FOOT-PROPELLED DIVERS ARE THE MOST COMMON LATEST CRETACEOUS NEORNITHINE FOSSILS, BUT WHERE ARE THE SHORE BIRDS AND SEA BIRDS?

When it comes to shallow marine fossil deposits of Late Cretaceous age, the avian fossils present are few and specific. The fragmentary avian fossils that are excavated almost exclusively show a foot-propelled diving lifestyle. Other marine bird lifestyles, such as flying, running, or soaring birds, are not represented. Late Cretaceous avian fossils that show a foot-propelled diving lifestyle include Vegavis iaai and Polarornis gregorii from Antarctica, Neogaeornis wetzeli from Chile, and a grebe-like tarsometatarsus from New Jersey. It is odd that avians are only showing this specialized lifestyle when the members of Enantiornithes were also present during the Late Cretaceous and they occupied many different niches, as do the neornithine birds of today. While enantiornithines were abundant and diverse, they did not survive the K-Pg extinction event. Adding to this phenomenon are the Late Cretaceous Hesperornithiformes, which are a group of foot-propelled divers that, for the most part, have no wing elements. The hesperornithiforms also failed to survive the K-Pg extinctions. For an unknown reason, the neornithines present at the time, did survive. Could the neornithines survival be due to having specialized lifestyles in the water? But hesperornithiforms also lived in the water, so clearly there is more to the story here.

When looking for avian fossils in a shallow marine deposit, one would expect to find a mix of shore birds, sea birds, and foot-propelled divers rather than only one of those groups. Antarcticavis capelambensis is the geologically oldest bird (~72 Ma) from Antarctica, but it’s lifestyle is presently unknown. To find the lifestyle of Antarcticavis, this study compares the Antarcticavis bones with the bones of birds that represent different lifestyles, building on previous studies and adding more taxa and lifestyles such as the local Mergus merganser and other ducks, as well as ground birds (chicken and quail). As my access to specimens grows, so does the probability of finding the niche of Antarcticavis as well as progressing our understanding of avian evolution and survival. Perhaps Antarcticavis will turn out to fit into a shore bird or sea bird lifestyle rather than a foot-propelled diving lifestyle, making it different than the other fossil avians of that time.