Geometric Morphometric Analysis of the Pedal Claw of the Early Cretaceous Bird Confuciusornis sanctus (Confuciusornithidae) and Its Functional and Behavioral Implications
Date of Award
Master of Science (MS)
Kenshu Shimada, PhD
Windsor Aguirre, PhD
John Dean, PhD
onfuciusornis sanctus (Hou et al., 1995) is an Early Cretaceous bird from the Liaoning Province of northeastern China. Much work has been published on this species, but some details of its habitat and behavior remain unclear. In this study, a geometric morphometric analysis of the ungual of the second pedal digit of Confuciusornis sanctus was performed to determine how its morphology compares to that of extant birds and which morphological variables best distinguish between taxonomic and behavioral groups. A total of 128 specimens was examined, comprising 104 extant bird species across 15 orders and Confuciusornis sanctus. Three fixed landmarks and 50 sliding semilandmarks were used to define shape. A principal component analysis gave two axes explaining over 73% of the variation in shape. Principal component one, which varies in the angle of claw curvature, explains 56% of the morphological variation whereas principal component two, which varies in claw thickness, explains 17.44%. Specimens are relatively evenly spread across principal component one. There is a large amount of overlap between specimen groups across principal component two. When principal component one is plotted against centroid size, specimen groups become more distinguishable. When specimens are grouped by order, groups show a large amount of overlap, indicating that taxonomic order is not strongly correlated with pedal claw morphology. Behavioral groups show much less overlap, indicating that differences in pedal claw morphology are more strongly correlated to behavior than ordinal-level taxonomic relationship. Additionally, claw curvature and claw size are the variables that are most correlated with differences in behavior, whereas claw thickness is not an informative morphological variable. The claw of Confuciusornis sanctus is morphologically similar to extant birds displaying arboreal behaviors. C. sanctus had the capability for short-term flight, and other aspects of the morphology of C. sanctus also support an arboreal lifestyle. The claw of C. sanctus also shows similarities to extant terrestrial birds. Other morphological characteristics suggest that it was not completely specialized for perching behavior, and it likely spent time on the ground as well as in the trees. Its claw morphology was dissimilar to that of extant birds of prey, indicating that it was unlikely that C. sanctus used its claws to seize prey. The pedal claw morphology of C. sanctus was most similar to that of Passer griseus, which inhabits woodland areas and feeds on seeds, grains, and small insects in trees and on the ground. It is likely that C. sanctus also fed on similar food sources. Its short, robust, toothless beak is ideal for a granivorous diet. However, it would have also been suited for piscivory. There is little direct evidence of its diet with the exception of a previously reported specimen preserving fish remains in the alimentary canal. This specimen combined with my study suggest that C. sanctus likely had an omnivorous diet, and elicits interesting questions about the evolution of the bird digestive system.
McIntosh, Annie P., "Geometric Morphometric Analysis of the Pedal Claw of the Early Cretaceous Bird Confuciusornis sanctus (Confuciusornithidae) and Its Functional and Behavioral Implications" (2017). College of Science and Health Theses and Dissertations. 271.