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Avian respiratory system biology + Gastornis tracks from Eocene of Washington state (free pdfs)

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Ben Creisler

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Feb 27, 2025, 12:25:28 PMFeb 27
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Ben Creisler

New avian papers:

A special issue, currently with free pdfs:

The biology of the avian respiratory system
Philosophical Transactions of the Royal Society B 380(1920)
https://royalsocietypublishing.org/toc/rstb/2025/380/1920

Papers of special interest to the DMG:

Free pdf:

J. N. Maina (2025)
Structure and function of the avian respiratory system
Philosophical Transactions of the Royal Society B 380(1920): 20230435
doi: https://doi.org/10.1098/rstb.2023.0435
https://royalsocietypublishing.org/doi/10.1098/rstb.2023.0435

Free pdf:
https://royalsocietypublishing.org/doi/epdf/10.1098/rstb.2023.0435


Among the extant air-breathing vertebrates, the avian respiratory system is the most efficient gas exchanger. Novel morphological and physiological adaptations and specializations largely explain its exceptional functional superiority. Anatomically, the avian respiratory system is separated into lungs that serve as gas exchangers and air sacs that operate as ventilators. Utterly rigid, the avian lungs are deeply fixed to the ribs and the vertebrae. A thin blood–gas barrier (BGB), vast respiratory surface area and large pulmonary capillary blood volume generate high total pulmonary morphometric diffusing capacity of O2. The weak allometric scaling of the thickness of the BGB indicates optimization for gas exchange; the negative scaling and strong correlation between the surface density of the respiratory surface area and body mass show the extreme subdivision of the gas exchange tissue; and the respiratory surface area, the pulmonary capillary blood volume and the total pulmonary morphometric diffusing capacity of O2 correlate strongly and positively with body mass. The arrangement of the structural components of the exchange tissue form crosscurrent-, countercurrent-like- and multicapillary serial arterialization gas exchange designs. By synchronized actions of the air sacs, the palaeopulmonic part of the of the avian lung is efficiently ventilated continuously and unidirectionally in a caudocranial direction.


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Free pdf:

Maria Grace Burton, Juan Benito, Kirsty Mellor, Emily Smith, Elizabeth Martin-Silverstone, Patrick O'Connor and Daniel J. Field (2025)
The influence of soft tissue volume on estimates of skeletal pneumaticity: implications for fossil archosaurs
Philosophical Transactions of the Royal Society B 380(1920): 20230428
doi: https://doi.org/10.1098/rstb.2023.0428
https://royalsocietypublishing.org/doi/10.1098/rstb.2023.0428

Free pdf:
https://royalsocietypublishing.org/doi/epdf/10.1098/rstb.2023.0428


Air space proportion (ASP), the volume fraction in bone that is occupied by air, is frequently applied as a measure for quantifying the extent of skeletal pneumaticity in extant and fossil archosaurs. Nonetheless, ASP estimates rely on a key assumption: that the soft tissue mass within pneumatic bones is negligible, an assumption that has rarely been explicitly acknowledged or tested. Here, we provide the first comparisons between estimated air space proportion (where the internal cavity of a pneumatic bone is assumed to be completely air-filled) and true air space proportion (ASPt, where soft tissues present within the internal cavities of fresh specimens are considered). Using birds as model archosaurs exhibiting postcranial skeletal pneumaticity, we find that estimates of ASPt are significantly lower than estimates of ASP, raising an important consideration that should be acknowledged in investigations of the evolution of skeletal pneumaticity and bulk skeletal density in extinct archosaurs, as well as in volume-based estimates of archosaur body mass. We advocate for the difference between ASP and ASPt to be explicitly acknowledged in studies seeking to quantify the extent of skeletal pneumaticity in extinct archosaurs, to avoid the risk of systematically overestimating the volume fraction of pneumatic bones composed of air.

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Free pdf:

Andrew J. Moore and Emma R. Schachner (2025)
When the lung invades: a review of avian postcranial skeletal pneumaticity
Philosophical Transactions of the Royal Society B 380(1920): 20230427
doi: https://doi.org/10.1098/rstb.2023.0427
https://royalsocietypublishing.org/doi/10.1098/rstb.2023.0427


Birds are unique among extant tetrapods in exhibiting air-filled cavities that arise from the respiratory system and invade postcranial bones, a phenomenon called postcranial skeletal pneumaticity (PSP). These intraosseous cavities originate from diverticula of the ventilatory air sacs or directly from the gas-exchanging lung. Despite a long history of study, many of the basic characteristics of this system remain poorly understood. In this hybrid review, we synthesize insights from the anatomical, developmental, biomechanical and paleontological literature to review the functional and evolutionary significance of PSP. Leveraging new data, we confirm that the skeletons of pneumatic birds are not less heavy for their mass than those of apneumatic birds. Pneumatic skeletons may nonetheless be lightweight with respect to body volume, but this is a hypothesis that remains to be empirically tested. We also use micro-computed tomography scanning and deep learning-based segmentation to produce a pilot model of the pneumatized spaces in the neck of a Mallard (Anas platyrhynchos). This approach facilitates accurate modelling of bone architecture for quantitative comparative analysis within and between pneumatic taxa. Future work on PSP should focus on the cellular mechanisms and developmental processes that govern the onset and extent of pneumatization, which are essentially unknown.

