SVP 2021 abstracts – 26: Fossil bird diets

Miller and Pittman 2021 report:
“Birds are some of the most ecologically diverse organisms on Earth, with species filling a huge swath of niches across every major biome. As such, birds are vital to the study of extant ecosystems. Our understanding of the evolutionary history of extant ecosystems, thus, is
hampered by gaps in our knowledge of the origin of bird diversity and ecosystem ecology.”

Those gaps were filled by the large reptile tree (LRT, 1991 taxa; subset Fig. 1).

Miller and Pittman 2021 continue:
“A critical part of addressing these shortcomings is a better understanding of the earliest birds, the non-avian avialans (i.e. non-crown birds), particularly of their diet.”

Diet? Critical? Let’s stick with the cladogram and let that give us a better understanding. We’re going to find more fossil bones than fossil stomach contents.

“The diet of non-avian avialans has been a matter of much debate because of the ambiguous, qualitative approaches that have been used to reconstruct it. After reviewing methods for determining diet in extant and extinct avians (i.e. crown birds) as well as non-avian theropods, we propose a set of comparable, quantitative approaches to ascertain fossil bird diet.”

They just wrote, ‘ascertain.’ That’s a high bar.

“Using this and direct evidence, we summarize what is currently known about fossil bird diet. While no single approach can precisely predict diet in birds, each can narrow the dietary possibilities and reach precision in concert.”

The authors are backing away from their earlier claim to ‘ascertain’.

“We recommend combining: (1) dental microwear, (2) landmark-based muscular reconstruction, (3) stable isotope geochemistry, (4) body mass estimations, (5) traditional and/or geometric morphometric analysis, (6) lever modelling, and (7) finite element analysis to
accurately determine possible fossil bird diets.”

Now the authors are only recommending methods to determine, ‘possible fossil bird diets’.

“We note current applications of dental mesowear, skull traditional morphometrics, geometric morphometrics, and certain stable isotope systems have yet to be proven effective at discerning fossil bird diet. With this in mind, we know little about the diet of non-avian avialans.”

Now the authors are saying, “We know little.” They have come down a notch or two.

“The ancestral dietary condition in non-avian avialans remains unclear due to scarce data from early-diverging avialans and contradictory evidence in Archaeopteryx. Due to a scarcity quantitative studies of bird diet leading to a dearth of robust dietary assignments, trends in non-avian avialan dietary evolution are also unclear.”

You’re already getting the pattern, but I’ll point it out anyway: “Unclear.”

“We expect dietary knowledge and evolutionary trends of bird diet to become much clearer in the coming years with this new framework as a roadmap. This will allow for a better
understanding of the role birds played in Mesozoic ecosystems and how this developed into their pivotal role in extant ecosystems.”

Finishing on a positive note, the authors ‘expect… bird diet to become much clearer…”

Another way to do this
would be to use phylogenetic bracketing within a valid cladogram (Fig. 1). If a fossil bird is closer to hawks, it probably ate smaller birds and mammals. If closer to swifts: insects on the wing. If parrots: seeds, if penguins: fish. Etc. etc. You can figure bird diets out by nesting them phylogenetically, like paleontologists have always done in the absence of stomach and mouth contents.

References
Miller CV and Pittman M 2021. The diet of fossil birds and new framework for its reconstructions. Journal of Vertebrate Paleontology abstracts.