Insight into the growth pattern and bone fusion of basal birds from an Early Cretaceous enantiornithine bird

We report an Early Cretaceous bird from 120 My ago that has a completely fused carpometacarpus and pelvis, pushing back the date for these avian traits by over 40 My. We suggest that this taxon grew more rapidly than other basal birds, but the degree of bone fusion is not causally linked with growth pattern in primitive birds. We hypothesize that the surprisingly high degree of bone fusion in basal birds may have been environmentally induced pertinent to flight or alternatively resultant from genetic modifications. Future developmental studies focusing on the development of bone fusion are needed to test these hypotheses and illustrate how the skeletal system of living birds achieves its modern shape.