Markus Lambertz

Origin of the unique ventilatory apparatus of turtles

The turtle body plan differs markedly from that of other vertebrates and serves as a model system for studying structural and developmental evolution. Incorporation of the ribs into the turtle shell negates the costal movements that effect lung ventilation in other air-breathing amniotes. Instead, turtles have a unique abdominal-muscle-based ventilatory apparatus whose evolutionary origins have remained mysterious. Here we show through broadly comparative anatomical and histological analyses that an early member of the turtle stem lineage has several turtle-specific ventilation characters: rigid ribcage, inferred loss of intercostal muscles and osteological correlates of the primary expiratory muscle. Our results suggest that the ventilation mechanism of turtles evolved through a division of labour between the ribs and muscles of the trunk in which the abdominal muscles took on the primary ventilatory function, whereas the broadened ribs became the primary means of stabilizing the trunk. These changes occurred approximately 50 million years before the evolution of the fully ossified shell.

The anatomy of the respiratory system in Platysternon megacephalum Gray, 1831 (Testudines: Cryptodira) and related species, and its phylogenetic implications

We discuss the morphology of the respiratory system regarding the phylogenetic relation among selected Testudines (Tetrapoda: Amniota). Lung structure and the associated coelomic organization are compared in Platysternon megacephalum and in representatives of the most-likely closely related taxa Chelydridae and Testudinoidea (Emydidae+Testudinidae). P. megacephalum shows horizontal intrapulmonary septation in the medial chambers, dividing them into dorsal and ventral lobes. This structure is found only in Platysternon and in the Emydidae, and is interpreted as a possible synapomorphy for these two taxa. In addition to further suggested synapomorphies for Platysternon and the Testudinoidea, we found - in contrast to previous reports - a small post-pulmonary septum (PPS) and incomplete coelomic compartmentalization in the Chelydridae. Thus, all major taxa of Testudines possess a PPS. Since this structure is also present in mammals, archosaurs and some lepidosaurs, the plesiomorphy of a coelomic compartmentalization by the PPS in amniotes in general should be considered. These preliminary results indicate that further comparative study of the respiratory apparatus might help resolve the phylogenetic relationships among the Testudines, as well as to shed light on its evolution among the Amniota.

Lungs of the first amniotes: why simple if they can be complex?

We show—in contrast to the traditional textbook contention—that the first amniote lungs were complex, multichambered organs and that the single-chambered lungs of lizards and snakes represent a secondarily simplified rather than the plesiomorphic condition. We combine comparative anatomical and embryological data and show that shared structural principles of multichamberedness are recognizable in amniotes including all lepidosaurian taxa. Sequential intrapulmonary branching observed during early organogenesis becomes obscured during subsequent growth, resulting in a secondarily simplified, functionally single-chambered lung in lepidosaurian adults. Simplification of pulmonary structure maximized the size of the smallest air spaces and eliminated biophysically compelling surface tension problems that were associated with miniaturization evident among stem lepidosaurmorphs. The remaining amniotes, however, retained the multichambered lungs, which allowed both large surface area and high pulmonary compliance, thus initially providing a strong selective advantage for efficient respiration in terrestrial environments. Branched, multichambered lungs instead of simple, sac-like organs were part and parcel of the respiratory apparatus of the first amniotes and pivotal for their success on dry land, with the sky literally as the limit.

Chordate phylogeny and the meaning of categorial ranks in modern evolutionary biology

In a recent review, Satoh et al. [[1][1]] discuss the evolutionary relationships among chordates and several of the scenarios that have been proposed to elucidate their origin. While we believe that the article is interesting in principle, as is the topic itself, we see, however, a major conceptual

A caseian point for the evolution of a diaphragm homologue among the earliest synapsids

The origin of the diaphragm remains a poorly understood yet crucial step in the evolution of terrestrial vertebrates, as this unique structure serves as the main respiratory motor for mammals. Here, we analyze the paleobiology and the respiratory apparatus of one of the oldest lineages of mammal‐like reptiles: the Caseidae. Combining quantitative bone histology and functional morphological and physiological modeling approaches, we deduce a scenario in which an auxiliary ventilatory structure was present in these early synapsids. Crucial to this hypothesis are indications that at least the phylogenetically advanced caseids might not have been primarily terrestrial but rather were bound to a predominantly aquatic life. Such a lifestyle would have resulted in severe constraints on their ventilatory system, which consequently would have had to cope with diving‐related problems. Our modeling of breathing parameters revealed that these caseids were capable of only limited costal breathing and, if aquatic, must have employed some auxiliary ventilatory mechanism to quickly meet their oxygen demand upon surfacing. Given caseids’ phylogenetic position at the base of Synapsida and under this aquatic scenario, it would be most parsimonious to assume that a homologue of the mammalian diaphragm had already evolved about 50 Ma earlier than previously assumed.