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Free pdf:

Jingmai K. O’Connor (2025)
Insights into the early evolution of modern avian physiology from fossilized soft tissues from the Mesozoic
Philosophical Transactions of the Royal Society B 380(1920): 20230426
doi: 10.1098/rstb.2023.0426
doi: https://doi.org/10.1098/rstb.2023.0426
https://royalsocietypublishing.org/doi/10.1098/rstb.2023.0426


Modern birds (Neornithes) are the mostly highly modified group of amniotes, bearing little resemblance to other extant sauropsids. Archaeopteryx, with its nearly modern wings but plesiomorphic skeleton, demonstrated more than 160 years ago that soft tissue specializations preceded skeletal modifications for flight. Soft tissues are thus of great importance for understanding the early evolution of modern avian physiology. Most commonly, traces of the integumentary system are preserved; exceptional discoveries include remnants of organs. Together, these have helped to elucidate the evolution of the lungs, ovaries, plumage and beak in early diverging birds. These fossils reveal that many important adaptations for efficient digestion, high oxygen intake, reduced body mass and improved wing structure, all of which serve to improve aerial capabilities and/or meet the energetic demands of this costly form of locomotion, evolved within the first 20–30 Myr of avian evolution. Soft tissue preservation also provides important clues for understanding the ecology of early diverging birds and may even elucidate the extinction of certain groups. However, the current fossil record of Mesozoic avian soft tissues is almost entirely limited to the Early Cretaceous and thus, discoveries from the Late Cretaceous have the potential to drastically transform our interpretation of the available data.

====
Free pdf:

Emma R. Schachner and Andrew J. Moore (2025)
Unidirectional airflow, air sacs or the horizontal septum: what does it take to make a bird lung?
Philosophical Transactions of the Royal Society B 380(1920): 20230418
doi: https://doi.org/10.1098/rstb.2023.0418
https://royalsocietypublishing.org/doi/10.1098/rstb.2023.0418

Free pdf:
https://royalsocietypublishing.org/doi/epdf/10.1098/rstb.2023.0418


In this review, we evaluate the differences between the pulmonary anatomy of birds and other sauropsids, specifically those traits that make the avian respiratory system distinct: a fully decoupled and immobilized, isovolumetric gas-exchanging lung separated from compliant ventilatory air sacs by a horizontal septum. Imaging data, three-dimensional digital anatomical models and dissection images from a red-tailed hawk (Buteo jamaicensis), common ostrich (Struthio camelus), barred owl (Strix varia), African grey parrot (Psittacus erithacus) and zebra finch (Taeniopygia castanotis) are used to demonstrate the anatomical variation seen in the pulmonary air sacs, diverticula and the horizontal septum. We address the current state of knowledge regarding the avian respiratory system and the myriad areas that require further study, including the comparative and quantitative ecomorphology of the bronchial tree and air sacs, the non-ventilatory functions of the sacs and diverticula, the fluid dynamics and anatomical mechanisms underlying unidirectional airflow, post-cranial skeletal pneumaticity, and how all of these factors impact reconstructions of respiratory tissues in extinct archosaurs, particularly ornithodirans (i.e. pterosaurs + non-avian dinosaurs). Specifically, we argue that without evidence for the horizontal septum, a fully avian lung should not be reconstructed in non-avian ornithodirans, despite the presence of post-cranial skeletal pneumaticity.


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Free pdf:

Wilfried Klein, Vinícius Pereira Ribeiro and Ray Brasil Bueno de Souza (2025)
Avian air sacs and neopulmo: their evolution, form and function
Philosophical Transactions of the Royal Society B 380(1920): 20230421
doi: https://doi.org/10.1098/rstb.2023.0421
https://royalsocietypublishing.org/doi/10.1098/rstb.2023.0421

Free pdf:
https://royalsocietypublishing.org/doi/epdf/10.1098/rstb.2023.0421


The avian respiratory system is composed of an exchange structure (parabronchi) and a pump (air sacs) to perform gas exchange. While there are many studies dealing with the morphology and function of the palaeopulmonic parabronchi, the air sacs and the neopulmo have been somewhat neglected from a comparative and functional point of view, not always receiving a closer examination that they deserve. While a decent amount of data are available regarding air sac and neopulmo morphology on a family level or for domestic species, several orders of birds have yet to be investigated. Owing to the lack of detailed specific data, we did not perform a comparative phylogenetic analysis but compiled data regarding air sac and neopulmo morphology and analysed them from the viewpoint of current phylogenetic relations while also discussing aspects of these structures regarding avian physiology.

