Vertebrate Paleontologist & Morphologist
University of Florida, Postdoctoral Researcher
Research
Powered flight, a pivotal adaptation in vertebrate evolution, evolved independently three times. Pterosaurs evolved powered flight first in the late Triassic (~220 million years ago) and achieved the largest body size of any powered fliers. Powered flight evolved in birds by the Late Jurassic (~160 million years ago) and in bats by the Eocene (~52 million years ago). Few quantitative comparisons among these three clades exist for key structural attributes or functional parameters. Surveys of vertebrate flight tend to present analyses of the three clades into separate sections, and only comparing basic traits like aspect ratio, body mass, and wing loading. When they do discuss vertebrate fliers as a whole, the discussion turns to a theoretical volant animal instead of drawing comparisons between clades. Complicating such comparisons is their divergent wing structure.
My PhD research focused on the wing skeleton—its overall shape including integumental structures and the shape of the bony anchor (sternum) for the main muscles that power the wing. I aim to bring to light additional fundamental properties of vertebrate wings based in biological data, particularly those relating to possible constraints on bat maximum body size.
​
My current postdoc research involves CT scanning inflated dead birds to visualize in 3D the anatomy of their lungs and compare the different lung shapes across avian taxa and track which part of the lung (pneumatic diverticula) goes inside which bone. I am also working on a couple side projects involving pterosaurs, because they likely share similar lung characteristics, and confusion about pterosaur pneumaticity is what got me into bird lungs in the first place.
​​
I have also collaborated on a wide range of projects, from tadpole evolutionary development to Spinosaurus and other dinosaurs to oVert, a massive nationwide CT scanning endeavor.
Waterbird wing ecomorphology
co-authors: Paul Sereno and Mark Westneat
Left: A rail with broad, rounded wings. Right: An albatross with narrow, pointed wings. Illustrations: Stephanie Baumgart.
​Wing shape plays a critical role in flight function in birds and other powered fliers and is correlated with flight performance, migratory distance, and the biomechanics of generating lift during flight. Avian wing shape and flight mechanics have also been shown to be associated with general foraging behavior and habitat choice. To further explore the relationship between avian wing shape, biomechanics and ecology, we focused on 'waterbirds,' a diverse array of birds united by their coastal and aquatic habitats. We aim to determine if wing shape in this functionally and ecologically diverse assemblage of birds is correlated with various functional and ecological traits.
Paper available here!
S. L. Baumgart, P. C. Sereno, and M. W. Westneat, “Wing shape in waterbirds: Morphometric patterns associated with behavior, habitat, migration, and phylogenetic convergence,” Integrative Organismal Biology, vol. 3, no. 1, Jan. 2021.
Spinosaurus behavior
co-authors: Paul Sereno (lead), Nathan Myhrvold, Donald Henderson, Frank Fish, Daniel Vidal, Tyler Keillor, Kiersten Formoso, Lauren Bop
Spinosaurus aegyptiacus fishing one lovely Cretaceous day. Artist: James Gurney.
P. C. Sereno, N. Myhrvold, D. M. Henderson, F. E. Fish, D. Vidal, S. L. Baumgart, T. M. Keillor, K. K. Formoso, and L. L. Conroy, “Spinosaurus is not an aquatic dinosaur,” eLife, vol. 11, e80092, Nov. 2022.
Spinosaurus bone structure
co-authors: Nathan Myhrvold (co-lead), Paul Sereno (co-lead), Daniel Vidal, Frank Fish, Donald Henderson, Evan Saitta
A Cretaceous scene in the rivers. Artist: Dani Navarro.
​Abstract: The lifestyle of spinosaurid dinosaurs has been a topic of lively debate ever since the unveiling of important new skeletal parts for Spinosaurus aegyptiacus in 2014 and 2020. Disparate lifestyles for this taxon have been proposed in the literature; some have argued that it was semiaquatic to varying degrees, hunting fish from the margins of water bodies, or perhaps while wading or swimming on the surface; others suggest that it was a fully aquatic underwater pursuit predator. The various proposals are based on equally disparate lines of evidence. A recent study by Fabbri and coworkers sought to resolve this matter by applying the statistical method of phylogenetic flexible discriminant analysis to femur and rib bone diameters and a bone microanatomy metric called global bone compactness. From their statistical analyses of datasets based on a wide range of extant and extinct taxa, they concluded that two spinosaurid dinosaurs (S. aegyptiacus, Baryonyx walkeri) were fully submerged “subaqueous foragers,” whereas a third spinosaurid (Suchomimus tenerensis) remained a terrestrial predator. We performed a thorough reexamination of the datasets, analyses, and methodological assumptions on which those conclusions were based, which reveals substantial problems in each of these areas. In the datasets of exemplar taxa, we found unsupported categorization of taxon lifestyle, inconsistent inclusion and exclusion of taxa, and inappropriate choice of taxa and independent variables. We also explored the effects of uncontrolled sources of variation in estimates of bone compactness that arise from biological factors and measurement error. We found that the ability to draw quantitative conclusions is limited when taxa are represented by single data points with potentially large intrinsic variability. The results of our analysis of the statistical method show that it has low accuracy when applied to these datasets and that the data distributions do not meet fundamental assumptions of the method. These findings not only invalidate the conclusions of the particular analysis of Fabbri et al. but also have important implications for future quantitative uses of bone compactness and discriminant analysis in paleontology.
Paper available here!
