The lifestyle of Antarcticavis capelambensis through a study of Polar section modulus

<p>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 lifestyles, such as flying, running, soaring, or flapping birds, are not represented. The latest Cretaceous avian fossils that show a foot-propelled diving lifestyle include Vegavis iaai from Antarctica, Polarornis gregorii from Antarctica, Neogaeornis wetzeli from Chile, and a grebe-like tarsometatarsus from New Jersey. It is odd that avians have only shown this specialized lifestyle when the members of Enantiornithes were also present during the Late Cretaceous and they occupied many different niches, as the neornithine birds of today do. While enantiornithines were abundant and diverse, they did not survive the Cretaceous-Paleogene (K-Pg) mass 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 mass extinction. For an unknown reason, the neornithines present at the time, did survive. Living an aquatic lifestyle is not the deciding factor on neornithines survival due to the aquatically adapted hesperornithiformes extinction, perhaps other lifestyles were present that would give an edge to survival. 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, discovered in Antarctica, could be a ‘missing link’ in regards to lifestyles, and finding the lifestyle will give greater insight as to what niches would have been present within Neornithes during the Maastrichtian. To find the lifestyle, this study examined and compared the polar section modulus of Antarcticavis with the polar section modulus of birds that represent different lifestyles, such as the Mergus merganser as well as ground birds, wading birds, and shore birds. Eleven polar section modulus morphospace graphs were generated representing eleven different lifestyles to build on a previous study. Antarcticavis plotted into the amphibious bird and seabird morphospaces, closest to Mergus merganser and Larus marinus, showing Antarcticavis would live similarly to those modern avians. Vegavis iaai plotted similarly to Antarcticavis. Morphospace trends seen on the modern avian polar section modulus graphs range from continuous to dichotomous depending on the lifestyle. Most dichotomies appear to be due to humeri/femora rigidity being favorable in larger species of a lifestyle, while humeri/femora bendability is favorable in smaller species of a lifestyle.</p>

Name thesis:degree_name

Master of Science (MS) in Biology

Level thesis:degree_level

Thesis: EWU Only

Discipline thesis:degree_discipline

Biology

Year

2025

Author dc:creator

• Deckhut, Joseph Tyler

• Ornithology
• Paleobiology

Statement dc:rights

• Access perpetually restricted to EWU users with an active EWU NetID

Repository record dc:identifier

https://dc.ewu.edu/theses/962

OAI identifier oai:identifier

oai:dc.ewu.edu:theses-1962