Flying Archosaurs: Deciphering the Physiological Correlates of Sky Conquest

Project Information

FLAPS

Grant agreement ID: 101107135

DOI

10.3030/101107135

Project closed

EC signature date 29 June 2023

Start date 1 September 2023

End date 31 August 2025

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 195 914,88

Coordinated by

CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE CNRS
France

Periodic Reporting for period 1 - FLAPS (Flying Archosaurs: Deciphering the Physiological Correlates of Sky Conquest)

Reporting period: 2023-09-01 to 2025-08-31

Summary of the context and overall objectives of the project

Understanding the evolutionary origins of flight in vertebrates remains one of the most complex challenges in evolutionary biology. Flight is among the most energetically demanding forms of locomotion, and its independent emergence in birds, bats, and pterosaurs reflects profound physiological innovations across vertebrate evolution. However, their metabolic adaptations required to sustain powered flight and their evolutionary trajectories remain debated. This project addresses these critical gaps by focusing on extinct flying archosaurs: pterosaurs and early birds. Despite considerable advances in fossil discoveries and imaging technologies, it is still unclear when these animals became capable of flight, and how their developmental strategies (precocial vs. altricial) and metabolic regimes evolved in parallel with flight adaptations. Moreover, the physiological underpinnings that allowed such species to overcome the "metabolic barrier" to flight, especially in juveniles—have never been explored in a comprehensive phylogenetic and histological framework. Set within the broader goals of the European Research Area and aligned with EU priorities in open science and gender equity, this Marie Skłodowska-Curie Action (MSCA) aimed to deliver insights into the evolution of vertebrate flight using an innovative interdisciplinary approach that integrates paleontology, evolutionary physiology, comparative anatomy, imaging technology, and statistical modeling. Specifically, the project aimed:

- Investigate the developmental strategies and flight capabilities of extinct flying archosaurs using novel proxies for metabolic rate derived from bone microstructure and nutrient foramen morphology.

- Test hypotheses on the metabolic performance of extinct species in a phylogenetic context, comparing extinct taxa with modern precocial and altricial birds and cursorial species.

- Produce the first-ever comparative model estimating maximum and resting metabolic rates (RMR and MMR) for fossil flying vertebrates using non-destructive imaging and paleohistological techniques.

