cieri et al, 2014;Cieri & Farmer, 2016;Schachner et al, 2014). Recent work in gross anatomy, embryonic development, function, and in vascularization patterns has demonstrated potential homologies between the crocodilian and avian lung (Farmer, 2015b;Farmer & Sanders, 2010;Sanders & Farmer, 2012;Schachner et al, 2013).…”
The avian lung is highly specialized and is both functionally and morphologically distinct from that of their closest extant relatives, the crocodilians. It is highly partitioned, with a unidirectionally ventilated and immobilized gas‐exchanging lung, and functionally decoupled, compliant, poorly vascularized ventilatory air‐sacs. To understand the evolutionary history of the archosaurian respiratory system, it is essential to determine which anatomical characteristics are shared between birds and crocodilians and the role these shared traits play in their respective respiratory biology. To begin to address this larger question, we examined the anatomy of the lung and bronchial tree of 10 American alligators (Alligator mississippiensis) and 11 ostriches (Struthio camelus) across an ontogenetic series using traditional and micro‐computed tomography (µCT), three‐dimensional (3D) digital models, and morphometry. Intraspecific variation and left to right asymmetry were present in certain aspects of the bronchial tree of both taxa but was particularly evident in the cardiac (medial) region of the lungs of alligators and the caudal aspect of the bronchial tree in both species. The cross‐sectional area of the primary bronchus at the level of the major secondary airways and cross‐sectional area of ostia scaled either isometrically or negatively allometrically in alligators and isometrically or positively allometrically in ostriches with respect to body mass. Of 15 lung metrics, five were significantly different between the alligator and ostrich, suggesting that these aspects of the lung are more interspecifically plastic in archosaurs. One metric, the distances between the carina and each of the major secondary airways, had minimal intraspecific or ontogenetic variation in both alligators and ostriches, and thus may be a conserved trait in both taxa. In contrast to previous descriptions, the 3D digital models and CT scan data demonstrate that the pulmonary diverticula pneumatize the axial skeleton of the ostrich directly from the gas‐exchanging pulmonary tissues instead of the air sacs. Global and specific comparisons between the bronchial topography of the alligator and ostrich reveal multiple possible homologies, suggesting that certain structural aspects of the bronchial tree are likely conserved across Archosauria, and may have been present in the ancestral archosaurian lung.
“…; (e) Saguinus sp., (with a diagrammatic illustration of a standardized primate bronchial tree); (f) Iguana iguana (modified from Cieri et al, 2014); (g) Varanus exanthematicus (modified from Schachner et al, 2014); (h) Chelydra serpentina (modified from Schachner et al, 2017); (i) Alligator mississipiensis; and, (j) Struthio camelus. Images not to scale however, the recent discovery of unidirectional airflow patterns in the lungs of numerous species of crocodilians (Farmer, 2010(Farmer, , 2015bFarmer & Sanders, 2010;Schachner et al, 2013), a monitor lizard (Cieri & Farmer, 2019;Schachner et al, 2014), and the green iguana (Cieri et al, 2014), suggest that the origin of unidirectional airflow predates the evolution of avian flight, and is likely independent from the evolution of birds and endothermy (Cieri et al, 2014;Cieri & Farmer, 2016;Schachner et al, 2014). Recent work in gross anatomy, embryonic development, function, and in vascularization patterns has demonstrated potential homologies between the crocodilian and avian lung (Farmer, 2015b;Farmer & Sanders, 2010;Sanders & Farmer, 2012;Schachner et al, 2013).…”
The avian lung is highly specialized and is both functionally and morphologically distinct from that of their closest extant relatives, the crocodilians. It is highly partitioned, with a unidirectionally ventilated and immobilized gas‐exchanging lung, and functionally decoupled, compliant, poorly vascularized ventilatory air‐sacs. To understand the evolutionary history of the archosaurian respiratory system, it is essential to determine which anatomical characteristics are shared between birds and crocodilians and the role these shared traits play in their respective respiratory biology. To begin to address this larger question, we examined the anatomy of the lung and bronchial tree of 10 American alligators (Alligator mississippiensis) and 11 ostriches (Struthio camelus) across an ontogenetic series using traditional and micro‐computed tomography (µCT), three‐dimensional (3D) digital models, and morphometry. Intraspecific variation and left to right asymmetry were present in certain aspects of the bronchial tree of both taxa but was particularly evident in the cardiac (medial) region of the lungs of alligators and the caudal aspect of the bronchial tree in both species. The cross‐sectional area of the primary bronchus at the level of the major secondary airways and cross‐sectional area of ostia scaled either isometrically or negatively allometrically in alligators and isometrically or positively allometrically in ostriches with respect to body mass. Of 15 lung metrics, five were significantly different between the alligator and ostrich, suggesting that these aspects of the lung are more interspecifically plastic in archosaurs. One metric, the distances between the carina and each of the major secondary airways, had minimal intraspecific or ontogenetic variation in both alligators and ostriches, and thus may be a conserved trait in both taxa. In contrast to previous descriptions, the 3D digital models and CT scan data demonstrate that the pulmonary diverticula pneumatize the axial skeleton of the ostrich directly from the gas‐exchanging pulmonary tissues instead of the air sacs. Global and specific comparisons between the bronchial topography of the alligator and ostrich reveal multiple possible homologies, suggesting that certain structural aspects of the bronchial tree are likely conserved across Archosauria, and may have been present in the ancestral archosaurian lung.
