Forelimb feathering, soft tissues, and skeleton of the flying dromaeosaurid Microraptor
By: Maxime Grosmougin, Xiaoli Wang, Xiaoting Zheng, Thomas G. Kaye, Matthieu Chotard, Luke A. Barlow, T. Alexander Deccechi, Michael B. Habib, Juned Zariwala, Scott A. Hartman, Xing Xu, and Michael Pittman
Summarized by: Summarized by Brooke Sacks, an undergraduate student pursuing a B.S. in Biological Sciences at Binghamton University. Upon graduation this spring, she will be pursuing a master’s program before heading to law school. When she is not studying paleontology, Brooke enjoys playing golf, tennis, and traveling.
Data being used: Researchers analyzed the front limbs, or forelimbs (including the bone structure, soft tissue, and feathers), of ten new Early Cretaceous Microraptor specimens from northern China, stored in the Shandong Tianyu Museum of Nature. The researchers obtained measurements of the bone structures, observed the preserved soft tissue, and measured the feathers for classification; this data was compared to that of previously studied specimens, including early flying dinosaurs (such as Anchiornis, Archaeopteryx, and Confuciusornis), as well as modern birds.
What was the hypothesis being tested? The purpose of the paper is to investigate the feathering, soft tissues, and bones of the Microraptor forelimb. The researchers aimed to 1) reconstruct an accurate model of Microraptor forewing feathering, specifically including the layering of the different types of feathers, 2) observe skeletal characteristics (the thickness and length of pectoral girdle, humerus, ulna, radius, carpals, metacarpals, and phalanges- the bones from the arm closest to the shoulder to the wings) that may provide a deeper understanding of the organism’s flight capabilities, and 3) perform tests on forelimb soft tissues to uncover the functionality of the Microraptor forewing. Overall, this study provides insight into avian evolution of flight, which has not previously been fully known due to limited understanding of Microraptor anatomy.
Methods: In this study, the researchers used white light and Laser-Stimulated Fluorescence, which is a procedure used to cause fluorescence around the surface of the body tissues and illuminate the specimen for visual analysis. Specifically, this was used to illuminate areas of interest on the specimens: the soft tissue, bones, and feathers. The use of Laser-Stimulated Fluorescence allowed researchers to discern otherwise hidden details in feathers which aid in the classification of the different feather layers. Thirty-second time-exposed images were taken using a Nikon D810 DSLR camera to ensure high-quality photos to study, and the photos were processed for review using Photoshop CS6 software. Additionally, scientists took measurements of bone lengths and feather lengths, as well marked the number of preserved feathers broken down by type. Microraptor specimens and similar early flying dinosaurs (Anchiornis, Archaeopteryx, and Confuciusornis) were studied in this comparative analysis. These measurements were compared across all species by uniform standards.
Results: This study further organized previously discovered layers of feathering (called coverts; see Fig. 1 for details about the layers) by distinguishing these into primary greater, secondary greater, median and lesser coverts, all of which have different roles in the process of flying (Fig. 1). As a result of analyzing its wing structure, it is clear that Microraptor exhibits characteristics consistent with modern birds that fly continuously at high-speeds–its V-shaped wings and lack of wingtip slotting (i.e. the separation of outer feathers that lets air pass through when flying) are commonly associated with reduced drag and prolonged flight capabilities. Regarding the soft-tissue analysis, Laser-Stimulated Fluorescence revealed the outline and surface texture of Microraptor, indicating this species had a strong arm with tissue covering. Taken together with its wing morphology and bony/soft tissue anatomy, it may be supported that this species, Microraptor, was likely an aerial hunter that possessed a diet typical of modern falcons. Researchers also found that the claws of Microraptor were more curved than other related species.
Why is this study important? This study is significant because it draws connections between anatomical features and functional applications. In this study, the V-shaped primary regimes on the outermost feather layer indicate that this species was likely a fast-flying hunter, which had not been previously known. From this, we can draw conclusions about their diet as likely hunters, and this methodology can be applied to learn more about other avian species. Additionally, because the claws of Microraptor were so curved, researchers think that this species could have been climbing trees during their lifetime.
Broader implications beyond this study: By comparing this species of flying dinosaur to both modern and prehistoric organisms, scientists can gain a deeper understanding of avian evolutionary trends, as well as how this particular species once flew and interacted with their environment. Future studies may focus on how Microraptor hindwings, as opposed to their forewings, compare and contrast to the findings discussed in this study. This study adds to how the process of flying evolved in birds over the past ~ hundred million years.
Citation: Grosmougin, M., Wang, X., Zheng, X., Kaye, T. G., Chotard, M., Barlow, L. A., Deccechi, T. A., Habib, M. B., Zariwala, J., Hartman, S. A., Xu, X., & Pittman, M. (2025). Forelimb feathering, soft tissues, and skeleton of the flying dromaeosaurid Microraptor. BMC Ecology and Evolution, 25(1). https://doi.org/10.1186/s12862-025-02397-5