Recent advances on the functional and evolutionary morphology of the amniote respiratory apparatus

Increased organismic complexity in metazoans was achieved via the specialization of certain parts of the body involved in different faculties (structure–function complexes). One of the most basic metabolic demands of animals in general is a sufficient supply of all tissues with oxygen. Specialized structures for gas exchange (and transport) consequently evolved many times and in great variety among bilaterians. This review focuses on some of the latest advancements that morphological research has added to our understanding of how the respiratory apparatus of the primarily terrestrial vertebrates (amniotes) works and how it evolved. Two main components of the respiratory apparatus, the lungs as the “exchanger” and the ventilatory apparatus as the “active pump,” are the focus of this paper. Specific questions related to the exchanger concern the structure of the lungs of the first amniotes and the efficiency of structurally simple snake lungs in health and disease, as well as secondary functions of the lungs in heat exchange during the evolution of sauropod dinosaurs. With regard to the active pump, I discuss how the unique ventilatory mechanism of turtles evolved and how understanding the avian ventilatory strategy affects animal welfare issues in the poultry industry.

Boundary conditions for heat transfer and evaporative cooling in the trachea and air sac system of the domestic fowl: a two-dimensional CFD analysis.

Various parts of the respiratory system play an important role in temperature control in birds. We create a simplified computational fluid dynamics (CFD) model of heat exchange in the trachea and air sacs of the domestic fowl (Gallus domesticus) in order to investigate the boundary conditions for the convective and evaporative cooling in these parts of the respiratory system. The model is based upon published values for respiratory times, pressures and volumes and upon anatomical data for this species, and the calculated heat exchange is compared with experimentally determined values for the domestic fowl and a closely related, wild species. In addition, we studied the trachea histologically to estimate the thickness of the heat transfer barrier and determine the structure and function of moisture-producing glands. In the transient CFD simulation, the airflow in the trachea of a 2-dimensional model is evoked by changing the volume of the simplified air sac. The heat exchange between the respiratory system and the environment is simulated for different ambient temperatures and humidities, and using two different models of evaporation: constant water vapour concentration model and the droplet injection model. According to the histological results, small mucous glands are numerous but discrete serous glands are lacking on the tracheal surface. The amount of water and heat loss in the simulation is comparable with measured respiratory values previously reported. Tracheal temperature control in the avian respiratory system may be used as a model for extinct or rare animals and could have high relevance for explaining how gigantic, long-necked dinosaurs such as sauropoda might have maintained a high metabolic rate.

On the origin of feathers—Response

Mayr questions the plausibility of our hypothesis that structural color signaling was the initial selective advantage in the evolution of pennaceous feathers. Our hypothesis is grounded in the accepted phylogenetic framework for theropods, which shows that pennaceous feathers evolved before flight

Phylogenetic placement, developmental trajectories and evolutionary implications of a feathered dinosaur tail in Mid-Cretaceous amber

In a recent report in Current Biology, Xing and colleagues [1] present a small fragment of a vertebrate tail preserved in amber that bears integumentary appendages (DIP-V-15103, Dexu Institute of Paleontology, Chaozhou, China; Figure 1). Following several analyses using cutting-edge technology the authors conclude that: the tail belongs to a non-avian theropod dinosaur (non-avialan according to the authors, but non-avian used synonymously here); the dinosaur most likely was a member of the Coelurosauria, possibly even Maniraptora; and, the integumentary appendages are feathers that support a barbule-first evolutionary pattern for feathers. DIP-V-15103 is indeed an intriguing specimen with potential implications for contributing to understanding the evolution of feathers among dinosaurs, which remains a current and undoubtedly controversial topic [2,3]. However, I would like to raise several concerns about the available evidence for the phylogenetic hypothesis concerning the placement of DIP-V-15103 as concluded by Xing and colleagues [1], and furthermore discuss the developmental trajectories predicted by them in light of their far-reaching evolutionary implications.

Again on the meaning of categorial ranks in modern evolutionary biology

1) BFor the great majority of systematists, however, taxa have an objective basis because of the requirement of monophyly.^ (p. 1, right column, first paragraph) 2) BThe Linnaean system is in fact robust to accommodating new organisms, unlike the Bideal^ system proposed by Lambertz and Perry (2015).^ (p. 2, left column, second paragraph) 3) BBut when the new taxa are to be accommodated into a pre-existing classification system (e.g., a new species that cannot be placed phylogenetically within any known genus or family), there is little one can do than to utilize such ranks.^ (p. 2, right column, fourth paragraph)