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Also:

Free pdf:

George E. Mustoe (2025)
Giant Bird Tracks (Family Gastornithidae) from the Paleogene Chuckanut Formation, Northwest Washington, USA, with a Review of Gastornis Distribution
Fossil Studies 3(1): 4
doi: https://doi.org/10.3390/fossils3010004
https://www.mdpi.com/2813-6284/3/1/4


Giant Paleogene groundbirds named Gastornis have long been known from Europe, with similar fossils from North America being placed in the genus Diatryma. A more recent discovery in China is evidence that these birds had wide geographic distribution. The name Gastornis is now generally considered to be the name that has historical precedence. Historically, Gastornis has been interpreted as being a fierce predator, but anatomical and isotopic evidence suggests that the giant birds were herbivores. Gastornithid tracks preserved in Lower Eocene fluvial sediments of the Chuckanut Formation in northwest Washington State, USA, support the herbivore interpretation. These tridactyl footprints preserve broad triangular toenails rather than talons. The Chuckanut Formation gastornithid tracks have been given the ichnotaxonomic name Rivavipes giganteus Mustoe et al. (2012). In 2024, two important new discoveries were made. These are a trackway that preserves three adult tracks, and two tracks left by a gastornithid chick.The adult bird trackway has stride and pace distances that are consistent with the short lower limb bones (tarsometatarsals) observed in Gastornis skeletal remains. The reproductive strategies of gastornithids remain enigmatic; the evidence consists of numerous egg shell fragments found at sites in France and the newly discovered Chuckanut tracks.

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Mickey Mortimer

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Mar 4, 2025, 3:34:14 AMMar 4
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"Free pdf:

Jingmai K. O’Connor (2025)
Insights into the early evolution of modern avian physiology from fossilized soft tissues from the Mesozoic
Philosophical Transactions of the Royal Society B 380(1920): 20230426
doi: 10.1098/rstb.2023.0426
doi: https://doi.org/10.1098/rstb.2023.0426
https://royalsocietypublishing.org/doi/10.1098/rstb.2023.0426


Modern birds (Neornithes) are the mostly highly modified group of amniotes, bearing little resemblance to other extant sauropsids. Archaeopteryx, with its nearly modern wings but plesiomorphic skeleton, demonstrated more than 160 years ago that soft tissue specializations preceded skeletal modifications for flight. Soft tissues are thus of great importance for understanding the early evolution of modern avian physiology. Most commonly, traces of the integumentary system are preserved; exceptional discoveries include remnants of organs. Together, these have helped to elucidate the evolution of the lungs, ovaries, plumage and beak in early diverging birds. These fossils reveal that many important adaptations for efficient digestion, high oxygen intake, reduced body mass and improved wing structure, all of which serve to improve aerial capabilities and/or meet the energetic demands of this costly form of locomotion, evolved within the first 20–30 Myr of avian evolution. Soft tissue preservation also provides important clues for understanding the ecology of early diverging birds and may even elucidate the extinction of certain groups. However, the current fossil record of Mesozoic avian soft tissues is almost entirely limited to the Early Cretaceous and thus, discoveries from the Late Cretaceous have the potential to drastically transform our interpretation of the available data."

This paper is not free.

Mickey mortimer

Gregory Paul

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Mar 4, 2025, 8:00:34 AMMar 4
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Whales are more modified amniotes than birds

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Jason Brougham

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Mar 4, 2025, 8:38:51 AMMar 4
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good point. They certainly are super-modified. A few years ago I had the great privilege of installing the Te Papa New Zealand Whales exhibition. Confronting whale skeletons in person really struck me much more than images online. It finally dawned on me that baleen whales are basically hammerheads! Their orbits are out on two pylons!

I wonder if there is a way to actually quantify how modified a large clade is. It is relative to some ancestor or basal sister group, I suppose. Then count how many, and what percentage, of scored characters are apomorphies, and how many are plesiomorphies? It would differ for different subgroups. 
From: 'Gregory Paul' via Dinosaur Mailing Group <DinosaurMa...@googlegroups.com>
Sent: Tuesday, March 4, 2025 8:00:28 AM
To: dinosaurma...@googlegroups.com <dinosaurma...@googlegroups.com>
Subject: Re: [DMG] Re: Avian respiratory system biology + Gastornis tracks from Eocene of Washington state (free pdfs)
 
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Ben Creisler

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Mar 4, 2025, 10:25:49 AMMar 4
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Ben Creisler

It was free at least when first posted. I was able to download it, but the link is down paywalled.

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Jura

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Mar 4, 2025, 12:29:46 PMMar 4
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If we're playing the most modified amniote game, then I'd say turtles win it hands down. They can't even lay their scales down the same way that other reptiles do.

Cheers,

Jason

Gregory Paul

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Mar 4, 2025, 12:32:53 PMMar 4
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I'm still going for whales. Heck, they don't even have scales. 

GSPaul

Mike Taylor

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Mar 4, 2025, 12:39:58 PMMar 4
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Turtles are straight up perverts, with their misplaced scapulae.

-- Mike.


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