To achieve these goals, the project used cutting-edge imaging platforms (e.g. micro-CT), quantitative bone histology, and phylogenetic eigenvector mapping (PEM). Specimens include key fossils from UNESCO listed sites in Brazil, Spain and China. This integrated analysis enabled an unprecedented reconstruction of physiological traits, ontogenetic stages, and evolutionary transitions tied to flight.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project successfully addressed the long-standing evolutionary and physiological question regarding the origin of vertebrate flight by reconstructing the metabolic profiles of extinct flying archosaurs using advanced paleohistological and imaging methodologies.
WP2 – Quantification of Histological Variables
• Histological variables such as osteocyte lacunae size, primary osteon area, and vascular canal density were extracted from both real and virtual thin-sections.
• Datasets were created, integrating samples from international collections (China, Brazil, Spain and Sweden).
• ImageJ (Fiji) was used for precise morphometric quantifications, forming the foundation for metabolic rate inference models.
WP3 – CT Data Acquisition and Nutrient Foramina Analysis
• High-resolution micro-CT scans of long bones from Archaeopteryx, Caiuajara, and Enantiornithes were obtained using the CT-scan platform at MNHN in France and National Museum in Brazil.
• Three-dimensional reconstructions were performed with Mimics® software, with manual segmentation of nutrient foramina.
• Blood flow rates were computed based on nutrient foramen dimensions.
WP4 – Phylogenetic Comparative Methods and Model Development
• Phylogenetic eigenvector maps (PEM) were constructed to model the evolution of resting metabolic rate (RMR) and maximum metabolic rate (MMR) in extinct taxa.
• Statistical models were validated using a dataset of extant birds and non-avian sauropsids.
• Three core hypotheses were tested:
1. That enantiornithine birds and pterosaurs exhibited superprecocial flight capacities at hatching.
2. That Archaeopteryx possessed metabolic rates indicative of flapping-powered flight.
3. That pterosaurs had intermediate metabolic capacities between cursorial and volant modern birds.
Key Scientific Outcomes:
• Developed and validated a novel, non-destructive methodology to estimate metabolic rates in extinct vertebrates based on nutrient foramen size and bone histology.
• Reconstructed the ontogenetic and physiological profiles of extinct flying archosaurs using integrated CT and histological data.
• Established a new phylogenetically-informed model to infer thermoregulatory strategies and developmental modes in fossil taxa.
• Provided new empirical evidence supporting early flight capability in hatchlings of enantiornithines and pterosaurs, challenging previous assumptions of delayed flight onset.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Scientific Outcomes
1. Novel Symposium Presentation (II Meeting in Vertebrate Paleophysiology)
◦ In September 2024, project members organized and presented findings at the II Meeting in Vertebrate Paleophysiology: The Legacy of Roger Seymour, held at Sorbonne Université in Paris (https://vertpaleophysio.sciencesconf.org/)
2. Innovative Exhibition Integration (MUPA, Cuenca)
◦ The “Fósiles con otra mirada – Paleobiología de los vertebrados de Las Hoyas” exhibit, hosted at MUPA in Cuenca, Spain, showcased fossil specimens alongside displays of histological slides and CT-derived imagery for a diverse audience
(https://cultura.castillalamancha.es/museos/actualidad/el-museo-de-paleontologia-de-castilla-la-mancha-acoge-la-muestra-fosiles-con-otra-mirada)
Methodological Advances
• Multimodal Analytical Pipeline
◦ For the first time, bone histology, micro-CT segmentation of nutrient foramina, and Phylogenetic Eigenvector Maps (PEMs) were combined into a seamless analytical workflow. This new pipeline enables the estimation of RMR and MMR in extinct taxa.
• Expanded Comparative Dataset
◦ Calibration against extant archosaurs (birds and crocodylians) allowed validation of methodological accuracy. Applying this to Archaeopteryx, enantiornithines, and juvenile pterosaurs generated reliable physiological inferences.
• Empirical Evidence for Early Flight
◦ Data presented at the Paris symposium and the MUPA exhibit confirm:
▪ Precocial flight in enantiornithines and pterosaurs
▪ Metabolically-supported flapping flight in Archaeopteryx
▪ Intermediate respiratory physiology in pterosaurs, distinct from modern bird analogues
Potential Impacts & Uptake
◦ Tools (CT workflows, histological morphometry scripts, PEM software) will be made available via open science platforms (e.g. GitHub, Zenodo), fostering reproducibility.
◦ Scaling method application requires further access to:
▪ CT-scanning facilities (e.g. MNHN, ESRF)
▪ Expanded taxonomic sampling across museum collections
▪ Future calls for funding under Horizon Europe and MSCA could fund demonstrations on non-avian dinosaurs.
2. Commercial and Educational Applications
◦ Though raw data pipelines remain non-patented, there is potential commercial value in: ‘‘Digital paleohistology’’ educational tools,
◦ The hybrid exhibition model (as at MUPA) serves as a blueprint for science communication, museum outreach, and public engagement with paleobiology.
3. Standardization & Policy Engagement
◦ Adoption of histo‑CT‑PEM methods could contribute to standard protocols and guidelines for invertebrate and vertebrate paleophysiological research.
◦ Policymakers and funding agencies can leverage these findings to support research infrastructures, museum digitization, and cross-border EU science collaboration.

Photo of executive committee of the fossil exposition at the MUPA

Exhibition poster of the fossil exposition at the MUPA

Poster promoting our talk for the American Association for Anatomy (AAA) webinar

Logo of the II MVP symposium

Diner offered for the key-speakers of the II MVP at Boisson Ardent in Paris

Talk of the MSCA at the II MVP

Final group photo of all participants and the executive committee at the II MVP