“…Even larger varanids such as V. varius and V. giganteus are active foragers and can chase down prey (Pianka and King, 2004). Compared to other reptiles, varanids have slightly elevated standard and highly elevated maximal metabolic rates (Thompson et al ., 1997), as well as respiratory (Owerkowicz et al ., 1999; Schachner et al ., 2013; Cieri and Farmer, 2019) and circulatory (Burggren and Johansen, 1982; Munns et al ., 2004; Hanemaaijer et al ., 2019) adaptations that may increase active foraging capacity.…”
There is a functional trade-off in the design of skeletal muscle. Muscle strength depends on the number of muscle fibers in parallel, while shortening velocity and operational distance depend on fascicle length, leading to a trade-off between the maximum force a muscle can produce and its ability to change length and contract rapidly. This trade-off becomes even more pronounced as animals increase in size because muscle strength scales with area (length 2) while body mass scales with volume (length 3). In order to understand this muscle trade-off and how animals deal with the biomechanical consequences of size, we investigated muscle properties in the pectoral girdle of varanid lizards. Varanids are an ideal group to study the scaling of muscle properties because they retain similar body proportions and posture across five orders of magnitude in body mass and are highly active, terrestrially adapted reptiles. We measured muscle mass, physiological cross-sectional area, fascicle length, proximal and distal tendon lengths, and proximal and distal moment arms for 27 pectoral girdle muscles in 13 individuals across 8 species ranging from 64 g to 40 kg. Standard and phylogenetically informed reduced major axis regression was used to investigate how muscle architecture properties scale with body size. Allometric growth was widespread for muscle mass (scaling exponent >1), physiological cross-sectional area (scaling exponent >0.66), but not tendon length (scaling exponent >0.33). Positive allometry for muscle mass was universal among muscles responsible for translating the trunk forward and flexing the elbow, and nearly universal among humeral protractors and wrist flexors. Positive allometry for PCSA was also common among trunk translators and humeral protractors, though less so than muscle mass. Positive scaling for fascicle length was not widespread, but common among humeral protractors. A higher proportion of pectoral girdle muscles scaled with positive allometry than our previous work showed for the pelvic girdle, suggesting that the center of mass may move cranially with body size in varanids, or that the pectoral girdle may assume a more dominant role in locomotion in larger species. Scaling exponents for physiological cross-sectional area among muscles primarily associated with propulsion or with a dual role were generally higher than those associated primarily with support | 1115 CIERI Et al.
“…Recent advances in VR enable researchers to interact with fully immersive, affordable, interactive digital environments, and have revolutionized our study of pulmonary airflow patterns (Cieri & Farmer, 2020). Unidirectional pulmonary airflow, a condition where lung gases travel in the same direction through most of the airways throughout the respiratory cycle, has recently been shown to be present beyond Aves, including crocodilians (Farmer, 2015; Farmer & Sanders, 2010; Schachner, Hutchinson, & Farmer, 2013), green iguanas (Cieri et al, 2014), and monitor lizards (Cieri & Farmer, 2020; Schachner, Cieri, et al, 2013), and has raised new questions about the underlying fluid dynamical phenomena occurring in unidirectional lungs. Direct measurements of airflow can be difficult because lungs are complex, delicate organs (Figure 3a,b) and many portions of the respiratory system are inaccessible with conventional instruments (Cieri et al, 2014).…”
Section: Discussionmentioning
confidence: 99%
“…Virtual reality environments give a “particle's eye view” (d), allowing for a more intuitive appreciate of local flow environments. It is also possible to follow streamlines through the simulation (e) to visualize where flow paths diverge from the main streams while maintaining a broad perspective.(a–c) Adapted from Cieri and Farmer (2020)…”
Section: Discussionmentioning
confidence: 99%
“…Models can also be viewed in AR using the mobile app, or natively by downloading the USDZ version of the model in iOS or through an enterprise account. The free Sketchfab account allows multiple uploads, and it is possible to link to Sketchfab in research papers (e.g., Cieri & Farmer, 2020). Without VR hardware, Sketchfab still allows traditional 3D viewing.…”
Virtual and augmented reality (VR/AR) are new technologies with the power to revolutionize the study of morphology. Modern imaging approaches such as computed tomography, laser scanning, and photogrammetry have opened up a new digital world, enabling researchers to share and analyze morphological data electronically and in great detail. Because this digital data exists on a computer screen, however, it can remain difficult to understand and unintuitive to interact with. VR/AR technologies bridge the analog‐to‐digital divide by presenting 3D data to users in a very similar way to how they would interact with actual anatomy, while also providing a more immersive experience and greater possibilities for exploration. This manuscript describes VR/AR hardware, software, and techniques, and is designed to give practicing morphologists and educators a primer on using these technologies in their research, pedagogy, and communication to a wide variety of audiences. We also include a series of case studies from the presentations and workshop given at the 2019 International Congress of Vertebrate Morphology, and suggest best practices for the use of VR/AR in comparative morphology.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