N. P. Myhrvold, S. L. Baumgart, D. Vidal, F. E. Fish, D. M. Henderson, E. T. Saitta, and P. C. Sereno, “Diving dinosaurs? Caveats on the use of bone compactness and pFDA for inferring lifestyle,” PLOS ONE, vol. 19, no. 3, e0298957, Mar. 2024.
Avian sternum ecomorphology
co-author: Leon Claessens
​
Sterna from bird specimens at the Field Museum of Natural History. Photographs: Stephanie Baumgart.
The avian sternum anchors the main muscles powering flight and is highly disparate in morphology. For instance, some birds feature long, narrow sternal plates with deep keels, others have almost square sternal plates and shallow keels, and some have very reduced or non-existent keels. Little work has focused on the relationship between the complex sternum shape and a bird’s ecomorphology. Here, we aim to examine relationships between sternal form and function using three-dimensional (3D) geometric morphometrics on a sample of sterna across Aves.
​
Society of Integrative and Comparative Biology 2020 Annual Meeting abstract
Bird bone tissue distribution
Co-authors: Emma Schachner, Andrew Moore
CT scan of a vulture humerus, showing the spongy bone inside (purple). Rendering: Stephanie Baumgart.
Most birds have some bones filled with air instead of marrow. These air-filled (pneumatic) bones help redistribute the bird's body mass and lighten the bones, making it easier and more efficient to fly. It is known from the literature that gliding and soaring birds tend to have the majority of their bones filled with air, while more agile flapping birds tend to have some vertebrae and their humerus filled with air. Diving birds reduce the air in their bones, preferring marrow or thicker-walled bones to decrease buoyancy. I aim to use CT scans of a sampling of birds across a variety of body masses and behaviors to begin quantifying bone tissue distribution in relation to skeletal pneumaticity in wing bones of birds. Ultimately, this data would be compared back to wing bones of pterosaurs, because they too have air-filled bones but grew to a much larger size than birds. More extreme skeletal pneumaticity might have enabled these animals to grow to much larger body sizes.
​
Society of Integrative and Comparative Biology 2024 Annual Meeting abstract
Ontogeny of the anuran urostyle
Co-authors: Gayani Senevirathne (lead author), Nathaniel Shubin, James Hanken, Neil Shubin
Left: cleared and stained adult Xenopus, bone is pink, cartilage is blue; IL = ilium, UR = urostyle, HL = hindlimb. Right: CT rendering of the pelvic region of adult Xenopus; CX = coccyx, RV = renal vein, DA = dorsa aorta, IA = iliac artery, HY = hypochord. Images from Figures 1A and 5C in Senevirathne et al. 2020.
Anurans (frogs and toads) have a distinctive skeleton - adults fuse their tail bones to make what is called a urostyle, part of a unique hip structure which enhances an anuran's ability to jump. The urostyle is composed of two parts, fused tail bones and a hypochord, a structure unique to anurans. As part of her Ph.D. thesis, Gayani Senevirathne set out to study the developmental mechanisms behind the formation of the anuran urostyle, and I was recruited to help CT scan a series of tadpoles at different growth stages in metamorphosis and visualize the change in blood vessel structure in the pelvic region as the tadpole turns into a frog.
​
Check out the paper here!
​
Senevirathne, G., Baumgart, S., Shubin, N., Hanken, J., & Shubin, N. H. (2020). Ontogeny of the anuran urostyle and the developmental context of evolutionary novelty. Proceedings of the National Academy of Sciences, 117(6), 3034-3044.
openVertebrate (oVert) Thematic Collections Network
Lead PI: David Blackburn
A cool video showing a fraction of the specimens that were CT scanned for this project and the 3d models made to show surprises inside.
For four years in grad school, I worked with the oVert team to CT scan as many vertebrate genera as possible for free access through MorphoSource.org. Many museums and universities across the country are engaged with this NSF-funded project, and we have CT scanned over 13,000 vertebrate genera!
​
Press release: Scientists CT scanned thousands of natural history specimens, which you can access for free
Paper here!
Wiki: https://www.idigbio.org/wiki/index.php/OVert:_Open_Exploration_of_Vertebrate_Diversity_in_3D
​
Reproducible Digital Restoration of Fossils Using Blender
Co-authors: Raina DeVries (lead author), Paul Sereno, Daniel Vidal
Figure 7 from DeVries et al. (2022) showing the use of armatures in Blender to record the retrodeformation and reconstruction of a dinosaur frontal bone.
Abstract: Digital restoration of fossils based on computed tomographic (CT) imaging and other scanning technologies has become routine in paleontology. Digital restoration includes the retrodeformation and reconstruction of a fossil specimen. The former involves modification of the original 3D model to reverse post-mortem brittle and plastic deformation; and the latter involves the infilling of fractures, addition of missing pieces, and smoothing of the mesh surface. The restoration process often involves digital editing of the specimen in ways that are difficult to document and reproduce. To record all actions taken during the digital restoration of a fossil, we outline a workflow that generates both the restored bone and the sequence of steps involved in its retrodeformation and reconstruction. Our method can also generate an animation showing the transformation of the original digital model into its final form. We applied this method to a dorsal rib and frontal bone of a small-bodied Jurassic-age armored dinosaur from Africa, the digital restoration of which engaged all modalities of deformation (translation, rotation, scaling, distortion) and reconstruction (fracture infilling, adding missing bone, surface smoothing).
​
Check out the paper here!
​
DeVries, R.P., Sereno, P.C., Vidal, D., Baumgart, S.L. (2022). Reproducible digital restoration of fossils using Blender. Front. Earth Sci. 138.